Process for synthesizing active esters of carboxylic acids

Description

The invention relates to a new synthesis of active esters of carboxylic acids. It also relates to the new alpha-halogenated carbonates which are useful for this synthesis, and to the method of producing them.
Active esters of carboxylic acids are much sought after, especially in the field of peptide synthesis. Thus, esterified, N-protected amino acids are stable products which may be stored and marketed. It is subsequently only necessary to react them with an amino compound in order to form the peptide bond.
The various types of active esters are well described in the literature (Houben Weyl Vol. 15, 2nd part, or Specialist Periodical Reports "Amino-acides Peptides and Protein" Vol. 1-14).
Among the most common esters, substituted aryl esters, such as 2,4,5-trichlorophenyl esters, and esters of hydroxyamines, such as N-succinimidyl esters, may be mentioned.
These active esters can also be used for coupling biologically active molecules to proteins or to solid or liquid supports (German Patent Application No. 2,631,656, European Patent Application No. 2,677).
They are also used for grafting amino acids onto biologically active molecules (European Patent Application No. 10,297).
A number of processes have already been proposed for preparing them [Tetrahedron 36 2409 (1980)].
The most widely used process consists of condensing the acid and the hydroxyl compound in the presence of dicyclohexylcarbodiimide as a dehydrating agent, but the yields are variable and there is formed, as by-product, dicyclohexylurea, which is very difficult to remove completely, and N-acylureas [Chem. Ber. 100, 16 (1967)].
According to another process, the hydroxylated compound is reacted with the mixed anhydride formed from the acid to be esterified and a carboxylic, carbonic or phosphoric acid chloride. Two stages are then generally necessary. Acid chlorides are unpleasant reagents to handle and are frequently toxic.
It is also possible to obtain active esters by reaction of the acid with a symmetrical carbonate formed from the hydroxylated compound. However, one equivalent of the hydroxylated compound is then lost, and this is frequently an expensive product which it is difficult to remove from the medium and recover.
It has also been proposed to replace the hydroxylated compound, in the case of 2,4-dinitrophenol, by its fluoride, which reacts with the sodium salt of the acid. However, this method is highly specific.
Some authors have, in fact, employed more sophisticated reagents such as 2-halopyridinium salts or the triphenylphosphine/diethyl azodicarboxylate system.
The very large number of processes proposed in the literature for producing these active esters tends to substantiate the view that none is entirely satisfactory, and that, in view of the value of these compounds, a better solution is still being sought.
The object of the invention is specifically to provide a process in which this expectation is fulfilled.
According to the process of the invention, a carboxylic acid is reacted, in the presence of an agent for binding hydrohalic acid, with an alpha-halogenated carbonate of the formula ##STR3## in which R.sup.1 denotes either a radical of formula ##STR4## in which R.sup.3 and R.sup.4, which may be identical or different, are not hydrogen atoms and denote highly diverse organic radicals which may be substituted or unsubstituted and saturated or unsaturated, and may or may not be bound to a polymer, and which can be joined together to form a heterocyclic system with the nitrogen atom,
or a substituted or unsubstituted aryl radical which may or may not be bound to a polymer,
R.sup.2 denotes a hydrogen atom, an aliphatic or cycloaliphatic radical which may be substituted or unsubstituted and saturated or unsaturated, or a substituted or unsubstituted aromatic radical,
and X denotes a halogen atom.
The reaction scheme is as follows: ##STR5## This reaction is surprising since, in effect, it is known that alpha-halogenated carbonates react with acids to give ester carbonates according to the scheme: ##STR6## This reaction is described, in particular, in Patents FR No. 2,201,870 and 82,404, and is very useful for improving the efficacy of certain drugs.
The mechanism of the reaction according to the invention is completely different, and an advantage of the invention is that the conditions have been discovered whereby active esters may be obtained.
The process according to the invention is applied to a very large number of simple or complex acids, saturated or unsaturated aliphatic, cycloaliphatic and heterocyclic acids, as well as aromatic acids. By way of example, acetic, acrylic, thiophenecarboxylic and benzoic acids may be mentioned.
It is especially useful for the esterification of N-protected natural or synthetic amino acids.
If the acids bear especially reactive groups, it is preferable to protect these but it is generally not necessary.
The alpha-halogenated carbonates of formula ##STR7## which R.sup.1 and R.sup.2 have the above meanings and which are reacted with the acids, are new compounds which also form the subject of the present invention.
R.sup.3 and R.sup.4 can, for example, be aliphatic or aromatic radicals, and they are frequently joined together and R.sup.1 then denotes one of a number of heterocyclic radicals. This heterocyclic system can comprise one or more hetero atoms which may be identical or different, and it can be saturated or unsaturated, may or may not be condensed with an aromatic system and can be substituted or unsubstituted.
R.sup.1 also frequently denotes a substituted or unsubstituted phenyl radical.
The substituents of R.sup.1 can be hydrocarbon groups, halogen atoms, especially chlorine or fluorine atoms, or functional groups such as nitro.
The radicals which are regarded as good activating groups in the active esters are the preferred radicals. These are, for example, N-succinimidyl, para-nitrophenyl, 2,4-dinitrophenyl, 2,4,5-trichlorophenyl, pentachloro or -fluorophenyl, and N-phthalimidyl radicals.
X is a halogen atom, a fluorine, chlorine, bromine or iodine atom, and is preferably chlorine.
R.sup.2 generally denotes a C.sub.1 to C.sub.5 aliphatic radical, especially a methyl radical which can be substituted with one or more halogen atoms, or a phenyl radical which is unsubstituted or substituted with, for example, one or more halogen atoms.
The trichloromethyl radical is very suitable.
The alpha-halogenated carbonates of the invention are generally crystalline, stable at room temperature and of little or no toxicity.
The method of producing them, which also forms the subject of the invention, will be described shortly.
One of the applications thereof is the preparation of active esters as described above.
In this application, one equivalent of carbonate is generally used for one equivalent of acid. If necessary, it is possible to depart from this proportion.
The carbonate and the acid are reacted in a solvent which is inert with respect to them. This solvent is generally chosen from cyclic or acyclic ethers, such as tetrahydrofuran or dioxane, esters such as, for example, ethyl acetate, nitriles such as acetonitrile, alcohols such as, for example, isopropanol, amides such as, for example, dimethylformamide and ketones such as, for example, acetone. Tetrahydrofuran is very suitable.
The presence of an agent for binding hydrohalic acid is necessary, to remove the acid which forms during the reaction. All the customary means can be employed. This will generally be an inorganic base, for example potassium carbonate, or an organic base, for example a tertiary amine.
Among preferred bases, N-methylmorpholine or triethylamine may be mentioned.
One equivalent of base is generally used per equivalent of acid, but an excess of base is no disadvantage.
The reaction temperature is generally between -20.degree. and 100.degree. C. It is chosen according to the reactivity of the carbonate used. It is most frequently between 20.degree. and 30.degree. C.
As regards the reaction time, this varies from a few minutes to a few hours. In general, two hours are sufficient to obtain good results. A simple means for establishing the completion of the reaction is to observe the cessation in the evolution of carbon dioxide.
The esterified acid obtained is purified by conventional, simple methods. The by-products of the reaction, which are the hydrochloride of the base used and the aldehyde, are readily removed, for example by washing with water. Then, by evaporation of the solvent, a product is obtained which is already of high purity and which can be recrystallised in a suitable solvent. The yields are excellent.
The invention also relates to the method of producing the new alpha-halogenated carbonates described above.
This method of production consists in reacting the hydroxylated compound of formula R.sup.1 OH, in which R.sup.1 has the meaning given above, with an alpha-halogenated chloroformate of formula ##STR8## in which R.sup.2 and X have the meaning given above, in an inert solvent medium at a temperature between -20.degree. and 100.degree. C., in the presence of an organic or inorganic base.
The reaction is as follows: ##STR9##
The starting hydroxylated compounds and alpha-halogenated compounds are generally commercially available or are manufactured according to known methods. For example, the alpha-halogenated chloroformates are prepared by halogenation of the corresponding chloroformates, or as described in French Patent Applications Nos. 2,482,587 and 2,532,933, and European Patent Application No. 108,547.
As an organic or inorganic base, a base is generally employed which is known to bind hydrochloric acid. Pyridine or triethylamine is preferably used.
It is preferable to add the base to the mixture of the reagents, and also to add it gradually.
A stoichiometric amount of the base and the reactive components is generally used, but an excess of alcohol can be employed.
The solvent medium consists of one or more solvents which are inert towards the reagents. Chlorinated aliphatic solvents, for example dichloromethane and dichloroethane, cyclic or acyclic ethers, ketones such as acetone or 2-butanone, nitriles, esters and aliphatic or aromatic hydrocarbons are preferably chosen.
When certain hydroxylated compounds such as phenols are reacted, it is preferable to choose a solvent system in which the phenol is only slightly soluble and the hydrochloride of the base is insoluble. A benzene/petroleum ether mixture, for example, is very suitable.
The reaction temperature is preferably between -10.degree. and 40.degree. C.
When the introduction of the reagents is complete, the mixture is generally brought to room temperature. The reaction time is frequently between a few minutes and a few hours.
The carbonate obtained is readily isolated by the usual methods. For example, the mixture is washed wih iced water or acid sodium sulphate, or filtered on a celite bed and the solvent or solvents then evaporated. The crystals generally obtained can be recrystallised in the conventional manner.
Thus, the invention enables new carbonates to be prepared in a simple manner without a special installation. Due to the originality of their structure, these new carbonates may form the subject of highly diverse applications.
The application to the esterification of acids, which forms the subject of the present invention, is a very useful application. The active esters of the acids are thereby obtained without great difficulty and without racemization, by using in a simple manner reagents which are easy to obtain and handle. The by-products of the reaction, the hydrochloride of the base used and aldehyde, are readily removed. The yields are very good and the products of high purity.

The examples which follow are given by way of illustration.
EXAMPLES 1 TO 10: SYNTHESIS OF ALPHA-HALOGENATED CARBONATES
The carbonates are prepared according to one or more of the following methods. The results are collated in Table 1.
METHOD A
12.35 g (0.05 mol) of 1,2,2,2-tetrachloroethyl chloroformate are added in a single portion to a solution of 5.75 g (0.05 mol) of N-hydroxysuccinimide in dichloromethane (50 ml). The mixture is cooled to 0.degree. C. and 4 g (0.05 mol) of pyridine is added dropwise. When the addition is complete, the mixture is allowed to return to room temperature and stirred for 3 hours. 20 ml of iced water are then added, and the organic phase is separated and washed with 20-ml portions of iced water as many times as are necessary until the pH is no longer acid (generally 3 to 4 times). The organic phase is dried over magnesium sulphate and evaporated, and a white solid is obtained which is crystallised in petroleum ether. 13.5 g (yield Y=83%) of the expected carbonate are collected. This recrystallisation can be obmitted; the yield is then 94% and the product is of satisfactory purity.
METHOD B
The procedure is as in Method A, replacing pyridine by triethylamine. The reaction is carried out for one hour at 0.degree. C. and then one hour at room temperature. In this case, the organic phase is washed rapidly with saturated NaHSO.sub.4 solution. After evaporation, the N-hydroxysuccinimide carbonate is crystallised in ethyl ether (Y=83%).
METHOD C
27 g (0.11 mol) of 1,2,2,2-tetrachloroethylchloroformate are added to a suspension of 18.4 g (0.1 mol) of 2,4-dinitrophenol in 150 ml of benzene and 150 ml of petroleum ether. The mixture is cooled to 0.degree. C. and 11 g (0.11 mol) of triethylamine are added dropwise while vigorous stirring is maintained. The mixture is stirred for 4 hours at 20.degree. C. and then filtered on a celite bed. The solvents are evaporated and 26 g (Y=66%) of white crystals are obtained after being washed with a little petroleum ether.
TABLE 1 Crystallisation M.p. or B.p. Ex Product Method Yield solvent mm Hg .degree.C. .sup.1 H NMR ppm IR cm.sup.-1 Elementary analysis 1 ##STR10## AB 8383 Petroleum etherEthyl ether 104108 2,9(s)6,6(s) 1760 C 26,00; H 1,74; N 4,10; O 23,54; Cl 43,55;(calculated: C 25,87; H 1,55; N 4,31;O 24,6; Cl 43,55; 2 ##STR11## A 64 Petroleum ether 71 6,73(s)7,4(s) 1800 C 26,61; H 1,02; O 11,56; Cl 60,80;(calculated C 26,54; H 0,74; O 11,78; Cl 60,93) 3 ##STR12## A 92% crude70% dist. -- B.p. 0,02 =150-155 6,7(s)7,4(s)7,56(s) 1795 C 26,67; H 0,90; O 11,95; Cl 60,64;(calculated: C 26,54; H 0,74;O 11,78; Cl 60,93; 4 ##STR13## A 98 AcOEt 120 6,7(s) 1800 C 22,40; H trace; Cl 67,15;(calculated: C 22,66; H 0,27; Cl 67,05 5 ##STR14## A 91 -- B.p. 0,05 = 80 6,7(s) 1800 C 27,60; H 0,47; Cl 35,80; F 24,56;(calculated C 27,44; H 0,26; Cl 36,00; F 24,12); 6 ##STR15## C 75 Petroleum ether B.p. 0,05 = 165M.p. 69 6,7(s)7,5(d)8,36(d) 1790 C 30,87; H 1,53; N 3,81;O 22,23; Cl 41,15; (calculated C 30,97; H 1,44; N 4,01; O 22,92; Cl 40,64) 7 ##STR16## C 66 Petroleum ether 121-122 6,73(s)8,60(s)9,06(d)7,66(d) 1795 C 27,49; H 1,04; N 6,98;O 27,99; Cl 35,95;(calculated C 27,44; H 1,02;N 7; O 28,43; Cl 36,00) 8 ##STR17## A 75 B.p. 0,05 =115-131 2,8(s)7,2(s)7,3 to8(m) 1750 M.sup.+ + 18 = 335 9 ##STR18## B 85 CH.sub.2 Cl.sub.2 145-147 7,04(s)7,6(d) 7,8(dd)8,0(d)8,2(d) 17701790 C 31,38; H 1,37; N 12,16; Cl 41,03;(calculated C 31,30; H 1,45; N 12,17;Cl 41,16) 10 ##STR19## A 86 Petroleum ether 105-106 6,4(q)1,9(d)2,8(s) 1750 C 37,80; H 3,64; N 6,24;O 36,68; Cl 15,88;(calculated C 37,94; H 3,64; N 6,32;O 36,10; Cl 16,00
EXAMPLE 11: PREPARATION OF N-SUCCINIMIDYL N-TERT-BUTYLOXYCARBONYL-L-ALANINATE
0.95 g (5 mmol) of N-tert-butyloxycarbonyl-L-alanine and 0.66 ml (5.5 mmol) of N-methylmorpholine are dissolved in 6 ml of THF, and 1.8 g (5.5 mmol) of N-succinimidyl 1,2,2,2-tetrachloroethyl carbonate is added in a single portion. The mixture is stirred for two hours at 20.degree. C. Approximately 25 ml of ethyl acetate are added and the organic phase is washed rapidly with N HCl solution, then with potassium bicarbonate solution and finally twice with water. The organic phase is dried over magnesium sulphate and evaporated. The residue is crystallised in an ethyl acetate/petroleum ether mixture and 1.25 g (Y=87%) of white crystals are obtained. Evaporation of the mother liquors and crystallisation enables a further 0.1 g to be recovered, and this brings the yield to 94%.
M.p. (melting point)=158.degree. C. [.alpha.].sub.D.sup.20 =50.7 (c=2, dioxane)
EXAMPLE 12: PREPARATION OF N-SUCCINIMIDYL N.sup..alpha. -TERT-BUTYLOXYCARBONYL-N.epsilon.-BENZYLOXYCARBONYL-L-LYSINATE
1.64 g (5 mmol) of N-succinimidyl 1,2,2,2-tetrachloroethyl carbonate is added to a solution of 1.9 g (5 mmol) of N.sup..alpha. -BOC-N.epsilon.-Z-lysine and 0.7 ml (5 mmol) of triethylamine in 15 ml of THF. The mixture is stirred at room temperature for 2 hours. 20 ml of ethyl acetate are then added and the organic phase is washed with 0.5N citric acid solution, then three times with 5% strength sodium bicarbonate solution and finally with saturated sodium chloride solution. The organic phase is dried over sodium sulphate and evaporated to dryness. 2.03 g (Y=85%) of white crystals are obtained.
M.p 110.degree. C. [.alpha.].sub.D.sup.20 =-21.51 (c=2, dioxane)
Analysis calculated for C.sub.23 H.sub.34 N.sub.3 O.sub.6.5H.sub.2 O: C=56.79; H=6.79; N=8.64 Found C=56.32; H=6.44; N=8.77.
EXAMPLES 13 TO 29
Other N-succinimidyl esters are prepared as in Example 11 or 12. All the results are summarised in Table 2.
TABLE 2__________________________________________________________________________N--SUCCINIMIDYL ESTERS Litera- ture Yield M.p. yield M.p.EX Amino acid % .degree.C. [.alpha.].sub.D.sup.20 (, solvent) % .degree.C. [.alpha.].sub.D.sup.20 (c, solvent) REF__________________________________________________________________________11 BOC-- Ala 94 158 -50,7 (2, dioxane) 71 161 -49,0 (2, dioxane) 112 BOC-- (Z)-- Lys 85 110 -21,51 (2, dioxane) -- 110 -21,12 (2, dioxane) 213 BOC-- Phe 91 147 -19,8 (2, dioxane) 81 152 -20,7 (2,2 dioxane) 114 BOC-- Gly 91 162 -- 62 168 -- 115 BOC-- Val 92 125 -37,4 (2, dioxane) 74 125 -37 (2, dioxane) 116 BOC-- Pro 82 133 -54,7 (2, dioxane) 74 135 -55,3 (2, dioxane) 117 BOC-- Tyr 69-74 181 -12,12 (1, dioxane) 180 -12,5 (1, dioxane) 218 BOC-- Trp 89 140 -23,13 (2, dioxane) 37 153 -22,4 (2, dioxane) 119 BOC-- Met 92 124 -21,6 (2, dioxane) 59 128 -20,6 (2, dioxane) 120 BOC-- (SBzl) Cys 61 106 -54,0 (2, dioxane) 49 117 -54,0 (2, dioxane) 121 BOC-- (OBzl)-- Ser 78 -- +5,8 (0,5, dioxane) 52 112-113 -[.alpha.].sub.D.sup.26 +6,5 (0,5 dioxane) 222 BOC-- (OBzl)-- Thr 85 -- +9,38 (2, dioxane) -- 94 -8,5 (1, methanol) 223 BOC-- (OBzl) Tyr 73 144 -6,2 (2, dioxane) -- 149 -6,3 (2, dioxane) 224 Z-- Ala 86 123 -36,9 (2, dioxane) 65 123 -37,2 (2, dioxane) 125 Z-- Pro 97 90 -54,9 (2, dioxane) 74 90 -54 (2, dioxane) 126 Z-- Met 72 102 -16,2 (2, dioxane) 59 102 -15,9 (2, dioxane) 127 FMOC-- Ala 70 102 -- -- -- -- --28 FMOC-- Phe 97 137 -- -- -- -- --29 FMOC-- Pro 100 -- -- -- -- --__________________________________________________________________________ Ref. 1 J. Am. Chem. Soc. 86, 1839 (1964) 2 HoubenWeyl: Methoden der Org. Chemie Vol. 15(2) p. 165 and loc. cit.
EXAMPLE 30: PREPARATION OF N-SUCCINIMIDYL N-TERT-BUTYLOXYCARBONYL-N-PHENYLALANINATE
To a solution of 1.33 g (5 mmol) of BOC-L-phenylalanine in 6 ml of THF, 0.8 g of anhydrous potassium carbonate and 1.8 g of 1,2,2,2-tetrachloroethyl N-succinimidyl carbonate are added. The mixture is stirred for two hours at 20.degree. C. and treated as in Example 11. 1.15 g (Y=63%) of 80C-L-PheOSu is obtained. M.p. 135.degree. C.
If 1 ml of aqueous potassium carbonate solution is used in place of anhydrous potassium carbonate, 1.3 g (Y=72%) of the above ester is obtained.
EXAMPLE 31: PREPARATION OF N-SUCCINIMIDYL N-TERT-BUTYLOXYCARBONYLGLYCINATE
The procedure is as in Example 11, replacing THF by acetonitrile. Starting with 1.76 g of BOC-glycine, 2.1 g (Y=77%) of BOC-Gly-OSu is obtained.
M.p. 158.degree. C. M.p. lit 168.degree. C.
EXAMPLE 32: PREPARATION OF N-SUCCINIMIDYL N-TERT-BUTYLOXYCARBONYL-N-PHENYLALANINATE
To a solution of 1.33 g (5 mmol) of BOC-L-phenylalanine in 6 ml of THF, 0.66 ml of N-methylmorpholine and 1.11 g (5 mmol) of 1-chloroethyl N-succinimidyl, carbonate are added. The mixture is stirred for 16 hours at 20.degree. C. and treated as in Example 11. 1.40 g (Y=77%) of BOC-L-Phe-OSu is obtained.
M.p. 143.degree. C. [.alpha.].sub.D.sup.20 =-16.6 (c=2,2 dioxane).
EXAMPLE 33: PREPARATION OF (2-CHLOROPHENYL)CHLOROMETHYL N-TERT-BUTYLOXYCARBONYL-L-ALANINATE
To a solution of 0.95 g (5 mmol) of BOC-L-alanine and 0.66 ml of N-methylmorpholine in 6 ml of THF, 2.0 g of (2-chlorophenyl)chloromethyl N-succinimidyl carbonate are added. The mixture is stirred for 1 hour 30 minutes at 20.degree. C. and treated as in Example 11. 1.25 g (Y=90%) of BOC-L-Ala-OSu is obtained.
M.P. 158.degree.-159.degree. C. [.alpha.].sub.D.sup.20 =-49.5 (c=2, dioxane).
EXAMPLES 34 TO 42: PREPARATION OF 2,4,5-TRICHLOROPHENYL ESTERS
These esters are prepared as in Example 11 or 12, starting with 1,2,2,2-tetrachloroethyl 2,4,5-trichlorophenyl carbonate. The results are collated in Table 3.
EXAMPLE 43: PREPARATION OF PENTACHLOROPHENYL N-TERT-BUTYLOXYCARBONYL-L-ALANINATE
The procedure is as in Example 12. Starting with 0.84 g (5 mmol) of BOC-L-alanine and 2.27 g (5 mmol) of pentachlorophenyl 1,2,2,2-tetrachloroethyl carbonate, 2.06 g (Y=94%) of white crystals are obtained (recrystallisation solvent: ethyl acetate/hexane).
M.p. 170.degree. C. [.alpha.].sub.D.sup.20 =-24.47 (c=1, CHCl.sub.3)
literature
M.P. 166.degree. C. [.alpha.].sub.D.sup.20 =-22.2 (c=5.1, CHCl.sub.3).
EXAMPLE 44: PREPARATION OF PENTACHLOROPHENYL N.sup..alpha. -TERT-BUTYLOXYCARBONYL-N.epsilon.-BENZYLOXYCARBONYL-L-LYSINATE
The procedure is as in Example 12. Starting with 1.9 g of N.sup..alpha. -BOC-N.epsilon.-Z-L-lysine, 2.4 g (Y=77%) of N.sup..alpha. -BOC-N.epsilon.-Z-L-lysine-OPCP are obtained.
TABLE 3__________________________________________________________________________2,4,5-TRICHLOROPHENYL ESTERS Litera- Yield M.p. ture M.p. [.alpha.].sub.D.sup.20 (c, solventEX Amino acid % .degree.C. [.alpha.].sub.D.sup.20 (c, solvent) yield .degree.C. literature Ref__________________________________________________________________________34 BOC-- Ala 79 82 -43,5 (2, acetic ac.) 73 82 -44 (2, acetic ac.) 135 BOC (SBzl) Cys 60 -- 86 77 -- 136 BOC (DNP) Hist 58 98 +1,87 (2, dioxane) -- -- --37 BOC-- (OBzl) Glu 60 107 -33,5 (2, methanol) 60 108 -33,5 (2, methanol) 238 BOC-- (Z) Lys 85 99 -19,13 (2, dioxane) 86 99 -- 139 BOC-- Met 79 90 -38,0 (2, DMF) 71 91 -38,5 (2, DMF) 140 BOC-- Ser 22 105 -42,0 (2, DMF) 5 105 -41 (2, DMF) 341 BOC-- (OBz-l) Ser 77 oil + 0,3 (2, dioxane) -- -- -- --42 BOC-- Tyr. 73 168 -31,4 (3,5, acetic ac.) 40 158 -26,4 (3,5 acetic 2c.)__________________________________________________________________________ Ref. 1 J. Chem. Soc (C) (1967) 2 Tetrahedron Suppl. 8,39 (1966) 3 J. Med. Chem. 10, 1047 (1977)
M.p. 142.degree. C. [.alpha.].sub.D.sup.20 =-16.7 (c=1, CHCl.sub.3).
literature:
M.p. 141.degree. C. [.alpha.].sub.D.sup.20 =-15.0 (c=4.99, CHCl.sub.3).
EXAMPLE 45: PREPARATION OF 4-NITROPHENYL N-TERT-BUTYLOXYCARBONYL-L-PHENYLALANINATE
0.73 g (2.75 mmol) of BOC-L-phenylalanine and 0.3 ml of N-methylmorpholine are dissolved in 6 ml of THF, and 87 g (2.5 mmol) of 1,2,2,2-tetrachloroethyl 4-nitrophenyl carbonate are added. The mixture is stirred for one hour at room temperature 15 ml of ethyl acetate are then added and the mixture is washed with normal hydrochloric acid solution and then with saturated sodium chloride solution. The organic phase is dried over magnesium sulphate. It is evaporated to dryness and the product is crystallised in 95% strength ethanol. 0.6 g (Y=62%) of white crystals are obtained.
M.p. 118.degree. C. [.alpha.].sub.D.sup.20 =-20.9 (c=2, DMF).
literature:
M.p. 132.degree. C. [.alpha.].sub.D.sup.20 =-21 (c=2, DMF).
EXAMPLE 46: PREPARATION OF 2,4-DINITROPHENYL N-TERT-BUTYLOXYCARBONYL-L-ALANINATE
The procedure is as in the example above. Starting with 0.945 g (5 mmol) of N-BOC-L-alanine, 1.45 g (Y=82%) of N-BOC-L-Ala-O-2,4-DNP, crystallised in 95% strength ethyl alcohol, is obtained.
M.p. 95.degree.-96.degree. C. [.alpha.].sub.D.sup.20 =-51.5 (c=0.2, DMF).
EXAMPLES 47 TO 54: PREPARATIONS OF PENTAFLUOROPHENYL ESTERS
The procedure is as in Example 11. The results are collated in Table 4.
TABLE 4__________________________________________________________________________PENTAFLUOROPHENYL ESTERS Lit. Yield M.p. M.p. LiteratureEX Amino acids % .degree.C. .degree.C. [.alpha.].sub.D.sup.20 (c, solvent) [.alpha.].sub.D.sup.20 (c, REF.ent)__________________________________________________________________________47 BOC-- Ala 90 85 83 -34,6 (1, dioxane) -31,2 (1, dioxane) 148 BOC-- Gly 90 80 80 -- --49 BOC-- Phe 86 112 112 -16,9 (1, dioxane) -26,9 (1, dioxane) 150 BOC-- Val 94 64 64 -31,8 (1, dioxane) -18,4 (1, dioxane) 151 BOC-- Pro 98 50 51 -48,2 (1, dioxane) -53 (1, dioxane) 152 BOC-- Trp 91 111 111 -12,8 (1, dioxane) -28,1 (1, dioxane) 153 BOC-- Met 81 79 80 -20,7 (1, dioxane) -22,5 (1, dioxane) 154 Z-- Pro 100 oil oil -55,08 (1, dioxane) -55,05 (1, dioxane) 1__________________________________________________________________________ Ref. 1 Ann. 1421 (1973)
EXAMPLE 55: PREPARATION OF PENTAFLUOROPHENYL N-TERT-BUTYLOXYCARBONYL-L-PHENYLALANINATE
The procedure is as in Example 48, but varying the reaction solvent. The results obtained are collated in the following table:
______________________________________SOLVENT YIELD M.P. .degree.C. [.alpha.].sup.20______________________________________THF 86 112 -16.9DIOXANE 86 113 -16.4ETHYL ACETATE 83 112 -15.4DMF 65 107 -14.2______________________________________
EXAMPLES 56 AND 57
These examples illustrate the use of the active esters of the amino acids in the synthesis of di- and tripeptides.
56. Preparation of ethyl N-BOC-L-phenylalanylglycinate (BOC-Phe-Gly-OEt)
To a solution of 0.86 g (2 mmol) of pentafluorophenyl N-t-butyloxycarbonyl-L-phenylalaninate, prepared according to Example 48, in 10 ml of dioxane, 0.28 g (2.2 mmol) of ethyl glycinate (hydrochloride) and 0.31 g (3 mmol) of triethylamine are added simultaneously. The mixture is stirred for one hour at room temperature. It is diluted with 10 ml of ethyl acetate and washed with aqueous 0.1N hydrochloric acid, potassium bicarbonate and sodium chloride solutions. The organic phase is dried over magnesium sulphate and evaporated. The residue is taken up with a 4:6 ethyl acetate/hexane mixture and filtered on silica. After evaporation, 0.53 g (Y=76%) of BOC-Phe-Gly-OEt is obtained.
M.p. 89.degree. C. [.alpha.].sub.D.sup.20 =-4.8 (c=5.0, EtOH)
M.p..sub.lit =89.5.degree. C. [.alpha.].sub.D.sup.20 -4.2 (c=5.0, EtOH) [J. Amer. Chem. Soc. 82, 4596 (1960)].
57 Preparation of ethyl N-benzyloxycarbonylprolinylglycylglycinate
Z-Pro-GlyOH.fwdarw.Z-Pro-Gly-OPFP.fwdarw.Z-Pro-Gly-Gly-OEt
1.4 g (3.6 mmol) of 1,2,2,2-tetrachloroethyl pentafluorophenyl carbonate is added to a solution of 1.07 g (3.6 mmol) of N-benzyloxycarbonylprolinylglycine and 0.4 ml of N-methylmorpholine in 5 ml of dioxane. The mixture is stirred for one hour at 20.degree. C. and treated as in Example 55. 0.82 g (Y=45%) of Z-Pro-Gly-OPFP is obtained:
[.alpha.].sub.D.sup.20 =-36.8 (c=1, dioxane).
This 0.8 g is dissolved in 10 ml of dioxane, and 0.23 g (1.8 mmol) of ethyl glycinate hydrochloride and 0.25 g of triethylamine are added simultaneously. The procedure is then as in Example 55. 0.55 g (Y=94%) of Z-Pro-Gly-Gly-OEt is obtained.
M.p. 95.degree.-96.degree. C. [.alpha.].sub.D.sup.20 =-21.4 (c=1, EtOH)
which is recrystallised in an ethyl acetate/hexane mixture.
M.p. 117.degree.-118.degree. C. [.alpha.].sub.D.sup.20 =-24.6 (c=1, EtOH)
M.p..sub.lit 120.degree. C. [.alpha.].sub.D.sup.20 =-26 (c=1, EtOH).
EXAMPLE 58: PREPARATION OF N-SUCCINIMIDYL 2,2-DIMETHYLACRYLATE
0.5 g of 2,2-dimethylacrylic acid in 15 ml of THF, 1.63 of 1,2,2,2-tetrachloroethyl N-succinimidyl carbonate and 0.7 ml of triethylamine are added. The mixture is stirred for 2 hours at 20.degree. C. and washed with sodium chloride solution. The organic phase is dried over magnesium sulphate and the solvent is evaporated. 0.6 g (Y=56%) of the expected ester is obtained. .sup.1 H NMR (CDCl.sub.3, TMS): 2.05 (s, CH.sub.3); 2.2 (s, CH.sub.3); 2.8 (s, CH.sub.2 CH.sub.2); 5.9 (m, H--C.dbd.).
EXAMPLE 59: PREPARATION OF N-SUCCINIMIDYL 2-THIOPHENECARBOXYLATE
The procedure is as in the example above. Starting with 0.64 g of 2-thiophenecarboxylic acid, 0.62 g (Y=51%) of the expected ester is obtained.
M.p 140.degree.-142.degree. C.
.sup.1 H NMR (CDCl.sub.3, TMS): 2.8 (CH.sub.2 CH.sub.2), 7.0-7.2 (m, H--C.dbd.); 7.6 (m, H--C.dbd.); 7.8 (m, H--C.dbd.).

Claims

1. A method for the preparation of an active ester of formula ##STR20## from an N-blocked aminocacid of formula YCOOH, wherein Y contains an N-protected amino group, which consists of reacting said aminoacid with a carbonate of formula ##STR21## wherein R.sup.1 is:
(1) an N-succinimidyl
(2) an N-phthalimidyl
(3) 1-benzotriazolyl radical;
(4) phenyl substituted by 1-5 chlorine, fluorine or one or two nitro groups;
R.sup.2 is: a saturated alkyl of 1 to 5 carbon atoms, unsubstituted or substituted by chlorine atoms, or an unsubstituted phenyl or phenyl substituted by chlorine atoms,
in the presence of an agent for binding hydrochloric acid which is a tertiary amine or an alkali metal carbonate in the presence of an inert solvent which is a member selected from the group consisting of cyclic or acyclic ethers, esters, nitriles, alcohols, amides and ketones wherein the reaction proceeds as follows: ##STR22## and isolating said active ester from the reaction mixture.
2. The process according to claim 1, wherein the carboxylic acid is an amino acid, the amino group of said amino acid being protected.
3. Process according to claim 1, wherein R.sup.1 is a N-succinimidyl, 2,4,5-trichlorophenyl, 2,4,6-trichlorophenyl, pentachloro- or pentafluorophenyl, 4-nitrophenyl, 2,4-dinitrophenyl or N-phthalimidyl group.
4. The process according to claim 1, wherein the tertiary amine is triethylamine or N-methylmorpholine.
5. The process according to claim 1, wherein the solvent is tetrahydrofuran.
6. The process according to claim 1, wherein the radical R.sup.2 is trichloromethyl.
7. The process according to claim 1, wherein the reaction temperature is between -20.degree. C. and 100.degree. C.
8. The process according to claim 2, wherein said amino acid is alanine, lysine, phenylalanine, glycine, valine, proline, tyrosine, tryptophan, methionine, cysteine, serine, threonine, histidine or glutamic acid and the amino group of said aminoacid is protected by a benzyloxycarbonyl group, tertiary butyloxycarbonyl, fluorenylmethyloxycarbonyl.
9. A method for the preparation of an active ester of formula ##STR23## from a carboxylic acid of formula RCOOH, wherein said carboxylic acid is acetic acid, an acrylic acid, thiophenecarboxylic acid or benzoic acid, which consists of reacting said carboxylic acid with a carbonate of formula ##STR24## wherein R.sup.1 is:
(1) an N-succinimidyl;
(2) an N-phthalimidyl;
(3) benzotriazolyl radical;
(4) phenyl substituted by 1-5 chlorine, fluorine or one or two nitro groups;
R.sup.2 is: a saturated alkyl of 1 to 5 carbon atoms, unsubstituted or substituted by chlorine atoms, or an unsubstituted phenyl or phenyl substituted by chlorine atoms,
in the presence of an agent for binding hydochloric acid which is a tertiary amine or an alkaline metal carbonate in the presence of an inert solvent which is a member selected from the group consisting of cyclic or acyclic ethers, esters, nitriles, alcohols, amides and ketones, wherein said reaction proceeds as follows: ##STR25## and isolating said active ester from the reaction mixture.

Priority Claims (1)

Number	Date	Country	Kind
84 18433	Dec 1984	FRX

US Referenced Citations (1)

Number	Name	Date	Kind
3218346	Baker etal.	Nov 1965

Foreign Referenced Citations (1)

Number	Date	Country
0002677	Jul 1979	EPX

Non-Patent Literature Citations (4)

Entry
Bodansky-"Principles of Peptide Synthesis", Springer-Verlag, 1984, pp. 28 and 35.
Houben-Weyl-"Methoden der Organischen Chemie", vol. 15, 1974-Index Pages.
Chemical Abstracts, vol. 88, 1978-Abstract No. 105128.
Haslam-"Recent Developments in Methods for the Esterification and Protection of the Carboxyl Group"-Tetrahedron Report No. 93-1980, pp. 2409-2433.

Process for synthesizing active esters of carboxylic acids

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