Patent Application
20160288090
The present application claims priority from Australian Provisional Application No. 2009900328 the content of which is incorporated herein by reference.
The present invention is directed to methods of designing molecularly imprinted polymers (MIPs) which have applications in extracting bioactive compounds from a range of bioprocessing feedstocks and wastes. The present invention is further directed to MIPs designed by the methods of the present invention.
Molecularly imprinted polymers (MIPs) can be designed with variable levels of cross-linking to produce polymers with controlled rigidity or flexibility, dependent upon the functional requirement, which contain cavities (binding sites) that can be tailor made to be specific for any target analyte. Using a pure sample of templates, MIPs can be prepared that are specific for the template compound or selective for other molecules having a similar chemical structure. MIPs are a polymeric network having high selectivity and specificity, which can be likened to that of an antibody for its antigen. MIPs offer the benefits of enhanced resistance to temperature, extremes of pH, solvents, proteases, and degradation or denaturation processes, which makes them reusable materials for the pre-concentration, extraction and separation of potential value-add biomolecules from complex feedstocks.
Strong epidemiological evidence exists for the health benefits of fruit and vegetables on cardiovascular disease, gastrointestinal tract cancers, cataracts and other diseases and ailments. Phytochemicals are candidates for contributing to a major part of this effect. Although knowledge of the mechanisms of uptake, metabolism and how these molecules exert their biological effects in vivo is uncertain, the health benefits afforded by these bioactive compounds is widely recognised and accepted.
One class of phytochemicals which are of considerable interest are the polyphenols, of which resveratrol is an example. Other interesting classes are the chalcones, indoles, coumarins, flavanones and flavanols, anthocyanins and the phytosterols and phytostanols.
With regard to resveratrol and its analogues or phytosterols and their analogues, there has been little published literature examining ways to produce MIPs of the required specificity. The literature that does exist predominately emphasises only the analytical mode of separation. Where attempts have been made to use the produced MIP in a preparative separation context, no attempt has been made to optimise the MIP performance or address some of the key challenges for larger scale use. For example, the work of Xiang et al.1 is based on the concept that non-covalent molecular imprinting techniques are unsuitable for templates, such as resveratrol, dissolved in polar solvents, and hence it was necessary for acrylamide to be used as the monomer, whilst in the work of Ma et al.2 no attention was given to control the selectivity of the derived MIP, with the consequence that the resveratrol derivatives, trans-polydatin and emodin, bound more strongly to the MIP despite their glucosidated or modified structures. The work of Cao et al.3 to a large extent simply restates the same conclusions of Xiang et al.1 or Ma et al.2, a situation which is not surprising in view of the use of very similar methods and an identical set of test compounds. There is thus a need for specific MIPs to be developed, which have been tailored and optimised for a particular template or class of templates with the derived molecularly imprinted polymers suitable for industrial-type applications. Specifically, there is a need to make suitable MIPs that are compatible with systems currently employed by the manufacturing industries, permitting the isolation of target compounds of commercial importance within the food and similar industries.
The present inventors have designed a resveratrol-selective MIP (described as MIP 8 in this document) using resveratrol as template. They have also designed a number of other molecularly imprinted polymers with resveratrol analogue templates, including an imine analogue of resveratrol (called “green resveratrol” by the inventors), and an amide analogue. They have demonstrated the application of their MIP 8 in a solid phase extraction technique, allowing the selective enrichment of resveratrol from grape seed and peanut meal extract. This outcome can be contrasted to the low purification factors obtained with the MIP systems of the prior art, such as those described by Ma et al.2, Xiang et al.1 or Cao et al.3. In addition, they have demonstrated the ability to scale up the molecularly imprinted solid phase technique, thereby illustrating the scalability of the process.
In a first aspect, the present invention provides a method of preparing a molecularly imprinted polymer (MIP) having a desired level of specificity for a compound, the method comprising the steps of polymerizing a monomer comprising one or more non-covalent bonding sites and a cross-linking agent in the presence of a template molecule and porogen and subsequently removing the template, wherein the template is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound, and wherein the template comprises one or more non-covalent bonding sites wherein said non-covalent bonding sites are complementary to the non-covalent bonding sites of the monomer, and further wherein the template has either more or less non-covalent bonding sites than the compound, whereby the MIP has a different level of specificity for the compound than if the compound itself was used as the template.
In one embodiment, the present invention provides a method of preparing a molecularly imprinted polymer (MIP) having a desired level of specificity for a compound, the method comprising the steps of polymerizing a monomer comprising one or more hydrogen-bonding sites and a cross-linking agent in the presence of a template and porogen and subsequently removing the template, wherein the template is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound, and wherein the template comprises one or more hydrogen-bonding sites complementary to the one or more hydrogen-bonding sites of the monomer, and further wherein the template has either more or less hydrogen-bonding sites than the compound, whereby the MIP has a different level of specificity for the compound than if the compound itself was used as the template.
In a second aspect, the present invention provides a method of guiding the selection of a monomer for use in a molecularly imprinted polymer (MIP) which is to be imprinted with a template comprising one or more non-covalent bonding sites, wherein the MIP is to be prepared by polymerizing the selected monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template, said method comprising the steps of providing a group of monomers having one or more non-covalent bonding sites which are complementary to the non-covalent bonding sites of the template, assessing the energy of formation of the complex formed between each monomer of the group of monomers and the template, and selecting the selected monomer from the number of monomers using the energy of formation of the complex as a factor in the selection.
In one embodiment, the present invention provides a method of guiding the selection of a monomer for use in a molecularly imprinted polymer (MIP) which is to be imprinted with a template comprising one or more hydrogen-bonding sites, wherein the MIP is to be prepared by polymerizing the selected monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template, said method comprising the steps of providing a group of monomers having one or more hydrogen-bonding sites which are complementary to the hydrogen-bonding sites of the template, assessing the energy of formation of the hydrogen-bonded complex formed between each monomer of the group of monomers and the template, and selecting the selected monomer from the number of monomers using the energy of formation of the hydrogen-bonded complex as a factor in the selection.
In a third aspect, the present invention provides a method of selecting the ratio of monomers to template in the preparation of a molecularly imprinted polymer (MIP) which is to be imprinted with the template, wherein the MIP is to be prepared by polymerizing the monomer with a cross-linking agent in the presence of the template and porogen and subsequently removing the template, said method comprising the step of assessing the energy of formation of the complex formed between the template and a varying number of the monomers, and selecting the ratio of monomers to template using the energy of formation of the complex as a factor in the selection.
In a fourth aspect, there is provided a pre-polymerisation complex for use in preparing a MIP comprising one or more monomers each comprising one or more non-covalent bonding sites and a template wherein the template comprises one or more non-covalent bonding sites complementary to the one or more non-covalent bonding sites of the monomer.
In one embodiment, there is provided a pre-polymerisation hydrogen-bonded complex for use in preparing a MIP comprising one or more monomers each comprising one or more hydrogen-bonding sites and a template wherein the template comprises one or more hydrogen-bonding sites complementary to the one or more hydrogen-bonding sites of the monomer.
In a fifth aspect, there is provided a MIP prepared according to the method of the first aspect.
In one embodiment, the monomer comprising one or more non covalent-bonding sites is selected by the process of the second aspect.
In a sixth aspect, there is provided a MIP prepared by polymerizing a monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template wherein the selection of the monomer is guided by the process of the second aspect or the ratio of monomer to template is selected by the process of the third aspect.
In a seventh aspect, there is provided a method of designing an analogue of a compound comprising a trans-ethylene linker, the method comprising replacing the trans-ethylene linker with an imine, amide or secondary amine linker.
Preferably, the trans-ethylene link is replaced with an imine link. The imine link is structurally equivalent to the ethylene link but is far simpler to synthesise.
In an eighth aspect, there is provided a method of preparing a MIP which is specific for a compound having a trans-ethylene linker, the method comprising the steps of polymerizing a monomer and a cross-linking agent in the presence of a template and porogen and subsequently removing the template, wherein the template is an analogue of the compound.
In a ninth aspect, the present invention provides a molecularly imprinted polymer (MIP) imprinted with a polyphenol or an analogue thereof wherein the MIP comprises polymerised 4-vinylpyridine together with a polymerised cross-linking agent.
In a tenth aspect, the present invention provides a method of preparing a MIP according to the ninth aspect, said method comprising the steps of
In a eleventh aspect, the present invention provides a method of extracting one or more polyphenols from a sample by exposing the sample to a MIP according to the first aspect.
In a preferred form, the sample is plant based, and sourced from foodstuffs such as grapes and their seeds, skins, and juice (and wine), apples, pears, berries, and other fruits, tea, peanuts (or peanut meal), and cereals such as wheat, corn, rice and their oils, and byproducts thereof.
In one embodiment, the MIP is encased in a permeable mesh.
In an twelfth aspect, the present invention provides a method of at least partially separating the constituents of a sample by chromatography, the method comprising the step of (i) preparing a chromatographic column comprising a MIP according to the first aspect; (ii) passing the sample through the column; and (iii) collecting fractions of the sample from the column.
In a thirteenth aspect, the present invention provides a MIP imprinted with one or more compounds selected from the group consisting of sterols and stanols, and analogues or derivatives thereof, wherein said MIP comprises a polymerised monomer.
Preferably, the derivative is a polyphenol ester such as a ferulic acid ester or a gallic acid ester. The polyphenol provides hydrogen-bonding and π-π bonding sites.
In a fourteenth aspect, the present invention provides a method of preparing a MIP according to the thirteenth aspect, said method comprising the steps of
(i) polymerising the MIP in the presence of the sterol(s) or stanol(s), or analogue(s) or derivative(s) thereof, and a porogen; and
(ii) removing the sterol(s) or stanol(s), or analogue(s) or derivative(s) thereof, thereof from the MIP.
In a fifteenth aspect, the present invention provides a method of extracting one or more sterol(s) or stanol(s), or analogue(s) or derivative(s) thereof, from a sample by exposing the sample to a MIP according to the thirteenth aspect.
In one embodiment, the MIP is encased in a permable mesh.
In a sixteenth aspect, the present invention provides a method of at least partially separating the constituents of a sample by chromatography, the method comprising the step of (i) preparing a chromatographic column comprising a MIP according to the thirteenth aspect; (ii) passing the sample through the column; and (iii) collecting fractions of the sample from the column.
In the course of investigations into the functional polymers of this invention, the present inventors have prepared a number of novel and inventive compounds. The seventeenth aspect of this invention is directed to these novel compounds.
In an eighteenth aspect, there is provided a method of at least partially separating components of a sample comprising two or more of said components, said method comprising sequentially exposing the sample to at least two MIPs wherein each MIP has been imprinted with a different template.
In a nineteenth aspect, there is provided a MIP encased in a permeable mesh.
In a twentieth aspect, there is provided a method of extracting a component from a sample comprising exposing the sample to a MIP according to the nineteenth aspect.
In a twenty first aspect, there is provided a MIP imprinted with (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol or 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide.
In a twenty second aspect, there is provided a method of extracting resveratrol from a sample, said method comprising exposing the sample to a MIP according to the twenty first aspect.
The formation of a MIP typically involves the following steps: a template is mixed together with a monomer (typically in excess) to form pre-polymerisation complexes comprising a single template associated with a number of monomer molecules; these pre-polymerisation complexes are then cross-linked into a polymer by polymerisation of the monomers with a cross-linking agent; and the template is subsequently removed from the cross-linked complexes. The cross-linked monomers of the complexes comprise surfaces and cavities which are complementary to the shape of the template. The cross-linking reaction is generally carried out in the presence of porogen which ensures that the MIP has an open structure comprising a number of pores. These pores allow the molecules of a solution to move through the MIP so that the molecules are able to interact with the surfaces and cavities. An analyte which has the same or similar shape to the template will more strongly interact with the MIP than other molecules in the solution, so that the MIP can be used to capture, concentrate and/or separate the analyte.
Various different types of manufacture can be employed, e.g. (a) monolith type preparation, (b) particles made by grinding and sizing, (c) precipitation polymerization procedures.
The present inventors have synthesised a series of compounds based on resveratrol to generate a library of compounds, which may be present in crude bioprocessing feedstocks, and which have been used as templates for creating and investigating MIPs as tailor-made affinity adsorbents for bioactives derived from plant and other biological sources. All of these molecules can be synthesised to incorporate variable functionality characteristics, based on hydrophobicity, hydrophilicity and other physicochemical parameters, to produce molecules with defined composition-of-matter. These chemical compounds can be designed, synthesised and derivatised with a variety of different functionalities to include inter alia amino, carboxyl, hydroxyl, alkyl or aryl substituents distributed throughout the points of diversity on the respective scaffolds to create a subset of compound analogues which can be used as templates for the design and characterisation of MIPs. These functionalities may be selected on the basis of both steric and electronic considerations. Compounds with an increased number of polar functional groups or “points” are more likely to be instructive in probing and defining the created MIP cavities. Increasing the number of points available for interaction with functional monomer molecules during the MIP templating process potentially increases the specificity of the cavity formed for any defined template.
As an illustration of the generality of methods of the present invention, the present inventors have also demonstrated that sterols and stanols esterified with polyphenol acids, such as gallic acid and ferulic acid, can be used as templates having additional “points” when compared to the sterol or stanol as such.
As would be clear to those skilled in the art, the techniques used are applicable to molecules other than resveratrol, the sterols and stanols.
Accordingly, in a first aspect, the present invention provides a method of preparing a molecularly imprinted polymer (MIP) having a desired level of specificity for a compound, the method comprising the steps of polymerizing a monomer comprising one or more non-covalent bonding sites and a cross-linking agent in the presence of a template and porogen and subsequently removing the template, wherein the template is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound, and wherein the template comprises one or more non-covalent bonding sites wherein said non-covalent bonding sites are complementary to the non-covalent bonding sites of the monomer, and further wherein the template has either more or less non-covalent bonding sites than the compound, whereby the MIP has a different level of specificity for the compound than if the compound itself was used as the template.
The term ‘non-covalent bonding site’ means a group or region of the molecule which is capable of a non-covalent bonding interaction. Examples of non-covalent bonding interactions include hydrogen bonding interactions, π-π bonding interactions, Lifshitz force interactions and van der Waals interactions.
Preferably, the non-covalent bonding site is a hydrogen-bonding site or a π-π bonding interaction site. More preferably, the non-covalent bonding site is a hydrogen-bonding site.
The term “complementary” means that a site on the template is able to bind via the non-covalent bonding interaction to a site on the monomer and vice versa.
In the circumstance where the template comprises a moiety which is structurally analogous to the compound, then the non-covalent bonding site(s) may be located (i) on the moiety, (ii) on the remaining part of the template, or (iii) if there are two or more non-covalent bonding sites, on both the moiety and on the remaining part of the template.
For instance, as will be seen in the Examples, the present inventors have used ferulic acid esters of sterols and stanols to prepare MIPs according to the present invention. These compounds comprise a moiety which is structurally analogous to the sterol or stanol (i.e. the sterol or stanol itself) with the remaining part of the molecule providing non-covalent bonding sites. The ferulic acid moiety provides two hydrogen-bonding sites and a π-π bonding interaction site.
In one embodiment, the present invention provides a method of preparing a molecularly imprinted polymer (MIP) having a desired level of specificity for a compound, the method comprising the steps of polymerizing a monomer comprising one or more hydrogen-bonding sites and a cross-linking agent in the presence of a template and porogen and subsequently removing the template, wherein the template is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound, and wherein the template comprises one or more hydrogen-bonding sites complementary to the one or more hydrogen-bonding sites of the monomer, and further wherein the template has either more or less hydrogen-bonding sites than the compound, whereby the MIP has a different level of specificity for the compound than if the compound itself was used as the template.
In one embodiment, the hydrogen-bonding site of the template is a phenolic hydroxyl group.
In another embodiment, the hydrogen-bonding site of the monomer is a pyridine nitrogen.
In a preferred form, the template further comprises one or more π-π bonding interaction sites and the monomer further comprises one or more complementary π-π bonding interaction sites.
In one embodiment, the π-π bonding interaction site of the template is the aromatic ring of a phenol. In another embodiment, the π-π bonding interaction site of the monomer is the aromatic ring of a pyridine.
The present inventors have found that a MIP formed using a template which is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound and further wherein the template comprises more hydrogen bonding sites than the compound will tend to be more specific for the compound (and for compounds with a very closely related structure) than if the compound itself is used as the template. This is because the additional hydrogen-bonding sites on the template will attract more monomer units to the pre-polymerisation complex so that the cavity formed by the template will conform more closely to the template and hence the compound and compensates for the loss of a potential binding site in cases where the opening of the cavity by chance is positioned such that one binding site of the template has no complementary binding site in the polymer.
Accordingly, in one embodiment, the template has more hydrogen-bonding sites than the compound, whereby the MIP has a greater level of specificity for the compound than if the compound itself was used as the template.
Further, if the MIP is formed using a template which is structurally analogous to the compound or comprises a moiety which is structurally analogous to the compound and the template comprises less hydrogen-bonding sites than the compound, then the MIP will tend to be less specific for the compound than if the compound itself is used as the template. Although the MIP is less specific for the compound itself, it will still possess a degree of specificity for the compound and also for compounds which have some structural similarities. This provides a means of extracting classes of potentially useful compounds from complex feed stocks. If desired, the extracted mixture comprising such a class of compounds can then be subjected to further purification techniques, such as extraction with more selective MIPs, to isolate sub-classes or individual molecules.
Accordingly, in another embodiment, the template has less hydrogen-bonding sites than the compound, whereby the MIP has a lower level of specificity for the compound than if the compound itself was used as the template.
As would be appreciated by the person skilled in the art, the methods of the present invention allows for the formation of MIPs which show improved levels of specificity for compounds which have no or fewer hydrogen-bonding sites by using, as templates, appropriately chosen structurally analogous compounds which do have a greater number of hydrogen-bonding sites. This provides a useful means of isolating compounds which are otherwise difficult to extract from complex mixtures.
In terms of relative abundance, a majority of compounds of interest as high value products within the food, fine chemical and pharmaceutical industries are likely to contain at least one hydrogen bonding site. Some contaminants, particularly toxic or hazardous compounds, such as polycyclic aromatics, are likely to fall into those families that lack hydrogen bonding sites and thus it will be essential in these cases to exploit other modes of molecular interaction. As would be understood to those skilled in the art, the approach taken with hydrogen-bonding is equally applicable to other types of non-covalent bonding and can be used to design MIPs which are selective for compounds such as polycyclic hydrocarbons.
In a second aspect, the present invention provides a method of guiding the selection of a monomer for use in a molecularly imprinted polymer (MIP) which is to be imprinted with a template comprising one or more non-covalent bonding sites, wherein the MIP is to be prepared by polymerizing the selected monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template, said method comprising the steps of providing a group of monomers having one or more non-covalent bonding sites which are complementary to the non-covalent bonding sites of the template, assessing the energy of formation of the complex formed between each monomer of the group of monomers and the template, and selecting the selected monomer from the number of monomers using the energy of formation of the complex as a factor in the selection.
The design of molecularly imprinted polymers (MIPs) requires the selection of a monomer species that will interact favourably with the intended template species, such that a pre-polymerisation complex is formed between template and monomer. The use of tools such as molecular modelling and NMR spectroscopy of the pre-polymerisation complexes allow the selection of appropriate monomers by performing a ‘virtual screen’, which reduces the number of actual polymer preparations that are required to achieve optimised MIP development.
In one embodiment, the present invention provides a method of guiding the selection of a monomer for use in a molecularly imprinted polymer (MIP) which is to be imprinted with a template comprising one or more hydrogen-bonding sites, wherein the MIP is to be prepared by polymerizing the selected monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template, said method comprising the steps of providing a group of monomers having one or more hydrogen-bonding sites which are complementary to the hydrogen-bonding sites of the template, assessing the energy of formation of the hydrogen-bonded complex formed between each monomer of the group of monomers and the template, and selecting the selected monomer from the number of monomers using the energy of formation of the hydrogen-bonded complex as a factor in the selection.
In a third aspect, the present invention provides a method of selecting the ratio of monomers to template in the preparation of a molecularly imprinted polymer (MIP) which is to be imprinted with the template, wherein the MIP is to be prepared by polymerizing the monomer with a cross-linking agent in the presence of the template and porogen and subsequently removing the template, said method comprising the step of assessing the energy of formation of the complex formed between the template and a varying number of the monomers, and selecting the ratio of monomers to template using the energy of formation of the complex as a factor in the selection.
In a preferred form of the second and third aspects, the energy of formation of the complex is assessed by molecular modeling techniques.
For instance, PM3 geometry optimization may be used to yield theoretical energy of formation values for the complex.
In another preferred form of the second and third aspects, the energy of formation is assessed by NMR-spectroscopy techniques. For instance, in the case of phenolic hydroxyl groups, the magnitude of the downfield shift of the 1H NMR signal for that group is indicative of the strength of the hydrogen-bonding interactions. Typically, the downfield shift would be in the order of about 0.5 to about 1.5 ppm although, as would be understood by those skilled in the art, the choice of NMR solvent will be a important factor in determining the magnitude of the shift.
In a fourth aspect, there is provided a pre-polymerisation complex for use in preparing a MIP comprising one or more monomers, each comprising one or more non-covalent bonding sites, and a template wherein the template comprises one or more non-covalent bonding sites complementary to the one or more non-covalent bonding sites of the monomer.
In a preferred form, the monomers are selected by the method according to the second aspect.
In another preferred form, the ratio of monomer to template is selected by the process of the third aspect.
In one embodiment, there is provided a pre-polymerisation hydrogen-bonded complex for use in preparing a MIP comprising one or more monomers each comprising one or more hydrogen-bonding sites and a template wherein the template comprises one or more hydrogen-bonding sites complementary to the one or more hydrogen-bonding sites of the monomer.
In a fifth aspect, there is provided a MIP prepared according to the method of the first aspect.
In one embodiment, the monomer comprising one or more non-covalent bonding sites is selected by the process of the second aspect.
In a sixth aspect, there is provided a MIP prepared by polymerizing a monomer with a cross-linking agent in the presence of a template and porogen and subsequently removing the template wherein the selection of the monomer is guided by the process of the second aspect or the ratio of monomer to template is selected by the process of the third aspect.
The monomers used in the methods and MIPs of the present invention include those that promote or facilitate hydrogen-bonding interactions and/or π-π bonding interactions and include:
where R is selected from the group consisting of C1-4alkyl, amide, nitrile, carboxylic acid, primary or secondary amine, CO2C1-4alkyl, C1-4OH, hydroxyalkyl acrylate, benzene, benzyl amine, naphthalene, anthracene, pyridine, pyrimidine, purine, N-imidazole; and
where R′ is selected from the group consisting of H and CH3;
and R″ is selected from the group consisting of C1-4alkyl, amide, nitrile, carboxylic acid, primary or secondary amine, CO2C1-4alkyl, C1-4OH, and hydroxyalkyl methacrylate.
In a preferred form, the monomer is selected from the group consisting of:
The person skilled in the art would be aware of a wide range of cross-linking agents that would be suitable for use in the methods and MIPs of the present invention. In a preferred embodiment, the cross-linking agent is selected from the group consisting of:
where R is an alkyl chain, preferably 1 to 4 carbons in length
In certain embodiments, the monomer and the cross-linking agent may be the same compound. Porogens suitable for use in the methods and MIPs of the present invention include those that promote or facilitate hydrogen-bonding interactions and those that promote or facilitate hydrophobic interactions or a combination of both.
Porogens that facilitate hydrogen bond formation include acetonitrile, acetone, ethyl acetate and dimethyl formamide (DMF) or a combination thereof, in addition to mixtures of the above with suitable quantities of ethanol, methanol or dimethyl sulfoxide (DMSO).
Porogens that facilitate hydrophobic interactions include aqueous mixtures of acetonitrile, acetone, ethyl acetate, DMF, ethanol, methanol, DMSO or a combination thereof.
With respect to phytosterols (or other classes or families of compounds) the above list can be extended with the inclusion also of water, optionally mixed with trifluoroacetic acid. Organic solvents such as chloroform, dichloromethane, hexane, toluene and the more polar organic solvents such as isopropanol, tertiary butyl alcohol and cyclohexanol may also be used.
In a seventh aspect, there is provided a method of designing an analogue of a compound comprising a trans-ethylene linker, the method comprising replacing the trans-ethylene linker with an imine, amide or secondary amine linker.
Preferably, the compound is resveratrol.
In an eighth aspect, there is provided a method of preparing a MIP which is specific for a compound having a trans-ethylene linker, the method comprising the steps of polymerizing a monomer and a cross-linking agent in the presence of a template and porogen and subsequently removing the template, wherein the template is an analogue of the compound and further wherein the analogue is designed according to the method of the seventh aspect.
In a ninth aspect, the present invention provides a molecularly imprinted polymer (MIP) imprinted with a polyphenol or an analogue thereof wherein the MIP comprises polymerised 4-vinylpyridine together with a polymerised cross-linking agent.
Preferably, the polyphenol or an analogue thereof is resveratrol or an analogue thereof. More preferably, the polyphenol or analogue thereof is an analogue of resveratrol where the trans-ethylene linker is replaced with an imine, amide or secondary amine linker. In certain embodiments, the analogue has more or less hydroxyl groups than resveratrol. In a more preferred form, the analogue of resveratrol is the imine (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol or the amide 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide.
The imine and amide anlogues of resveratrol analogues are simpler and cleaner to synthesise than resvertrol itself. MIPs prepared using these templates have been shown to have a comparable binding affinity for resveratrol as MIPs prepared using resveratrol as a template.
In a preferred from, the MIP is for use in isolating resveratrol.
Preferably, when resveratrol is used as a template, the ratio of resveratrol to 4-vinylpyridine is 1:3. This ratio has been shown by modelling studies and by empirical results to be the optimum ratio for a resveratrol binding MIP. Similarly, the ratio of the imine (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol and the amide 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide to 4-vinylpyridine is preferably 1:3.
Various classes of compounds can be used as templates for resveratrol. These include:
(a) the chalcones
(b) the amide analogue linked by —NH—C(O)—;
(c) cyclic systems such as the flavanols and coumarins, ie
(d) alkaloids such as the nitrogen containing indoles, the rings of the indoles being substituted with R groups;
(e) other cyclic analogues are also relevant, such as the products from the following model reaction
generating benzimidazoles, which are analogues of resveratrol. Each phenyl ring of the bezimidazole can additionally bear an R substituent.
In these compounds; each R may be zero (O) to three (3) substituents each of which is independently selected from the group consisting of: H, OH, CH3, NH2, SH, NO2, COOH, C(O)NH2, CHO, CN, NC, OCH3, OC1-4alkyl, SC1-4alkyl, O-Sugar, N-Sugar, P(O)(OH)2, S(O)2(OH), OAr, NHAr, SAr, NHC1-4alkylAr, OC(O)Ar, C(O)Oar, C(O)Ar, C(O)Nar, CF3, OCF3, Halogen, NHC1-4alkyl, N(C1-4alkyl)2, SC1-4alkyl, C(O)C1-4alkyl, OC(O)C1-4alkyl, C(O)OC1-4alkyl, C(O)NHC1-4alkyl, C(O)N(C1-4alkyl)2, C1-4alkoxy, C1-4alkylenedioxy, P(O)(OH)2, P(O)(OC1-4alkyl)2, S(O)(OC1-4alkyl)2, C(NH2)═C(NH2)2, C(NH2)═C(CN)2, C(CN)═C(CN)2, C(CN)═C(NH2)2, C(NH2)═C(C1-4alkyl)2, C(C1-4alkyl)═C(NH2)2, C(CN)═C(C1-4alkyl)2, C(C1-4alkyl)═C(CN)2; and OR1
wherein R1 may be selected from the group consisting of H, Ac, glucose, galactose, gallate, ferulate.
X and Y indicate appropriate substituents. Typically, H or C1-6alkyl. In the case of the coumarins, X or Y may be ═O and the oxygen containing ring may contain an additional double bond.
Conditions have been established and optimized for the synthesis of a small library of polyfunctionalized (E)-stilbene (resveratrol) analogues using a convergent methodology. The synthetic procedures have introduced various functional groups into the core scaffolds, which has resulted in the production of a library of low molecular weight compounds having unique compositions of matter. A summary of the molecules produced to date is shown in Table 1. These compounds, together with their saturated diphenethyl analogues, have been used as templates for the creation of molecularly imprinted polymers and as probes to investigate the binding characteristics of these MIPs.
Additional compounds evaluated and templated are shown below. Examples have been used both as MIP templates and as MIP test compounds.
In a further preferred form, the analogue of resveratrol is a compound of Formula I or of Formula II wherein:
Even more preferably, the compound is a compound of Formula I and X is N.
Suitable cross-linking agents are described above. Preferably, the cross-linking agent is EDGA.
In another preferred form, the ratio of polymerised 4-vinylpyridine to polymerised cross-linking agent is from three to fifteen. More preferably, five.
An expanded repertoire of templates used in MIP preparation could confer the potential to form a chemical class-selective MIP rather than a molecule-selective MIP.
Accordingly, in one embodiment, the MIP is imprinted with a mixture of two or more different polyphenols or analogues thereof.
In a tenth aspect, the present invention provides a method of preparing a MIP according to the ninth aspect, said method comprising the steps of
In a preferred form, the ratio of the polyphenol(s) or analogue(s) thereof to 4-vinylpyridine to cross-linking agent is 1:3:15.
The temperature of the polymerisation and the period of time over which it occurs may be important. The present inventors have found that the preferred temperature range for preparing MIPs of the present invention is between 50-55° C., whereas the imprinted polymers prepared in the cited literature were at a single temperature of 45° C. (Xiang et al.1) for excessive periods of time, such as 24 hours, or at a single temperature of 60° C. (Ma et al.2 and Cao et al.3). In a preferred form, the porogen is selected from porogens that promote or facilitate hydrogen-bonding interactions.
More preferably, the porogen comprises one or more solvents selected from the group consisting of acetonitrile, acetone, ethyl acetate, and dimethylformamide. Even more preferably, the porogen further comprises one or more solvents selected from the group consisting of ethanol, methanol and dimethylsulfoxide.
In a preferred form, the porogen comprises a mixture of acetonitrile and ethanol. In an even more preferred form, the ratio of acetonitrile to ethanol is about 5 to 1.
In a eleventh aspect, the present invention provides a method of extracting one or more polyphenols from a sample by exposing the sample to a MIP according to the present invention or designed or prepared according to the methods of the present invention.
A sample could include, but not be limited to, agricultural waste, agricultural products, chemical reaction mixture, or a prepared mixture of compounds.
The extraction could be carried out using any suitable means including but not limited to a chromatographic column system, a batch adsorption (tank) system, a fluidised/expanded bed system, a membrane-related system and a “tea-bag” type of separation device.
In a preferred form, the sample is a foodstuff such as grape seed, grape skin, peanuts or peanut meal.
In a preferred form, the polyphenol is resveratrol.
In an twelfth aspect, the present invention provides a method of at least partially separating the constituents of a sample by chromatography, the method comprising the step of (i) preparing a chromatographic column comprising a MIP according to the first aspect; (ii) passing the sample through the column; and (iii) collecting fractions of the sample from the column.
In a thirteenth aspect, the present invention provides a MIP imprinted with one or more compounds selected from the group consisting of sterols and stanols, and analogues or derivatives thereof, wherein said MIP comprises a polymerised monomer.
Preferably, the monomer has one or more hydrogen-bonding sites and/or π-π bonding interaction sites. Suitable monomers are described above.
In one embodiment, the monomer is selected from the group consisting of 4-vinylpyridine, methylmethacrylic acid and other types of functional monomers, exemples of which are given above.
In another embodiment, the monomer is ethylene glycol dimethacrylate. Although often used as a cross-linking agent, ethylene glycol dimethacrylate has also been used by the present inventors as the sole monomer in certain MIPs.
In a preferred form, the MIP further comprises a polymerised cross-linking agent.
Suitable cross-linking agents are described above. A particularly preferred cross-linking agent is ethylene glycol dimethacrylate.
Preferably, the sterol and stanols are phytosterols and phytostanols.
Suitable sterols and stanols include: cholesterol, brassicasterol, beta-sitosterol, stigmasterol, campesterol, beta-sitostanol, and campestanol.
Preferably, the derivative is a ferulic acid ester of the sterol or stanol such as the components of γ-oryzanol. Suitable derivatives include: campersterylferulate, beta-sitosterylferulate, cycloartanylferulate, campestanylferulate, cycloartenylferulate and 24-methylen-cycloartanylferulate.
In a fourteenth aspect, the present invention provides a method of preparing a MIP according to the thirteenth aspect, said method comprising the steps of
Suitable porogens are described above. In a preferred form, the porogen is selected from the group consisting of chloroform, trifluoroacetic acid, water; and mixtures of trifluoroacetic acid and water.
In a fifteenth aspect, the present invention provides a method of extracting one or more sterol(s) or stanol(s), or analogue(s) or derivative(s) thereof, from a sample by exposing the sample to a MIP according to the present invention or prepared or designed according to the methods of the present invention.
A sample could include, but not be limited to, agricultural waste, agricultural products, chemical reaction mixture, or a prepared mixture of compounds.
The extraction could be carried out using any suitable means including but not limited to a chromatographic column system, a batch adsorption (tank) system, a fluidised/expanded bed system, a membrane-related system and a “tea-bag” type of separation device.
In a preferred form, the sample is a foodstuff such as avocado oil, sesame seed oil, wheat oil, or grapeseed oil.
In a sixteenth aspect, the present invention provides a method of at least partially separating the constituents of a sample by chromatography, the method comprising the step of (i) preparing a chromatographic column comprising a MIP according to the thirteenth aspect; (ii) passing the sample through the column; and (iii) collecting fractions of the sample from the column.
In the methods and MIPs of the present invention, the template may be incorporated in the polymer by non-covalent means, eg by hydrogen-bonding, π-π interactions, donor-acceptor interactions and van der Waals interactions or by covalent means such as by covalent attachment to monomers of the MIP.
Removal of the template from a covalent MIP can be achieved by any means known to be suitable to those in the art. The means include, but are not limited to, acid hydrolysis, base hydrolysis, reduction (using NaBH4 or LiAIH4), washing with a weak acid (to remove metal co-ordination bonds) and thermal cleavage to remove a reversible urethane bond. The latter procedure follows an adaptation of a method to cleave urethane bonds at elevated temperatures, such as 60° C. in DMSO, although the very harsh conditions of 180° C. in DMSO as describe by Ki and coworkers4 for the preparation of molecularly imprinted silica spheres, would not be suitable for the types of fully organic based monomers as detailed above. Additionally, enzymatic cleavage can be considered to be possible using e.g. esterases.
In the course of investigations into the functional polymers of this invention, the present inventors have prepared a number of novel and inventive compounds. The seventeenth aspect of this invention is directed to these novel compounds.
A list of various compounds used in the methods and compositions of the present invention are set out in Table 2 and Table 3 below. The novel compounds in the Table also form part of the present invention.
In a preferred form, the present invention provides novel compounds of Formula I and Formula II wherein:
each of R1, R2, R3, R4, R5 and R6 is independently selected from: H, OH, CH3, NH2, SH, NO2, COOH, C(O)NH2, CHO, CN, NC, OCH3, OC1-4alkyl, SC1-4alkyl, O-Sugar, N-Sugar, P(O)(OH)2, S(O)2(OH), OAr, NHAr, Sar, C1-4alkylAr, NHC1-4alkylAr, OC(O)Ar, C(O)Oar, C(O)Ar, C(O)NAr, CF3, OCF3, Halogen, NHC1-4alkyl, N(C1-4alkyl)2, SC1-4alkyl C(O)C1-4alkyl, OC(O) C1-4alkyl, C(O)OC1-4alkyl, C(O)NHC1-4alkyl, C(O)N(C1-4alkyl)2, C1-4alkoxy, C1-4alkylenedioxy, P(O)(OH)2, P(O)(OC1-4alkyl)2, S(O)(OC1-4alkyl)2, C(NH2)═C(NH2)2, C(NH2)═C(CN)2, C(CN)═C(CN)2, C(CN)═C(NH2)2, C(NH2)═C(C1-4alkyl)2, C(C1-4alkyl)=C(NH2)2, C(CN)═C(C1-4alkyl)2, C(C1-4alkyl)═C(CN)2; and OR1
wherein R1 may be selected from the group consisting of H, Ac, glucose, galactose, gallate, ferulate.
Even more preferably, the compound is a compound of Formula I and X is N.
In an eighteenth aspect, there is provided a method of at least partially separating components of a sample comprising two or more of said components, said method comprising sequentially exposing the sample to at least two MIPs wherein each MIP has been imprinted with a different template.
The present inventors have further shown that MIPs can be used to extract components from samples by using MIPs encased in “teabags” ie a permeable mesh that allows the MIP to be readily inserted or “dipped” into the sample and then removed. Suitable meshes include cotton-based materials, Gilson® 63 μm sieve mesh and Sigma Aldrich dialysis tubing cellulose membrane (12 kDa MWCO).
Accordingly, in a nineteenth aspect, there is provided a MIP encased in a permeable mesh. The MIO can include, but need not be limited to, the MIPs of the present invention or prepared or designed according to the methods of the present invention.
In a twentieth aspect, there is provided a method of extracting a component from a sample comprising exposing the sample to a MIP according to the nineteenth aspect.
In a twenty first aspect, there is provided a MIP imprinted with (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol or 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide, wherein said MIP comprises a polymerised monomer.
In one embodiment, the MIP comprises a cross-linking agent.
Preferably, the MIP is for use in the extraction of resveratrol.
The monomer, cross-linking agent and porogen used in preparation of the MIP may be selected from those described in relation to the other aspects of the invention.
Preferably, the monomer is 4-vinylpyridine and the cross-linking agent is EDGA. More preferably, the ratio of template to 4-vinylpyridine used in preparation of the MIP is 1:3.
Preferably, the MIP comprises one or more features of one or more of the other aspects of the invention.
In a twenty second aspect, there is provided a method of extracting resveratrol from a sample, said method comprising exposing the sample to a MIP according to the twenty first aspect.
Preferably, the resveratrol is subsequently washed or elute from the MIP.
It would be understood by those skilled in the art that the aspects of the present invention are closely interrelated and that therefore the features of one aspect of the present invention may also be relevant to another aspect of the present invention.
In order that the nature of the present invention may be more clearly understood preferred forms thereof will now be described by reference to the following non-limiting Examples.
A number of polyfunctionalized (E)-stilbene analogues 1 have been synthesised as templates around which new molecularly imprinted polymers (MIPs) can be generated. These compounds, along with their “saturated” diphenethyl analogues 2, were also used as probes to investigate the characteristics of these MIPs. These compounds were synthesized using a convergent methodology where the key step was the palladium catalysed coupling of a functionalized benzoyl chloride 3 with a functionalized styrene 4. Best results were obtained when the acid chlorides were freshly generated from the parent benzoic acids 5, which were then immediately on-reacted. This synthetic methodology is described in Scheme 1.
The key coupling step for generating the nitrogen isosteres is shown below in Scheme 2.
Most AR solvents were used as purchased from the manufacturer except for dimethylformamide (DMF), which was dried over 4 Å molecular sieves and toluene which was dried over sodium wire. Milli-Q distilled water was used for aqueous manipulations. Saturated aqueous solutions of reagents were written, for example, as sat. NaHCO3. Solvent extracts of aqueous solutions were dried over anhydrous sodium sulfate, filtered and then rotary evaporated to dryness at low pressure (10-400 mbar) and 30-35° C. in a temperature-controlled water bath.
Analytical thin layer chromatography (TLC) was performed using aluminium sheets (Merck) coated with silica gel 60 F254. The components were visualised by (i) fluorescence at 254 nm and (ii) exposure to iodine vapour or dipping into an ethanolic phosphomolybdic acid solution and heating until charred.
Column chromatography was conducted using silica gel 60 (Merck), 0.040-0.063 mm (230-400 mesh): eluent mixtures are expressed as volume/volumes.
Melting points were determined using a Büchi B-545 melting point apparatus.
Proton nuclear magnetic resonance (1H NMR) spectra were recorded at (i) 200 MHz on a Bruker AC-200 spectrometer, (ii) 300 MHz with a Bruker DPX-300 spectrometer, or (iii) 400 MHz with a Bruker DRX-400 spectrometer. The 1H NMR spectra refer to solutions in deuterated solvents as indicated. The residual solvent peaks have been used as an internal reference. Resonances were assigned according to the following convention: chemical shift (δ) measured in parts per million (ppm) relative to the residual solvent peak, multiplicity, number of protons, coupling constants (J Hz), and assignment. Multiplicities are denoted as (s) singlet, (d) doublet, (dd) doublet of doublets, (ddd) doublet of doublet of doublets, (t) triplet, (dt) doublet of triplets, (td) triplet of doublets, (q) quartet, or (m) multiplet and prefixed (b) broad where appropriate.
Carbon nuclear magnetic resonance (13C NMR) spectra were recorded at (i) 50 MHz on a Bruker AC-200 spectrometer, (ii) 75 MHz on a Bruker DPX-300 spectrometer, or (iii) 100 MHz on a Bruker DRX-400 spectrometer with the spectra referring to deuterated solutions in solvents indicated.
Low resolution electrospray ionisation mass spectra (ESI) were recorded on a Micromass Platform II API QMS Electrospray mass spectrometer. Analyses were conducted in both positive (ESI+) and negative (ESI−) polarity. Principle ion peaks (m/z) are reported with their intensities expressed as percentages of the base peak in brackets. High-resolution electrospray mass spectra (HRMS) were recorded on a Brucker BioApex 47e Fourier Transform mass spectrometer.
The following examples serve to illustrate these synthetic methodologies.
Trans-stilbene and 10% Pd/C in methanol was hydrogenated overnight at 95 psi. The reaction was then filtered through a Celite pad and the clear filtrate concentrated by rotary evaporation. Purification of the resultant product with column chromatography (isocratically eluted with hexane) gave an absolute yield of 1,2-diphenylethane as a clear oil. This solidified upon standing at room temperature. Rf 0.95 (4:1 hexane/EtOAc), 0.30 (hexane); mp 49.5-50.0° C., 1H NMR (CDCl3): δ 2.95 (s, 4H, 2×CH2), 7.18-7.23 (m, 6H, H-2, H-4, H-6, H-2′, H-4′, H-6′), 7.28-7.33 ((m, 4H, H-3, H-5, H-3′, H-5′); 13C JMOD NMR (CDCl3): δ 37.18 (2×CH2), 125.18 (4,4′), 127.59 (2,6,2′,6′), 127.71 (3,5,3′,5′), 141.01 (1,1′); LREI mass spectrum; m/z 182 (M., 100%), 183 (16%), 91 (51%).
Freshly distilled benzoyl chloride, 4-acetoxystyrene, N-ethylmorpholine and palladium diacetate (2.00 mole %) were added to toluene and this mixture heated overnight at 120° C. After cooling to room temperature, ethyl acetate was added and the solution washed twice each with 0.1M HCl and water. The organic layer was then dried, filtered and rotary evaporated to give a brown solid. Recrystallization from EtOAc/hexane produced (E) 4-acetoxyphenethene benzene as beige coloured fine needles. Rf 0.53 (2:1 hexane/EtOAc); mp 150-151° C.; 1H NMR (CDCl3): δ 2.28 (s, 3H, OAc), 6.99-7.10 (m, 4H), 7.21-7.26 (m, 1H), 7.30-7.36 (m, 2H), 7.46-7.50 (m, 4H); 1H NMR (CD3OD): δ 2.24 (s, 3H, OAc), 7.03-7.23 (m, 5H, J=13.5 Hz, Htrans), 7.28-7.34 (m, 2H), 7.49-7.57 (m, 4H); 13C JMOD NMR (CDCl3): δ 20.13 (OCOCH3), 120.81 (3,5), 125.55 (2′,6′), 126.44 (3′,5′), 126.72 (2×Ctrans), 127.72 (2,6), 127.99 (4′), 134.18 (1), 136.22 (1′), 149.13 (4′), 168.390 (OCOCH3); LRESI positive ion mass spectrum; m/z 261 (MNa+, 100%), 293 (MNa++MeOH, 95%).
A solution of potassium hydroxide in methanol was added to 4-acetoxyphenethene benzene dissolved in methanol. This reaction was heated under an argon atmosphere to 65° C. for 60 minutes. The solution was poured into water and then acidified to pH 4 with dilute HCl. Sodium chloride was added and the solution extracted with EtOAc. The organic layer was then separated, washed three times with water, then dried, filtered and rotary evaporated to return a pale pink coloured solid. This was purified with column chromatography (isocratically eluted with 2:1 hexane/EtOAc) to give 4-hydroxyphenethene benzene as a white solid. Rf 0.42 (2:1 hexane/EtOAc); mp: 189.6-190.0° C.; 1H NMR (CDCl3): δ 4.71 (s, 1H, OH), 6.79-6.82 (m, 2H, Jortho=8.7 Hz, H2, H6), 6.93 (d, 1H, Jtrans=16.4 Hz, Halkene), 7.02 (d, 1H, Jtrans=16.4 Hz, Halkene), 7.18-7.23 (m, 1H, H4′), 7.29-7.32 (m, 2H, H3′, H5′), 7.37-7.40 (m, 2H, H3, H5), 7.44-7.47 (m, 2H, H2′, H6′); LRESI negative ion mass spectrum; m/z 195 ([M−H]−, 100%), 196 (16%).
(E) 4-Acetoxyphenethene benzene and 10% Pd/C in methanol was hydrogenated overnight at 95 psi. Filtration through a Celite pad gave a clear filtrate that was rotary evaporated to a viscous oil. Gradient elution column chromatography (4:1 hexane/EtOAc to 2:1 hexane/EtOAc) gave 4-phenethyl-acetoxybenzene as a clear viscous oil. Rf 0.53 (2:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.26 (s, 3H, OAc), 2.89 (s, 4H, 2×CH2), 6.95-6.99 (m, 2H), 7.13-7.20 (m, 5H), 7.23-7.29 (m, 2H); 13C JMOD NMR (CDCl3): δ 20.15 (CH3), 36.35, 36.93 (2×CH2), 120.45 (2,6), 125.11 (4′), 127.48 (2′,6′), 127.56 (3′,5′), 128.46 (3,5), 138.37 (4), 140.64 (1′), 148.04 (1), 168.56 (C═O); LRESI positive ion mass spectrum; m/z 263 (MNa+, 100%), 264 (18%).
A solution of potassium hydroxide in methanol was added to 4-phenethyl-acetoxybenzene dissolved in methanol. This reaction was heated to 65° C. for 2 hours under an argon atmosphere. The clear solution was then poured into water, acidified to pH 2 with 1M HCl, and extracted with EtOAc. The organic layer was separated and washed three times with water, then dried, filtered and rotary evaporated to give a pale pink coloured solid. Purification by isocratic elution on column chromatography using 2:1 EtOAc/hexane gave 4-phenethyl-phenol as a white solid. Rf 0.55 (2:1 EtOAc/hexane); 1H NMR (CDCl3): δ 2.84 (s, 4H, 2×CH2), 6.69-6.74 (m, 2H, J=8.6 Hz, ArHortho), 6.99-7.04 (m, 2H, J=8.6 Hz, ArHortho), 7.12-7.19 (m, 3H), 7.22-7.28 (m, 2H); 13C JMOD NMR (CDCl3): δ 36.09, 37.24 (2×CH2), 114.29 (2,6), 124.99 (4′), 127.42 (2′,6′), 127.59 (3′,5′), 128.67 (3,5), 133.20 (4), 140.90 (1′), 152.55 (1); LRESI negative ion mass spectrum; m/z 197 ([M−H]−, 100%), 198 (16%).
A suspension of 3-hydroxybenzoic acid in ethyl acetate was cooled in an ice-bath. Acetic anhydride and pyridine were added and the reaction allowed proceeding for 60 minutes. The resultant homogenous solution was then stirred at room temperature overnight. Formic acid and further ethyl acetate were then added and the reaction poured onto ice-water. The organic phase was separated and washed six times with water, then dried, filtered and rotary evaporated to give a white solid. This solid was recrystallized from EtOAc/hexane (1:1) to produce 3-acetoxybenzoic acid as a white powder. Rf 0.46 (2:1 EtOAc/hexane); mp 133.0-133.5° C.; 1H NMR (CDCl3): δ 2.33 (s, 3H, OAc), 7.34-7.38 (m, 1H, H-4), 7.49 (t, 1H, Jortho=7.8 Hz, H-4), 7.84 (t, 1H, Jmeta=2.0 Hz, H-2), 8.00 (dt, 1H, H-6); 13C JMOD NMR (CDCl3): δ 20.00 (OC(O)CH3), 122.42 (2), 126.21 (4), 126.60 (6), 128.56 (5), 129.84 (1), 149.70 (3), 168.19 (COCH3), 170.27 (COOH); LRESI positive ion mass spectrum; m/z 203 (MNa+, 100%), 204 (11%).
A suspension of 3-acetoxybenzoic acid in dry toluene N,N-DMF and thionyl chloride was heated at 100° C. for three hours under an argon atmosphere. The solvents were removed by vacuum distillation to give a yellow oil. This material was dissolved in dry toluene and the solution was sonicated under vacuum for 30 minutes to remove dissolved gases. Styrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added and this mixture was heated at 120° C. for 22 hours under an argon gas atmosphere. The solution was cooled to room temperature and ethyl acetate was added. The solution was then washed three times with 0.1 M HCl and twice with water then dried, filtered and rotary evaporated to give a brown solid. Gradient elution column chromatography (9:1 hexane/EtOAc to 4:1 hexane/EtOAc) gave a white solid. This was recrystallized from 2:3 EtOAc/hexane (50 mL) to return (E)-3-acetoxystilbene as white fine needles. Rf 0.45 (hexane/EtOAc 9:1), 0.75 (hexane/EtOAc 4:1); mp 106.5-107.0° C.; 1H NMR (CDCl3): δ 2.30 (s, 3H, OAc), 6.94-7.00 (m, 1H, H-4), 7.04 (d, 1H, Jtrans=16.4 Hz, Halkene)9 7.08 (d, 1H, Halkene), 7.23-7.28 (m, 2H), 7.30-7.37 (m, 4), 7.45-7.50 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CDCl3): δ 20.16 (OC(O)CH3), 118.30 (4), 119.68 (2), 123.21 (6), 125.67 (2′,6′), 126.76, 126.92 (2×Calkene), 127.75 (3′,5′), 128.61 (4′), 128.84 (5), 136.05 (1), 138.11 (1′), 150.17 (3), 168.41 (C═O); LRESI positive ion mass spectrum; m/z 261 (MNa+, 100%), 293 ((MNa++MeOH, 74%); HRESI positive ion mass spectrum; C16H14O2Na+; calc. 239.1072.
A solution of potassium hydroxide in methanol was added to a suspension of 3-acetoxystilbene in methanol. This solution was heated to 70° C. for 2 hours under an argon atmosphere. The clear solution was then acidified to pH 4 with dilute hydrochloric acid. Water was added, and the volume reduced by rotary evaporation until the first appearance of a precipitate. Further water was added and the solution then extracted four times with EtOAc. The combined organic extracts were dried, filtered and rotary evaporated to give a pale yellow coloured solid. This was purified by gradient elution column chromatography (4:1 hexane/EtOAc to 2:1 hexane/EtOAc) to give (E)-3-hydroxystilbene as a white solid. Rf 0.36 (4:1 hexane/EtOAc), 0.74 (2:1 hexane/EtOAc); mp: 125.0-125.5° C., 1H NMR (CD3OD): δ 6.70-6.74 (m, 1H, H-4), 7.00-7.05 (m, 2H), 7.12 (s, 2H), 7.16-7.28 (m, 2H), 7.33-7.39 (m, 2H), 7.53-7.56 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CD3OD): δ 114.77 (2), 116.60 (4), 120.17 (6), 128.34 (2′,6′), 129.37, 130.45, 130.59 (2×Calkene, 4′), 130.50 (3′,5′), 131.49 (5), 139.61 (1′), 141.05 (1), 159.54 (3); LRESI negative ion mass spectrum; m/z 19504-Hr, 100%), 196 (16%), 391 ([2M−H]−);
HRESI negative ion mass spectrum; [M−H]− calc. 195.0810.
A mixture of (E)-3-acetoxtstilbene and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. Filtration through a Celite pad gave a solution which was rotary evaporated to return a grey coloured oil. This was purified by gradient elution column chromatography (9:1 EtOAc/hexane to 4:1 EtOAc/hexane) to return 2 major products comprising 3-phenethyl-acetoxybenzene as a white powder and 3-phenethyl phenol as a white solid.
Rf 0.32 (9:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.30 (s, 3H, OAc), 2.96 (s, 4H, 2×CH2), 6.94-6.98 (m, 2H), 7.05-7.08 (m, 1H), 7.19-7.25 (m, 3H), 7.27-7.34 (m, 3H).
Rf 0.16 (9:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.83-2.95 (m, 4H, 2×CH2), 4.84 (bs, 1H, OH), 6.64-6.68 (m, 2H), 6.75-6.78 (m, 1H), 7.12-7.31 (m, 6H).
A suspension of 3,5-dihydroxybenzoic acid in ethyl acetate was cooled in an ice-bath. Acetic anhydride and pyridine were added and the reaction allowed proceeding for 60 minutes. The homogenous solution was stirred overnight at room temperature. Formic acid was added and the solution then poured onto ice-water. Further ethyl acetate was added and the organic phase separated and successively washed twice each with sat. NaHCO3 and water, then dried, filtered and rotary evaporated to give a white solid. Recrystallization from EtOAc/hexane produced 3,5-diacetoxybenzoic acid as a white powder. Rf 0.20 (1:1 hexane/EtOAc), 0.39 (3:1 hexane/EtOAc); mp 161-162° C., lit mp: 157-159° C. Turner et al, Macromolecules, 1993, 26, 4617-4623; 1H NMR (CDCl3): δ 2.29 (s, 6H, 2×OAc), 7.18 (pseudo t, 1H, J=2.1 Hz, H4), 7.70 (pseudo d, 2H, J=2.1 Hz, H2, H6); 13C JMOD NMR (CD3OD): δ 18.43 (2×CH3), 118.94 (C4), 119.02 (C2,6), 131.70 (C1), 150.19 (C5), 165.46 (COOH), 168.17 (2×OCOCH3); LRESI positive ion mass spectrum; m/z 261 (MNa+, 100%).
3,5-Diacetoxybenzoic acid was suspended in dry toluene. N,N-DMF and thionyl chloride were added and the reaction heated under an argon atmosphere to 100° C. for 3 hours. The solvents were removed by vacuum distillation to give a pale yellow solid, which was suspended in dry toluene and sonicated under vacuum for 15 minutes. Styrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added and the reaction mixture heated overnight at 120° C. under an argon gas atmosphere. Upon cooling to room temperature, ethyl acetate was added and the solution washed successively three times with 0.1 M HCl and twice with water, then dried, filtered and rotary evaporated to give a brown solid. Purification with column chromatography (gradient elution starting with 6:1 hexane/EtOAc and finished with 2:1 hexane/EtOAc) produced (E)-5-styryl-1,3-phenylene diacetate as a white powder. Further recrystallisation from EtOAc/hexane produced the compound as white fine needles. Rf 0.44 (4:1 hexane/EtOAc); mp 90.0-90.5° C., 1H NMR (CDCl3): δ 2.31 (s, 6H, 2×OAc), 6.83 (pseudo t, 1H, J=2.1 Hz, H-4), 7.04 (d, 1H, J=16.3 Hz, Htrans), 7.09 (d, 1H, J=trans, 16.3 Hz, Htrans), 7.12-7.14 (m, 2H, H-2, H-6), 7.25-7.30 (m, 1H, H-4′), 7.34-7.39 (m, 2H, H-3′, H-5′), 7.47-7.50 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CDCl3): δ 20.09 (3×CH3), 113.32 (4), 115.89 (2,6), 125.73 (2′,6′), 125.98, 127.13 (2×Ctrans), 127.75 (3′,5′), 129.72 (4′), 135.69 (1′), 138.72 (1), 150.35 (3, 5), 167.93 (2×C═O); LRESI positive ion mass spectrum; m/z 319 (MNa+, 100%); HRESI positive ion mass spectrum; C18H16O4Na+; calc. 319.0946. measured 319.0943.
A solution of potassium hydroxide in methanol was added to (E)-5-styryl-1,3-phenylene diacetate suspended in methanol. The solution was heated under a nitrogen atmosphere to 70° C. for 100 minutes. Upon cooling to room temperature, the solution was acidified to pH 3 by addition of 1 M HCl. Water was added, and the volume reduced by rotary evaporation and stopped at the first appearance of a precipitate. Ethyl acetate was added and the organic layer was separated and washed four times with water until the aqueous washings were neutral. The organic material was then dried, filtered and rotary evaporated to give an orange oil. Purification by gradient elution column chromatography (2:1 hexane/EtOAc to 1:1 hexane/EtOAc) gave (E)-5-styrylbenzene-1,3-diol as a white solid. Rf 0.17 (hexane/EtOAc 4:1), 0.62 (hexane/EtOAc 1:1); mp 157.0-157.5° C., 1H NMR (CD3OD): δ 6.18 (pseudo t, 1H, J=2.2 Hz, H-4), 6.46 (d, 2H, J=2.2 Hz, H-2, H-6), 6.95 (d, 1H, J=16.3 Hz, Htrans), 7.01 (d, 1H, J=16.3 Hz, Htrans), 7.15-7.21 (m, 1H, H-4′), 7.26-7.32 (m, 2H, H-3′, H-5′), 7.44-7.48 (m, 2H, 2′,6′); 13C JMOD NMR (CD3OD): δ 100.91 (4), 103.92 (2,6), 125.13 (2′,6′), 126.19, 127.27, 127.48 (2×Ctrans, 4′), 127.31 (3′,5′), 136.32 (1′), 138.52 (1), 157.28 (3, 5); LRESI positive ion mass spectrum; m/z 213 (MH+, 100%), 214 (18%); HRESI positive ion mass spectrum; C14H12O2Na+; calc. 235.0735. measured 235.0729.
A mixture of (E)-5-styryl-1,3-phenylene diacetate and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. Filtration through a Celite pad gave a clear solution which was rotary evaporated to return a clear gum, which was subsequently subjected to gradient elution column chromatography (4:1 EtOAc/hexane to 2:1 EtOAc/hexane). This procedure resulted in two major products (i) 5-phenethyl-1,3-phenylene diacetate as a clear oil, that solidified on standing and (ii) 3-hydroxy-5-phenethylphenyl acetate as a clear viscous oil.
Rf 0.61 (2:1 hexane/EtOAc); mp 48.0-48.5° C., 1H NMR (CDCl3): δ 2.25 (s, 6H, 2×OAc), 2.90 (s, 4H, 2×CH2), 6.75 (pseudo t, 1H, J=2.1 Hz, H-4), 6.80 (pseudo d, 2H, J=2.1 Hz, H-2, H-6), 7.13-7.30 (m, 5H, H-2′, H-3′, H-4′, H-5′, H-6′); 13C JMOD NMR (CDCl3): δ 20.07 (OCOCH3), 36.26, 36.59 (2×CH2), 112.04 (4), 118.01 (2,6), 125.13 (4′), 127.43, 127.47 (2′,3′,5′,6′), 140.16 (1′), 143.21 (1), 150.04 (3,5), 167.99 (OCOCH3); LRESI positive ion mass spectrum; m/z 321 (MNa+, 100%), 322 (20%); HRESI positive ion mass spectrum; C18H18O4Na+; calc. 321.1103. measured 321.1095.
Rf 0.42 (2:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.25 (s, 3H, OAc), 2.79-2.91 (m, 4H, 2×CH2), 6.41 (pseudo t, 1H, J=2.2 Hz, H-4), 6.48 (pseudo d, 2H, J=2.3 Hz, H-2, H-6), 7.13-7.20 (m, 3H, H-2′, H-4′, H-6′), 7.23-7.29 (m, 2H, H-3′, H-5′); 13C JMOD NMR (CDCl3): δ 20.19 (OCOCH3), 36.26, 36.59 (2×CH2), 105.82 (2), 112.47 (4), 112.50 (6), 125.04 (4′), 127.42, 127.45 (2′,3′,5′,6′), 140.48 (1′), 143.61 (5), 150.32 (1), 155.66 (3), 169.43 (OCOCH3); LRESI positive ion mass spectrum; m/z 279 (MNa+, 100%), 280 (20%).
Potassium hydroxide dissolved in methanol was added to a solution of 5-phenethyl-1,3-phenylene diacetate in methanol and heated to 70° C. for 150 minutes under an argon atmosphere. Upon return to room temperature, the solution was acidified to pH 3 by addition of 1M HCl. Water was then added and the volume reduced by rotary evaporation. The solution was then extracted four times with ethyl acetate and the combined extracts dried, filtered and rotary evaporated to give a brown oil. Purification with column chromatography (gradient elution starting with 4:1 hexane/EtOAc and finishing with 2:1 hexane/EtOAc) gave 5-phenethylbenzene-1,3-diol as a clear oil. Rf 0.36 (2:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.75-2.81 (m, 2H, CH2), 2.84-2.90 (m, 2H, CH2), 4.70 (bs, 2H, 2×OH)), 6.17 (pseudo t, 1H, J=2.2 Hz, H-4), 6.22 (d, 2H, J=2.2 Hz, H-2, H-6), 7.13-7.19 (m, 3H, H-2′, H-4′, H-6′), 7.23-7.29 (m, 2H, H-3′, H-5′); 13C JMOD NMR (CDCl3): δ 36.25, 36.61 (2×CH2), 99.85 (4), 107.41 (2,6), 125.00 (4′), 127.41 (2′,6′), 127.49 (3′,5′), 140.72 (1′), 144.16 (1), 155.47 (3,5); LRESI negative ion mass spectrum m/z 213 ([M−H]−, 100%), 214 (14%), 427 ([2M−H]−, 13%).
A suspension of 3-acetoxybenzoic acid in dry toluene, N,N-DMF and thionyl chloride was heated to 100° C. under an argon atmosphere and maintained for 3 hours. The solvents were removed by vacuum distillation and the resultant solid redissolved in dry toluene, then this solution was sonicated under vacuum for 20 minutes. 4-Acetoxystyrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added and the mixture heated overnight at 120° C. under an argon gas atmosphere. Upon cooling to room temperature, ethyl acetate was added, which was subsequently washed three times with 0.1 M HCl and twice with water, then dried, filtered and rotary evaporated to give of a brown liquid. Purification by column chromatography (gradient elution starting with 4:1 hexane/EtOAc and finishing with 2:1 hexane/EtOAc) gave a white solid. 1H NMR showed this to be mostly (E)-3,4′-diacetoxystilbene and a small amount of unreacted 4-acetoxystyrene. Recrystallization from EtOAc/hexane gave (E)-3-(4-acetoxystyryl)phenyl acetate exclusively as white mica plates. Rf 0.32 (4:1 hexane/EtOAc), 0.59 (2:1 hexane/EtOAc); mp 124.5-125.0° C., 1H NMR (CDCl3): δ 2.28 (s, 3H, OAc), 2.29 (s, 3H, OAc), 6.93-7.09 (m, 5H, H-4, 2×Htrans, H-3′, H-5′), 7.21-7.22 (m, 1H, H-2), 7.30-7.34 (m, 2H, H-5, H-6), 7.45-7.50 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CDCl3): δ 20.11 (2×OC(O)CH3), 118.27 (4), 119.74 (2), 120.86 (3′,5′), 123.19 (6), 126.55 (2′,6′), 126.96, 127.76 (2×Ctrans), 128.61 (5), 133.79 (1′), 137.92 (1), 149.32 (4′), 150.15 (3), 168.35 (2×C═O).
A solution of potassium hydroxide in methanol was added to (E)-3-(4-acetoxystyryl)phenyl acetate suspended in methanol and heated to 70° C. for 100 minutes under an argon atmosphere. Upon cooling to room temperature, the solution was acidified to pH 3 by addition of 1M HCl. Water was then added and the volume reduced by rotary evaporation until the first appearance of a precipitate. Further water and ethyl acetate were added and the 2 phases separated. The organic phase was washed three times with water until the aqueous washings were neutral, then dried, filtered and rotary evaporated to return a cream coloured solid. Purification by column chromatography (gradient elution starting with 2:1 hexane/EtOAc and finishing with 1:1 hexane/EtOAc) gave (E)-3,4′-(ethene-1,2-diyl)diphenol as a cream coloured powder. Rf 0.35 (2:1 hexane/EtOAc); mp 213.0-213.5° C., 1H NMR (CD3OD): δ 6.60-6.63 (m, 1H, H-2), 6.74 (d, 2H, Jortho=8.7 Hz, H-3′, H-3′), 6.85 (d, 1H, J=16.3 Hz, Htrans), 6.89-6.94 (m, 2H, H-4, H-6), 6.98 (d, 1H, J=16.3 Hz, Htrans), 7.09 (pseudo t, 1H, Jortho=7.9 Hz, H-5), 7.33 (d, 2H, H-2′, H-6′); 13C JMOD NMR (CD3OD): δ 111.21 (2), 112.79 (4), 114.15 (3′,5′), 116.68 (6), 124.51 (5), 126.49 (2′,6′), 127.14 (Ctrans), 128.12 (1′), 128.22 (Ctrans), 138.35 (1), 155.90 (4′), 156.20 (3); LRESI negative ion mass spectrum; m/z 211 ([M−H]−, 100%), 212 (13%); HRESI positive ion mass spectrum; C14H12O2Na+; calc. 235.0735. measured 235.0730.
A mixture of (E)-3,4′-(ethene-1,2-diyl)diphenol and 10% Pd/C in methanol was hydrogenated overnight at 85 psi. Filtration through a Celite plug gave a clear solution which was rotary evaporated to return a clear viscous oil. This material was purified by isocratic elution from column chromatography with 2:1 hexane/EtOAc to give 3-(4-acetoxyphenylethyl)phenyl acetate as a clear viscous oil. This material slowly solidified upon standing overnight at room temperature. Rf 0.69 (2:1 hexane/EtOAc); mp 69.5-70.0° C., 1H NMR (CDCl3): δ 2.259 (s, 3H, OAc), 2.263 (s, 3H, OAc), 2.89 (s, 4H, 2×CH2), 6.88-6.92 (m, 2H, H-4, H-6), 6.94-7.02 (m, 3H, Jortho=8.6 Hz, H-2, H-3′, H-5′), 7.12-7.16 (m, 2H, H-2′, H-6′), 7.22-7.28 (m, 1H, H-5); 13C JMOD NMR (CDCl3): δ 20.07 (2×OCOCH3), 35.91, 36.55 (2×CH2), 118.23 (4), 120.38 (3′,5′), 120.96 (2), 124.99 (6), 128.30 (5), 128.38 (2′,6′), 137.96 (1′), 142.25 (1), 148.03 (4′), 149.85 (3), 168.43, 168.51 (2×OCOCH3); LRESI positive ion mass spectrum; m/z 321 (MNa+, 100%), 299 (MH+, 10%).
Potassium hydroxide dissolved in methanol was added to 3-(4-acetoxyphenylethyl)phenyl acetate suspended in methanol and heated to 80° C. under an argon atmosphere for 2 hours. Upon cooling to room temperature, the solution was acidified to pH 3 by addition of 1 M HCl. Water was then added and the volume reduced by rotary evaporation, The solution was then extracted four times with ethyl acetate and the combined extracts dried, filtered and rotary evaporated to give a viscous yellow oil. Purification by isocratic elution from column chromatography with 2:1 hexane/EtOAc) gave 3,4′-(ethane-1,2-diyl)diphenol as a white solid. Rf 0.41 (2:1 hexane/EtOAc); mp 108.0-108.5° C., 1H NMR (CDCl3): δ 2.84 (s, 4H, 2×CH2), 4.60 (s, 1H, OH), 4.65 (s, 1H, OH), 6.63-6.78 (m, 5H, H-2, H-4, H-6, H-3′, H-5′), 7.00-7.07 (m, 2H, H-2′, H-6′), 7.10-7.18 (m, 1H, H-5); 1H NMR (CD3OD): δ 2.79 (s, 4H, 2×CH2), 6.58-6.73 (m, 5H, H-2, H-4, H-6, H-3′, H-5′), 6.97-7.02 (m, 2H, H-2′, H-6′), 7.15-7.10 (m, 1H, H-5); 13C JMOD NMR (CD3OD): δ 34.19, 35.45 (2×CH2), 109.81 (4), 112.13 (3′,5′), 112.52 (2), 117.17 (5), 126.38 (6), 126.56 (2′,6′), 130.24 (1′), 140.94 (1), 152.24 (4′), 154.13 (3); LRESI negative ion mass spectrum m/z 213 ([M−H]−, 100%), 427 ([2M−H]−, 66%)
3,5-Dimethylbenzoic acid was suspended in dry toluene. N,N-DMF and thionyl chloride were added and the reaction heated at 100° C. under an argon atmosphere for 3 hours. After cooling to room temperature the solvents were removed by vacuum distillation. The residual yellow oil was dissolved in dry toluene and the solution sonicated under vacuum. 4-Acetoxystyrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added and the mixture heated overnight at 120° C. under an argon atmosphere. Upon cooling to room temperature, ethyl acetate was added and the solution washed successively three times with 0.1 M HCl and twice with water, then dried, filtered and rotary evaporated to give a brown oil. Purification by gradient elution column chromatography (9:1 hexane/EtOAc to 7:1 hexane/EtOAc) gave 4-acetoxystyrene as a major product and a cream coloured solid as a secondary product. This solid was subsequently triturated with hexane to give (E)-4-(3,5-dimethylstyryl)phenyl acetate as a white solid. Recrystallization of this product from hexane produced translucent fine needles. Rf 0.34 (9:1 hexane/EtOAc), 0.59 (2:1 hexane/EtOAc); mp 84.9-85.0° C., 1H NMR (CDCl3): δ 2.28 (s, 3H, OAc), 2.31 (s, 6H, 2×CH3), 6.89 (bs, 1H, H4), 6.97 (d, 1H, J=16.4 Hz, Htrans), 7.02-7.07 (m, 3H, H3′, H5′, Htrans), 7.10 (bs, 2H, 2,6), 7.45-7.50 (m, 2H, Jortho=8.7 Hz, H2′, H6′); 13C JMOD NMR (CDCl3): δ 20.12 (OCOCH3), 20.32 (2×CH3), 120.79 (3′,5′), 123.49 (2,6), 128.20, 128.55 (4, 2×Calkene), 134.38 ((1′), 136.14 (1), 137.14 (3,5), 149.02 (4′), 168.40 (3×C═O); LRESI positive ion mass spectrum; m/z 555 (2M+Na+, 14%), 321 (MNa++MeOH, 53%), 289 (MNa+, 100%), 267 (MH+, 12%).
A solution of potassium hydroxide in methanol was added to (E)-4-(3,5-dimethylstyryl)phenyl acetate dissolved in methanol and heated to 65° C. under a nitrogen atmosphere for 2 hours. The solution was then poured onto ice-water, then acidified to pH 3 with 1 M HCl. Sodium chloride was added and the solution then extracted three times with ethyl acetate. The combined extracts were dried, filtered and rotary evaporated to give a yellow solid. Purification by flash chromatography (gradient elution starting with 9:1 hexane/EtOAc and finishing with 4:1 hexane/EtOAc) gave (E)-4-(3,5-dimethylstyryl)phenol as a white amorphous powder. Rf 0.29 (4:1 hexane/EtOAc); mp: 142.0-142.2° C., 1H NMR (CDCl3): δ 2.31 (s, 6H, 2×CH3), 4.66 (s, 1H, OH), 6.77-6.81 (m, 2H, Jortho=8.7 Hz, 3′,5′), 6.86 (bs, 1H, 4), 6.88 (d, 1H, Ttrans=16.1 Hz, alkene), 7.00 (d, 1H, alkene), 7.08 (s, 2H, 2,6), 7.34-7.39 (m, 2H, 2′,6′); 13C JMOD NMR (CDCl3): δ 19.25 (2×CH3), 114.22 (3′,5′), 122.82 (2,6), 124.88 (Calkene), 126.55 (2′,6′), 126.72 (Calkene), 127.43 (4), 128.39 (1′), 136.58 (3,5), 136.66 (1), 155.74 (4′); LRESI negative ion mass spectrum; m/z 223 ([M−H]−, 100%), 224 (18%); HRESI negative ion mass spectrum; m/z [M−H]− calc. 223.1123. measured 223.1126.
A mixture of (E)-4-(3,5-dimethylstyryl)phenyl acetate and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. Filtration through a Celite pad gave a clear solution which was rotary evaporated to a viscous oil. Purification by gradient elution column chromatography (9:1 EtOAc/hexane to 4:1 EtOAc/hexane) gave 4-(3,5-dimethylphenethyl)phenyl-acetate as a clear viscous oil. Rf 0.64 (2:1 hexane/EtOAc), 0.32 (4:1 hexane/EtOAc), 0.18 (9:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.267, 2.270, 2.271 (3×s, 9H, 2×CH3, OAc), 2.77-2.90 (m, 4H, 2×CH2), 6.79 (bs, 2H, 2,6), 6.82 (bs, 1H, 4), 6.95-7.00 (m, 2H, Jortho=8.6 Hz, 2′,6′), 7.14-7.19 (m, 2H, 3′,5′); 13C JMOD NMR (CDCl3): δ 20.13 (OCOCH3), 20.40 (2×CH3), 36.52, 36.92 (2×CH2), 120.47 (3′,5′), 125.44 (2, 6), 126.78 (4), 136.89 (3,5), 138.65 (1′), 140.64 (1), 148.06 (4′), 168.57 (OCOCH3); LRESI positive ion mass spectrum; m/z 291 (MNa+, 100%), 292 (20%), 269 (MH+, 5%).
A solution of potassium hydroxide in methanol was added to 4-(3,5-dimethylphenethyl)phenyl-acetate dissolved in methanol and heated for 3 hours at 65° C. under an argon atmosphere. The volume was reduced by rotary evaporation and the concentrated solution was poured into water, then acidified to pH 3 with 1M HCl and extracted three times with EtOAc. The combined extracts were then dried, filtered and rotary evaporated to give a clear viscous oil. Purification by column chromatography (gradient elution starting with 9:1 hexane/EtOAc and finishing with 4:1 hexane/EtOAc) gave 4-(3,5-dimethylphenethyl)phenol as a clear viscous oil. Rf 0.71 (2:1 EtOAc/hexane), 0.59 (2:1 hexane/EtOAc), 0.39 (4:1 hexane/EtOAc); 1H NMR (CD3OD): δ 2.28 (s, 4H, 2×CH3), 2.78-2.84 (m, 1H, 2×CH2), 4.59 (bs, 1H, OH), 6.71-6.76 (m, 2H, Tortho=8.5 Hz, 2,6), 6.80 (bs, 2H, 2′,5′), 6.82 (bs, 1H, 4′), 7.03-7.07 (m, 2H, 3,5); 13C JMOD NMR (CDCl3): δ 20.57 (2×CH3), 36.42, 37.36 (2×Calkene), 114.64 (3,5), 125.65 (2′,6′), 126.88 (4′), 128.86 (2,6), 133.72 (1), 137.06 (3′,5′), 141.14 (1′), 152.67 (4); LRESI negative ion mass spectrum; m/z 225 ([M−H]−, 100%), 226 (17%); HRESI positive ion mass spectrum; m/z MH+ calc. 227.1436. measured 227.1438.
A suspension of 3,5-diacetoxybenzoic acid in dry toluene, N,N-DMF and thionyl chloride was heated at 100° C. for three hours under a nitrogen atmosphere. The solvents were removed by vacuum distillation and the remaining viscous liquid treated with hexane to precipitate a yellow solid. Hexane was removed by rotary evaporation to give a pale yellow powder. This compound was immediately on-reacted. Rf 0.88 (2:1 EtOAc/hexane). Rf 0.88 (2:1 EtOAc/hexane).
3,5-diacetoxybenzoyl chloride, 4-acetoxystyrene, N-ethylmorpholine and palladium diacetate (0.45 mole %) were dissolved in dry toluene (20 mL) and heated overnight at 120° C. under a nitrogen atmosphere. Upon cooling to room temperature, ethyl acetate was added and the reaction washed twice each with 0.1 M HCl and water, then dried, filtered and rotary evaporated to give a brown solid. Purification by isocratic elution from column chromatography with 1:1 hexane/Et2O gave a white solid. This material was purified by gradient elution chromatography (4:1 hexane/EtOAc to 2:1 hexane/EtOAc) to give E-5-(4-acetoxystyryl)-1,3-phenylene diacetate as a white solid. Rf 0.29 (2:1 hexane/EtOAc); mp 112.5-113.0° C., 1H NMR (CDCl3): δ 2.27 (s, 9H, 3×OAc), 6.80 (pseudo t, 1H, J=2.1 Hz, 4′), 6.93 (d, 1H, J=16.3 Hz, Htrans), 7.03 (d, 1H, J=16.3 Hz, Htrans), 7.04-7.09 (m, 4H, 3,5,2′,6′), 7.44-7.47 (m, 2H, 2,6); 13C JMOD NMR (CDCl3): δ 20.07 (3×CH3), 113.39 (4′), 115.88 (2′,6′), 120.88 (3,5), 126.19, 126.64, 128.64 (2×Ctrans, 2, 6), 133.45 (1), 138.53 (1′), 149.46 (4), 150.34 (3′,5′), 167.91, 168.30 (3×C═O); LRESI positive ion mass spectrum; m/z 377 (MNa+, 100%), 378 (21%).
A mixture of 3,5-diacetoxybenzoic acid, N,N-DMF and thionyl chloride in dry toluene was heated to 100° C. under an argon atmosphere for 3 hours. The solvents were removed by vacuum distillation and the solid white residue subsequently suspended in dry toluene and sonicated under vacuum. 4-acetoxystyrene, N-ethylmorpholine and palladium diacetate (2.0 mole %) were added and this mixture was heated overnight at 120° C. Upon cooling to room temperature, ethyl acetate was added and the solution washed three times with 0.1 M HCl, then, dried, filtered and rotary evaporated to give a brown solid. Purification by gradient elution column chromatography (2:1 hexane/EtOAc to 100% EtOAc) gave (E)-5-(4-acetoxystyryl)-1,3-phenylene diacetate as a white solid. Rf 0.29 (2:1 hexane/EtOAc); mp 112.5-113.0° C., 1H NMR (CDCl3): δ 2.27 (s, 9H, 3×OAc), 6.80 (pseudo t, 1H, J=2.1 Hz, 4′), 6.93 (d, 1H, J=16.3 Hz, Htrans), 7.03 (d, 1H, J=16.3 Hz, Htrans), 7.04-7.09 (m, 4H, 3,5,2′,6′), 7.44-7.47 (m, 2H, 2,6); 13C JMOD NMR (CDCl3): δ 20.07 (3×CH3), 113.39 (4′), 115.88 (2′,6′), 120.88 (3,5), 126.19, 126.64, 128.64 (2×Ctrans, 2, 6), 133.45 (1), 138.53 (1′), 149.46 (4), 150.34 (3′,5′), 167.91, 168.30 (3×C═O); LRESI positive ion mass spectrum; m/z 377 (MNa+, 100%), 378 (21%).
3,5-diacetoxybenzoyl chloride, 4-acetoxystyrene, N-ethylmorpholine and palladium diacetate (0.45 mole %) were dissolved in dry toluene and heated overnight at 120° C. under a nitrogen atmosphere. Upon cooling to room temperature, ethyl acetate was added and the reaction washed twice with 0.1 M HCl, then water and dried, filtered and rotary evaporated to a brown solid. Purification by isocratic elution from column chromatography (1:1 hexane/Et2O) gave a white solid. This material was purified by gradient elution chromatography (4:1 hexane/EtOAc to 2:1 hexane/EtOAc) to give (E)-5-(4-acetoxystyryl)-1,3-phenylene diacetate as a white solid. Rf 0.29 (2:1 hexane/EtOAc); mp 112.5-113.0° C., 1H NMR (CDCl3): δ 2.27 (s, 9H, 3×OAc), 6.80 (pseudo t, 1H, J=2.1 Hz, 4′), 6.93 (d, 1H, J=16.3 Hz, Htrans), 7.03 (d, 1H, J=16.3 Hz, Htrans), 7.04-7.09 (m, 4H, 3,5,2′,6′), 7.44-7.47 (m, 2H, 2,6); 13C JMOD NMR (CDCl3): δ 20.07 (3×CH3), 113.39 (4′), 115.88 (2′,6% 120.88 (3,5), 126.19, 126.64, 128.64 (2×Ctrans, 2, 6), 133.45 (1), 138.53 (1′), 149.46 (4), 150.34 (3′,5′), 167.91, 168.30 (3×C═O); LRESI positive ion mass spectrum; m/z 377 (MNa+, 100%), 378 (21%).
Potassium hydroxide dissolved in methanol was added to (E)-5-(4-acetoxystyryl)-1,3-phenylene diacetate suspended in methanol and heated to 65° C. under a nitrogen atmosphere for 1 hour. The volume was reduced by rotary evaporation and the solution then acidified to pH 3 with 1 M HCl. Ethyl acetate was added and the solution then washed three times with saturated brine, then dried, filtered and rotary evaporated to give a dark red solid. Purification by isocratic elution from column chromatography (0,040-0,063 mm SiO2) with EtOAc gave (E)-5-(4-hydroxystyryl)benzene-1,3-diol as a pale beige coloured solid. Rf 0.65 (EtOAc); 1H NMR (CD3OD): δ 6.13 (pseudo t, 1H, J=2.2 Hz, 4), 6.41-6.42 (m, 2H, 2,6), 6.71-6.79 (m, 3H, Htrans, 3%5% 6.93 (d, 1H, J=16.3 Hz, Htrans), 7.29-7.36 (m, 2H, Jortho=8.6 Hz, 2′,6′). 13C JMOD NMR (CD3OD): δ. LRESI positive ion mass spectrum; m/z 229 (MH+, 100%), 230 (23%).
A mixture of (E)-4-(3,5-diacetoxyphenethylene)-acetoxybenzene and 10% Pd/C in methanol was hydrogenated overnight at 95 psi. Filtration through a Celite pad gave a clear solution which was rotary evaporated to give a viscous oil. Purification by isocratic elution from column chromatography (0,040-0,063 mm SiO2) with 2:1 EtOAc/hexane) gave 4-(3,5-diacetoxyphenethyl)-acetoxybenzene as a clear viscous oil, which solidified to a white solid after standing at room temperature. Rf 0.68 (2:1 EtOAc/hexane), 0.52 (2:1 Et2O/hexane); mp 52.0-52.5° C., 1H NMR (CDCl3): δ 2.25 (s, 6H, 2×OAc), 2.26 (s, 3H, OAc), 2.88 (s, 4H, 2×CH2), 6.75-6.77 (m, 3H), 6.95-6.98 (m, 2H, Jortho=8.4 Hz, ArH), 7.12-7.14 (m, 2H, ArH); 13C JMOD NMR (CDCl3): δ 20.03 (3×CH3), 35.57, 36.47 (2×CH2), 112.08 (4′), 118.00 (3,5), 120.46 (2′,6′), 128.33 (2, 6), 137.64 (1), 142.91 (1′), 148.02 (4), 150.01 (3′,5′), 167.98, 168.53 (3×C═O); LRESI positive ion mass spectrum; m/z 379 (MNa+, 100%), 380 (21%).
A solution of potassium hydroxide in methanol was added to 4-(3,5-diacetoxyphenethyl)-acetoxybenzene in methanol then heated to 65° C. for 30 minutes under an argon atmosphere. The solution was then poured into water, acidified to pH 4 with 1 M HCl. NaCl was added and the solution extracted with EtOAc. The organic layer was separated and washed twice with saturated brine, then dried over anhydrous Na2SO4, filtered and rotary evaporated to give an orange solid. Purification by isocratic elution from column chromatography (0,040-0,063 mm SiO2) with 2:1 EtOAc/hexane gave 4-(3,5-diahydroxyphenethyl)-phenol as a white solid. Rf 0.44 (2:1 EtOAc/hexane); Mp: 160.5-161.0° C., 1H NMR (CD3OD): δ 2.61-2.75 (m, 4H, 2×CH2), 6.05 (pseudo t, 1H, J=2.2 Hz, 4′), 6.09-6.10 (m, 2H, 2′,6′), 6.61-6.66 (m, 2H, Jortho8.6 Hz, 3,5), 6.91-6.96 (m, 2H, 2,6); 13C JMOD NMR (CD3OD): δ 35.56, 37.08 (2×CH2), 98.81 (4′), 105.82 (2′,6′), 113.66 (3,5), 128.01 (2, 6), 131.82 (1), 143.33 (1′), 153.85 (4), 156.80 (3′,5′); LRESI positive ion mass spectrum; m/z 231 (MH+, 100%), 232 (12%), 253 (MNa+, 11%); HRESI positive ion mass spectrum; MH+ calc. 231.1021. measured 231.1014.
3,5-Dinitrobenzoyl chloride, 4-acetoxystyrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added to dry toluene and heated overnight at 120° C. under an argon gas atmosphere. Upon cooling to room temperature, ethyl acetate was added and the solution washed four times with 0.1M HCl and twice with water. The organic layer was then dried over anhydrous Na2SO4, filtered and rotary evaporated to give a dark brown solid. This material was suspended in CH2Cl2 and silica added before removing the solvent by rotary evaporation. The remaining powder was then loaded as a narrow band onto a column and purified by isocratic elution chromatography (0.040-0,063 mm SiO2) with CH2Cl2 to give (E)-4-(3,5-dinitrostyryl)phenyl acetate as a bright yellow solid. Rf 0.42 (CH2Cl2); mp, 217.5-218.0° C., 1H NMR (CDCl3): δ 2.30 (s, 3H, OAC), 7.08-7.17 (m, 3H, H3′, H5′), 7.32 (d, 1H, Jtran=16.3 Hz, Halkene), 7.54-7.58 (m, 2H, Jortho=8.5 Hz, H2′, H6′), 8.60-8.61 (m, 2H, Jmeta=2.0 Hz, H2, H6), 8.87 (pseudo t, 1H, H4); 13C JMOD NMR (CDCl3): δ 20.31 (CH3), 115.92 (4); 121.75 (3′,5′), 124.22 (Calkene), 125.48 (2,6), 127.66 (2′,6′), 132.42 (Calkene), 133.15 (1′), 140.39 (1), 148.05 (3,5), 150.28 (4′), 168.55 (CO); EI MS: m/z 328 (M+, 6%), 286 (100%), 147 (30%).
A solution of potassium hydroxide in methanol was added to (E)-4-(3,5-dinitrostyryl)phenyl acetate suspended in methanol and heated to 65° C. under an argon atmosphere for 2 hours. The reaction solution volume was halved by rotary evaporation, then poured onto ice-water and then acidified to pH 3 with 1M HCl. The resultant bright yellow solid was then extracted with ethyl acetate and the organic layer was removed and washed three times with water. The extract was dried over anhydrous Na2SO4, then filtered and rotary evaporated to give a bright orange solid. Purification by gradient elution chromatography (absolute CH2Cl2 to 9:1 CH2Cl2/MeOH) gave (E)-4-(3,5-dinitrostyryl)phenol as a bright orange powder. Rf 0.31 (CH2Cl2); 1H NMR (CD3OD): δ 6.79 (m, 2H, Jortho=8.5 Hz, H3′, H5′), 7.16 (d, 1H, Jtran=16.2 Hz, Halkene), 7.40-7.49 (m, 3H, Halkene, H2′, H6′), 8.67-8.69 (m, 2H, H2, H6), 8.73 (m, 1H, H4); 13C JMOD NMR (CD3OD): δ. ESI MS: m/z 286 (100%), 147 (53%).
A mixture of 3,5-dihydroxybenzaldehyde, 4-aminophenol and anhydrous sodium sulphate in dichloromethane was vigorously stirred at room temperature for 3 hours. Further anhydrous sodium sulphate was added and stirring continued for 1 hour. Dichloromethane was removed by rotary evaporation. The remaining white powder was resuspended in boiling ethanol, then removed by vacuum filtration. The recovered solid was rinsed with further boiling ethanol. The clear filtrates were combined and rotary evaporated to dryness to give (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol as a pale pink solid. Lit (WO 2006/108864 A2) 162° C. (dec); 1H NMR (d6-DMSO): δ 6.36 (pseudo t, 1H, J=2.2 Hz, H-4), 6.80-6.85 (m, 4H, H-2, H-6, H-3′, H-5′), 7.16-7.22 (m, 2H, Jortho=8.8 Hz, H-2′, H-6′), 8.43 (s, 1H, imine-H), 9.47 (bs, 3H, 3×phenolic-OH); 13C JMOD NMR (d6-DMSO): δ 106.27 (4), 107.41 (2,6), 116.70 (3′,5′), 123.42 (2′,6′), 139.35 (1), 143.61 (1′), 157.16 (4′), 158.38 (imine-C), 159.62 (3,5); LRESI positive ion mass spectrum; m/z 230 (MH+, 100%), 231 (13%); HRESI positive ion mass spectrum; C13H11NO3Na+; calc. 252.0637. measured 252.0633.
A suspension of 3,4,5-trihydroxybenzoic acid in ethyl acetate was cooled in an ice-bath, then acetic anhydride and pyridine were added. The reaction was allowed to proceed for 45 minutes and then the solution was then heated to reflux for 3 hours. Further acetic anhydride was then added and the solution stirred overnight at room temperature. Formic acid was added and the solution poured onto ice-water. The organic layer was removed, then washed four times with sat. NaHCO3 and twice with water, dried, filtered and rotary evaporated to give a white solid. Recrystallization from 1:1 EtOAc/hexane gave 3,4,5-triacetoxybenzoic acid as a white powder. Rf 0.47 (EtOAc); mp 167.5-168.0° C., 1H NMR (CDCl3): δ 2.279 (s, 6H, 2×OAc), 2.284 (s, 3H, OAc), 7.84 (s, 2H, arom); 13C JMOD NMR (CDCl3): δ. LRESI positive ion mass spectrum; m/z 319 (M+Na+, 100%), negative ion mass spectrum; m/z 295 ([M−H]−, 100%).
3,4,5-Triacetoxybenzoic acid was suspended in dry toluene. N,N-DMF and thionyl chloride were added and the reaction heated to 100° C. for 3 hours under an argon atmosphere. Solvents were removed by vacuum distillation to give a pale yellow solid. This acid chloride was suspended in dry toluene and the mixture sonicated under vacuum for 30 minutes. 4-Acetoxystyrene, N-ethylmorpholine and palladium diacetate (2 mole %) were added and the mixture heated overnight at 120° C. under an argon atmosphere. Upon cooling to room temperature, ethyl acetate was added and the solution washed successively once with water, three times with 0.1 M HCl, and again with water, then dried, filtered and rotary evaporated to give a dark brown viscous oil. Purification by gradient elution column chromatography (absolute hexane to absolute EtOAc) separated and recovered 4-acetoxystyrene and (E)-3,4,5,4′-tetra acetoxystilbene. Recrystallisation of (E)-3,4,5,4′-tetra acetoxystilbene from hexane:ethyl acetate (3:2) gave (E)-3,4,5,4′-tetra acetoxystilbene as fine white needles. Rf 0.49 (1:1 hexane/EtOAc), 0.23 (2:1 hexane/EtOAc); mp 162.5-163.0° C., 1H NMR (CDCl3): δ 2.26 (s, 3H, OAc), 2.27 (s, 6H, 2×OAc), 2.28 (s, 3H, OAc), 6.91 (d, 1H, J=16.2 Hz, Htrans), 6.99 (d, 1H, Htrans), 7.04-7.08 (m, 2H, Jortho=8.6 Hz, Jmeta=1.9 Hz, H-3′, H-5′), 7.20 (bs, 2H, H-2, H-6), 7.42-7.47 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CDCl3): δ 19.12, 19.62, 20.08 (OCOCH3), 117.45 (2,6), 120.87 (3′,5′), 125.65 (Calkene), 126.64 (2′,6′), 128.70 (Calkene), 132.76 (1), 133.39 (4), 134.89 ((1′), 142.61 (3,5), 149.47 (4′), 165.99, 166.82, 168.30 (OCOCH3); LRESI positive ion mass spectrum; m/z 435 (MNa+, 100%); HRESI positive ion mass spectrum; calculated for m/z C22H20O8Na+, 435.1056. measured 435.1061.
A solution of p-toluene sulphonic acid monohydrate (4 mg, 0.021 mmol) in methanol (1.0 mL) was added to (E)-3,4,5,4′-tetraacetoxystilbene (150 mg, 0.3623 mmol) suspended in methanol (9 mL). The reaction was heated to reflux for 4 hours under an argon atmosphere. The solvent was removed by rotary evaporation and the remaining pink solid then triturated with hexane. The solid was filtered off and air dried to give a pink coloured powder. Purification by gradient elution column chromatography (2:1 EtOAc/hexane to absolute EtOAc) gave (E)-3,4,5,4′-tertahydroxystilbene as a pale yellow powder. Rf 0.34 (2:1 EtOAc/hexane); 1H NMR (CD3OD): δ 6.50 (bs, 2H, H-2, H-6), 6.70 (d, 1H, Jtrans=16.2 Hz, Halkene), 6.69-6.76 (m, 2H, Jortho=8.7 Hz, H-3′, H-5′), 6.77 (d, 1H, Halkene), 7.25-7.30 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CD3OD): δ 104.12 (2,6), 114.07 (3′,5′), 124.55, 124.90 (2×Calkene), 126.01 (2′,6′), 128.45 (1′), 128.56 (1), 131.62 (4), 144.63 (3, 5), 155.42 (4′); LRESI negative ion mass spectrum; m/z 243 ([M−H]−, 100%), 244 (17%).
A mixture of (E)-3,4,5,4′-tetraacetoxystilbene and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. The solution was filtered through a Celite pad, then rotary evaporated to a grey oil. This oil was then dissolved in ethyl acetate, then cooled in an ice-bath before addition of acetic anhydride and pyridine. The reaction was allowed to proceed for 60 minutes before addition of further acetic anhydride and subsequent heating at 80° C. for 3 hours. This mixture was then stirred at room temperature overnight. The reaction solution was then poured onto ice-water, and extracted with ethyl acetate. The organic layer was subsequently removed, washed four times with water, then dried, filtered and rotary evaporated to give an orange oil. This oil was purified by gradient elution chromatographically (4:1 hexane/EtOAc to 1:1 hexane/EtOAc) to give 5-(4-acetoxy phenethyl)benzene-1,2,3-triyltriacetate as a white powder. Rf 0.36 (1:1 hexane/EtOAc); mp 121.5-122.0° C., 1H NMR (CDCl3): δ 2.24 (s, 6H, 2×OAc), 2.25 (s, 3H, OAc), 2.26 (s, 3H, OAc), 2.87 (bs, 4H, 2×CH2), 6.89 (bs, 2H, H-2, H-6), 6.95-6.99 (m, 2H, Jortho=8.4 Hz, Jmeta=2.0 Hz, H-3′, H-5′), 7.11-7.16 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CDCl3): δ 19.11, 19.59, 20.06 (4×OCOCH3), 35.54, 36.23 (2×CH2), 119.56 (2,6), 120.49 (3′,5% 128.32 (2′,6′), 131.72 (4), 137.54 (1′), 139.02 (1), 142.19 (3, 5), 148.04 (4′), 166.08, 166.86, 168.51 (4×OCOCH3); LRESI positive ion mass spectrum; m/z 437 (MNa+, 100%), 438 (22%); HRESI positive ion mass spectrum; C22H22O8Na+; calc. 437.1212. measured 437.1196.
A solution of p-toluene sulphonic acid monohydrate in methanol was added to a suspension of 1-(3,4,5-tri-O-acetylphenethyl)-4-O-acetylbenzene in methanol. The reaction was heated to 85° C. overnight under an argon gas atmosphere. The solvent was removed by rotary evaporation and the oil purified with column chromatography (isocratically eluted with 2:1 EtOAc/hexane) to return 5-(4-hydroxyphenethyl)benzene-1,2,3-triol as a white solid. Rf 0.55 (2:1 EtOAc/hexane); mp 180.0-188.5° C., 1H NMR (CD3OD): δ 2.55-2.61 (m, 2H, CH2), 2.66-2.72 (m, 2H, CH2), 6.13 (bs, 2H, H-2, H-6), 6.61-6.65 (m, 2H, Jortho=8.5 Hz, H-3′, H-5′), 6.90-6.93 (m, 2H, H-2′, H-6′); 13C JMOD NMR (CD3OD): δ 39.03 (CH2), 39.75 (CH2), 109.36 (2,6), 116.74 (3′,5′), 131.14 (2′,6′), 132.74 (4), 135.11 (1′), 131.37 (1), 147.43 (3,5), 156.83 (4′); LRESI negative ion mass spectrum; m/z 245 ([M−H]−, 100%), 246 (18%); HRESI negative ion mass spectrum; calculated m/z for C14H14O4—H− 245.0814. measured 245.0814.
The reaction was conducted under an argon gas atmosphere. Diisopropylethylamine was added to a solution of 3,5-dihydroxybenzaldehyde dissolved in dried N,N-DMF. After The solution was well agitated at room temperature for 20 minutes and then tert-butyldimethylsilylchloride dissolved in dry N,N-DMF was added drop-wise over 15 minutes and the mixture stirred at room temperature overnight. The reaction was then poured into ice-water, extracted with dichloromethane, and the combined extracts dried (anhyd. Na2SO4) and rotary evaporated to return a brown oil. Purification with column chromatography (gradient eluted beginning with hexane (100%) and finishing with 9:1 hexane/EtOAc) 3,5-di(tert-butyldimethylsilyloxy)benzaldehyde as a clear oil. Rf 0.80 (4:1 hexane/EtOAc), 0.50 (19:1 hexane/EtOAc); 1H NMR (CDCl3): δ 0.22 (s, 12H, 2×Si(CH3)2), 0.99 (s, 18H, 2×SiC(CH3)3), 6.59 (pseudo t, 1H, J=2.3 Hz, H4), 6.96 (pseudo d, 2H, J=2.3 Hz, H2, H6), 9.86 (s, 1H, CHO); 13C JMOD NMR (CDCl3): δ −4.15 (SiCH3). 18.46 (C(CH3)3), 25.90 (C(CH3)3), 114.61 (2,6), 118.59 (4), 138.73 (1), 157.55 (3,5), 191.80 (CHO).
The reactions were conducted under an argon gas atmosphere. Methylenetriphenylphosphorane was first generated in situ by heating to reflux a mixture of methyltriphenylphosphonium bromide (34.787 g, 97.443 mmol, Aldrich Chem. Co.) and potassium tert-butoxide (9.010 g, 73.856 mmol, Aldrich Chem. Co.) in anhydrous THF. On return to room temperature, a solution of 3,5-di(tert-butyldimethylsilyloxy)benzaldehyde in anhydrous THF was added drop wise and the reaction heated to reflux overnight. Ethyl acetate (600 mL) was then added and the solution washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to a brown oil. Purification with column chromatography (gradient eluted beginning with hexane (100%) and finishing with 7:1 hexane/EtOAc) gave (5-vinyl-1,3-phenylene)bis(oxy)bis(tert-butyldimethylsilane) as a pale yellow oil; Rf 0.44 (50:1 hexane/EtOAc), 0.75 (25:1 hexane/EtOAc); 1H NMR (CDCl3): δ 0.21 (s, 12H, 2×Si(CH3)2), 0.99 (s, 18H, 2×SiC(CH3)3), 5.02 (dd, 1H, J=12.8 Hz, J=1.5 Hz, Halk), 5.66 (dd, 1H, J=13.2 Hz, J=0.7 Hz, Halk), 6.59 (pseudo t, 1H, J=1.6 Hz, H2), 6.96 (pseudo d, 2H, J=1.6 Hz, H4, H6), 6.58 (dd, 1H, Halk); 13C JMOD NMR (CDCl3): δ −8.03 (SiCH3). 18.56 (C(CH3)3), 26.06 (C(CH3)3), 111.80 (4,6), 112.02 (2), 114.20 (═CH2), 137.12 (CH═), 139.78 (5), 156.97 (1,3); LRESI positive ion mass spectrum; m/z 365 (MH+, 100%), 366 (37).
The reaction was conducted under an argon gas atmosphere. Tetrabutylammonium fluoride dissolved in THF was added over 15 minutes to (5-vinyl-1,3-phenylene)bis(oxy)bis(tert-butyldimethylsilane) in anhydrous THF, and the reaction left at room temperature for 90 minutes. The volume was then reduced by rotary evaporation and the volume replaced with ethyl acetate. The solution was then washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to a brown oil. Purification with column chromatography (isocratically eluted with 1:1 hexane/EtOAc) gave a viscous pale yellow oil. Further column chromatography (gradient eluted beginning with 4:1 hexane/EtOAc and finishing with 1:1 hexane/EtOAc) returned 5-vinylbenzene-1,3-diol as a pale yellow oil; Rf 0.58 (1:1 hexane/EtOAc), 0.76 (1:2 hexane/EtOAc); 1H NMR (CD3OD): δ 5.16 (dd, 1H, J=10.8 Hz, J=1.1 Hz, Halk), 5.66 (dd, 1H, J=17.6 Hz, J=1.2 Hz, Halk), 6.22 (pseudo t, 1H, J=2.2 Hz, H2), 6.40 (pseudo d, 2H, J=2.2 Hz, H4, H6), 6.58 (dd, 1H, Halk); 13C JMOD NMR (CD3OD): δ 102.24 (2), 104.92 (4,6), 112.95 (═CH2), 137.11 (CH═), 140.07 (5), 158.31 (1,3); LRESI negative ion mass spectrum; m/z 13504-Hr, 100%), 136 (17%).
The reaction was conducted under an argon gas atmosphere. 5-Vinylbenzene-1,3-diol was dissolved in ethyl acetate. Pyridine and acetic anhydride were added and the reaction heated to reflux for 4 hours and left overnight at room temperature. The volume was increased with further ethyl acetate and the solution washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to a yellow semisolid. Purification with column chromatography (isocratically eluted with 4:1 hexane/EtOAc) gave 5-vinyl-1,3-phenylene diacetate as a clear oil; Rf 0.29 (4:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.30 (s, 6H, 2×OAc), 5.33 (d, 1H, J=10.9 Hz, Halk), 5.75 dd, 1H, J=17.5 Hz, Halk), 6.66 (dd, 1H, Halk), 6.84 (pseudo t, 1H, J=2.1 Hz, H2), 7.03 (pseudo d, 2H, J=2.1 Hz, H4, H6); 13C JMOD NMR (CDCl3): δ 21.37 (2×CH3), 114.93 (2), 116.18 (═CH2), 117.04 (4,6), 135.66 (CH═), 140.27 (5), 151.54 (1,3), 169.22 (2×CO);
LRESI positive ion mass spectrum; m/z 243 (MH+, 100%), 244 (13%).
Attempted preparation of the (2+2) adduct; (E)-3,5,3′,5′-Tetraacetoxystilbene. Systematically named as (E)-5,5′(ethene-1,2-diyl)bis(benzene-5,3, 1-triyl)tetraacetate.
3,5-Diacetoxybenzoic acid (1.841 g, 7.735 mmol, batch BDp125-21-9-07) was suspended in sodium wire dried toluene (50 mL). Dry N,N-DMF (0.5 mL) and thionyl chloride (5.0 mL, 69 mmol) were added and the reaction was heated to reflux for three hours under an Argon gas atmosphere. All the material dissolved within 20 minutes. The solvents were removed by vacuum distillation (0.1 mm/60° C.) and the resultant yellow solid then redissolved in dry toluene (25 mL) and sonicated under vacuum for 15 minutes to remove dissolved gases. 3,5-Diacetoxystyrene (1.547 g, 7.032 mmol, batch BDp143-18-10-07), N-ethylmorpholine (983 μL, 7.735 mmol) and palladium diacetate (35 mg, 0.0155 mmol, 2 mole %) were added and the mixture heated to reflux overnight under an Argon gas atmosphere. On return to room temperature, ethyl acetate (200 mL) was added and the solution washed successively with water (5×50 mL), dried (anhyd. Na2SO4), filtered and rotary evaporated to give 3.269 g of dark brown gum. TLC of this crude material showed a number of products. 1H NMR (300 MHz, CDCl3) showed no obvious trans-stilbene product, and styrene starting material. ESI mass spectroscopy suggested no penta-O-acetate or partially deacetylated adduct(s). The positive mode showed a m/z 243 [MNa+] consistent for the styrene starting material. The negative ion mode showed a m/z 237 [M−H]− consistent for the acid starting material.
The crude product was then re-acetylated. The whole 3.269 g was dissolved in ethyl acetate (150 mL) and pyridine (40 mL) and acetic anhydride (40 mL) added. This reaction was heated to reflux for 5 hours and left overnight at room temperature. Water (50 mL) was added and the solution reduced to half volume with rotary evaporation. Dichloromethane (500 mL) was then added and the solution washed with water (6×400 mL), dried (anhyd. Na2SO4), filtered and rotary evaporated to give 5.253 g of dark brown viscous oil (This still had a residual pyridine smell). Purification with column chromatography (0,040-0,063 mm SiO2, gradient eluted starting with 4:1 hexane/EtOAc and finished with 2:1 hexane/EtOAc EtOAc) returned as major product recovered 3,5-diacetoxystyrene (1.506 g) as a clear oil
1H NMR (CDCl3): δ 2.30 (s, 6H, 2×OAc), 5.32 (d, 1H, J=10.8 Hz, Halk), 5.74 dd, 1H, J=17.5 Hz, Halk), 6.65 (dd, 1H, Halk), 6.77 (pseudo t, 1H, J=2.1 Hz, H2), 7.03 (pseudo d, 2H, J=2.1 Hz, H4, H6).
The general methodology was sourced from Spencer, A., “Selective Preparation of Non-Symmetrically Substituted Divinylbenzenes by Palladium Catalysed Arylations of Alkenes with Bromobenzoic Acid Derivatives”, J. Organomet. Chem., 1984, 265, 323-3315. An increased amount of catalyst was used because of the failure of the (2+2) preparation BDp145-22-10-07.
3,4,5-Triacetoxybenzoic acid (2.294 g, 7.75 mmol, batch BDp79-1-8-07) was suspended in sodium wire dried toluene (500 mL) and thionyl chloride (10.0 mL, 138 mmol) added. The reaction was heated to reflux under an Argon gas atmosphere for three hours. All the material dissolved within 30 minutes. The solvents were removed by vacuum distillation (0.1 mm/60° C.) to give a white solid, which was redissolved in dry toluene (20 mL) and sonicated under vacuum for 30 minutes to remove dissolved gases. 3,5-Diacetoxystyrene (1.365 g, 6.205 mmol, batch BDp143-18-10-07), N-ethylmorpholine (985 μL, 7.775 mmol) and palladium diacetate (87 mg, 0.3875 mmol, 5 mole % with respect to the acid chloride) were added and the mixture heated to reflux overnight under an Argon gas atmosphere. Further palladium diacetate (87 mg, 0.3875 mmol, 5 mole %) was added and the heating continued for an additional 4 hours. On return to room temperature, ethyl acetate (500 mL) was added and the solution washed successively with 0.1M HCl (300 mL) and water (3×300 mL), dried (anhyd. Na2SO4), filtered and rotary evaporated to give 3.371 g of dark brown gum. TLC of this crude material showed a number of products. 1H NMR (400 MHz, CDCl3) showed no obvious trans-stilbene product, and styrene starting material. ESI mass spectroscopy: both positive and negative ion modes, suggested no penta-O-acetate or partially deacetylated adduct(s). 3,4,5-Triacetoxybenzoic acid (2.294 g, 7.75 mmol, batch BDp79-1-8-07) was suspended in sodium wire dried toluene (500 mL) and thionyl chloride (10.0 mL, 138 mmol) added. The reaction was heated to reflux under an Argon gas atmosphere for three hours. All the material dissolved within 30 minutes. The solvents were removed by vacuum distillation (0.1 mm/60° C.) to give a white solid, which was redissolved in dry toluene (20 mL) and sonicated under vacuum for 30 minutes to remove dissolved gases. 3,5-Diacetoxystyrene (1.365 g, 6.205 mmol, batch BDp143-18-10-07), N-ethylmorpholine (985 μL, 7.775 mmol) and palladium diacetate (87 mg, 0.3875 mmol, 5 mole % with respect to the acid chloride) were added and the mixture heated to reflux overnight under an Argon gas atmosphere. Further palladium diacetate (87 mg, 0.3875 mmol, 5 mole %) was added and the heating continued for an additional 4 hours.
1H NMR (CDCl3): δ 2.28 (s, 6H, 2×OAc), 5.32 (d, 1H, J=10.8 Hz, Halk), 5.73 dd, 1H, J=17.5 Hz, Halk), 6.64 (dd, 1H, Halk), 6.82 (pseudo t, 1H, J=2.1 Hz, H2), 7.01 (pseudo d, 2H, J=2.1 Hz, H4, HO.
A mixture of (E)-3,5-dinitro-4′-acetoxystilbene and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. Filtration through a Celite pad gave a pale pink coloured solution which was rotary evaporated to dryness to give a pale pink solid.
A suspension of 3,4,5-trihydroxybenzoic acid in ethyl acetate was cooled in an ice-bath and acetic anhydride and pyridine added. After 1 hour, the resultant solution was then heated to reflux for 3 hours. Further acetic anhydride was added and the solution stirred overnight at room temperature. Formic acid was then added, and the solution poured onto ice-water. The organic layer was separated and washed with saturated aqueous sodium bicarbonate and water, dried (anhyd. Na2SO4), filtered and rotary evaporated to a white solid. Recrystallization from a 1:1 mixture of EtOAc/hexane gave two crops of 3,4,5-triacetoxybenzoic acid; Rf 0.47 (EtOAc); mp 167.5-168.0° C.; 1H NMR (300 MHz, CDCl3): δ 2.279 (s, 6H, 2×OAc), 2.284 (s, 3H, OAc), 7.84 (s, 2H, arom); 13C JMOD NMR (75 MHz, CDCl3): δ 20.48, 20.87 (3×OCOCH3), 123.16 (2,3), 127.75 (1), 139.71 (4), 143.89 (3,5), 166.72, 167.93 (3×OCOCH3), 169.96 (CO2H); LRESI positive ion mass spectrum; m/z 319 (M+Na+, 100%), negative ion mass spectrum; m/z 295 ([M−H]−, 100%).
3,4,5-Triacetoxybenzoic acid was suspended in dried toluene and N,N-DMF and thionyl chloride added. The reaction was heated to 100° C. under a nitrogen atmosphere for three hours and the solvents removed by vacuum distillation to return a yellow solid. This was suspended in dry toluene and sonicated under vacuum for 30 minutes to remove dissolved gases. Styrene, N-ethylmorpholine, and palladium (II) diacetate 2 mole %, Aldrich) were added and the mixture heated to reflux overnight under a nitrogen atmosphere. On return to room temperature, ethyl acetate was added and the solution washed successively with water, 0.1M HCl and water, dried (anhyd. Na2SO4), filtered and rotary evaporated to a dark brown viscous oil. Purification with column chromatography (gradient eluted starting with 3:1 hexane/EtOAc and finished with 2:1 hexane/EtOAc) returned (E)-3,4,5-triacetoxy stilbene as a cream coloured solid; Rf 0.86 (1:1 hexane/EtOAc), 0.34 (2:1 hexane/EtOAc); mp 119.0-119.5° C.; 1H NMR (300 MHz, CDCl3): δ 2.30 (s, 3H, OAc), 2.31 (s, 6H, 2×OAC), 7.02 (d, 1H, J=16.3 Hz, Htrans), 7.05 (d, 1H, Htrans), 7.26 (bs, 2H, H-2, H-6), 7.26-7.32 (m, 1H, H-4′), 7.34-7.40 (m, 2H, H-3′, H-5′), 7.47-7.52 (m, 2H, Jortho=8.6 Hz, H-2′, H-6′); 13C JMOD NMR (75 MHz, CDCl3): δ 20.38, 20.87 (OCOCH3), 118.70 (2,6), 126.68 (Calkene), 126.96 (2′,6′), 128.34 (Calkene), 128.99 (3′,5′), 131.02 (4′), 133.97 (4), 136.32 (1), 136.88 (1′), 143.87 (3,5), 167.25 (OCOCH3), 168.09 (2×OCOCH3); LRESI positive ion mass spectrum; m/z 377 (MNa+, 100%), 393 (MK+, 41%).
A methanolic solution of p-toluene sulphonic acid monohydrate was added to (E)-3,4,5-triacetoxystilbene suspended in methanol (50 mL) and the reaction then heated to 85° C. overnight under a positive pressure nitrogen gas atmosphere The solvent was removed by rotary evaporation to give a salmon pink coloured solid which was purified with column chromatography (isocratically eluted with 2:1 EtOAc/hexane) to return (E)-3,4,5-trihydroxystilbene as a pale beige coloured powder. Rf 0.63 (2:1 EtOAc/hexane); mp 172.0-172.5° C., 1H NMR (300 MHz, CD3OD): δ 6.61 (bs, 2H, H-2, H-6), 6.90 (d, 1H, Jtrans=16.3 Hz, Halkene), 6.96 (d, 1H, Halkene), 7.18-7.23 (m, 1H, H-4′), 7.30-7.35 (m, 2H, H-3′, H-5′), 7.46-7.50 (m, 2H, H-2′, H-6′); 13C JMOD NMR (75 MHz, CD3OD): δ 107.71 (2,6), 127.82 (Calkene), 127.91 (2′,6% 128.78 (Calkene), 130.39 (3′,5′), 130.83 (4′), 131.11 (1), 135.32 (4), 139.95 (1′), 147.82 (3,5); LRESI negative ion mass spectrum; m/z 227 ([M−H]−, 100%), 228 (15%).
(E)-3,4,5-Triacetoxystilbene and 10% Pd/C in methanol was hydrogenated overnight at 90 psi. The reaction was then filtered through a Celite pad and the filtrate rotary evaporated to a grey solid. This was dissolved in ethyl acetate, cooled in an ice-bath and acetic anhydride and pyridine added and the reaction heated to 80° C. for 3 hours. Further acetic anhydride was added and solution stirred overnight at room temperature. The reaction was then poured onto ice-water and extracted with ethyl acetate. The extract was washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to return a yellow oil. This was chromatographed (isocratically eluted with 2:1 hexane/EtOAc) to give 5-phenethylbenzene-1,2,3-triyl triacetate as a cream coloured solid. Rf 0.49 (1:1 hexane/EtOAc), 0.66 (1:2 hexane/EtOAc); mp 79.5-80.0° C.; 1H NMR (300 MHz, CDCl3): δ 2.28 (s, 6H, 2×OAc), 2.29 (s, 3H, OAc), 2.93 (bs, 4H, 2×CH2), 6.95 (bs, 2H, H-2, H-6), 7.16-7.24 (m, 3H, H-2′, H-4′, H-6′), 7.26-7.33 (m, 2H, H-3′, H-5′); 13C JMOD NMR (75 MHz, CDCl3): δ 20.23 (OCOCH3), 20.70 (2×OCOCH3), 37.30, 37.44 (2×CH2), 120.70 (2,6), 126.26 (4′), 128.53 (2′,6′), 128.60 (3′,5′), 132.83 (4), 140.40 (1), 141.16 (1′), 143.33 (3, 5), 167.22 (OCOCH3), 168.00 (2×OCOCH3); LRESI positive ion mass spectrum; m/z 379 (MNa+, 100%).
p-Toluene sulphonic acid monohydrate dissolved in methanol was added to a solution of 5-phenethylbenzene-1,2,3-triyl triacetate in methanol. The reaction was heated to 85° C. overnight under a positive pressure nitrogen gas atmosphere and the solvent then removed by rotary evaporation. The remaining salmon pink coloured solid was purified with column chromatography (isocratically eluted with 1:1 EtOAc/hexane) to return 5-phenethylbenzene-1,2,3-triol as a cream coloured solid. Rf 0.50 (1:1 EtOAc/hexane); mp 124.0-124.5° C.; 1H NMR (300 MHz, CD3OD): δ 2.67-2.76 (m, 2H, CH2), 2.79-2.87 (m, 2H, CH2), 6.23 (bs, 2H, H-2, H-6), 7.12-7.17 (m, 3H, H-2′, H-4′, H-6′), 7.23-7.28 (m, 2H, H-3′, H-5′); 13C JMOD NMR (75 MHz, CD3OD): δ 39.39 (CH2), 39.82 (CH2), 109.32 (2,6), 127.44 (4′), 129.93 (2′,6′), 130.17 (3′,5′), 132.80 (4), 135.15 (1), 143.95 (1′), 147.46 (3,5); LRESI negative ion mass spectrum; m/z 229 ([M−H]−, 100%).
A further “three point” exemplar has been generated with the synthesis of 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide (17). The procedure used was that described by S. J. Kim et al., (Amorepacific Corporation; Applicant), “Hydroxybenzamide derivatives, the method for preparing thereof and the cosmetic composition containing the same”, WO2007/021067 A1. The below scheme summarizes this preparation, starting from commercially available 3,5-dihydroxybenzoic acid (25) and 4-aminophenol.
Reagents and conditions: (i) Ac2O, Et3N, EtOAc, reflux, 4 hours, 34% yield; (ii) Et3N, THF, CH3SO2Cl, 30 minutes; (iii) 4-aminophenol, 0° C., 4 hours, 82% yield; (iv) Ac2O, pyridine, DMAP, EtOAc, reflux, 2 hours, 76% yield; (v) (a) KOH(aq), reflux, 75 minutes. (b) HCl(aq), 55% yield; (vi) (a) KOH(aq), reflux, 2 hours. (b) HCl(aq), 60% yield
The reaction was conducted under a positive pressure of Argon gas. Triethylamine was added to a solution of 3,5-diacetoxybenzoic acid in anhydrous THF cooled to 0° C. Methane sulphonyl chloride was then slowly added by syringe and the reaction stirred for a further 25 minutes. 4-Aminophenol was then added, and the reaction kept at 0° C. for a further 4 hours before being stored overnight at −20° C. The reaction was then acidified (pH 2) with 1M HC and the solvents removed by rotary evaporation. The residual gum was dissolved in EtOAc and washed with water. dried (anhyd. Na2SO4), filtered and rotary evaporated to return a white solid. 1H NMR (CD3OD) showed this to be at best 75% pure 5-(4-hydroxyphenylcarbamoyl)-1,3-phenylene diacetate. This material was used as is for ongoing reactions. Rf 0.56 (2:1 EtOAc/hexane).
“Crude” 5-(4-hydroxyphenylcarbamoyl)-1,3-phenylene diacetate was suspended in ethyl acetate. 4-(Dimethylamino)pyridine, pyridine and acetic anhydride were then added and the solution then heated to reflux for 2 hours and left to stand at room temperature overnight. Further ethyl acetate was added and the reaction washed with 0.1M HCl and water, dried (anhyd. Na2SO4), filtered and rotary evaporated to return a white solid. This was re-dissolved in ethyl acetate, silica added and the solvent rotary evaporated off. The remaining powder was loaded onto a silica column as a dry plug and chromatographed (gradient eluted beginning with 2:1 EtOAc/hexane and finishing with 5:1 EtOAc/hexane) to give 5-(4-acetoxyphenylcarbamoyl)-1,3-phenylene diacetate as a white powder. 1H NMR (d6-DMSO) showed this to be ca. 80% pure. This material was used as is for the ongoing hydrolysis reaction. Rf 0.63 (2:1 EtOAc/hexane).
The reaction was conducted under a positive pressure of Argon gas. An aqueous solution of potassium hydroxide was added to “crude” 5-(4-hydroxyphenylcarbamoyl)-1,3-phenylene diacetate. The reaction was heated to reflux for 75 minutes, returned to room temperature and 1M HCl added until a precipitate formed (pH approx. 3). This was vacuum filtered off and the solid repeatedly washed in the funnel with water, and then dried under vacuum to return 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide as fluffy small white needles. Rf 0.39 (4:1 EtOAc/hexane); mp 266.0-266.5° C.; 1H NMR (CD3OD): δ 6.47 (pseudo t, 1H, Jmeta=2.2 Hz, H-4), 6.77-6.82 (m, 4H, H-3′, H-5′, H-2, H-6), 7.43-7.46 (m, 2H, Jortho=8.9 Hz, H-2′, H-6′); 1H NMR (d6-DMSO): δ 6.42 (pseudo t, 1H, Jmeta=2.2 Hz, H-4), 6.72-6.78 (m, 4H, H-3′, H-5′, H-2, H-6), 7.51-7.56 (m, 2H, Jortho=8.9 Hz, H-2′, H-6′), 9.20 (s, 1H), 9.51 (s, 2H), 9.83 (s, 1H); 13C JMOD NMR (CD3OD): δ 104.41 (4), 104.67 (2,6), 113.92 (3′,5′), 122.13 (2′,6′), 129.10 (1′), 136.08 (1), 153.26 (4′), 157.41 (3,5), 166.70 (C═O); LRESI negative ion mass spectrum; m/z 244 ([M−H]−, 100%), 489 ([2M−H]−, 29%); HRESI positive ion mass spectrum; m/z for C13H11NO4, calculated [MH]+ 246.0766. measured 246.0764.
The reaction was conducted under a positive pressure of Argon gas. A solution of potassium hydroxide in water was added to “crude” 5-(4-acetoxyphenylcarbamoyl)-1,3-phenylene diacetate. The reaction was heated to reflux for 2 hours and on return to room temperature, 1M HCl was then added until a precipitate formed (pH approx. 3). This was vacuum filtered off and repeatedly washed with water. The white solid then dried under vacuum to return 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide as fluffy small white needles. Melting point and spectroscopic data were identical to the previously prepared material.
Additional compounds sourced/evaluated/templated are shown below. Examples have been used both as MIP templates and as MIP test analytes.
The compounds which have been synthesized and sourced externally provide useful templates for (i) constructing MIPs around defined templates, (ii) assessment of binding using pure and complex mixtures of compounds, and (iii) full characterisation of the selectivity of said MIPs for target compounds. with the synthesised templates as test compounds and with real bioprocess waste materials.
Development of MIP systems centred around more complex resveratrol analogues as templates, such as the flavone class of molecules, and different classes of polyphenols.
Other molecules, and their analogues, currently being investigated as potential templates for MIPs include inter alia cacatechin, morin, ellagic acid, procyanidin which is being targeted with MIPAmide. Another possible class of molecules for MIP templating are naturally occurring resveratrol derivatives such as the glucuronides. Romero-Peréz et al6 have reported significant amounts of these glucuronides in grape berry skins, quantities that typically exceed that of resveratrol, (J. Agric. Food Chem., Vol. 49, No. 1, 2001, 210-215). Development of a MIP specific for such compounds could have considerable value for concentrating, separating and extracting these bioactive molecules as secondary downstream products from the same feedstock used to isolate resveratrol. If required, these glucuronides could then be either chemically or enzymatically converted to resveratrol. D. A. Learmonth (Bioconjugate Chem., 2003, 14, 262-267)7 has reported a synthetic methodology for preparing these glucuronide templates (
We have also explored the development of a new class of MIPs, called “covalently bound” MIPs, which are expected to have both greater selectivity and capacity for individual target molecules. Trial experiments have already generated a small quantity of (E)-5-(4-(methacryloyloxy)styryl)-1,3-phenylene bis(2-methylacrylate), shown in
The reaction was conducted under an Argon gas atmosphere. Resveratrol was dissolved in dry acetonitrile, to which anhydrous sodium sulphate was added. The solution was vigorously stirred for 30 minutes and the solid material was filtered off. Triethylamine was then added to the filtrate and immediately cooled in an ice-bath. Methacryloyl chloride dissolved in acetonitrile was slowly added and the reaction solution was allowed to cool to room temperature, then stirred overnight. The reaction was then cooled again in an ice-bath and further triethylamine added, followed by ice-water and the solution stirred for a further 20 minutes. Ethyl acetate was added and the phases separated. The organic layer was washed four times with water, then dried, filtered and rotary evaporated to give a brown gum. This gum was purified by gradient elution chromatography (9:1 hexane/EtOAc to 4:1 hexane/EtOAc) to give pure (E)-3,4′,5-tri(methacryloyl)oxystilbene as a clear oil. Rf 0.47 (4:1 hexane/EtOAc); 1H NMR (CDCl3): δ 2.04 (s, 9H, 3×CH3), 5.72-5.76 (m, 3H, 3×vinyl), 6.33-6.34 (m, 3H, 3×vinyl), 6.88 (pseudo t, 1H, Jmeta=2.1 Hz, H-4), 6.97 (d, 1H, J=16.3 Hz, Htrans), 7.10 (d, 1H, Htrans), 7.10-7.15 (m, 4H, H-2, H-6, H-3′, H-5′), 7.47 (dt, 2H, Jortho=8.6 Hz, H-2′, H-6′). LRESI positive ion mass spectrum; m/z 455 (MNa+, 100%), 456 (31%).
Ferulic acid was added to an aqueous solution of sodium hydroxide cooled in an ice-bath. The suspension was well stirred until all the solid had dissolved, and then acetic anhydride was then added. After 5 minutes, the cooling bath was removed and the solution stirred at room temperature for a further 90 minutes. The reaction was returned back to 0° C., 2M aq. HCl added to precipitate a white solid (pH ca. 4), and this vacuum filtered and repeatedly washed in the funnel with further water. Recrystallization from hexane/ethyl acetate collected 2 crops of trans-4-O-acetylferulic acid as a white powder. Rf 0.52 (4:1 EtOAc/hexane); mp 197.5-198.0° C.; lit mp 192° C. (Roberts et al, Eur. J. Med. Chem., (1994), 29, 841-8548); 1H NMR (300 MHz, CDCl3): δ 2.33 (s, 3H, OAc), 3.88 (s, 3H, OMe), 6.40 (d, 1H, Jtrans=15.9 Hz, Halkene), 7.06-7.17 (m, 3H, arom), 7.73 (d, 1H, Jtrans 15.9 Hz, Halkene).
Ferulic acid was dissolved in pyridine. Acetic anhydride (15.0 mL) was added and the reaction stirred overnight at room temperature overnight. The solution was then poured onto ice and acidified with 2M HCl (pH 2). The resultant white solid was filtered off, washed in the funnel with further water and then dried. Recrystallized from boiling dichloromethane and ethanol gave two crops of trans-4-0-acetylferulic acid as a white powder. Mp 201.0-201.5° C.; lit mp 192° C. (Roberts et al, Eur. J. Med. Chem., (1994), 29, 841-8548); Rf and 1H NMR (300 MHz, CDCl3) were identical to the earlier prepared material.
trans-4-O-Acetylferulic acid was dissolved in dry dichloromethane and 4-dimethylaminopyridine and N,N-dicyclohexylcarbodiimide added. The reaction was stirred at room temperature for 60 minutes to generate the activated acid, and ergosterol was then added and washed in with further dichloromethane. The solution was stirred at room temperature overnight and the resultant white solid removed by filtration. The filtrate was rotary evaporated to return a white solid which was purified with column chromatography (gradient eluted starting with 50:1 CHCl3/MeOH and finished with 50:4 CHCl3/MeOH) to give 3-O-(trans-4-O-acetylferuloyl)-ergasterol as a white solid. Rf 0.58 (2:1 hexane/EtOAc), 0.90 (49:1 CHCl3/MeOH); mp 181.5-182.05° C.; 1H NMR (300 MHz, CDCl3): δ 0.64 (s, 3H, CH3), 0.83 (d, 3H, J=6.8 Hz, CH3), 0.85 (d, 3H, J=6.8 Hz, CH3), 0.93 (d, 3H, J=6.8 Hz, CH3), 0.99 (s, 3H, CH3), 1.04 (d, 3H, J=6.6 Hz, CH3), 1.20-2.60 (broad multiplet with an indeterminate number of protons), 2.32 (s, 3H, OAc), 3.86 (s, 3H, OCH3), 4.80-4.90 (m, 1H, H-3), 5.14-5.28 (m, 2H, H-22, H-23), 5.38-5.42 (m, 1H, H-6/5), 5.59-5.61 (m, 1H, H-5/6), 6.40 (d, 1H, Jtrans=15.9 Hz, Halkene), 7.03-7.14 (m, 3H, arom), 7.65 (d, 1H, Jtrans=15.9 Hz, Halkene); 13C JMOD NMR (75 MHz, CDCl3): δ 12.30 (18), 16.43, 17.84, 19.89, 20.18, 20.82 (5×CH3), 21.28 (11), 21.35 (CH3), 23.24 (15), 28.48, 28.50 (2,16), 33.33 (25), 37.01, 37.37, 38.19, 39.29 (10,4,13,1,12), 40.64 (20), 43.07 (24), 46.31 (9), 54.77, 55.99, 56.10 (14, OCH3, 17), 73.22 (3), 111.47 (2arom), 116.59 (7), 119.08 (6), 120.55 (Calkene), 121.41 (6arom), 123.44 (5arom), 132.23 (23), 133.70 (1arom), 135.80 (22), 138.72 (5), 141.65 (8), 141.71 (4arom), 143.97 (Calkene), 151.63 (C—OCH3), 166.36 (C3-OCOCH═), 168.89 (Ar—OCOCH3).
3-O-(trans-4-O-Acetylferuloyl)-ergasterol was dissolved in a 2:1 mixture of chloroform and methanol and potassium carbonate added and the reaction heated to 65° C. for 6 hours. On return to room temperature, saturated aqueous ammonium chloride was added and the solution repeatedly extracted with dichloromethane. The combined extracts were washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to return a white solid. Purification with column chromatography (gradient eluted started with CH2Cl2 and finished with 98:2 CH2Cl2/MeOH) returned 3-O-(trans-feruloyl)-ergasterol as a white solid. Rf 0.31 (4:1 hexane/EtOAc), 0.49 (100% CH2Cl2), 0.84 (98:2 CH2Cl2/MeOH); mp 182.0-182.5° C.; 1H NMR (400 MHz, CDCl3): δ 0.64 (s, 3H, CH3), 0.84-0.85 (m, 6H, 2×CH3), 0.92 (d, 3H, J=6.8 Hz, CH3), 0.99 (s, 3H, CH3), 1.04 (d, 3H, J=6.6 Hz, CH3), 1.26-2.08 (broad multiplet with an indeterminate number of protons), 2.41-2.48 (m, 1H), 2.56-2.61 (m, 1H), 3.93 (s, 3H, OCH3), 4.82-4.86 (m, 1H, H-3), 5.15-5.26 (m, 2H, H-22, H-23), 5.39-5.40 (m, 1H, H-6/5), 5.59-5.60 (m, 1H, H-5/6), 5.83 (s, 1H, OH), 6.28 (d, 1H, Jtrans=15.9 Hz, Halkene), 6.91 (d, 1H, Jortho=8.2 Hz, H6arom), 7.03-7.10 (m, 2H, Harom), 7.60 (d, 1H, Jtrans=15.9 Hz, Halkene); 13C JMOD NMR (100 MHz, CDCl3): δ 12.41 (18), 16.55, 17.95, 19.99, 20.29, 21.46 (5×CH3), 21.40 (11), 23.35 (15), 28.62 (2,16), 33.44 (25), 37.17, 37.49, 38.32, 39.41 (10,4,13,1,12), 40.75 (20), 43.17 (24), 46.42 (9), 54.88, 56.10, 56.26 (14, OCH3, 17), 73.09 (3), 109.70 (2arom), 115.08 (7), 116.36 (Calkene), 116.69 (6), 120.59 (5arom), 123.36 (6arom), 127.44 (1arom), 132.34 (23), 135.92 (22), 138.96 (5), 141.83 (8), 144.93 (Calkene), 147.13 (4arom), 148.28 (C—OCH3), 166.99 (C═O).
To the best of the inventor's knowledge, this compound is novel.
trans-Cinnamic acid was dissolved in dry dichloromethane. 4-Dimethylaminopyridine and N,N-dicyclohexylcarbodiimide were added and the reaction was stirred at room temperature for 15 minutes. Ergosterol was then added along with further dry dichloromethane and the reaction stirred at room temperature overnight. The resultant white solid was filtered off and the solid washed with further dichloromethane The combined filtrates were rotary evaporated and the resultant white solid then purified with column chromatography (gradient eluted starting with CH2Cl2 (100%) and finished with 97:3 (v/v) CH2Cl2/MeOH) to return a white solid. 1H NMR (300 MHz, CDCl3) showed this to be ca. 95% pure title compound. A sample was taken and recrystallized from a 2:1 hexane and ethyl acetate mixture to give 3-O-ergasteryl cinnamate as “glistening” white mica plates. Rf 0.68 (4:1 hexane/EtOAc), 0.89 (99:1 CH2Cl2/MeOH); mp 171.0-171.1° C., 1H NMR (300 MHz, CDCl3): δ 0.64 (s, 3H, CH3), 0.83 (d, 3H, J=6.8 Hz, CH3), 0.85 (d, 3H, J=6.7 Hz, CH3), 0.93 (d, 3H, J=6.8 Hz, CH3), 0.99 (s, 3H, CH3), 1.04 (d, 3H, J=6.6 Hz, CH3), 1.23-2.62 (broad multiplet with an indeterminate number of protons), 4.80-4.91 (m, 1H, H-3), 5.14-5.28 (m, 2H, H-22, H-23), 5.38-5.42 (m, 1H, H-6/5), 5.59-5.61 (m, 1H, H-5/6), 6.43 (d, 1H, Jtran=16.0 Hz, Halkene), 7.36-7.40 (m, 3H, 3arom, 4arom, 5arom), 7.51-7.55 (m, 2H, 2arom, 6arom), 7.68 (d, 1H, Halkene); 13C JMOD NMR (75 MHz, CDCl3): δ 12.42 (18), 16.56, 17.97, 20.01, 20.31, 21.48 (5×CH3), 21.41 (11), 23.36 (15), 28.60, 28.63 (2,16), 33.45 (25), 37.14, 37.50, 38.33, 39.42 (10,4,13,1,12), 40.76 (20), 43.19 (24), 46.44 (9), 54.90 (14), 56.11 (17), 73.26 (3), 116.72 (7), 119.02 (6), 120.64 (Calkene), 128.38 (2arom,6arom), 129.20 (3arom,5arom), 130.50 (4arom), 132.35 (23), 134.90 (1arom), 135.93 (22), 138.92 (5), 141.81 (8), 144.81 (Calkene), 166.68 (C═O).
p-Coumaric acid was suspended in pyridine and acetic anhydride and DMAP were added. All the solids rapidly dissolved and the solution was stirred overnight at room temperature. The reaction was then poured onto ice and acidified (to pH 3) by addition of 2M HCl. The resultant white solid was filtered off, washed in the funnel with further water, and then dried under vacuum over desiccant. The dry material was recrystallized from ethyl acetate to give (E)-4-O-acetoxycinnamic acid as white needles, and a second crop was obtained from the volume reduced filtrate. Rf 0.52 (4:1 EtOAc/hexane); mp 201.1-201.2° C.; lit mp 205-208° C. (Roberts et al, Eur. J. Med. Chem., (1994), 29, 841-8547); 1H NMR (300 MHz, CD3OD): δ 2.31 (s, 3H, OAC), 6.48 (d, 1H, Jtrans=16.0 Hz, Halkene), 7.17-7.20 (m, 2H, Jorthos=8.6 Hz, 3arom, 5arom) 7.64-7.73 (m, 3H, Halkene 2arom, 6arom); LRESI negative ion mass spectrum; m/z 205 ([M−H]−, 100%), 206 (12%).
A mixture of (E)-4-O-acetoxycinnamic acid, 4-dimethylaminopyridine and N,N-dicyclohexylcarbodiimide in dry dichloromethane was stirred at room temperature for 20 minutes. Ergosterol was then added and washed in with further dry dichloromethane and the reaction stirred at room temperature overnight. The resultant white solid was filtered off, washed well in the funnel with further dichloromethane and the combined filtrates rotary evaporated to return a yellow solid. Purification with column chromatography (gradient eluted starting with CH2Cl2 and finished with 97:3 CH2Cl2/MeOH) returned 3-O-(trans-4-O-acetoxycinnamoyl)-ergasterol as a white solid. Rf 0.60 (4:1 hexane/EtOAc), 0.56 (CH2Cl2 100%); mp 181.1-181.2° C.; 1H NMR (300 MHz, CDCl3): δ 0.64 (s, 3H, CH3), 0.82-0.86 (m, 6H, 2×CH3), 0.92 (d, 3H, J=6.8 Hz, CH3), 0.99 (s, 3H, CH3), 1.04 (d, 3H, J=6.6 Hz, CH3), 1.22-2.57 (broad multiplet with an indeterminate number of protons), 2.31 (s, 3H, OAc), 4.79-4.90 (m, 1H, H-3), 5.10-5.28 (m, 2H, H-22, H-23), 5.38-5.41 (m, 1H, H-6/5), 5.58-5.61 (m, 1H, H-5/6), 6.38 (d, 1H, Jtrans=16.0 Hz, Halkene), 7.10-7.14 (m, 2H, Jortho=8.6 Hz, 3arom,5arom), 7.51-7.56 (m, 2H, 2arom,6arom), 7.67 (d, 1H, Halkene); 13C JMOD NMR (75 MHz, CDCl3): δ 12.34 (18), 16.46, 17.90, 19.94, 20.24, 21.34, 21.41 (5×CH3, OC(O)CH3), 21.32 (11), 23.29 (15), 28.52, 28.55 (2,16), 33.37 (25), 37.05, 37.40, 38.23, 39.34 (10,4,1,12), 40.69 (20), 43.09 (13), 43.11 (24), 46.35 (9), 54.81 (14), 56.03 (17), 73.24 (3), 116.66 (7), 119.08 (6), 120.59 (Ccinn alkene), 122.34 (3arom,5arom), 129.39 (2arom,6arom), 132.27 (23), 132.49 (1arom), 135.85 (22), 138.78 (5), 141.69 (8), 143.58 (Ccinn alkene), 152.32 (4arom), 166.42 (C3-OCOCH3), 169.22 (Ar—OCOCH3).
Potassium carbonate was added to 3-O-(trans-4-O-acetylferuloyl)-ergasterol dissolved in a 2:1 mixture of chloroform and methanol. This was then heated to 70° C. for 6 hours, further 2:1 chloroform (10.0 mL) and methanol (5.0 mL) added, and the reaction left to stir at room temperature overnight. Saturated aqueous ammonium chloride and additional dichloromethane were added and the two phases separated. The organic material was repeatedly washed with water, dried (anhyd. Na2SO4), filtered and rotary evaporated to return a cream coloured solid. Recrystallization from ethyl acetate gave pure 3-O-(trans-coumaroyl)-ergasterol as a white solid. The filtrate was reduced in volume to return a second crop. Rf 0.28 (100% CH2Cl2); mp 213.1-213.2° C.; 1H NMR (400 MHz, CDCl3): δ 0.64 (s, 3H, CH3), 0.82-0.85 (m, 6H, 2×CH3), 0.92 (d, 3H, J=6.8 Hz, CH3), 0.99 (s, 3H, CH3), 1.04 (d, 3H, J=6.6 Hz, CH3), 1.24-2.09 (broad multiplet with an indeterminate number of protons), 2.41-2.47 (m, 1H), 2.56-2.60 (m, 1H), 4.81-4.85 (m, 1H, H-3), 5.15-5.26 (m, 3H, H-22, H-23, OH), 5.39-5.41 (m, 1H, H-6/7), 5.59-5.60 (m, 1H, H-7/6), 6.29 (d, 1H, Jtrans=15.9 Hz, Halkene), 6.80-6.86 (d, 2H, Jortho=8.6 Hz, H3arom, H5arom), 7.41-7.45 (m, 2H, H2arom, H6arom), 7.62 (d, 1H, Halkene); 13C JMOD NMR (75 MHz, CDCl3): δ 12.43 (18), 16.58, 17.96, 20.01, 20.30, 21.47 (5×CH3), 21.42 (11), 23.34 (15), 28.62 (2,16), 33.46 (25), 37.17, 37.51, 38.33, 39.43 (10,4,1,12), 40.76 (20), 43.19 (24), 43.21 (13), 46.45 (9), 54.91 (14), 56.12 (17), 73.23 (3), 116.24, 116.44, 116.69, (7, Ccinn alkene,3arom,5arom), 120.61 (6), 127.73 (1arom), 130.29 (2arom,6arom), 132.37 (23), 135.94 (22), 138.98 (5), 141.89 (8), 144.62 (Ccinn alkene), 158.02 (4arom), 167.28 (C3-OCOCH3); LRESI negative ion mass spectrum; m/z 541 ([M−H]−, 100%), 542 (51%); HR EI negative ion mass spectrum; calculated for [C37H49O3—H]−1 541.36817. measured 541.36801.
The reaction was done under a positive pressure nitrogen gas atmosphere. Ergosterol was dissolved in dry pyridine and this solution cooled in an ice-bath. Freshly distilled benzoyl chloride was added and the reaction allowed to return back to room temperature, and left to stir overnight. The reaction was then poured onto ice-water and the white solid extracted with dichloromethane. The organic extract was then washed successively with water and saturated aqueous NaHCO3, dried (anhyd. Na2SO4), filtered and rotary evaporated to return a pale brown solid. Purification with column chromatography (isocratically eluted with CH2Cl2, 100%) gave ergosteryl benzoate as a white solid. Rf 0.69 (100% CH2Cl2); mp 157.1-157.2° C.; lit mp 169-171° C. [Done, R. E.; Kruse, L. I. J. Org. Chem. 1985, 51, 4047-40539]; 1H NMR (400 MHz, CDCl3): δ 0.65 (s, 3H, CH3), 0.83 (d, 3H, J=6.6 Hz, CH3), 0.85 (d, 3H, J=6.6 Hz, CH3), 0.93 (d, 3H, J=6.8 Hz, CH3), 1.01 (s, 3H, CH3), 1.05 (d, 3H, J=6.6 Hz, CH3), 1.26-2.67 (broad multiplet with an indeterminate number of protons), 4.92-5.01 (m, 1H, H-3), 5.16-5.27 (m, 2H, H-22, H-23), 5.40-5.42 (m, 1H, H-6/5), 5.60-5.62 (m, 1H, H-5/6), 7.39-7.45 (m, 2H, 3arom, 5arom), 7.53-7.57 (m, 1H, 4arom), 8.01-8.06 (m, 2H, 2arom, 6arom); 13C JMOD NMR (100 MHz, CDCl3): δ 12.43 (18), 16.59, 17.96, 20.01, 20.30, 21.47 (5×CH3), 21.42 (11), 23.36 (15), 28.59, 28.63 (2,16), 33.45 (25), 37.13, 37.27, 37.52, 38.32 (10,4,12), 40.76 (20), 43.19 (24), 43.20 (13), 46.44 (9), 54.91 (14), 56.11 (17), 73.74 (3), 116.72 (7), 120.68 (6), 128.61 (2arom,6arom), 129.89 (3arom,5arom), 131.17 (1arom), 132.36 (23), 133.07 (4arom), 135.92 (22), 138.88 (5), 141.87 (8), 166.31 (C═O).
The procedure used was that reported for β-sitostanol described by Condo Jr, A. M.; Baker, D. C.; Moreau, R. A.; and Hicks, K. B., J. Agric. Food Chem., (2001), 49, 4961-4964, “Improved Method for the Synthesis of trans-Feruloyl-β-sitostanol.”10
3,4-Dimethoxy cinnamic acid (1.765 g, 8.475 mmol, Aldrich Chem. Co.) was dissolved in dichloromethane (30.0 mL, dried by passage through alumina) and 4-dimethylaminopyridine (105 mg, 0.861 mmol, Sigma) and N,N-dicyclohexylcarbodiimide (1.925 g, 9.345 mmol, Aldrich) added. The reaction was stirred at room temperature for 20 minutes to generate the activated acid. Ergosterol (3.360 g, 8.470 mmol, Aldrich) was then added along with further dry dichloromethane (10.0 mL) and the solution stirred at room temperature overnight. The resultant white solid was filtered off and washed with further dichloromethane (3×30 mL). The filtrates were combined and rotary evaporated to return 5.478 g of a pale yellow solid
TLC showed this to be predominantly a mixture of higher Rf new product and ergosterol starting material.
Rf 0.45 (4:1 hexane/EtOAc), 0.58 (CH2Cl2 100%);
The design of molecularly imprinted polymers (MIPs) requires the selection of a monomer species that will interact favourably with the intended template species, such that a pre-polymerisation complex is formed between template and monomer. The use of tools such as molecular modelling and NMR spectroscopy assist in the selection of appropriate monomers by performing a ‘virtual screen’, which reduces the number of polymer preparations required in MIP development.
Modelling calculations were performed using PM3 geometry optimisation without solvent considerations to yield theoretical energy of formation values, ΔHf. The geometry optimisation and surface electron potential of resveratrol was generated (
Monomer clusters were modelled, with clusters sizes ranging from 1 to 6 monomer units. These calculations yielded predictive ΔHf values for the interaction of the monomer with itself at these cluster sizes (Table 4). Introduction of the theoretical geometry optimisation and surface electron parameters for resveratrol parameters permit estimation of the average energy of formation for the complex (
4Ei=(ΔHf_Complex−(ΔHf_Template+ΔHf_Monomer)).
The presence of cross-linking monomers were not included in these modelling calculations.
4VP is expected to interact through both hydrogen bonding and aromatic π-π interactions (
Table 4 shows that the optimum ratio of resveratrol to 4VP in the formation of a MIP should theoretically be 1:3. Similar studies for the imine (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol or the amide 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide also show 1:3 ratios.
Both Ma et al and Zhuang et al (J. Chromatographic Sci. (2008), 46 (8), pp 739-742, have reported the preparation of MIPs from reseveratrol and 4-vinylpyridine. However, they did not identify the optimal 1:3 resveratrol:4-VP ratio either by empirical or modelling techniques.
Modelling titration experiments were conducted using various other functional monomers, including acrylamide (AAM) and 4-vinylbenzoic acid (4VBA) for which the data are shown below, as well as with 4-vinylpyridine (4VPyr). Because AAM has been employed by Xiang et al.1 in a unsystematic experiment based on a resveratrol:AAM:EGDMA ratio of 1:6:30, we replicated this preparation for comparison purposes, despite the fact that our modelling studies indicating the requirement for only 3 equivalents AAM were needed for optimal MIP construction.
Static binding evaluation data for the AAM-based MIP derived with the 1:6:30 ratio confirmed our conclusion from the modelling studies, with the results indicating that although some low affinity for resveratrol was observed, the selective performance was significantly poorer than for MIPs employing 4-vinylpyridine. A molecularly imprinted polymer was also prepared using 4VBA as functional monomer based on the preparation conditions used to make MIP 8 (the most successful 4VP-based MIP). In this case, the modelling data failed to show any reliable minimum for the monomer ratio and in most cases predicted unfavourable interactions (for 2, 3 and 4 equivalents 4VBA). The static binding evaluation data supported this prediction with no recognition of resveratrol and negligible affinity observed (
Resveratrol was dissolved in CD3CN, and was titrated with increasing molar equivalents of 4VP. Upon each addition, 1H NMR spectra were recorded, and the change in aromatic —OH shifts followed. The presence of H bonding interactions was evidenced by the consistent downfield movement of the aromatic —OH shift (Table 5 and
1H NMR titration for Resveratrol against increasing amounts of 4VP.
Resveratrol imprinted monoliths were prepared using 4VP and EGDMA as functional and cross-linking monomers respectively in various porogenic mixtures (Table 6) After polymerisation monoliths were ground, sieved to a particle size of 60-90 μm, followed by repeated washing in methanol containing acetic acid (10% v/v) to remove the template.
Molecularly Imprinted Polymers (MIPs) Templated with Resveratrol
First and Second generation molecularly imprinted polymers (MIPs) were prepared as described in Table 6, using the following procedure. In a glass test tube fitted with a suba seal, the template (resveratrol) and functional monomer (4VP) were sonicated for 10 minutes prior to the addition of cross-linker (ethylene glycol dimethacrylate, EGDMA) and free radical initiator (AIBN) followed by N2(g) purge for 10 minutes. Thermal polymerization for 1st generation MIPs was carried out at 45° C. for 12 hours, then at 50° C. for 24 hours, and for 2nd generation MIPs thermal polymerization was performed at 50° C. for 16 hours, then 55° C. for 5 hours and 60° C. for 4 hours, resulting in bulk monolith polymers. Non-imprinted control polymers (NIPs) were prepared in exactly the same manner, but in the absence of the template. Monolith polymers were removed from reaction tubes and ground using a Reutsh 200 ball mill, then sieved to size (60-90 μm). Fines were removed by repeated suspension of polymer particles in acetone and filtering through a 20 μm glass frit. The resveratrol template was removed by repeated washing in methanol/acetic acid (10%) until no template was present as observed by UV-VIS spectrophotometry at vmax of 235 nm, 307 nm and 321 nm UV-Vis analysis of the washing extracts showed that >99% of the template had been removed.
An example of a Typical MIP preparation is described below:
228.2 mg of resveratrol (1 mmol) and 321 μL of 4VP (3 mmol) were dissolved in 1 mL of EtOH and 5 mL of ACN in a 15 mL test tube and sealed with a suba seal. The solution was purged with N2(g) for 2 minutes and then sonicated for 20 minutes. To the solution was added 2.83 mL of EGDMA (15 mmol) and 51 mg of AIBN (0.31 mmol) radical initiator. The reaction mixture was then purged with N2(g) for a further 2 minutes prior to being submersed into a 50° C. water bath for 18 hours. The water temperature was then increased to 60° C. for 24 hours. As the polymerisation initiation liberates N2(g), the test tube was fitted with a needle and syringe barrel with plunger to act as a pressure valve. This was repeated for the NIP control polymer without the addition of the resveratrol template.
The bulk polymer monolith was then removed from the test tube, crushed and ground to a particle size of 60-90 μm using a Restch 200 ball mill. The resulting polymer particles were the washed repeatedly in MeOH/AcOH (10%) (v/v) to remove the template and any unreacted monomer species. The MIP and NIP materials were then washed with MeOH to remove any traces of AcOH and dried under reduced pressure.
Initial MIP binding studies were performed using 4.5 mL fitted polypropylene reaction tubes fitted to a Mettler Toledo MiniBlock™ system. Using this apparatus, first generation MIPs were rapidly evaluated for resveratrol affinity after a short incubation period, followed by vacuum assisted filtration into fraction collection tubes. These evaluations were designed to identify the most suitable template to functional monomer ratio. The rebinding studies were performed as follows:
(1) 50 mg of MIP (or respective NIP control) was measured into a reaction tube fitted with a 25 μm polypropylene porous frit;
(2) a rebinding solution of resveratrol (0.05 min) in acetonitrile was added and the reaction mixture was incubated for 30 min at room temperature with continuous shaking;
(3) the filtrate was collected, diluted five-fold with acetonitrile—a 3 mL aliquot was analysed by UV-VIS spectroscopy at vmax 235 nm, 307 nm and 321 nm using a quartz cuvette with a 1 cm path length and the concentration of free resveratrol calculated from an experimentally determined a five point calibration curve. The concentration of resveratrol bound to the MIP (or respective NIP) was then determined as the difference between the initial resveratrol concentration and the final free resveratrol concentration. This was then expressed as the amount bound, B, in μmoles/g polymer.
(4) MIPs were washed sequentially with acetonitrile methanol and methanol containing acetic acid (10% v/v) and again with methanol to remove bound resveratrol.
MIP negative control experiments for resveratrol binding were performed identically to the above procedure, with the exception that the rebinding solution did not contain resveratrol.
To further ascertain the most appropriate template to functional monomer ratio, an assay employing a 10 fold increase in resveratrol concentration (0.5 min) was employed. The results are set out in
The relative imprinting factor (IF), relating the performance of the MIP with respect to the NIP control, was determined for each MIP, from
IF=BMIP/BNIP,
where BMIP and BNIP is the amount of resveratrol bound to the MIP and NIP respectively.
Thus, in accordance with the modeling data, the most suitable template:monomer ratio was identified to be 1:3 for the preparation of a resveratrol imprinted polymer using 4VP as the functional monomer (Table 7). MIPs prepared in this manner demonstrated maintained high performance levels (highest capacity and IF values) after consecutive repeated binding studies at both low and intermediate resveratrol concentrations (0.05 and 0.5 min respectively).
MIPs based on this formulation were subsequently prepared with varying amounts of EGDMA to assess the effect of cross-linking on binding affinity. Example MIPs are MIP 2, MIP 5, MIP 7, MIP 8, MIP 9 and MIP 10).
However it was observed that MIP 7 resulted in a pseudo precipitation polymerisation that produced a talc-like polymer which was physically soft or weak and was reduced to fines or beads of a particle size <20 μm. This was due to the low amount of cross-linking and large porogen volume which was required to dissolve the resveratrol template. Although such sizes are useful for analytical techniques, this polymer was deemed unsuitable for future large scale or industry scale separation techniques, as the small particle size would result in unacceptably high back-pressures regardless of binding performance (data not shown).
Therefore a small amount of EtOH was included in the ACN porogen (MIP 8) which increased the solubility of the template resveratrol thus affording a smaller porogenic volume and the preparation of a monolithic polymer which could be ground and sieved to a suitable particle size.
An example preparation for a polymer containing an ACN/EtOH (5:1 v/v) porogenic mixture is described below for MIP 8 (LS2-6p10-7-2-07):
Static binding assays were employed to evaluate the effect of cross-linking. An example of an assay is detailed below:
Into a 1.7 mL eppendorf tube was measured 30 mg of MIP, 1.5 mL of resveratrol (0.5 mM) in acetonitrile and the resulting sample mixture was mixed for 18 hours using a rotary suspension mixer at 28° C. Each sample was prepared in duplicate and repeated with NIP control samples. In addition to this blank control samples were prepared using 30 mg of the respective polymer with 1.5 mL of blank acetonitrile solution. The samples was then centrifuged at 13000 rpm for 15 minutes and a 200 μL aliquot removed for reverse phase HPLC analysis under isocratic conditions with UV-Vis detection at a wavelength of γ=321 nm. The area under the curve was determined and the concentration of free resveratrol determined using an experimental five point calibration curve. The concentration of resveratrol bound to the MIP was calculated by subtracting the free resveratrol concentration from the concentration of the binding solution. The results are set out in
An important aspect of this invention is the ability to replicate the MIP preparation and subsequent binding affinity. As an example of this MIP 8 was prepared in multiple batches (
Further studies into binding characteristics of MIPs discussed within this invention include the static capacity and static cross-reactivity studies for which examples using MIP 8 are discussed below. Static Capacity Binding Assay: into 1.7 mL eppendorf tubes was weighed 30 mg of polymer (both MIP and NIP) to which was added increasing concentrations of resveratrol solution at constant volume (1.5 mL) in acetonitrile. The resulting mixture was incubated while mixing at approximately 40 rpm for 18 hours (unless stated otherwise), after which the mixture was centrifuged at 13000 rpm for 15 minutes. A 200 μL aliquot of the supernatant was removed and analysed by reverse phase HPLC analysis with UV detection, and the concentration of resveratrol in the supernatant determined via a 5 point calibration curve. This was subtracted from the initial binding solution to give the amount of resveratrol bound. Binding (B) was expressed as analyte bound, B in μmol/g polymer.
Preliminary data shows no clear capacity (as would be evidenced by a plateau in the curve) while the non-specific binding on the NIP control polymer was observed to be quite variable over repeat binding experiments (
For static cross-reactivity studies the binding procedure was the same as above with the exception that the concentration of analyte binding solutions was kept at 0.5 min.
Cross-reactivity studies on MIPE (LS 2-6p10-7-1-07) were continued with a range of zero, one, two, three and four point compounds. Compounds included in the study were: Resveratrol (1), 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide (BDp105-21-8-07) (2), ‘Green’ Resveratrol (BDp55-11-12-2006) (3), (E)-5-(4-hydroxystyryl)benzene-1,2, 3-triol (BDp75-23-7-2007) (4), (E)-4-(3,5-dinitrostyryl)phenol (BDp15-2-11-06) (5), (E)-4-(3,5-dimethylstyryl)phenol (BDp127-22-9-06) (6), (E)-5-styrylbenzene-1, 3-diol (BDp123-8-3-07) (7), Caffeic acid (8), (E)-3,4′-(ethene-1,2-diyl)diphenol (BDp35-23-5-07) (9), (E)-4-styrylphenol (BDp81-5-10-2007) (10), (E)-3-styrylphenol (BDp47-15-6-07) (11), (E)-Stilbene (12), 5-(4-hydroxyphenethyl)benzene-1,3-diol (BDp55-12-7-2006) (13), 5-(4-hydroxyphenethyl)benzene-1,2,3-triol (BDp67-16-7-2007) (14), 3-(4-hydroxyphenethyl)phenol (BDp35-23-5-07) (15), Bisphenol A (16), 3-phenethylphenol (BDp55-27-6-07) (17), 4-phenethylphenol (BDp89-9-8-06) (18).
The numbering scheme used in this section corresponds to the numbering scheme in
Cross-reactivity binding data (
Other notable observations were the loss of affinity upon removal of two or more —OH units such as with the nitro (5), dimethyl (6) and stilbene (12) analogues for which minimal affinity was observed.
Some of the resveratrol analogues that showed affinity towards MIP 8, such as the amide and the imine analogues (
Examples of molecularly imprinted polymers templated with resveratrol analogues are shown in
In order to successfully apply MIP technology to the separation and enrichment of bioactives such as polyphenols at the industry scale, a format affording good separation and high flow is required. As such it was anticipated that an example of an appropriate format for this technology would be a scaleable liquid chromatography technique such as solid phase extraction.
Initial MISPE and non-imprinted solid phase extraction (NISPE) columns were prepared in 3.5 mL syringe barrels capped with 20 μm glass frits. 100 mg of dry MIP were slurry packed into the syringe barrels, allowed to settle overnight. A second glass frit cap was placed on the top of the wet packed column, which was then gently compressed using a plunger, with care taken to keep the column wet, thus preventing the formation of voids and cracks in the column packing. This was repeated for the respective NIP control materials. Columns were successively washed with methanol, methanol containing acetic acid (10% v/v), methanol and acetonitrile.
The MIP columns were pre-conditioned with, successively, methanol containing acetic acid (10% v/v), methanol and acetonitrile). After loading of 1 mL resveratrol (or analyte) solution (0.5 min) onto the MISPE columns, the eluate and solvent from subsequent washing steps were collected in a single fraction tube. Elution of the bound molecules was achieved by several washes with methanol containing acetic acid (10% v/v). Samples were clarified by centrifugation and an aliquot of the supernatant was analysed by reversed-phase HPLC. Samples comprising solvents other than acetonitrile or acetonitrile/H2O were evaporated under vacuum at 30° C. then reconstituted in acetonitrile prior to analysis. All samples were chromatographed via isocratic elution in acetonitrile/H2O (7:3) as mobile phase at a flow rate of 0.5 mL/min with UV-VIS detection at 321 nm for detection and quantification of resveratrol.
The preparation of MISPE materials have been further improved using a modified procedure and apparatus, which has resulted in MIPs that have demonstrated enhanced adsorption selectivity for resveratrol in multiple, reproducible MISPE assays. This procedure has been applied to several different MIPs prepared using various template:functional monomer:cross-linker (T:FM:XL) ratios and alternative porogens. The retention of resveratrol on these MISPE columns is shown in
The performance of MIP 8 was subsequently examined under semi-aqueous conditions (ethanol (20% v/v in water) in MISPE format with a clean up step comprising two washes with 20% (v/v) ethanol in water, followed by successive washes with 1% (v/v) acetonitrile in methanol, and acetonitrile.
The effect of ethanol and water content on resveratrol affinity to MIP 8 was examined by increasing the ethanol content under aqueous binding conditions. The amount of resveratrol bound expressed as a percentage of the initial loading solution for ease of comparison (
Application of a Complex Sample from Agricultural Feedstocks
In order to assess the ability of MIP 8 to concentrate resveratrol from a complex feedstock such as grape press waste and thus be an effective value adding process to the Australian food industry, a grape seed sample was applied to a 100 mg MISPE column packed with MIP 8.
Raw grape seed was provided by CSIRO, Food Science Australia Werribee (Batch No. 02VIN03). 2×10 g samples were measured out, one of which was spiked with 200 μg of resveratrol, and continuously extracted in acetone via soxhlet based on procedure reported by Romero-Perez et al.6 yielding control BDp119-14-9-2006 and spiked BDp119-14-9-2006 extracts. 1 g of each extract were separately suspended in 80% (v/v) ethanol, then sonnicated for 30 minutes and centrifuged at 3000 rpm for 30 minutes. 1 mL aliquots of the respective soluble extracts were applied to off-line MISPE columns packed with 100 mg of MIP 8, the washed with 80% (v/v) ethanol followed by successive washes with acetonitrile and final elution with 10% (v/v) AcOH in methanol. A resveratrol standard solution in 80% (v/v) ethanol in water was applied to a separate MISPE column packed with MIP 8 and treated identically to the grape seed extracts. Non-imprinted control columns (NISPE) were treated exactly the same as their respective MIP counterparts. Aliquots of recovered bound material from MIPSE columns were analyzed by HPLC (see
10 g of peanut meal extract (BDp63-9-7-07) made up in 500 mL EtOH/H2O (50/50 v/v). Mixture was centrifuged and filtered after which 100 mL aliquot was treated by molecularly imprinted solid phase extraction (MISPE) using 1 g of MIP 8 material (1s3-26p62-1-4-08). The MIP column was then washed with 4 column volumes (4×10 mL) of aqueous ethanol (EtOH/H2O 50/50 v/v), followed by a selective clean up wash using 3 column volumes of aqueous acetone (acetone/H2O 50/50 v/v). The remaining bound analytes were eluted via 5×5 mL 10% AcOH in MeOH and 2×5 mL acetone. This procedure was repeated using a column packed with 1 g of non-imprinted control polymer (NIP). The elution fractions were combined, evaporated to dryness and made up to 1 mL in 50% aqueous EtOH of which 200 μL aliquots were analysed by reversed-phase HPLC employing isocratic elution at a flow rate of 0.5 mL/min (Table 9).
Reversed-phase HPLC generated chromatograms of untreated and MISPE treated peanut meal extract (
Peanut meal extract (10 g) was made up in 500 mL EtOH/H2O (50/50 v/v). The mixture was centrifuged and filtered after which 100 mL aliquot was treated by molecularly imprinted solid phase extraction (MISPE) using 1 g of molecularly imprinted polymer (MIP) material. The MIP column was then washed with 4 column volumes (4×10 mL) of aqueous ethanol (EtOH/H2O 50/50 v/v), followed by a selective clean up wash using 3 column volumes of aqueous acetone (acetone/H2O 50/50 v/v). The remaining bound analytes were eluted via 5×5 mL 10% AcOH in MeOH and 2×5 mL acetone. This procedure was repeated using a column packed with 1 g of non-imprinted control polymer (NIP). The elution fractions were combined, evaporated to dryness and made up to 1 mL in 50% aqueous EtOH of which a 200 μL aliquots were analysed by reverse phase HPLC employing gradient elution at a flow rate of 0.5 mL/min (Table 10).
Reversed phase HPLC generated chromatograms of untreated and MISPE treated peanut meal extract (
Phytosterols and Phytostanols are known to lower low density lipoprotein-cholesterol (LDL-C) levels in humans by up to 15%, and there are several products now on the market that are naturally derived fatty acid esters of phytostanols (stanol esters) and phytosterols. Phytosterols are plant fats that are structurally similar to the animal fat cholesterol. All plants including inter alia fruits, vegetables, grains, spices, seeds and nuts contain these sterol compounds or sterolins. Some of the most commonly found phytosterols include beta-sitosterol, stigmasterol and campesterol. Plant oils are a particularly rich source of phytosterols, however all sources are thought to be effective in the treatment or prevention of high cholesterol or hypercholesterolemia.
γ-Oryzanol is a mixture of ferulic acid esters of triterpene alcohols such as cycloartenol and 24-methylene cycloartanyl. γ-Oryzanol has been suggested to have potential functionality such as antioxidant activity, reduction of serum cholesterol, reduction of cholesterol absorption and decrease of early atherosclerosis, inhibition on platelet aggregation, inhibition of tumor promotion, menopausal syndrome treatment and antiulcerogenic activity.
Since the functionality of γ-Oryzanol is promising, rice bran or γ-Oryzanol may have great market potential and can be applied to a wide range of products and functional foods that may provide cholesterol-lowering and antioxidant effects.
The various formulations of different noncovalent and covalent MIPs that have been prepared are summarized in Table 11.
Molecularly imprinted polymers (MIPs) have been prepared using cholesterol and stigmasterol separately as the templating molecule. MIPs and their respective non-imprinted control polymers (NIPs) were prepared according to the following procedure. Template (cholesterol or stigmasterol: 1 eq), functional monomer (4VP or methylacrylic acid: 3 eq) were dissolved in porogen (CHCl3), then sonicated for 10 minutes. The crosslinker (ethyleneglycol dimethacrylate, EGDMA: 30 eq) and free radical initiator (AIBN: 0.25 eq) were subsequently added and thermal polymerisation was performed at 60° C. for 24 hours. NIPS were prepared in an identical manner in the absence of template.
Molecularly imprinted polymers (MIPs) have been prepared using cholesterol as the templating molecule. MIPs and their respective NIPS were prepared according to the following: Template (cholesterol 1 eq), functional monomer (MMA: 3 eq) were dissolved in porogen (H2O:TFA, 9:1), then sonicated for 10 minutes. The crosslinker (ethyleneglycol dimethacrylate, EGDMA: 30 eq) and free radical initiator (AIBN: 0.25 eq) were subsequently added and thermal polymerisation was performed at 65° C. for 24 hours. NIPS were prepared in an identical manner in the absence of template.
Similar rebinding experiments demonstrated that both of these MIPs were capable of binding stigmasterol as shown in
A second series of MIPs was and NIPs were prepared using stigmasterol as template to determine whether the chemical structure differences between stigmasterol and cholesterol affected the overall recognition of the MIP. MIPS were prepared as above using T:MMA:EDGMA in the ratio 1:3:30. The results of rebinding experiments are shown in
Assessment of the “Green Polymer” (MIP21 and NIP21) with porogen 9:1 H2O:TFA with cholesterol and stigmasterol in comparison to MIP19 and MIP20.
The preliminary conclusion which can be drawn is that the “Green Polymer” has a certain degree of recognition for both stigmasterol and cholesterol (see
Attempts to recycle the polymer were promising and are summarized in
A mixture of the phytosterols containing stigmasterol, sitosterol, campesterol and β-sitosterol were derivatised to the corresponding ferrulate esters using readily available ferrulic acid (
Ferullic acid was acetylated using Ac2O/NaOH in water to produce trans-4-O-acetylferrulic acid. The product was purified by adjusting the solution pH to 4-5 with 1 M HCl to form a white precipitate, which was washed subsequently with H2O, dried and collected as a crystalline solid.
1H (300 MHz, CDCl3) 7.0-7.5 (m, 3H, Ar), 6.2 (m, 1H), 3.70 (s, 3H, OCH3), 2.0 (s, 3H, CH3).
Trans-4-O-acetylferulic acid and cholesterol were dissolved in dry CH2Cl2. DCC in CH2Cl2 and DMAP were added and the mixture was stirred at room temperature for 18 hours. Solid by-product was removed by filtration and the solution was successively extracted once with H2O, then twice with 10% HOAc and twice with H2O. The organic extracts were combined and dried over anhydrous MgSO4 and evaporated to yield a white solid. The solid was dissolved in minimal THF and chilled at 0° C. overnight to precipitate any residual by-product. The solution was filtered and the solvent evaporated to form a solid which was purified by isocratic elution in 25% EtOAc/Hexane by column chromatography to give the final product as an off white crystalline solid.
1H (300 MHz, CDCl3) 7.62 (d, 1H, J=16 Hz, Ar), 7.10 (m, 2H, Ar), 6.37 (d, 1H), 4.83 (m, 1H), 3.86 (s, 3H), 2.33 (s, 3H), 0.6-2.0 (m, 50H).
Trans-4-O-acetylferulic acid and β-sitosterol were dissolved in dry CH2Cl2. DCC in CH2Cl2 and DMAP were added and the mixture was stirred at room temperature for 18 hours. Solid by-product was removed by filtration and the solution was successively extracted once with H2O, then twice with 10% HOAc and twice with H2O. The organic extracts were combined and dried over anhydrous MgSO4 and evaporated to yield a white solid. The solid was dissolved in minimal THF and chilled at 0° C. overnight to precipitate any residual by-product. The solution was filtered and the solvent evaporated to form a solid which was purified by isocratic elution in 25% EtOAc/Hexane by column chromatography to give the final product as an off white crystalline solid.
1H (300 MHz, CDCl3) 7.62 (d, 1H, J=16 Hz, Ar), 7.10 (m, 2H, Ar), 6.37 (d, 1H), 4.83 (m, 1H), 3.86 (s, 3H), 2.33 (s, 3H), 0.6-2.0 (m, 50H).
3-O-(trans-4-O-Acetylferuloyl) cholesterol was dissolved in 2:1 CHCl3:MeOH and K2CO3 (0.2 eq) was added and the mixture refluxed for 6 hours. The reaction was subsequently quenched by the addition of satd aq. NH4Cl and the layers organic layer was separated and washed twice with H2O, then dried over MgSO4. The final product was obtained as an off white crystalline solid after recrystallization from 3:1 CHCl3: MeOH
1H (300 MHz, CDCl3) 7.62 (d, 1H, J=16 Hz, Ar), 7.10 (m, 2H, Ar), 6.91 (d, 1H), 6.2 (d, 1H), 5.96 (s, 1H), 4.83 (m, 1H), 3.86 (s, 3H), 0.6-2.0 (m, 50H).
Molecularly imprinted polymers (MIPs) have been prepared using cholesteryl ferrulate as the templating molecule. MIPs and their respective NIPs were prepared according to the following procedure. Template (cholesteryl ferrulate: 1 eq), functional monomer (4VP or methylacrylic acid: 3 eq) were dissolved in porogen (CHCl3), then sonicated for 10 minutes. The crosslinker (ethyleneglycol dimethacrylate, EGDMA: 30 eq) and free radical initiator (AIBN: 0.25 eq) were subsequently added and thermal polymerisation was performed at 60° C. for 24 hours. NIPs were prepared in an identical manner in the absence of template.
The preliminary rebinding studies were performed as follows:
MIP controls were treated the same, except the rebinding solution did not contain the template.
Binding data was analyzed as the percentage of the applied cholesteryl ferrulate, cholesterol or stigmasterol bound to the polymer. The concentration of the free cholesteryl ferulate, cholesterol or stigmasterol was determined from the 4-point calibration curve. The percentage of cholesteryl ferulate bound (
Polymerisation Using “Covalent Approach” with Cholesteryl Ferrulate as a Template for Imprinting:
Molecularly imprinted polymers and their respective non-imprinted control polymers (NIPs) were prepared as follows: (4VP:crosslinker (1:10) where crosslinker is EGDMA) in CHCl3 as a porogen using AIBN as radical initiator.
The performance is detailed in
Future investigations will involve investigation in effects of porogen (such as ethanol, H2O/TFA) in order to optimize the performance of the polymers and the selectivity.
The “hybrid polymer” was prepared with ratios of T:M:C as 1:3:30 for consistency. Where T is cholesterol, M is (E)-3-(4-(methacryloxy)-3-methoxyphenyl)acrylic acid and C is EDGMA.
The performance of the polymer indicates that the “hybrid approach” adds increased flexibility and selectivity in the substrates of interest.
The hybrid polymer shows good selectivity with ester-like substrates and low-moderate levels of nonspecific binding (
In this example, the design and preparation of a (E)-resveratrol imprinted polymer via non-covalent self-assembly and the assessment of its selectivity for (E)-resveratrol over structurally similar analogues is described.
Resveratrol-3-β-D-glucopyranoside (3,4′,5-trihydroxystilbene-3-β-D-glucopyranoside) 5, (E)-stilbene 8, 4-Vinylpyridine (4VP), ethyleneglycol dimethacrylate (EGDMA) and 2,2′-azobis(2-methylpropionitrile) (AIBN) were purchased from Sigma-Aldrich. All solvents used for MIP preparation and evaluation were HPLC grade.
An Agilent Technologies 1100 LC system (Waldbronn, Germany) consisting of a binary pump with a vacuum degasser, auto-sampler with a 900 μL sample loop, thermostated column compartment and a diode-array detector was employed for the HPLC separation of the sample. Injected samples were analysed by RP-HPLC on a Zorbax Eclipse XDB-C18 column (4.6×150 mm, 5 μm particle size).
The selected compounds were chosen to enable the comparative investigation of the number of potential binding sites and their relative positions, around a central E-stilbene core. The general synthetic process is summarized below in
A detailed description for the preparation of (E)-resveratrol 1 and the hydroxylated stilbene analogues (E)-5-(4-hydroxystyryl)benzene-1,2,3-triol 2, (E)-5-styrylbenzene-1,3-diol 3, (E)-3-(4-hydroxystyryl)phenol 4, (E)-4-styrylphenol 6, (E)-3-styrylphenol 7, (and further polyphenols) is reported above. The process entailed conversion of a functionalized benzoic acid to its more activated acid chloride, which after distillation to remove solvents, was immediately on-reacted with an appropriate styrene. The coupling reaction was satisfactorily promoted with catalytic amounts of palladium acetate. This coupling reaction is reported to proceed via a chalcone intermediate. However, only the stilbene adduct was isolated under these conditions, indicating that complete decarbonylation has occurred simultaneously during the reaction. The E stereochemistry of the product was readily confirmed by the characteristic Jtrans=16 Hz coupling constant in the 1H NMR and no Z isomer was detected (expected Jcis=≦12 Hz).
All modelling calculations were conducted using Spartan '08 for Windows V100 software package on a Pentium IV 2.0 GHz. Modelling procedures were based on previously described methods, whereby the semi-empirical equilibrium geometry level theory was applied using a PM3 force field to calculate the energy of formation values (ΔHf), for template, monomer clusters and monomer-template clusters in the gas phase without consideration of solvent effects. Monomer cluster sizes ranging from 1 to 6 monomer units were modelled and the ΔHf values determined for the interaction of the monomer with itself at these cluster sizes. The (E)-resveratrol structural file was then inserted into each cluster file with no pre-defined orientation imposed upon either template or monomer cluster. Equilibrium geometry was determined using an iterative approach. A minimum of three iterations yielded theoretical estimates of the average energy of formation (ΔEi) for the complex, which was determined using the following equation:
ΔEi=Hf_Complex−(ΔHf_Template+ΔHf_Monomer)
(E)-Resveratrol (23 mg, 0.1 min) dissolved in CD3CN was titrated with increasing molar equivalents of 4-vinylpyridine (4VP). The 1H NMR spectrum was recorded after each addition and the change in aromatic —OH shifts followed until the presence of H bonding interactions was evidenced by the consistent downfield shift of this aromatic —OH signal with increased additions. This process was continued until the aromatic —OH signal was no longer detectable due to peak broadening.
MIPs were prepared by dissolving the template (E)-resveratrol (228 mg, 1 mmol) in CH3CN/EtOH (6 mL, 5:1 v/v) in a glass test tube to which the functional monomer 4VP (322 μL, 3 mmol) was added. The mixture was sonicated for 10 minutes and the cross-linker EGDMA (2.314 mL, 15 mmol) and the free radical initiator AIBN (51 mg, 0.31 mmol) were added. This pre-polymerisation mixture was sparged with N2 (g) for 5 minutes and placed in a thermostatic water bath at 50° C. for 24 hours. A number of polymer products were annealed by heating at 60° C. for a further 24 hours. Polymers were then removed from reaction tubes, then crushed and ground using a Retsch 200 ball mill. The ground particles were subsequently sieved and the 63-100 μm size particles retained. Fines were removed by repeated cycles of suspension of the polymer particles in acetone and decanting the supernatant. The (E)-resveratrol template was removed from the MIP resin by repeated washings in MeOH containing 10% AcOH by volume (50 mL) with gently stirring. The washings were monitored by UV-Vis spectroscopy at 321 nm and repeated at least 3 times or until the template could no longer be detected. MIPs were then washed with MeOH to remove traces of AcOH, filtered and dried in vacuo. Non-imprinted control polymers (NIPs) were prepared in exactly the same manner but in the absence of the template molecule. A summary of MIP and NIP preparations is outlined in Table 12.
(E)-Resveratrol saturation studies over the concentration range of 0-4 min in CH3CN were conducted using both MIPs and NIPs at constant polymer weight. Comparison of binding events observed with the MIP and NIP reference materials revealed the extent to which imprinting has influenced adsorption of (E)-resveratrol. The polymer (30 mg) was weighed into a 1.7 mL Eppendorf tube and incubated with analyte solution (1.5 mL, 0-4 min) on a rotary mixer at 40 rpm for 18 hours. The mixture was then centrifuged at 13000 rpm for 15 minutes to pellet the ligand-bound polymer: an aliquot (200 μL) of the supernatant was removed and analysed by RP-HPLC with UV detection at 321 nm and the concentration of unbound (E)-resveratrol was determined from a linear 5 point calibration curve. This concentration was Subtraction of this value from the initial total analyte concentration yielded the amount of analyte bound (B), expressed as μmol/g polymer.
To further investigate non-specific surface binding resulting from interactions with the cross-linker and randomly dispersed functional monomer, static binding assays were conducted on both the MIP and NIP in parallel. The polymer (30 mg) was weighed into a 1.7 mL Eppendorf tube and (E)-resveratrol solution (1.5 mL, 0.5 min in CH3CN) added. The resulting mixture was then treated and analysed as above.
A number of techniques were used to assist in the rational design of an (E)-resveratrol imprinted polymer. Molecular modelling techniques were employed to estimate the strength of intermolecular interactions between (E)-resveratrol and a range of potential functional monomer clusters. This approach identified 4-vinylpyridine (4VP) as a suitable functional monomer (FM) and predicted that a 3:1 molar ratio of 4VP:(E)-resveratrol was optimal for the formation of the most stable pre-polymerisation complex (
Solid imprinted block copolymer monoliths were prepared by incorporating a small amount of EtOH into the porogen solution (CH3CN:EtOH, 5:1 v/v) to increase the solubility of (E)-resveratrol without compromising H-bonding capabilities. This polar protic solvent may contribute to enhancement of aromatic π-π interactions between aromatic groups already clustered in close proximity, while also stabilising existing interactions within the phenolic-pyridinyl cluster systems.
Scatchard analysis revealed a nonlinear concave-upward curve with two distinct linear regions that is typically illustrative of (i) heterogeneity of binding sites, (ii) cooperativity of binding or (iii) multivalent ligand binding, of which (i) is typically considered to describe the binding of molecules to non-covalently prepared imprinted polymers.
To confirm that non-specific surface interactions with randomly dispersed 4VP were responsible for the binding response of the non-imprinted polymer N1, the polymers P2 ((E)-resveratrol imprinted poly-EGDMA, no FM), N2 (non-imprinted poly-EGDMA, no FM) and N3 (non-imprinted poly-4VP, no cross-linker) were prepared. The respective affinity of these polymers for binding of (E)-resveratrol under the same conditions is shown in
Single analyte (non-competitive) cross reactivity studies were employed to examine the influence of positions and numbers of hydrogen bonding OH groups present on the target molecule upon molecular recognition. The static binding affinities of (E)-resveratrol and a range of structural analogues towards the (E)-resveratrol imprinted polymer P1 were determined using equilibrium binding assays. The concentration of the bound analyte was determined by the difference between the initial analyte concentration and the concentration of remaining analyte in solution (
The binding of polyphenol analogues to polymer P1 was investigated under competitive conditions. Results from a competitive static cross-reactivity assay for an equimolar mixture of (E)-resveratrol 1 and analogues 2, 3, 4, 6 and 8 at 0.5 min each are shown in Table 14. To reduce the complexity of the mixture, analogues 5 and 7 were not included in this mixture due to the above demonstrated negligible affinity of these analogues for P1. Polymer P1 retained good recognition for (E)-resveratrol with imprinting factor (IF 2.26) and selectivity (α 1.26) (where α=BMIP−BNIP)/BNIP) parameters that were virtually unchanged from the single analyte experiment (IF 2.35, a 1.36). This result clearly demonstrates that P1 preferentially binds (E)-resveratrol over its structurally similar analogues. Although the binding capacity of P1 for (E)-resveratrol from the mixture was reduced (7.78 μmol/g), this may be a consequence of competition for available binding sites by the tetra-ol analogue. The tetra-ol analogue displayed effectively unchanged binding to P1 (19.84 μmol/g) with improved recognition (IF 1.41) and selectivity (a 0.41) compared to the non-competitive studies (19.37 μmol/g, IF 1.17, a 0.17). The increased IF may be a consequence of reduced nonspecific binding of (E)-resveratrol to randomly distributed 4VP throughout the polymer arising from non-specific binding of other analytes present in the mixture. (E)-resveratrol analogues 3 and 4 that displayed good recognition in single analyte assays (IF 4.02 and 2.89 respectively) were unable to compete with (E)-resveratrol 1 and compound 2 for available binding sites on P1, as manifested by reduced IF and α for both analogues. In accordance with the above static binding results for single analytes, compounds 6 and 8 demonstrated essentially negligible binding. Compound 8 continued to show the lowest value consistent with the least amount of recognition. These results, in accordance with those obtained for single analyte assays, emphasise the importance of the —OH groups with respect to their number and position in the core molecule. Analogues of (E)-resveratrol having at least two —OH groups in the mew and para positions on the aromatic rings (compounds 1, 2, 3, 4) clearly demonstrated moderate to good affinity, with good correlation between binding affinities and the number of aromatic-linked OH groups present.
An (E)-resveratrol-imprinted polymer has been prepared via non-covalent self-assembly and shown with both single and mixed analyte samples to have a highly specific molecular recognition for the template over similar polyphenolic analogues. Recognition of the compounds was influenced by the presence of aromatic OH groups and required at least two such groups in the mew and or para positions. Compounds with more than three aromatic OH groups exhibited strong affinity for the (E)-resveratrol imprinted polymer, but their molecular recognition was inhibited by a high level of non-specific binding. Superior recognition was observed for resveratrol which was able to interact with the binding cavity through three mew and para positioned aromatic OH groups having complementarity with the 3-dimensional binding cavity
Reported here is the synthesis of the imine and amide selectophores of (E)-resveratrol. These selectophores are more easily and efficiently prepared than (E)-resveratrol, as both can be synthesized by a “single-pot” preparation. The performances of the new polyphenolic selectophore-imprinted polymers relative to (E)-resveratrol-imprinted polymer is also reported.
(E)-Resveratrol 1 can be visualized as a polyphenolic compound with an alkene constraint. Analogues with a variation at this constraint were then selected for synthesis, namely the imine, (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol 2 and the amide, 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide 3. All three compounds have two resorcinol hydroxyls that are able to occupy the same 3-dimensional spaces, with the third phenolic hydroxyl then likely to adopt very similar but not identical positions.
Earlier studies in this laboratory used (E)-resveratrol as the original template for the preparation of MIPs. There are numerous reported methods for the synthesis of (E)-resveratrol, but most of these synthetic methods contravene both the Principles of Green Chemistry and modern industrial practicality. All of these methods invariably require multistep syntheses with resultant significant losses of materials, along with consequential purification processes, multiple handlings of noxious reagents, protection and deprotection processes and energy to drive the chemical reactions.
The process used for the synthesis of (E)-resveratrol is summarized in Scheme 5 and was used to transform 3,5-dihydroxybenzoic acid 4 to (E)-resveratrol 1.
This multistep process returned the desired product in a 29% overall yield, but typically required >5 days to complete, and necessitated the generation and handling of corrosive and noxious materials, as well as chromatographic purifications.
The imine selectophore (E)-5-[(4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol 2 was prepared from commercially available 4 aminophenol 5 and 3,5-dihydroxybenaldehyde 6 as shown in Scheme 6.
We have found this method to be highly advantageous in that it rapidly gave quantitative yields of clean product after a simple filtration workup. The stability of this imine product was confirmed by 1H NMR studies in d6-DMSO and CD3CN, which showed that this compound remained unchanged in these solutions over a 6 day period. This imine selectophore also remained intact when used as the template molecule under the conditions employed for MIP preparation, and when used as an analyte to evaluate the binding properties of these MIPs.
The third selectophore example was the amide 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide 3. An authentic sample was initially prepared by the multistep procedure shown in Scheme 7.
Full experimental details for this multistep preparation have been included in the attached electronic supplementary information. This multistep preparation of this amide 3 clearly suffered from the same “non-green” issues that were encountered in the synthesis of (E)-resveratrol 1. Our ongoing requirement for larger amounts of this amide 3 encouraged us to develop an alternative improved process, which is summarized in Scheme 8.
Workup by removal of the solvent followed by trituration and washing with water rapidly returned the pure amide 3 in 76% yield. The ‘green’ advantage of this carbodiimide activated coupling is that the same starting reagents were used as for the reported multistep synthesis, but now the amide was produced in an improved overall yield, using a single-pot procedure, and did not require added energy, functional group protection and deprotection, or chromatographic purification.
The three selectophores synthesized were used as templates for the preparation of MIPs, and as analytes to interrogate the binding characteristics of the new polymers. The preparation of the molecularly imprinted polymers (MIPs) briefly involved the thermally initiated free radical polymerization of a mixture of the selectophore template, the functional monomer and the crosslinker in a porogen. The resultant solid material was then ground and appropriate sized particles sieved off and washed with acid to desorb the template. Non-imprinted polymers (NIPs) were identically prepared in the absence of template molecule. Single analyte binding studies where performed using the (E)-resveratrol imprinted polymer (MIPRES) and the corresponding NIP. in these studies, the polymers were incubated overnight with a freshly prepared solution of analyte, and the supernatant was then removed and its concentration determined by RP-HPLC. Subtraction from the original concentration gave the amount of analyte bound (B) by the polymer, and these results are summarized in
Within this experimental design, MIPRES displayed both similar binding capacity and comparable selective affinities (BMIP−BNIP) for the alkene, the amide and the imine molecules. The similarity of these binding parameters suggests that MIPRES displays generic cross-reactivity towards each of these polyphenolic selectophores. This result is consistent with similar spatial conformations that all of these molecules adopt in solution. These selectophores are also likely to possess similar electronic characteristics as inductive variations associated with these three different linkages are likely to be moderated by both distance from the aromatic hydroxyl groups and the aromatic it clouds. Consequently, these selectophores are similarly bound at the recognition surfaces within these MIP cavities.
The suitability of the amide and imine selectophores as (E)-resveratrol template mimics was then assessed. Each of these compounds was used as templates for the preparation of new MIPs (i.e. MIPAMIDE and MIPIMINE respectively) using a similar protocol to that employed for the preparation of MIPRES. Static binding assays were conducted as before, and the ability of these MIPs to recognise (E)-resveratrol are reported in
The selectophore-imprinted MIPAMIDE and MIPIMINE both displayed selective affinity for (E)-resveratrol, but with reduced capacity compared to MIPRES. Despite the fact that these molecules may have similar conformations in solution, the stereotopological spaces occupied by the pyridyl nitrogens of 4-vinylpyridine, which are the complementary functional binding groups during imprinting, must differ for all three MIPs. The decreased binding capacity and lower selective affinity observed for both MIPAMIDE and MIPIMINE may also reflect that these imprinted polymers have a diminished ability to bind and maintain a favoured conformation of the alkene (E)-resveratrol, a finding that may be a consequence of the increased relative structural rigidity of the alkene constraint.
Methodologies to synthesize structural analogues with spatially defined functionalities, or selectophores, of the polyphenol (E)-resveratrol have been developed. These compounds were more easily and conveniently prepared using “greener” single-pot procedures. The selectophores were then used as template mimics for the preparation of MIPs, and these new polymers were found to display comparable, but not identical binding, towards this representative polyphenolic compound.
The approach is a technique that can be used to explore and characterize new MIPs, and our findings suggest that appropriate selectophores may be suitable templates to enable the more convenient preparation of generic MIPs which are capable of extracting structurally similar compounds.
AR solvents were used as purchased from the manufacturer except for dimethylformamide (DMF) which was dried over 4 Å molecular sieves, toluene over sodium wire, and pyridine and triethylamine over KOH pellets. Milli-Q distilled water was used for aqueous manipulations. Solvent mixtures are expressed as volume/volumes. Solvent extracts were dried over anhydrous sodium sulfate, filtered and then rotary evaporated to dryness at low pressures (>10 mbar) at 30-35° C. Analytical thin layer chromatography (TLC) was conducted on silica gel using Merck® 1.05554.001 plates. The components were visualised by (i) fluorescence at 254 nm and (ii) ethanolic phosphomolybdic acid solution dip and char. Silica gel column chromatography was conducted using Merck® 1.09385.1000. Melting points were determined by open glass capillary method and are uncorrected. NMR spectra were recorded on a Bruker DPX-300; 1H at 300 MHz and 13C JMOD at 75 MHz. Deuterated solvents were used as indicated and the residual solvent peaks used for internal reference. J values are given in Hz. Low resolution electrospray ionisation mass spectra (ESI) were recorded using a Micromass Platform II API QMS Electrospray mass spectrometer in both positive (ESI+) and negative (ESI−) polarity. High-resolution electrospray mass spectra (HRMS) were recorded on a Bruker BioApex 47e Fourier Transform mass spectrometer. Mixtures were sonicated in a 37 kHz/150 W Elmasonic 5100 ultrasonic cleaning unit. Polymers were ground using a Retsch PM 200 Planetary Ball Mill and sized on a Retsch AS 200 sieve shaker.
A suspension of 3,5-dihydroxybenzoic acid (15.40 g, 0.100 mol) in ethyl acetate (220 mL) was cooled in an ice-bath. Acetic anhydride (24.52 mL, 0.2421 mol), pyridine (16.16 mL, 0.1998 mol) and 4-(dimethylamino)pyridine (100 mg, 0.81855 mmol) were added and the reaction stirred at 0° C. for 60 minutes and then at room temperature overnight. Formic acid (5.12 mL, 0.1357 mmol) was added and the reaction poured onto ice (ca. 500 g). Further ethyl acetate (300 mL) was added and the organic phase separated and washed with water (2×200 mL), sat. aq. NaHCO3 (100 mL), further water (2×200 mL), and then dried and evaporated to a white solid. Recrystallization from 5:1 EtOAc/hexane (120 mL) gave 2 crops of 3,5-diacetoxybenzoic acid (combined weight 17.07 g, 72%) as a white powder. Rf 0.20 (1:1 EtOAc/hexane), 0.39 (3:1 EtOAc/hexane); mp 161-162° C. (from EtOAc/hexane) (lit. mp: 157-159° C.); δH(CDCl3) 2.29 (s, 6H, 2×OAc), 7.18 (pseudo t, 1H, J 2.1, 4-H) and 7.70 (pseudo d, 2H, J 2.1, 2-H, 6-H); δC(CD3OD) 18.43, 118.94, 119.02, 131.70, 150.19, 165.46 and 168.17; m/z (ESI) 261 (MNa+, 100%).
3,5-Diacetoxybenzoic acid (8.022 g, 33.706 mmol) suspended in a mixture of toluene (130 mL), DMF (500 μL) and thionyl chloride (16.00 mL, 220.6 mmol) was heated at 100° C. for three hours under an argon gas atmosphere. The solvents were removed by vacuum distillation and the residue re-suspended in toluene (85 mL) and sonicated under vacuum to remove dissolved gases. 4-Acetoxystyrene (5.74 mL, 37.5 mmol), N-ethylmorpholine (4.31 mL, 33.9 mmol) and palladium diacetate (35 mg, 0.16 mmol, 0.46 mole %) were added and the reaction heated to reflux for 2 hours. Further palladium diacetate (116 mg, 0.52 mmol, 1.54 mole %) was added and the reaction left to reflux overnight. On return to room temperature, ethyl acetate (500 mL) was added, the solution was washed with 0.1 M HCl (2×300 mL) and water (300 mL) and then dried and evaporated to return a brown solid. Purification with column chromatography (isocratically eluted with 2:1 Et2O/hexane) gave 7.888 g of a white solid, shown by 1H NMR to be predominantly the desired adduct. Further chromatography (gradient eluted starting with 4:1 hexane/EtOAc and finishing with 2:1 hexane/EtOAc) returned pure (E)-3,4′,5-triacetoxystilbene (6.071 g, 51%) as a white solid. Rf 0.29 (2:1 hexane/EtOAc); mp 112.5-113.0° C. (lit mp 116° C.); 511 (CDCl3) 2.27 (s, 9H, 3×OAc), 6.80 (pseudo t, 1H, J 2.1, 4′-H), 6.93 (d, 1H, J 16.3, Htrans), 7.03 (d, 1H, J 16.3, Htrans), 7.04-7.09 (m, 4H, 3-H, 5-H, 2′-H, 6′-H) and 7.44-7.47 (m, 2H, 2-H, 6-H); δC(CDCl3) 20.07, 113.39, 115.88, 120.88, 126.19, 126.64, 128.64, 133.45, 138.53, 149.46, 150.34, 167.91 and 168.30; m/z (ESI) 377 (MNa+, 100%), 378 (21).
The reaction was conducted under an argon gas atmosphere. Potassium hydroxide (22 mg, 0.3922 mmol) dissolved in methanol (3.0 mL) was added to a suspension of (E)-3,4′,5-triacetoxystilbene (113 mg, 0.319 mmol) in methanol (10 mL). The solid immediately dissolved and the clear solution was gently heated to reflux for 60 minutes and a marked darkening in colouration noted. The volume was then reduced to half with rotary evaporation and the remaining solution acidified (pH 2) with 1M aq. HCl. Ethyl acetate (150 mL) was added and the reaction washed with sat. brine (3 20×20 mL), dried and evaporated to return a dark red solid. Purification with column chromatography (isocratically eluted with 100% EtOAc) gave (E)-resveratrol (58 mg, 79%) as a pale beige coloured solid. Rf 0.65 (EtOAc); mp 261.0-263.0° C. (lit mp 255-260° C.); δH(CD3OD) 6.13 (pseudo t, 1H, J 2.2, 4-H), 6.41-6.42 (m, 2H, 2-H, 6-H), 6.71-6.79 (m, 3H, Htrans, 5′-H), 6.93 (d, 1H, J 16.3, Htrans) and 7.29-7.36 (m, 2H, Jortho 8.6, 2′-H, 6′-H); δC (CD3OD) 100.30, 103.47, 114.12, 124.64, 126.43, 127.06, 128.07, 138.97, 155.89 and 157.20; m/z (ESI) 229 (MH+, 100%), 230 (23).
A mixture of 3,5-dihydroxybenzaldehyde (300 mg, 2.174 mmol), 4-aminophenol (237 mg, 2.174 mmol) and anhyd. sodium sulphate (309 mg, 2.176 mmol) in dichloromethane (15 mL) was vigorously stirred at room temperature for 3 hours. Further anhyd. sodium sulphate (309 mg, 2.176 mmol) was added and the stirring continued for an additional one hour. Dichloromethane was removed by rotary evaporation and the white residue re-suspended in boiling ethanol (10 mL) and filtered whilst hot. The solid was washed in the funnel with further hot ethanol (10 mL). The clear filtrates were combined and rotary evaporated to dryness to give (E)-5-[(4-hydroxy-phenylimino)-methyl]benzene-1,3-diol (501 mg, 100%) as a pale pink solid. Rf 0.48 (2:1 EtOAc/hexane); darkens with heating with mp>340° C.; δH (d6-DMSO) 6.36 (pseudo t, 1H, J 2.2, 4-H), 6.80-6.85 (m, 4H, 2-H, 6-H, 3′-H, 5′-H), 7.16-7.22 (m, 2H, Jortho 8.8, 2′-H, 6′-H), 8.43 (s, 1H, imine-H), 9.47 (bs, 3H, 3×phenolic-OH); δC (d6-DMSO) 106.27, 107.41, 116.70, 123.42, 139.35, 143.61, 157.16, 158.38 and 159.62; m/z (ESI) 230 (MH+, 100%), 231 (13); m/z (HRESI) 252.0633 ([M+Na]+ C13H11NO3Na+ requires 252.0637).
The reaction was conducted under a positive pressure of argon gas. 3,5-Dihydroxybenzoic acid (2.310 g, 15.000 mmol) and 4-aminophenol (1.962 g, 18.000 mmol) were dissolved in DMF (90.0 mL). N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride (3.450 g, 17.997 mmol) was added and the reaction stirred at room temperature overnight. The solvent was removed by rotary evaporation under high vacuum and the oily residue co-distilled with water until a solid formed. This solid was triturated with cold 0.01 M HCl (50 mL), filtered, and the pale purple coloured product washed in the funnel with cold water (4×20 mL). The solid was dried with desiccant under vacuum to give pure 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide (2.791 g, 76%); Rf 0.39 (4:1 EtOAc/hexane); mp 266.0-266.5° C.; δH(CD3OD) 6.47 (pseudo t, 1H, Jmeta 2.2, 4-H), 6.77-6.82 (m, 4H, 3′-H, 5′-H, 2-H, 6-H), 7.43-7.46 (m, 2H, Jortho 8.9, 2′-H, 6′-H); δH (d6-DMSO) 6.42 (pseudo t, 1H, Jmeta 2.2, 4-H), 6.72-6.78 (m, 4H, 3′-H, 5′-H, 2-H, 6-H), 7.51-7.56 (m, 2H, Jortho 8.9, 2′-H, 6′-H), 9.20 (s, 1H), 9.51 (s, 2H) and 9.83 (s, 1H); δC(CD3OD) 104.41, 104.67, 113.92, 122.13, 129.10, 136.08, 153.26, 157.41 and 166.70; m/z (ESI) 244 ([M−H]−, 100%), 489 ([2M−H]−, 29); m/z (HRESI) 246.0764 ([M+H]+C13H12N1O4+ requires 246.0766).
Molecularly imprinted polymers (MIPs) were prepared by dissolving the selectophore template (1 mmol) in porogen (5:1 acetonitrile/EtOH, 6 ml) in a disposable glass test tube. Acetone (6 mL) was the preferred porogen with the amide 3 due to its incomplete solubilization in the original mixture volume.10 The functional monomer 4 vinylpyridine (322 μL, 3 mmol) was added and the mixture sonicated for 10 minutes. Ethyleneglycol dimethacrylate (2.314 mL, 15 mmol) was then added as cross-linker and 2,2-azobis(isobutyro)nitrile (51 mg, 0.31 mmol) added as radical initiator. This pre-polymerisation mixture was sparged with nitrogen gas for 5 minutes before being heated in a thermostatic water bath at 50° C. for 24 hours. The solid polymers were removed from the reaction tubes, crushed with a mortar and pestle and finely ground using a Retsch 200 ball mill. Grounds were sieved and the 63-100 μm size particles retained. This size range was repeatedly suspended in acetone and the supernatant poured off to remove fines. Bound template was then removed from the polymer by repeated washings with methanolic 10% acetic acid until the washings were free of template (monitored by UV-Vis spectroscopy at 321 nm). Non-imprinted control polymers (NIPs) were prepared using the same procedure in the absence of a template molecule.
Experiments were conducted on both MIP and NIP in parallel under identical conditions.
Analyte solution (1.5 mL, 0.5 min in acetonitrile) was added to the polymer (30 mg) in an Eppendorf tube. This was mixed at 40 rpm for 18 hours and the polymer settled by centrifugation for 15 minutes at 13000 rpm. A 200 μL aliquot of the supernatant was removed and analysed by RP-HPLC with UV detection at 321 nm. Concentration was determined by comparison with a linear 5 point calibration curve. The amount of analyte bound (B) was determined as the difference between this and the initial value and reported in units of μmol/g polymer.
F. Enrichment of the Bioactive Polyphenol (E)-Resveratrol from Peanut by-Products Via Molecular Imprinting
A rapid technique for the isolation and enrichment of (E)-resveratrol and the determination of related polyphenols from peanut press waste using molecular imprinting technology is reported.
4-Vinylpyridine (4VP), ethyleneglycol dimethacrylate (EGDMA) and 2,2′-azobis(2-methylpropionitrile) (AIBN), (+)-catechin hydrate (lyophilized prior to use), caffeic acid and (E)-piceid were obtained from Sigma-Aldrich (Sydney, NSW, Australia). 4-VP and EGDMA were purified immediately prior to use via vacuum distillation and alumina column chromatography, respectively. All solvents used were HPLC grade.
(E)-Resveratrol 1 was synthesized using the methodology reported above.
An (E)-resveratrol imprinted polymer (MIPRES) was prepared by dissolving (E)-resveratrol and 4-VP (in ratio 1:3 mole equivalents) in acetonitrile/EtOH (5:1 v/v). The resulting mixture was purged with N2 (g) for 2 minutes and sonicated for 20 minutes prior to the addition of EGDMA (15 mole equivalents) and the free radical initiator AIBN. The mixture was then sealed and purged with N2(g) for 2 minutes and then placed in a 50° C. water bath (18 hrs) followed by a thermal annealing treatment at 60° C. (24 hrs). A non-imprinted polymer (NIP) was prepared as a control in the same manner without the inclusion of the (E)-resveratrol template. The resulting hard bulk monoliths were ground using a Retsch 200 ball mill to produce a particle size distribution of 60-100 μm which were isolated by sieving. The template molecule was extracted by repeated washings with MeOH/AcOH (9:1 v/v) until the template was no longer visible in the extraction media by absorbance at 321 nm. The MIP particles were then washed with MeOH to remove traces of AcOH and the fines removed by repeated sedimentation in acetone. The remaining MIP particles were subsequently dried in vacuo at 40° C. overnight.
Selectivity studies were conducted for both MIP and NIP using a constant polymer amount of 30 mg. The NIP was used to determine the extent of non-specific binding resulting from interactions with the cross-linker and randomly dispersed functional monomer. The polymer was incubated in 1.5 mL of analyte solution (0.5 min) in acetonitrile. The resulting mixture was mixed at 40 rpm for 18 hours and then centrifuged at 13000 rpm for 15 minutes. An aliquot (200 μL) of the supernatant was removed and analysed by RP-HPLC by UV spectroscopy at 321 nm and the concentration of free analyte was determined from a linear 5 point calibration curve. The amount of bound analyte (B), expressed as μmol/g polymer, was calculated by subtracting the free analyte concentration from the initial total analyte solution concentration.
Small scale MISPE studies were conducted on SPE columns containing 100 mg of either MIP or NIP stationary phases. Polymeric stationary phase (100 mg) was slurry packed in MeOH into 3 mL syringe barrels fitted with polypropylene frits (20 μm pore size). The resulting SPE columns were subsequently conditioned with 1.5 mL (3 column volumes) of either acetonitrile or EtOH/H2O (1:1, v/v) for organic and aqueous studies respectively, after which 1 mL of an (E)-resveratrol (0.5 min) solution in acetonitrile or EtOH/H2O (1:1, v/v) was loaded on-column. Multiple selective clean up steps (1 mL each) were then applied to each column using either acetonitrile or 1% AcOH in EtOH/H2O (1:1, v/v) after which each column was eluted using 10% AcOH in MeOH (2 mL). The fractions collected from the clean up and elution steps were evaporated to dryness, reconstituted to 1 mL in EtOH/H2O (1:1, v/v) and analysed by RP-HPLC. The (E)-resveratrol concentration was determined using a 5 point calibration curve.
The RP-HPLC separation was performed on an Agilent Technologies 1100 LC system (Waldbronn, Germany) consisting of a binary pump with a vacuum degasser, auto-sampler with a 900 μL, sample loop, thermostated column compartment and a diode-array detector. Injected samples were analysed on a Zorbax Eclipse XDB-C18 column (4.6×150 mm, 5 μm particle size) at 40° C. The mobile phase consisted of 0.1% AcOH in H2O (solvent A) and 0.1% AcOH in EtOH/H2O applying the following gradient: 0-2 min: 25% B isocratic, 2-6 min: 25-37.5% B, 6-9 min: 37.5% B isocratic, 9-12 min: 37.5-62.5% B, 12-15 min: 62.5% B isocratic, 15-18 min: 62.5-100% B, 18-22 min: 100% B isocratic, 22-25 min: 100-25% B, 25-29 min: 25% B isocratic. The flow rate was 0.5 mL min−1. Injection volume was 5 μL with the UV-Vis diode array detector (80 Hz) set to the absorbance wavelengths of λ=280, 321 and 370 nm.
All chromatographic separations were performed using an Agilent 1100 Capillary LC system (Agilent Technologies, Palo Alto, Calif., USA) coupled to an ion-trap MS system (Agilent 1100 Series LC/MSD-SL). Separation of the MIP eluate was performed using a Zorbax 300SB-C18 (150 mm×0.3 mm I.D.) capillary column packed with 3.5 μm particles. The outlet of the column was directly connected to the electrospray source of the ion-trap mass spectrometer, with the UV detector bypassed. A 0.3 mg/mL MIP eluate sample in acetonitrile/H2O (60:40, v/v) containing 0.1% FA was separated using a mobile phase consisting of 0.1% FA in H2O (solvent A) and 0.1% FA in acetonitirle applying the following gradient: 0-15 min: 10% B, 15-65 min: 10-65% B, 65-70 min; 60-95% B. The flow rate was 4 μL mind Injection volume was 0.2 μL. ESI-MS/MS analysis was carried out in the positive ion mode. The mass spectrometer was operated in a data-dependent mode where the two most intense ions in the precursor ion scan were subjected to subsequent automated MS/MS. All system control and data acquisition were conducted with Agilent ChemStation and MSD Trap Control software.
Peanut press waste (200 g) in EtOH:H2O (1000 mL, 4:1 v/v) was sonicated for 60 min, after which the mixture was filtered and the solvent evaporated to return 17.9 g of extract. A 10.0 g amount of this peanut press waste extract was reconstituted to 500 mL in EtOH/H2O (1:1 v/v) in a volumetric flask and stored at 4° C. until required. Prior to use the peanut press waste extract was equilibrated at room temperature and sonicated to clarify the solution.
MISPE studies were conducted using 1.0 g of either MIPRES or the corresponding NIP as control stationary phase, to examine its ability to selectively retain and enrich (E)-resveratrol from the peanut press waste extract described above. Columns were conditioned using 3 column volumes each of MeOH, then EtOH and finally EtOH/H2O (1:1, v/v) containing 0.1% AcOH. Peanut press waste extract (2×50 mL) was applied to each column. The breakthrough fractions were collected under vacuum and recycled back through the columns to maximize the interaction between the stationary phase and the polyphenolic components within the peanut press waste extract. Each column was then washed with EtOH/H2O (1:1 v/v) (20 mL), followed by successive selective clean up steps comprising EtOH/H2O (1:1 v/v) containing 1% AcOH (20 mL) and then acetone/H2O (1:1 v/v) (30 mL) to disrupt non-specific binding. An acidic elution step with 10% AcOH in MeOH (25 mL) was then applied to desorb and remove the compounds of interest from each column. Elution fractions were combined, evaporated to dryness and made up to 1.0 mL in EtOH/H2O (1:1 v/v) and analysed by RP-HPLC.
(E)-resveratrol-imprinted polymer cavities were generated via an initial self-association between the acidic phenolic hydroxyl groups of (E)-resveratrol with the electron rich pyridinyl nitrogen of the 4VP functional monomer. The resultant pre-polymerization complex formed primarily from self-assembling hydrogen bonding interactions, may be stabilized by the participation of additional aromatic π-π interactions due to the close proximity of phenolic and pyridinyl aromatic groups. The self-assembled complex was then ‘frozen’ by polymerization of the styryl functionalities in the presence of the cross-linker EGDMA. Removal of the template molecule resulted in the generation of MIP cavities that are complementary to (E)-resveratrol.
The cross-reactivity of MIPRES was evaluated using several structurally related, naturally occurring polyphenols: E-resveratrol, caffeic acid, (=)-catechin and (E)-piceid. For MIPRES, the order of recognition (MIP-NIP) was (E)-resveratrol 1>caffeic acid 2>catechin 3>(E)-piceid 4 (Table 15). Although the binding capacity of MIPRES for both caffeic acid and (+)-catechin is comparable to that observed for the template molecule, this is offset by increased non-specific binding of these compounds by the NIP. It can be concluded that the greater number of groups on caffeic acid and (+)-catechin, compared to (E)-resveratrol, that can form hydrogen bonds with the NIP is responsible for stronger non-selective binding and thus greater affinity to the NIP control polymer, thereby leading to reduced recognition. Negligible recognition of the glucosylated resveratrol molecule (E)-piceid, was observed, which is presumably due to the presence of the bulky glucose substituent preventing access to the MIPRES binding cavities. Further, the reduced binding capacity of the NIP for (+)-catechin compared to (E)-resveratrol provides additional support for the involvement of H-bond interactions in non-specific binding to MIPs and NIPs. Based upon the selectivity displayed by MIPRES towards (E)-resveratrol over other structurally related molecules, typical of those found in polyphenol-rich sources, it was anticipated that a MIPRES based SPE extraction would selectively isolate the target (E)-resveratrol from a complex agricultural byproduct matrix.
To establish that the use of MIPRES as a MISPE sorbent for the refinement of (E)-resveratrol was viable, preliminary small scale experiments were conducted with MIPRES stationary phase in both organic and aqueous environments. The binding capacity of MIPRES for (E)-resveratrol was determined in this format, as was the effect of an aqueous clean up step to disrupt weak or non-specific binding compared to an organic clean up step (
Peanut press waste is a by-product of peanut oil preparation, constituting the remains of the peanut and husk after pressing that contains a range of bioactive constituents including phytosterols, flavanols and other polyphenols. However, as this by-product is regularly disposed of as landfill or stock feed, these bioactives often remain underutilized. As peanuts and peanut derivatives are consumed in large quantities globally, the resulting peanut meal by-product presents a significant reservoir of bioactive components such as the bioactive polyphenol (E)-resveratrol, which is present in amounts ranging from 0.02-1.79 μg/g in various peanut market types. Therefore, we have employed MIPRES in a MISPE format to selectively isolate and enrich (E)-resveratrol from a peanut meal liquid extract. RP-HPLC chromatograms of the peanut meal extract and subsequent MIP eluates are shown in
The MIPRES eluate was analysed by tandem liquid chromatography-ESI-mass spectrometry (LC-ESI-MS) in positive ion mode, which confirmed the presence of (E)-resveratrol (Rt=12.2 minutes, 229 m/z [M+H]+) by comparison to an (E)-resveratrol standard.
In addition to (E)-resveratrol, the MIPRES cavities also exhibited affinity for a secondary molecule as evidenced by the peak at Rt=9.9 min. This peak is associated with a more polar compound that was not retained by the NIP control polymer. LC-ESI-MS revealed the presence of mass peaks corresponding to [M+H]+ ions at 577 m/z and 865 m/z, both of which correlate with the expected mass of A-type procyanidin dimers and trimers, respectively.
The application of a molecularly imprinted solid phase extraction technique has been demonstrated for the isolation and enrichment of bioactive polyphenols from peanut by-products. The use of an (E)-resveratrol imprinted polymer as the stationary phase column afforded both significant sample clean up and a 60-fold enrichment of (E)-resveratrol from an aqueous peanut press waste extract with minimal sample preparation.
In this example, a rapid tandem MISPE approach for the isolation and concentration of (E)-resveratrol and related polyphenols in high purity from peanut meal is reported.
4-Vinylpyridine (4VP), ethyleneglycol dimethacrylate (EGDMA) and 2,2′-azobis(2-methylpropionitrile) (AIBN), catechin and piceid were obtained from Sigma-Aldrich (Sydney, NSW, Australia). 4-VP and EGDMA were purified immediately prior to use via vacuum distillation and alumina column chromatography, respectively. All solvents used were HPLC grade.
(E)-Resveratrol 1 and the structurally related polyphenolic analogue 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide 2 were synthesized as described above.
Several MIPs and their non-templated counterparts (NIPs) were prepared as summarized in Table 16. MIPRES was prepared at 50° C. (18 hours) followed by a thermal annealing treatment at 60° C. (24 hours). MIPAMIDE was produced with a different porogen at 55° C. (40 hours). Both these preparations produced MIPs having comparable binding performance.
+MIPRES
+NIPRES
+Prepared at 50° C. with thermal annealing treatment at 60° C. in 6 mL of porogen.
The RP-HPLC separation was performed on an Agilent Technologies 1100 LC system (Waldbronn, Germany) consisting of a binary pump with a vacuum degasser, auto-sampler with a 900 μL sample loop, thermostated column compartment and a diode-array detector. Injected samples were analysed on a Zorbax Eclipse XDB-C13 column (4.6×150 mm, 5 μm particle size) at 40° C. The mobile phase consisted of 0.1% AcOH in H2O (solvent A) and 0.1% AcOH in EtOH/H2O or MeOH/H2O (8:2 v/v) (solvent B), applying the following gradient: 0-2 min: 25% B isocratic, 2-6 min: 25-37.5% B, 6-9 min: 37.5% B isocratic, 9-12 min: 37.5-62.5% B, 12-15 min: 62.5% B isocratic, 15-18 min: 62.5-100% B, 18-22 min: 100% B isocratic, 22-25 min: 100-25% B, 25-29 min: 25% B isocratic. The flow rate was 0.5 mL mind The injection volume was 5 μL with the UV-Vis diode array detector (80 Hz) set to the absorbance wavelengths of λ=280, 321 and 370 nm.
Peanut meal (200 g) in EtOH:H2O (1000.0 mL, 4:1 v/v) was sonicated for 60 min, after which the mixture was filtered and the solvent evaporated to return 17.9 g of extract. A peanut meal extract for use in subsequent experiments was prepared by adding 10.0 g of this material to a solution of EtOH/H2O (1:1 v/v) and diluting to 500 mL in a volumetric flask and stored at 4° C. until required. Prior to use, the peanut meal extract was brought to room temperature and sonicated to clarify the solution.
(E)-Resveratrol saturation studies over the concentration range of 0-2 min were conducted for both MIPs and their NIP counterparts using a constant amount of polymer (30 mg). The NIP response was used to determine the extent of non-specific binding resulting from interactions with the cross-linker and randomly dispersed functional monomer. The polymers were incubated with mixing at 40 rpm for 18 hours in 1.5 mL of acetonitrile containing resveratrol and then centrifuged at 13000 rpm for 15 minutes to pellet the polymers. An aliquot (200 μL) of the supernatant was removed and analysed by RP-HPLC with UV detection at 321 nm, and the concentration of unbound (E)-resveratrol was determined from a linear 5 point calibration curve. This concentration was subtracted from the total analyte solution concentration to derive the amount of analyte bound (B) expressed as μmol/g polymer.
Selectivity studies were conducted for both MIPs and NIPs using a constant amount of polymer (30 mg). The polymers were separately incubated with either resveratrol or the structurally similar analogues 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide 2, catechin 3 and (E)-piceid 4. Binding of each of these compounds was evaluated as described above.
Preliminary MISPE studies were conducted using MIPRES or MIPAMIDE (250 mg) to investigate their ability to selectively retain and enrich resveratrol and other polyphenols from the peanut meal extract. A solution of the peanut meal extract (25 mL) was applied to each column and the breakthrough fractions were collected under vacuum and recycled back through the columns to maximize the interaction between the stationary phase and the polyphenolic components within the peanut meal extract. Each column was then washed with EtOH/H2O (1:1 v/v, 3 column volumes, 6 mL), then with H2O (10 mL) to remove unbound and/or weakly bound water-soluble components of the extract. A selective clean up step with aqueous acetone (acetone/H2O, 1:1 v/v, 2 mL) was used to disrupt non-specific binding. An acidic elution step with 10% AcOH in MeOH (10×1 mL) was then used to desorb and remove the specifically bound compounds of interest from each polymer. The elution fractions were combined, then evaporated to dryness and reconstituted in 1.0 mL in EtOH/H2O (1:1 v/v). These concentrated eluates were clarified by centrifugation and the supernatant removed for RP-HPLC analysis.
Separate MIPRES and MIPAMIDE columns (1000 mg each) were pre-conditioned with EtOH/H2O (1:1 v/v) containing 1% AcOH (15 mL). Peanut meal extract (100 mL) was loaded onto the first of two MIP columns in series (MIPRES) as illustrated in
Prior to the second cycle (
The processed extract from two cycles of tandem MISPE was subsequently reloaded onto a larger column of MIPRES (5 g) to extract any remaining polyphenolic compounds in the largest quantity possible. This column was pre-conditioned with MeOH containing 10% AcOH (3 column volumes), MeOH (3 column volumes) and 1% AcOH in EtOH/H2O (1:1, v/v) (3 column volumes). Remaining processed peanut meal extract (comprising the flowthrough and washes from first MISPE application described above) was applied (100 mL) and the subsequent flowthrough collected. The column was then eluted with 1% AcOH in EtOH/H2O (1:1, v/v) (50 mL).
Molecularly imprinted polymers templated with either resveratrol 1 or 3,5-dihydroxy-N-(4-hydroxyphenyl)benzamide 2 were prepared using the functional monomer 4VP. The use of 4VP provided the opportunity for hydrogen bonding or ionic interactions between the electron rich pyridine nitrogen and the acidic phenolic groups in both of these template compounds. Aromatic π-π interactions may also participate in stabilising the pre-polymerisation complex which is subsequently ‘frozen’ during polymerization in the presence of the cross-linker EGDMA. The binding characteristics and performance of MIPRES is reported above describing the preparation of an (E)-resveratrol selective MIP that is capable of the specific recognition of (E)-resveratrol present in a complex mixture comprising multiple structurally related analogues and other polyphenolics.
3,5-Dihydroxy-N-(4-hydroxyphenyl)benzamide 2 was synthesised as a template for preparing MIPAMIDE that should generate “pseudo” (E)-resveratrol cavities within an imprinted polymer that are capable of binding not only the template molecule, but also (E)-resveratrol and potentially other structurally related compounds that are present in complex food waste matrices.
(E)-resveratrol saturation studies were conducted to determine the (E)-resveratrol binding affinity of MIPAMIDE, (
The cross-reactivity of both MIPRES and MIPAMIDE was evaluated via binding site interrogation using several structurally related polyphenols (
Peanut meal or peanut press is generated during peanut oil preparation and constitutes the remains of the peanut and husk after pressing. Peanuts contain variable amounts of (E)-resveratrol (0.02-1.79 μg/g) (11), amounts which exceed what we have observed in grape marc. Accordingly, binding of components present in a peanut meal extract, a complex mixture of bioactive polyphenols including (E)-resveratrol and catechin-based oligomers, was evaluated using MIPRES and MIPAMIDE. A liquid peanut meal extract was prepared and separately applied to either MIPRES or MIPAMIDE columns or the respective NIP controls. RP-HPLC chromatograms of the peanut meal extract and subsequent MIP eluates are shown in
The eluate from MIPRES (
The concept of employing multiple MIPs in a tandem separation and isolation strategy, whereby multiple bioactive components may be captured and isolated from a single source, was explored as outlined in
Typical RP-HPLC chromatograms from the tandem MISPE treatment of peanut meal extract are shown in
The tandem combination of MIPRES and MIPAMIDE enabled the near quantitative (96%) recovery of resveratrol as summarised in Table 17. This result clearly signifies that both MIP columns are capable of selective retention and enrichment of (E)-resveratrol with almost complete recovery from the crude feed stock.
1Recovery determined for 1 mL reconstituted samples
2ND = Not detectable.
Surprisingly, the MIPAMIDE column also displayed preferential selectivity towards (E)-resveratrol over the likely type A procyanidins (Rt=15 minutes, 577 m/z [M+H]+), a result in contrast to observations that showed that MIPAMIDE preferentially bound the unknown compound compared to (E)-resveratrol (
Since the tandem MISPE columns had selectively removed most of the (E)-resveratrol (96%) from the initial feed stock, it was anticipated that with diminished competition for available MIP binding sites both MIPRES and MIPAMIDE would selectively bind the procyanidin remaining in the resveratrol-depleted peanut meal extract. Consequently, the flowthrough and wash fractions from the processed peanut meal extract were combined and re-applied to the reconditioned tandem MIPRES and MIPAMIDE columns. The RP-HPLC chromatograms of the extracts recovered from the MIPRES and MIPAMIDE columns, obtained using the same conditions as above, showed that (E)-resveratrol did not bind or elute from either column (
The findings reported here demonstrate the ability of molecularly imprinted polymers (MIPs) to selectively fractionate a mixture comprising polyphenols such as resveratrol and A-type procyanidins from peanut meal extract without the requirement for extensive sample pre-treatment. These MIPs may also be utilized in such a manner that more than one polyphenol may be separately isolated or enriched from the same feed stock with a rapid tandem MISPE (i.e., MIPs in series) approach.
This technology represents a new approach for the practical application of MIPs. Extraction of bioactives from processing waste streams (e.g., peanut by-products, winery grape seeds and skins, apple juice production wastes) may be a considerable logistic exercise, due to the large quantities of material, from geographically diverse locations, to isolate and return much smaller amounts of target bioactives. Therefore, it may be more advantageous to consider initial separation or pre-concentration of bulk-scale materials at the site of waste generation, which would result in material that is more easily handled and combined for final separations and purifications at a single dedicated processing facility. Alternatively, extraction may be performed at, or close to, the site of waste generation using low technology applications for the initial process of extraction of valuable materials from waste streams. An exemplar methodology could be based on the use of “tea bags” filled with MIPs for isolating target molecules from the feed stock.
“Teabags” for use in these investigations have been made from cotton-based materials, Gilson® 63 μm sieve mesh and Sigma Aldrich dialysis tubing cellulose membrane (12 kDa MWCO). The bags were held in an electroplated metal tea infuser to protect them from physical damage during stirring. They are robust for periods of several days and tolerate soaking in mixtures of ethanol, water and acetic acid.
Binding experiments using MIPs in a teabag were conducted. The MIPs used in the resveratrol binding experiments were MIP8 (as numbered in the patent application), MIPE, MIPAMIDE, and MIPIMINE as set out in the Examples above. The MIPs used in the phytosterol biding experiments were prepared using a 1:3:30 ratio of template:4-VP:EDGMA.
MIPs were templated with ergosterol, campesterol, cholesterol, stigmasterol, cholesteryl ferrulate, ferrulic acid and coumarin as described above. MIPs were packed in teabag polymer bags, and then placed in the crude plant extract for 18 hours. The teabag was subsequently removed from the mixture and transferred to a solution of 10% acetic acid in MeOH for 4 hours. The teabag was removed and the solution was evaporated to dryness; the resulting solid was reconstituted to approx 0.5 min in 20% ACN/MeOH, and analyzed by HPLC and ESI/MS. The performance MIPs were evaluated using extracts from avocado oil, sesame seed oil, wheat oil, grape seed oil, β-sitosterol vitamin supplement, and a green tea extract, derived from Lipton Green Tea™. The individual components extracted were identified. Several different polymers could be place singularly or severally in individual bags to simultaneously and concurrent extract the maximum amount and number of compounds of interest from the extract solutions. Recycling of individual MIPs was also established and the results demonstrated the reusability of these MIPs without significant deterioration in performance. The peaks in the 13C NMR spectrum allow for an analysis of the various captured and isolated phytosterols. For example, with the bound fraction eluted from a loaded campesterol-templated MIP, the peaks in the 13C NMR spectrum reveal only pure campesterol confirming that campesterol only has been specifically and selectively absorbed by this MIP. On the other hand with the cholesterol-templated MIP, the stigmasterol present in the crude extract was significantly bound suggesting that cholesterol can be used as a biomimetic template (in a manner analogous to the green resveratrol—the imine analogue of resveratrol), for molecular imprinting of more expensive and difficult to produce polymers.
A corresponding experiment was carried out for binding of resveratrol to “teabag” MIPs using MIP8 (as numbered in the patent application), MIPE, MIPAMIDE, and MIPIMINE using the following feedstock examples: peanut skin and mash by-products, winery grape seeds and skins, apple juice production wastes and a green tea extract, derived from Lipton Green Tea™.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia or elsewhere before the priority date of each claim of this application.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009900328 | Jan 2009 | AU | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13146970 | Nov 2011 | US |
| Child | 15017737 | US |
