Patent Application
20070066846
The present invention is directed to a process for the synthesis of (S)-Pregabalin, (S)-(+)-3-(aminomethyl)-5-methylhexanoic acid.
(S)-Pregabalin, (S)-(+)-3-(aminomethyl)-5-methylhexanoic acid, a compound having the chemical structure
is also known as γ-amino butyric acid or (S)-3-isobutyl GABA. (S)-Pregabalin has been found to activate GAD (L-glutamic acid decarboxylase). (S)-Pregabalin has a dose dependent protective effect on-seizure, and is a CNS-active compound. (S)-Pregabalin is useful in anticonvulsant therapy, due to its activation of GAD, promoting the production of GABA, one of the brain's major inhibitory neurotransmitters, which is released at 30 percent of the brain's synapses. (S)-Pregabalin has analgesic, anticonvulsant, and anxiolytic activity.
(S)-Pregabalin may be prepared according to the process disclosed in U.S. Patent Application Publication No. 2003/0212290, by an asymmetric hydrogenation of a cyano-substituted olefin of formula 7, to produce a cyano precursor of (S)-3-(aminomethyl)-5-methyl hexanoic acid of formula 8, which is further reduced to obtain (S)-Pregabalin, as described in Scheme 1.
However, the disclosed method requires the use of carbon monoxide under high pressure, raising serious problems in adapting this process for production scale.
Another process is disclosed in JACS 2003, 125, 4442, in which an aluminum salen catalyst is used in the conjugate addition of hydrogen cyanide to α,β-unsaturated imides.
This process is also not practical for large scale production due to the use of highly poisonous reagents. In addition, the last reduction step requires high pressure of hydrogen, which only adds to the difficulties required for adapting this process for production scale.
Therefore, there is a need in the art for a process that overcomes these limitations.
In one embodiment, the present invention provides the use of the compound of formula 15
for the preparation of (S)-Pregabalin.
In another embodiment, the present invention provides the compound of formula 16,
wherein R1 and R2 are independently H, a straight or branched C1-10 alkyl, C6-10 aryl, or C3-6 allyl. Preferably, R1 and R2 each is methyl, ethyl, or isopropyl.
In yet another embodiment, the present invention provides the compound of formula 18,
wherein, R1 and R2 are independently H, a straight or branched C1-10 alkyl, C6-10 aryl, or C3-6 allyl. Preferably, R1 and R2 each is methyl, ethyl, or isopropyl.
In one embodiment, the present invention provides a process for the preparation of (S)-Pregabalin, denominated process 1, comprising combining the compound of formula 15,
and a reducing agent; adding a copper salt and a solvent selected from a group consisting of: acetonitrile, toluene and mixtures of alcohol/acetonitrile; and heating, wherein R1 and R2 are independently H, a straight or branched C1-10 alkyl, C6-10 aryl, or C3-6 allyl. Preferably, each of R1 and R2 is methyl, ethyl, or isopropyl.
In another embodiment, the present invention provides another process for the preparation of (S)-Pregabalin, denominated process 2, comprising combining the compound of formula 15 and a reducing agent; adding a salt, and a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof; and heating.
In yet another embodiment, the present invention provides yet another a process for the preparation of (S)-Pregabalin, denominated process 3, comprising combining the compound of formula 15 a reducing agent, and a C1-6 alcohol; combining with an inorganic acid to form a mixture; heating the mixture; and passing the mixture through an ion exchange resin.
In one embodiment, the present invention provides another process for the preparation of (S)-Pregabalin, denominated process 4, comprising combining the compound of formula 15, a salt, and a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof; heating; adding a reducing agent; combining with an inorganic acid; heating, and passing through an ion exchange resin.
In another embodiment, the present invention provides another process for the preparation of (S)-Pregabalin, denominated process 5, comprising combining the compound of formula 15 a reducing agent, a Ni salt and a first solvent selected from a group consisting of: C1-6 alcohol and THF; adding an inorganic base and a second C1-6 alcohol; adding a C6-10 aromatic hydrocarbon; heating; combining with an inorganic acid; heating; and mixing with a third C1-6 alcohol and an organic base.
In yet another embodiment, the present invention provides a process for preparing pharmaceutical formulation comprising mixing (S)-Pregabalin, prepared according to the processes of the present invention, and a pharmaceutically acceptable carrier.
The process of the present invention provides a process for the preparation of (S)-Pregabalin that does not require an optical resolution step, and is also easy to conduct, efficient, and thus, can be easily adapted to larger scales.
The present invention provides the use of the compound of formula 15
for the preparation of (S)-Pregabalin.
The present invention also provides the compound of formula 16,
wherein R1 and R2 are independently H, a C1-10 straight or branched alkyl, C6-10 aryl, or C3-6 allyl. Preferably, each of R1 and R2 is methyl, ethyl, or isopropyl.
The present invention further provides the compound of formula 18,
wherein preferably, R1 and R2 are independently H, a C1-10 straight or branched alkyl, C6-10 aryl, or C3-6 allyl. Preferably, each of R1 and R2 is methyl, ethyl, or isopropyl.
The present invention provides a process for the preparation of (S)-Pregabalin, denominated process 1, comprising combining the compound of formula 15,
and a reducing agent; adding a copper salt and a solvent selected from a group consisting of: acetonitrile, toluene and mixtures of alcohol/acetonitrile; and heating, wherein each of R1 and R2 is independently H, a straight or branched C1-10 alkyl, C6-10 aryl, or C3-6 allyl. Preferably, each of R1 and R2 is methyl, ethyl, or isopropyl.
Preferably, the process may be done according to the following scheme
wherein R1 and R2 are as described above.
The compound of formula may be prepared, for example, according to the process disclosed in JACS, 2004, 126, 9906.
Preferably, the reduction step may be catalyzed by an acid; hence, an acid may be combined with the compound of formula 15 and a reducing agent. Preferably, the acid is an organic acid, more preferably, either acetic acid or formic acid. The acid may be used also as a solvent.
Preferably, the reducing agent is a combination of hydrogen and a catalyst. More preferably, the catalyst is a metal catalyst. The metal catalyst is selected from a group consisting of: Raney Ni, Pt and Rt. Preferably, the metal catalyst is palladium, and more preferably, palladium absorbed on carbon. Preferably, the hydrogen is bubbled at a pressure of about 1 to about 5 atmospheres, and more preferably, at a pressure of about 2 to about 5 atmospheres.
Preferably, combining the compound of formula 15, an acid and a reducing agent is performed at a temperature of about 15° C. to about 35° C., and more preferably, at about 25° C. to about 30° C., to provide a mixture. The mixture is maintained at the temperature for about 1 to about 10 hours, preferably, for about 2 to about 4 hours, and more preferably, for about 3 hours, to provide the compound of formula 16.
The compound of formula 16 may be recovered by filtering off the catalyst and evaporating the filtrate to obtain a residue.
Preferably, the copper salt is copper (I) salt, and more preferably, a copper oxide salt.
Preferably, adding the copper salt and a solvent selected from a group consisting of: acetonitrile, toluene and mixtures of alcohol/acetonitrile, provides a mixture, which is warmed at a temperature of about 60° C. to about 100° C., more preferably, of about 70° C. to about 90° C., and even more preferably, of about 80° C. The mixture is then maintained at the temperature for about 5 to about 10 hours, preferably, for about 7 to about 9 hours, and more preferably, for about 7.5 hours.
(S)-Pregabalin may be recovered by concentrating the maintained mixture, preferably, under vacuum, to obtain a residue. The residue may be purified by crystallization from a solvent selected from a group consisting of: mixtures of isopropyl alcohol and water, preferably, in a ratio of 65:30, of ethanol and water, of methanol and ethanol and of isopropanol and any other alcohol.
The present invention further provides another process, denominated process 2, for the preparation of (S)-Pregabalin comprising combining the compound of formula 15 and a reducing agent; adding a salt and a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof; and heating.
Preferably, the process is done according to the above scheme, but with altering the reaction from compound 16 to (S)-Pregabalin.
Preferably, the salt is either an organic salt or an inorganic salt. Preferably the inorganic salt is an alkali salt. Preferably, the alkali salt is selected from a group consisting of: LiI, LiCl, NaCl, and KCN. Preferably, the organic salt is Bu4NOAc. More preferably, the salt is an inorganic salt, most preferably, alkali salt, and even most preferably, NaCl.
Preferably, the water miscible organic solvent is selected from a group consisting of: dimethylsulfoxide (referred to as DMSO), N,N-dimethylformamide (referred to as DMF), dimethylacetamide (referred to as DMA), and hexamethylphosphoroustriamide (referred to as HMPT). The more preferred solvent is a mixture of water and DMSO.
Preferably, adding an alkali halide salt, a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof provides a mixture, which is heated at a temperature of about 100° C. to about 160° C., preferably, of about 120° C. to about 140° C., more preferably, of about 135° C. The mixture is maintained at the temperature for about 4 to about 12 hours, preferably, for about 6 to about 8 hours, and more preferably, for about 7 hours.
(S)-Pregabalin may be recovered by cooling the maintained mixture, preferably, gradually. First the mixture is cooled at a temperature of about 30° C. to about 60° C., preferably, of about 35° C. to about 55° C., and more preferably, of about 40° C., and then to about 10° C. to about 0° C. Prior to the second cooling step, a solvent selected from a group consisting of diethylether, diisopropylether (referred to as DIPE) and t-butylmethylether (referred to as TBME) is added. After reaching a temperature of about 10° C. to about 0° C., water is added, and the mixture is further maintained at the temperature for about 25 minutes. The mixture separates into two phases and the aqueous phase is extracted with a solvent selected from a group consisting of: diethylether, DIPE and TBME, followed by washing the organic phase with water, and evaporating the solvent. (S)-Pregabalin may be purified by crystallization from a mixture of isopropyl alcohol (referred to as IPA) and water or from a mixture of tetrahydrofuran (referred to as THF) and water.
The present invention also provides a process for the preparation of (S)-Pregabalin, denominated process 3, comprising combining the compound of formnula 15 a reducing agent, and a C1-6 alcohol; combining with an inorganic acid; heating; and passing through an ion exchange resign.
Preferably, the process is done according to the above scheme, but without isolating compound 16.
Preferably, the C1-6 alcohol is ethanol.
Preferably, the reducing agent is a combination of hydrogen and a catalyst, and more preferably, a metal catalyst. The metal catalyst is selected from a group consisting of: Raney Ni, Pt and Rt. Preferably, the metal catalyst is Raney Nickel. Preferably, the hydrogen is bubbled at a pressure of about 1 to about 6 atmospheres, and more preferably, at a pressure of about 1 to about 3 atmospheres.
Preferably, combining the compound of formula 15, a C1-6 alcohol and a reducing agent is done at a temperature of about 15° C. to about 40° C., and preferably, at about 25° C. to about 35° C., providing a mixture. The mixture is maintained at this temperature for about 3 to about 10 hours, preferably, for about 4 to about 6 hour, and more preferably, for about 5 hours, and then, preferably, a work-up step is done.
The work-up step is done by filtering off the catalyst and evaporating the filtrate to obtain a residue containing of compound of formula 16. The residue is then dissolved in the inorganic acid, and heated to a temperature of about 50° C. to about 100° C., preferably at about 80° C. to about 100° C., and more preferably, to about 100° C., for about 5 to about 20 hours, preferably, for about 10 to about 18 hours, and more preferably, for about 15 hours, to provide an inorganic acid salt of (S)-Pregabalin. The salt may be recovered by cooling the maintained mixture at a temperature of about 20° C. to about −10° C., and preferably, of about 10° C. to about 0° C., and evaporating water to dryness. Preferably, the inorganic acid is selected from a group consisting of: HCl, HBr, H2SO4 and H3PO4. More preferably, the inorganic acid is HCl. Preferably, the inorganic acid salt of (S)-Pregabalin is (S)-Pregabalin hydrochloride. The salt may be purified by slurry from a mixture of methanol and ether. (S)-Pregabalin hydrochloride may be converted to (S)-Pregabalin by passing it through an ion exchange resign, preferably, through Dowex 50W.
Optionally, the salt of (S)-Pregabalin may be converted to (S)-Pregabalin by dissolving it in isobutanol and adding an organic base, providing a mixture. The mixture is then maintained at a temperature of about 15° C. to about 55° C., preferably, of about 20° C. to about 35° C., for about 25 to about 80 minutes, preferably, for about 30 to about 55 minutes, and even more preferably, for about 45 minutes. (S)-Pregabalin may be recovered by filtering off the product, washing and drying. Preferably, the base is trialkylamine, more preferably, triisopropylamine, trimethylamine or triethylamine, most preferably, triethylamine.
The present invention provides another process for the preparation of (S)-Pregabalin, denominated process 4, comprising combining the compound of formula 15 a salt, and a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof; heating; adding a reducing agent; combining with an inorganic acid; heating; and passing through an ion exchange resin.
Preferably, the process may be done according to the following scheme
wherein R1 and R2 are described above.
The preferred salt, solvent and the inorganic acid are described a above.
Preferably, adding a salt, a solvent selected from a group consisting of water, water miscible organic solvent and mixtures thereof provides a mixture, which is heated at a temperature of about 145° C. to about 155° C. The mixture is maintained at the temperature, for about 3 to about 9 hours, preferably, for about 4 to about 6 hours, and more preferably, for about 5 hours, to provide the compound of formula 17.
The compound of formula 17 may be recovered by the same process as compound of formula 16 was recovered.
Preferably, the step from compound 17 to (S)-Pregabalin may be done by reducing the compound of formula 17 under the same conditions of the reduction of compound 15 to compound 16, as described in process No. 1, followed by obtaining the inorganic salt of (S)-Pregabalin, preferably, (S)-Pregabalin hydrochloride, which is then converted to (S)-Pregabalin. The inorganic salt of (S)-Pregabalin, preferably, (S)-Pregabalin hydrochloride, may be obtained by reacting the compound of formula 17 with an inorganic acid, preferably, HCl, under the same conditions of the reaction of compound of formula 16 with an inorganic acid, preferably, HCl, as described in process No. 3. The inorganic salt of (S)-Pregabalin, preferably, (S)-Pregabalin hydrochloride, may be converted to (S)-Pregabalin, by the methods disclosed in process No. 3, i.e. either by passing through an ion exchange resin, or by reacting with a base.
The present invention further provides another process for the preparation of (S)-Pregabalin, denominated process 5, comprising combining the compound of formula 15 a reducing agent, a Ni salt and a first solvent selected from a group consisting of: C1-6 alcohol and THF; adding an inorganic base and a second C1-6 alcohol; adding a C6-10 aromatic hydrocarbon; heating; combining with an inorganic acid; heating, mixing with a third C1-6 alcohol and an organic base,
Preferably, the process may be done according to the following scheme
wherein each of R1 and R2 is as described above.
Preferably, the reducing agent is a metal hydride. Preferably, the metal hydride is selected from a group consisting of: sodium borohydride, sodium cyanoborohydride and lithium cyanoborohydride. More preferably, the metal hydride is sodium borohydride.
Preferably, the Ni salt is a Ni halide salt. The Ni halide is either NiBr2 or NiCl2 sesquihydrate. More preferably, the Ni halide is NiCl2 sesquihydrate.
Preferably, the C1-6 alcohol is selected from a group consisting of: methanol, ethanol, and IPA. More preferably, the first solvent is methanol.
Preferably, combining the compound of formula 15, a reducing agent, a Ni salt and a first solvent selected from a group consisting of: C1-6 alcohol and THF is done at a temperature of about −10° C. to about 10° C., more preferably, at about 0° C. to about 5° C., and even more preferably, at about 0° C., providing a mixture. The mixture is then maintained at the temperature for about 3 to about 12 hours, preferably, for about 5 to about 8 hours, and more preferably, for about 6 hours, and quenched, providing compound 18; wherein R2 is an alkyl group.
Preferably, quenching is done using NH4Cl.
The compound of formula 18 may be recovered by adding a solvent selected from a group consisting of: CH2Cl2, toluene and dichloroethane, to the quenched mixture, and concentrating the organic phase.
Preferably, the inorganic base is an alkali hydroxide. Preferably, the alkali hydroxide is selected from a group consisting of: NaOH, KOH and LiOH. The preferred alkali hydroxide is NaOH.
Preferably, the second C1-6 alcohol is selected from a group consisting of: methanol, ethanol, and IPA. More preferably, the C1-6 alcohol is ethanol.
Preferably, adding an inorganic base and a second C1-6 alcohol is done at a temperature of about 15° C. to about 55° C., preferably, at about 20° C. to about 35° C., providing a reaction mixture, which is maintained at the temperature for about 25 to about 90 minutes, preferably, for about 30 to about 60 minutes, and more preferably, for about 30 minutes, providing the compound of formula 18, wherein R2 is H.
The compound of formula 18, wherein R2 is H, may be recovered by concentrating the maintained reaction mixture, and adding water and an acid selected from a group consisting of: HCl, HBr, H2SO4, and H3PO4. Preferably, the acid is HCl. Subsequently, the phases are separated, and the aqueous phase is extracted with CH2Cl2. The combined organic phases are then concentrated.
Preferably, the C6-10 aromatic hydrocarbon is either toluene or xylene.
Preferably, compound of formula 18, wherein R2 is H, is dissolved in C6-10 aromatic hydrocarbon. The solution is then heated at a temperature of about 90° C. to about 120° C., preferably, of about 100° C. to about 115° C., and more preferably, of about 110° C., and maintained for about 3 to about 12 hours, preferably, for about 6 to about 8 hours, and more preferably, for about 6 hours, providing compound 19.
The compound 19 may be recovered by concentrating the maintained mixture to dryness. Compound 19 may be purified by chromatography.
Preferably, the inorganic acid is selected from a group consisting of: HCl, HBr and H2SO4. More preferably, the inorganic acid is HCl.
Preferably, adding an inorganic acid provides a solution, which is warmed at a temperature of about 80° C. to about 105° C., preferably, to about 95° C. to about 100° C., and more preferably, to about 100° C., and maintained for about 10 to about 25 hours, preferably, for about 12 to about 18 hours, and more preferably, for about 15 hours, providing the inorganic salt of (S)-Pregabalin. The salt of (S)-Pregabalin is then converted to (S)-Pregabalin as described above.
The present invention also provides a process for preparing pharmaceutical formulation comprising mixing (S)-Pregabalin, prepared according to the processes of the present invention, and a pharmaceutically acceptable carrier.
Having described the invention with reference to certain preferred embodiments, other embodiments will become apparent to one skilled in the art from consideration of the specification. The invention is further defined by reference to the following examples describing in detail the preparation of the composition and methods of use of the invention. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the invention.
A solution of 10 g of compound 15 in 150 ml of acetic acid is hydrogenated over a 10 percent palladium on carbon catalyst for 3 hours at ambient temperature and pressure, e.g., about 25° C. and about 1 to about 5 atmospheres pressure. The catalyst is then filtered off, and the filtrate is evaporated under reduced pressure giving compound 16.
Method 1
First, 0.85 g of copper (I) oxide is added to a solution of 8.5 g of the dicarboxylic acid of compound 16 in 110 ml of CH3CN. The resulting solution is warmed to 80° C., stirred for 7.5 hours, and then concentrated in vacuo. The residue is recrystallized from isopropyl alcohol/water in a 65:30 ratio, producing (S)-Pregabalin.
Method 2
First, 6 g of sodium chloride and 3 ml of water are added to a solution of 12 g of the diester compound 16 in 90 ml of DMSO. The mixture is heated to 135° C., and stirred for 7 hours. The mixture is then cooled to 40° C., and treated with 50 ml of methyl tert-butyl ether. The mixture is then cooled to 0° to 10° C., and 50 ml of water are added, while maintaining the temperature below 40° C. After stirring for 25 minutes, the phases are separated, and the aqueous phase is extracted with 35 ml of methyl tert-butyl ether. The organic extracts are combined, extracted with water, and then dried over sodium sulfate. After separation, the salt solution is concentrated in vacuo to dryness to provide crude (S)-Pregabalin. Crystallization from isopropyl alcohol/water in a 55:20 ratio provides the pure product.
Method 3:
A mixture of 4 g of compound 15, 60 ml of ethanol, and Raney Ni is stirred at room temperature under an atmosphere of H2 for 5 hours. The resulting mixture is filtered through a pad of Celite, and the filtrate is concentrated. The residue is then suspended in 40 ml of 6 N HCl, and the mixture is heated at 100° C. for 15 hours. After cooling, the excess water is removed under reduced pressure, producing a solid residue. Triturating the residue in methanol/ether provides the final product of (S)-Pregabalin hydrochloride. The crude product is purified by ion exchange chromatography on Dowex 50W to obtain (S)-Pregabalin. (S)-Pregabalin can be obtained also as described in example 7.
First, 7 g of sodium chloride and 5 ml of water are added to a solution of 9.6 g of the diester of compound 15 in 65 ml of DMSO. The mixture is heated to 145° to 155° C., and stirred for 5 hours. The mixture is then cooled to 40° C., and treated with 50 ml of methyl tert-butyl ether. The mixture is cooled to 0° to 10° C., and 25 ml of water are added, while maintaining the temperature at less than 40° C. After stirring for 25 minutes the phases are separated. The aqueous phase is extracted with 15 ml of methyl tert-butyl ether, the organic extracts are combined and extracted with 20 ml water, and dried over sodium sulfate. After separation, the salt solution is concentrated in vacuo to dryness to providing crude compound 17 as a yellowish oil.
A solution of 10 g of 5-methyl-3-nitromethylhexanoic acid ethyl ester, compound 17, in 70 ml of acetic acid is hydrogenated over a catalyst of 10 percent palladium on carbon for 2.4 hours at ambient temperature and pressure, e.g., 25° C. and about 1 to about 5 atmospheres. The catalyst is then filtered off, the filtrate is evaporated under reduced pressure, and the residue is dissolved in 25 ml of 6 N HCl, followed by refluxing for 3 hours. The solution is evaporated under reduced pressure to dryness. The crude product is purified by ion exchange chromatography on Dowex 50W. Crystallization from isopropyl alcohol/water provides the pure product. It is important to note that first the initial product is the lactam, and the hydrolysis step provides the (S)-Pregabalin. In addition, this reduction can be performed with Raney nickel.
3.3 g of NaBH4 is added to a suspension of 14 g of compound 15 and 5 g of NiCl2.6H2O in 140 ml of methyl alcohol at 0° C. The reaction mixture is stirred for 6 hours, and then quenched with NH4Cl, followed by dilution with 55 ml of CH2Cl2. The organic phase is separated and dried over MgSO4, filtered, and concentrated in vacuo to provide compound 18.
135 ml of 1 N NaOH is added to a solution of 24 g of compound 18 in 350 ml of ethanol at room temperature. After 30 minutes of stirring at that temperature, the reaction mixture is concentrated in vacuo. Then, 250 ml of 6 N HCl in water are added to the residue, and the phases are separated. The aqueous phase is extracted with 120 ML OF CH2Cl2, and then the combined organic layers are dried over MgSO4, filtered, and evaporated under reduced pressure to provide the corresponding carboxylic acid (compound 18, wherein R2 is H). A solution of the carboxylic acid in 120 ml of toluene refluxed at 140° C. for 6 hours, and then the mixture is concentrated under reduced pressure to dryness. The crude compound 19 is purified by column chromatography on silica gel to give desired pure compound 19.
10 g of compound 19 is dissolved in 440 ml 6 N HCl, and the solution is warmed to 125° C. for 15 hours. After cooling, the mixture is diluted with water, and extracted three times with dichloromethane, then the aqueous phase is evaporated. After drying under high vacuum, the (S)-Pregabalin hydrochloride is obtained as crystals. (S)-Pregabalin is further resolved by dissolving (S)-Pregabalin hydrochloride in isobutanol, and then adding triethyl amine. The mixture is stirred for 45 minutes, and the product is filtered, washed with isobutanol.
This application claims the benefit of U.S. provisional application No. 60/670,425, filed Apr. 11, 2005; herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60670425 | Apr 2005 | US |
