Patent Application
20050043565
The present invention relates to processes for the production of Substituted acrylic acid esters and the use thereof to produce Substituted γ-amino acids, such as gabapentin and pregabalin.
Substituted v-amino acids, such as gabapentin of formula (A) below and pregabalin of formula (B) below, are used as medicines for the treatment of epilepsy and pain (J. S. Bryans, D. J. Wustrow; Medicinal Research Reviews 19, 149-177 (1999) and L. Martin, X. Rabasseda, P. Leeson, J. Castaner; Drugs of the Future 24, 862-870 (1999)).
A series of processes for the production of gabapentin and pregabalin are known from the prior art. Reference is made by way of example to a process described by J. S. Bryans et al. (J. Med. Chem. 41, 1838-1845 (1998)) for the production of gabapentin.
In accordance with this process, acrylic acid ethyl esters may be produced from ketones or aldehydes by Wadsworth-Emmons olefination with triethyl phosphonoacetate, in the presence of sodium hydride as base and in tetrahydrofuran as solvent. Nitromethane is then added by Michael Addition. The nitro group is reduced to the amino group, wherein the compounds formed cyclise to yield γ-lactams. The γ-amino acids may be obtained by acidic hydrolysis.
A disadvantage of this known process is the use of alkali metal hydrides for the production of substituted acrylic acid esters in the first reaction stage, which makes it necessary to use absolute organic solvents and to perform the procedure under protective gas.
The object of the present invention was accordingly to improve the first reaction stage for the production of substituted acrylic acid esters in such a way that the procedure may be performed Without absolute organic solvents and without protective gas and high purity substituted acrylic acid esters are obtained in high yields, so simplifying the above-described process for the production of substituted γ-amino acids, such as gabapentin and pregabalin.
According to the invention, the object is achieved by providing the hereinafter described processes for the production of substituted acrylic acid esters and of substituted γ-amino acids produced therefrom, such as gabapentin and pregabalin.
The present invention accordingly provides a process for the production of substituted acrylic acid esters of the genera' formula II,
in which
The compounds of the general formulae V and VI together with the alkali metal carbonate, preferably the potassium carbonate, are preferably combined at a temperature in the range from 0 to 10° C., preferably with ice cooling, and reacted at a temperature in the range of ≦25° C., preferably with ice cooling, to yield a substituted acrylic acid ester of the general formula II. The temperature is preferably regulated by ice cooling before and during the reaction.
After the reaction, the substituted acrylic acid ester of the general formula II may be purified, preferably by extraction, wherein diethyl ether is preferred as solvent.
A process is particularly preferred in which cyclohexanone or 3-methylbutanal as a compound of the general formula V is reacted with triethyl phosphonoacetate as a compound of the general formula VI in each case to yield cyclohexylideneacetic acid ethyl ester or 5-methylhex-2-ene carboxylic acid ethyl ester respectively.
High purity substituted acrylic acid esters of the general formula II are obtained in high yields by the process according to the invention. The olefination procedures may be performed both on the 0.5-molar scale and on the multi-molar scale without impairing purity or yield. The substituted acrylic acid esters of the general formula II produced according to the invention may be immediately further reacted after a purity check by GC/MS analysis. As synthesis proceeds for the production of substituted γ-amino acids, the above-listed synthesis steps may be performed without change. With regard to the corresponding production, the disclosure made by J. S. Bryans et al. (J. Med. Chem. 41, 1838-1845 (1998)) is hereby introduced as reference.
The present invention accordingly further provides processes for the production of a substituted γ-amino acid of the general formula I, in which R1 and R2 have the above-stated meaning,
in which
A process is particularly preferred in which cyclohexanone or 3-methylbutanal as a compound of the general formula V is reacted with triethyl phosphonoacetate as a compound of the general formula VI in each case to yield cyclohexylideneacetic acid ethyl ester or 5-methylhex-2-ene carboxylic acid ethyl ester respectively in the first reaction stage and is further processed as stated to yield gabapentin or pregabalin respectively.
In the process according to the invention for the production of substituted acrylic acid esters or in the first reaction stage for the production of substituted γ-amino acids, such as gabapentin and pregabalin, alkali metal carbonates are used as the base. Therefore, in the case of Wadsworth-Emmons olefination, it is possible according to the invention to dispense with protective gas and absolute organic solvents, and to use aqueous solvents, preferably water.
Substituted γ-amino acids, such as gabapentin and pregabalin are used as pharmaceutical preparations for the treatment of epilepsy and pain.
The invention is explained below with reference to Examples. These explanations are given merely by way of example and do not restrict the general concept of the invention.
The chemicals and solvents used were purchased from conventional suppliers (Acros, Aldrich, Fluka, Lancaster and Merck).
The NMR spectra were measured with spectrometers made by Bruker Analytik GmbH, Silberstreifen 4, D-76287 Rheinstetten. The instrument names are as follows: for 300 MHz: Avance DPX 300 MHz, for 600 MHz: Avance DRX 600 MHz.
GC analysis was performed on an HP 6890 gas chromatograph (with PTV injector) and a 5973 Mass Selective Detector made by Hewlett Packard coupled thereto.
The ESI mass spectra were measured with a Finnigan LCQ model instrument made by Thermoquest, Analytische Systeme GmbH, Boschring 12, D-63329 Egelsbach and evaluated with Xcalibur software.
31.1 ml (0.3 mol) of cyclohexanone, 72.1 ml (0.36 mol) of triethyl phosphonoacetate and 83 g (0.6 mol) of potassium carbonate were combined in 60 ml of water with ice cooling and stirred for 20 hours with the temperature slowly being raised to 25° C.
The reaction batch was diluted with 50 ml of water and extracted three times with ether. The organic phase was washed to neutrality with water, dried over MgSO4 and evaporated, and cyclohexylideneacetic acid ethyl ester was obtained as a pale yellowish liquid in a yield of 47.4 g (94% of theoretical).
MS (calculated: 168.34 g/mol): 168 (M+), 153 (M+-CH3), 139 (M+-CH2CH3), 123 (M+-OCH2CH3), 95 (M+-CO2CH2CH3).
1H-NMR (CDCl3/TMSint.): δ=1.27 ppm (3H, t, CH3, J=7.2 Hz); 1.64 ppm (6H, m, CH2); 2.19 ppm (2H, m, CH2); 2.83 ppm (2H, m, CH2); 4.14 ppm (2H, q, OCH2, J=7.1 Hz); 5.60 ppm (1H, s, olefin-H).
14.8 g (0.088 mol) of the cyclohexylideneacetic acid ethyl ester produced according to 1.1 were dissolved in 50 ml of tetrahydrofuran, 7.11 ml (0.132 mol) of nitromethane and 88 ml of tetrabutylammonium fluoride (1 molar in tetrahydrofuran) were added under a nitrogen atmosphere and refluxed for 20 hours. After cooling, the mixture was diluted with 50 ml of water and extracted three times with dieethyl ether. The organic phase was washed with 10 wt. % aqueous potassium hydrogensulfate solution and then washed with water, dried over magnesium sulfate and evaporated. (1-Nitromethylcyclohexyl)acetic acid ethyl ester was obtained as an orange-yellow oily liquid. The yield amounted to 19.8 g (98% of theoretical).
MS (calculated: 229.28 g/mol): 230 (M+), 184 (M+-OCH2CH3), 169 (M+-CH2NO2).
1H-NMR (CDCl3/TMSint.): δ=1.27 ppm (3H, t, CH3, J=7.2 Hz); 1.48-1.53 ppm (10, m, CH2); 2.54 ppm (2H, s, CH2); 4.15 ppm (2H, q, OCR2, J=7.2 Hz); 4.71 ppm (2H, s, CR2)
22 g (0.096 mol) of (1-nitronethylcyclohexyl)acetic acid ethyl ester produced according to 1.2. were dissolved in 150 ml of methanol, 2.20 g of Raney nickel were added and hydrogenation was performed for 20 hours with continuous supply of hydrogen. The reaction batch was filtered through diatomaceous earth, rewashed with methanol and evaporated in a rotary evaporator. 15.3 g (100% yield) of a yellowish mass of crystals were obtained.
By stirring with hexane and filtering out, 12.4 g (81% yield) of colourless crystals were obtained.
2-Azaspiro[4.5]decan-3-one was used as crude product for further synthesis.
MS (calculated: 153.22 g/mol): 153 (M+), 125 (M+-CO), 123 (M+-CH2NH), 96 (M+-CH2NHCO), 81 (M+-CH2NHCOCH3).
1H-NMR (CDCl3/TMSint.): δ=1.43 ppm (1OH, m, CH2); 1.98 ppm (2H, s, CH2); 2.99 ppm (2H, s, CH2); 7.20 ppm (1H, s (wide), NH).
12.4 g (0.81 mol) of the 2-azaspiro[4.5]decan-3-one produced according to 1.3. were redissolved in 4 N hydrochloric acid and stirred for 20 hours at a bath temperature of 110° C. After cooling, the mixture was diluted with water and extracted twice with dichloromethane. The aqueous phase was stirred with activated carbon, filtered through diatomaceous earth, evaporated and dried under a high vacuum. The colourless solid was dissolved in methanol/acetone (5/3, vol./vol.) and precipitated by addition of diethyl ether. After filtering out and washing with diethyl ether, 12.4 g (74% of theoretical) of (1-aminomethylcyclohexyl)acetic acid hydrochloride were obtained.
ESI-MS (calculated: 168.34 g/mol):
1H-NMR (d6-DMSO/TMSext.): δ=1.40 ppm (10H, m, 5×CH2); 2.40 ppm (2H, m, CH2); 2.90 ppm (2H, m, CH2); 8.00 ppm (3H, s (wide), NH3+); 12.30 ppm (1H, s (wide), CO2H).
1 mol (138 g) of potassium carbonate was dissolved in 100 ml of water and cooled in ice water. 0.6 mol (120 ml) of phosphonoacetic acid triethyl ester and 0.5 mol (43.1 g) of 3-methylbutanal were added and the mixture was stirred for 20 hours with the temperature slowly being raised to 25° C. The reaction batch was then diluted with 150 ml of water and extracted four times with diethyl ether. The organic phase was dried with magnesium sulfate and evaporated in a rotary evaporator. A clear liquid was obtained. The crude yield amounted to 75.8 g (97% of theoretical).
Gas-chromatographic investigation demonstrated that the crude product contained only traces of the two educts. It was used in the next synthesis stage without further purification steps.
MS (calculated: 156.23 g/mol): 156 (M+), 141 (M+-CH2), 128 (M+-CH2CH3), 111 (M+-OCH2CH3), 86 (M+-(CH3)2CHCH2)
1H-NMR (d6-DMSO/TMSext.) δ=0.89 ppm (6H, d, 2×CH3, J=6.8 Hz); 1.22 ppm (3H, t, CH3, J=7.2 Hz); 1.76 ppm (1H, h, CH(CH3)2, J=6.5 Hz, J=6.8 Hz); 2.01 ppm (2H, m, CH2, J=6.8 Hz); 4.11 ppm (2H, q, CH20, J=7.2 Hz); 5.83 ppm (1H, dd, CH, J=1.5 Hz, J=15.5 Hz); 6.85 ppm (1H, m, CH), J=7.5 Hz).
0.485 mol (75.8 g) of the (2E)-5-methyl-hex-2-ene carboxylic acid ethyl ester produced according to 2.1. were dissolved under a nitrogen atmosphere in THF (abs.). 0.73 mol (39.1 ml) of nitromethane and 0.49 mol (485 ml) of a 1 molar tetrabutylammonium fluoride solution in THF were added, wherein an orange solution arose. The mixture was refluxed for 20 hours. After cooling, the mixture was combined with 280 ml of water and extracted four times with diethyl ether. The organic phase was extracted three times with 10% aqueous potassium hydrogensulfate solution and washed to neutrality with water. The organic phase was dried with magnesium sulfate and evaporated in a rotary evaporator. An orange liquid was obtained. The crude yield amounted to 95.2 g (90% of theoretical).
Gas-chromatographic investigation demonstrated that, in addition to 91% product, the crude product contained 7% of tetrabutylammonium fluoride and 2% of unidentifiable secondary product.
For purification, the crude product was stirred for 4 hours in ether and the solution was filtered and evaporated.
MS (calculated: 217.27 g/mol): 202 (M-CH3), 172 (M-OCH2CH3), 156 (M-CH2NO2) 143 (M-CO2CH2CH3).
1H-NMR (d6-DMSO/TMSext.) δ=0.96 ppm (6H, t, 2×CH3, J=6.8 Hz); 1.14-1.21 ppm (5H, m, CH2 and CH3, J=7.2 Hz); 1.63 ppm (1H, sept, CH, J=6.8 Hz); 2.38 ppm (2H, d, CH2CO2Et, J=6.4 Hz); 2.58 ppm (1H, sept, CH, J=6.4 Hz, J=6.8 Hz); 4.07 ppm (2H, q, OCH2, J=7.0 Hz); 4.55 ppm (2H, d, CH2NO2, J=6.4 Hz),
0.39 mol (85.3 g) of the 5-methyl-3-nitromethylhexane carboxylic acid ethyl ester produced and purified according to 2.2. were dissolved in approx. 900 ml of methanol, 25 g of Raney nickel were added and hydrogenation was performed at a temperature of 35° C. and a pressure of 2 bar for 20 hours. The reaction batch was filtered through diatomaceous earth, washed carefully with methanol and evaporated in a rotary evaporator. After drying under a high vacuum, 59.3 g of a colourless liquid were obtained.
MS (calculated: 141.21 g/mol): 141 (M+), 126 (M+-CH3), 111 (M+-CO), 98 (M+-CH(CH3)2), 84 (M+-CH2NHCOCH3).
1H-NMR (d6-DMSO/TMSext.): δ=0.87 ppm (3H, d, CH3, J=6.4 Hz), 0.88 ppm (3H, d, CH3, J=6.4 Hz); 1.28 ppm (2H, t, CH2, J=7.2 Hz); 1.55 ppm (1H, sept, CH, J=6.4 Hz, 8.8 Hz); 1.79 ppm (1H, dd, CH, J=8.7 Hz); 2.20 ppm (1H, dd, CH, J=8.3 Hz); 2.40 ppm (1H, sept, CH, J=7.5 Hz, J=8.3 Hz); 2.83 ppm (1H, dd, CH, J=7.5 Hz); 3.33 ppm (1H, dd, CH, J=8.3 Hz), 7.46 ppm (s (wide), 1H, NH).
7.16 g (0.06 mol) of the 4-isobutyl-pyrrolidin-2-one produced according to 2.3. were redissolved in 550 ml of 4 N hydrochloric acid and heated for 20 hours at an oil bath temperature of 125° C. After cooling, the mixture was diluted with 500 ml of water and extracted three times with dichloromethane. The aqueous phase was stirred with activated carbon, filtered through diatomaceous earth and evaporated. After drying under a high vacuum, the 3-aminomethyl-5-methyl-hexanoic acid hydrochloride was obtained as an orange-yellow mass of crystals in a yield of 100%.
ESI-MS (calculated: 159.23 g/mol): 160 (MH+), 142 (MH+-H20).
1H-NMR (d6-DMSO/TMSext.): δ=0.88 ppm (6H, dd, 2×CH3) J=Hz); 1.18 ppm (1H, dd, CH2, J=Hz); 1.20 ppm (1 H, dd, CH2, J=Hz), 1.61 ppm (1 H, sept, CH, 3=Hz), 2.18 ppm (2H, m, CH2, J=Hz); 2.45 ppm (1H, dd, CH, J=Hz); 2.78 ppm (2H, m, CH2, J=Hz); 8.10 ppm (3H, s (wide), NH3+).
| Number | Date | Country | Kind |
|---|---|---|---|
| 102 03 122.3 | Jan 2002 | DE | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP03/00213 | Jan 2003 | US |
| Child | 10894389 | Jul 2004 | US |
