Method for introducing a 1,2 double bond into 4-azasteroids, and crystalline phroscor(R) and pharmaceutical compositions thereof

Abstract: A process for introducing a 1,2 double bond into a compound of the formula which comprises the process of (a) treating the compound of formula I with oxalyl chloride; (b) brominating the product of step (a) followed by in situ dehydrobromination; (c) deprotecting the product of step (b) to yield the α and β isomers; (d) dehydrobrominating the product of step (c), which results in the introduction of a double bond at the 1,2 position.

Description: This invention is concerned with a process for preparing crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one (finasteride), to crystalline finasteride prepared therefrom, to the crystalline finasteride thereby prepared for use in treating hyperandrogenic conditions, and to the use of the crystalline finasteride thereby prepared for the manufacture of a medicament for treating hyperandrogenic conditions. EP-A-0298652 describes inter alia a method for crystallizing finasteride from methylene chloride-isopropyl acetate. No other method is disclosed therein for preparing crystalline finasteride. A dehydrogenation process involving a silylation-mediated DDQ oxidation of 4-aza-3-ketosteroids to the corresponding Δ 1 -lactams is reported in Bhattacharya et al., J. Am. Chem. Soc. , 110, 3318 (1988). This publication specifically describes the crystallization of the 17β-carboxylic acid analogue of finasteride from methylene chloride-acetonitrile. However, there is no explicit disclosure therein of any method for crystallizing finasteride. The present invention provides a process for preparing crystalline finasteride which consists of dissolving finasteride to a concentration of 0.216 g/ml in 1 part by volume of acetic acid and slowly adding 10 parts by volume of water; ageing the mixture at room temperature for 10 hours with agitation; filtration and drying at 70°C in vacuo . In another aspect, the present invention provides crystalline finasteride obtainable from the process described above. In a further aspect, the present invention provides crystalline finasteride obtainable from the process described above for use in treating hyperandrogenic conditions. The crystalline finasteride obtainable from the process of the present invention is a testosterone-5α-reductase inhibitor useful for treating the hyperandrogenic conditions of acne vulgaris, seborrhea, female hirsutism, androgenic alopecia including male pattern alopecia, prostatic carcinoma and benign prostatic hypertrophy by topical or systemic administration. The schematic flow diagram which follows shows a generalized process for preparing 3-oxo-4-azasteroids having a double bond at the 1,2-position, including finasteride, which is the end-product wherein R is NH-tert-butyl and R 1 is hydrogen. Generally, in the above process both 5α-azaamide and 5α-azamethylester are suitable in this three-steps one-pot process. Since all intermediates leading to products such as 2-bromo-5α-azasteroids are water sensitive, water should be vigorously excluded from the reaction. The reaction of oxalyl chloride with 5α-azasteroids in methylene chloride in the presence of an amine base such as diisopropylethylamine or pyridine gives vinylidenyloxazolidinediones. Other solvents such as chloroform and carbon tetrachloride can also be utilized. On bromination, vinylidinyloxazolidinediones are converted to dibromooxazolidinediones which are unstable and dehydrobrominate spontaneously in solution on warming to give bromovinylidinyloxazolidinediones. Reaction of ethylenediamine, N, N 1 -dialkylethylenediamines or 2-(methylamino) ethanol with bromovinylidineoxazolidinediones gives 2-bromo-5α-azasteroids as chemically stable and easily isolable products. The dehydrobromination of 2-bromo-5α-azasteroids can be effected using potassium t-butoxide, DBN, DBU, tetrabutylammonium fluoride, and N, N, N 1 ,N 1 -tetramethylethylenediamine in THF, DMF and DMSO, but the yields of 1 Δ-5α-azasteroids vary substantially depending on starting 2-bromo-5α-azasteroids, dehydrobrominating agents, and solvents used. The best results were obtained using 2-bromo-5α-azaamide with potassium t -butoxide in DMF. The experimental procedure for this latter steroid is described below. The overall yield was 60%. The following example should be considered as not limiting the invention and will serve to illustrate the manner in which the present invention is accomplished. All temperatures are in °C. PREPARATIVE PROCEDURE Oxalylation/Bromination/De-Oxalylation A 500ml three-neck round bottom flask equipped with a stirrer, a thermometer, a nitrogen inlet and a distillation condenser was charged with 5α-azaamide (10 g , 26.7 mmol), pyridine (26.7 ml) and methylene chloride (300 ml). The methylene chloride solution was distilled under atmospheric pressure until 100 ml of methylene chloride was collected. The reaction mixture was cooled to -70°C and oxalyl chloride (2.56 ml, 29.4 mmol) was added dropwise over 10 min. The mixture was warmed to 0°C and aged at this temperature until the reaction was complete and no 5α-azaamide was observed (1 1/2 to 3 hrs.). HPLC Column: Dupont Zorbax C-8, 25 cm x 4.6 mm Solvent: 60% CH 3 CN - 40% H 2 O (0.1% H 3 PO 4 ) Flow: 1.5 ml/min Wavelength: 210 nm Detector: Kratos Spectroflow 757, AVFS = 0.02 RT: 5α-Azaamide 4.6 min Vinylidenyloxazolidinedione Amide 9.1 min 3-Hydroxyoxazolidinedione Amide 4.9 min. Epsilon-Caprolactam (0.226 g, 2 mmol) was added and the reaction further aged at 0°C for 1/2 hour. The mixture was then cooled to -70°C and neat bromine (4.48 g, 28.0 mmol) was added. The reaction was aged for 15 minutes and then sampled and checked by HPLC to ensure that all vinylidineoxazolidinedione amide have been consumed. More bromine could be added in small portions if necessary to complete the bromination reaction. HPLC Same conditions as above. RT: 2-Bromo-3-hydroxyoxazolidinedione amide 6.4 min, 6.7 min. 2-Bromovinylidenyloxazolidinedione amide 13.3 min. The reaction mixture was warmed to 0°C and aged (18-20 hrs) until all of the 2,3-dibromo-oxazolidinedione amides have converted to bromovinyloxazolidinedione amide. After cooling the mixture back to -65°C, 2-(methylamino) ethanol (9.02 g, 120.2 mmol) was added while maintaining the reaction temperature below -60°C. The reaction was checked for the complete disappearance of the starting material by HPLC. HPLC Same conditions as reported above RT: 2-Bromovinylidenyloxazolidinedione amide 13.3 min. 2-Bromo-5α-azaamide 4.7 min & 5.0 min. More 2-(methylamino) ethanol could be added in small portions (0.2 g) if the disappearance of bromovinylidineoxazolidinedione amide was not complete. The mixture was warmed to room temperature and aged until the aminoethanol intermediate adducts have converted to 2-bromo-5α-azaamides (2 to 3 hours). The solution was cooled to 0°C and 200 ml of cold 2N HCL solution was added slowly while maintaining the temperature at ≤5°C. After the addition the two layers were thoroughly mixed and separated. The organic layer was washed again with 2N HCL (200 ml) followed by 10% brine (2x200 ml). To the methylene choloride solution was added acetonitrile (100 ml) and the methylene chloride was removed in vacuo at ≤40°C while maintaining the liquid volume at ∼35 ml by addition of acetonitrile. When no more methylene chloride was detected in the distillate, the volume was further reduced to 35 ml of acetonitrile and the mixture was cooled to 0°C. Water (105 ml) was added slowly over 15 min. After aging for 1 1/2 hours at 0°C, the solid was collected by filtration and the filter cake washed with water (50 ml). The filter cake was suction dried to a free flowing solid and then further dried at 60°C in vacuo overnight (14 to 18 hours). The yield was 10.80 g, 85.1% corrected for 95.4 wt.% HPLC purity. Dehydrobromination In a 250 ml three-neck flask equipped with a stirrer, an internal thermometer, and a nitrogen inlet was charged potassium t -butoxide (6.15 g, 54.8 mmol) and 25 ml of dry DMF. After the potassium t -butoxide was completely dissolved, the mixture was cooled to 0°C and a solution of 2-bromo-5α-azaamide (4.00 g, 8.8 mmol) in DMF (12 ml) was added dropwise while maintaining the temperature at 0°C. After the addition was complete, the reaction was aged for an additional 10 min. and was then quenched by the dropwise addition of acetic acid (5.2 ml, 90 mmol) while keeping the temperature below 5°C. To the stirred solution was slowly added 200 ml of saturated sodium chloride. The suspension was stirred at 0°C for 4 hours and the solid was isolated by filtration and washed with 200 ml of distilled water. The crude product was dried overnight in vacuo at 70°C under a gentle nitrogen purge. The yield was 3.29 g, 80.2% corrected for 78.8% purity. The crude finasteride (MK906) was dissolved in isopropyl acetate (100 ml) with heating and the volume reduced to 15 ml by distillation under reduced pressure. The suspension was stirred overnight at 0°C. The solid was isolated by filtration and dried in the vacuum oven at 70°C. The yield was 2.16 g, 64.6% corrected for 95.4% purity. EXAMPLE The above solid was dissolved in 10 ml of acetic acid and 100 ml of water was added slowly. The product gradually crystallized out of solution. The mixture was aged at r.t. for 10 hours with agitation. After filtration and drying at 70°C in vacuo, 1.97 g of white crystalline finasteride (MK906) was obtained. The overall yield for the two steps was 60.2%, corrected for 98.0 wt. % purity. HPLC Same conditions as reported previously. RT: Finasteride (MK906) 4.25 min.

Claims: A process for preparing crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one which consists of dissolving 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one to a concentration of 0.216 g/ml in 1 part by volume of acetic acid and slowly adding 10 parts by volume of water; ageing the mixture at room temperature for 10 hours with agitation; filtration and drying at 70°C in vacuo. Crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one obtainable from the process as claimed in claim 1. Crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one as claimed in claim 2 for use in treating hyperandrogenic conditions. Crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one as claimed in claim 2 for use in treating hyperandrogenic conditions selected from acne vulgaris, seborrhea, female hirsutism, androgenic alopecia, prostatic carcinoma and benign prostatic hypertrophy. The use of crystalline 17β-(N-tert-butylcarbamoyl)-4-aza-5α-androst-1-en-3-one as claimed in claim 2 for the manufacture of a medicament for treating hyperandrogenic conditions. The use as claimed in claim 5 wherein the hyperandrogenic conditions are selected from acne vulgaris, seborrhea, female hirsutism, androgenic alopecia, prostatic carcinoma and benign prostatic hypertrophy.

Inventors: ANDERSON R KEVIN, KING ANTHONY O, SHUMAN RICHARD F, WEINSTOCK LEONARD M, ANDERSON, R. KEVIN, KING, ANTHONY O., SHUMAN, RICHARD F., WEINSTOCK, LEONARD M.
Applicants: MERCK & CO INC, MERCK & CO., INC.
Application year: 1990
Main classification: C07J73
IPC codes: C07J73