methyl (2S)-2-amino-5,5,5-trifluoropentanoate

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a stirred solution of 2-isopropyl-3,6-dimethoxy-2,5-dihydro-pyrazine (1 mL, 5.58 mmol) in THF (13.5 mL) under argon at −78° C. was added a solution of n-butyllithium (2.5 M, 2.3 mL, 5.75 mmol). The solution was stirred at −78° C. for 30 minutes. A solution of 1-Iodo-3,3,3-trifluoropropane (925 μL, 5.87 mmol) in THF (11.5 mL) was added slowly. The resulting solution was stirred at −78° C. for 5 hours, warmed to room temperature and diluted with ethyl acetate. The organic layer was washed successively with saturated aqueous NH4Cl solution, water and brine. The organic layer was then dried (MgSO4), concentrated and purified by flash chromatography to yield 2-Isopropyl-3,6-dimethoxy-5-(3,3,3-trifluoro-propyl)-2,5-dihydro-pyrazine (915 mg, 59%). 1H-NMR: 400 MHz, (CDCl3) δ: 4.04-3.99 (m, 1H), 3.98-3.95 (m, 1H), 3.71 (s, 3H), 3.68 (s, 3H), 2.29-2.20 (m, 1H), 2.18-2.04 (m, 3H), 1.94-1.84 (m, 1H), 1.03 (d, J=6.9 Hz, 3H), 0.71 (d, J=6.8 Hz, 3H) ppm. 5,5,5-Trifluoro-2-methoxycarbonylamino-pentanoic acid methyl ester: A solution of 2-Isopropyl-3,6-dimethoxy-5-(3,3,3-trifluoro-propyl)-2,5-dihydro-pyrazine (725 mg, 2.59 mmol) in 0.25N HCl was stirred at room temperature for 3 hours. The aqueous solution was washed once with ethyl acetate. The ethyl acetate rinsing was discarded and the aqueous layer was basified to pH-10 with saturated aqueous NaHCO3. The aqueous layer was extracted twice with ethyl acetate. The combined organics were washed with brine, dried (MgSO4) and concentrated to give crude (2S)-amino-5,5,5-trifluoro-pentanoic acid methyl ester contaminated with D-valine methyl ester. The crude material was dissolved in dichloromethane (20 mL) and cooled to 0° C. Triethylamine (1.75 mL, 12.6 mmol) and methyl chloroformate (480 μL, 6.2 mmol) were successively added to the solution. After 1 hour the reaction was concentrated and purified by flash chromatography to yield 5,5,5-Trifluoro-2-methoxy-carbonylamino-pentanoic acid methyl ester (465 mg, 74%). 1H-NMR: 400 MHz, (CDCl3) δ: 5.27 (br, 1H), 4.42 (br, 1H), 3.79 (s, 3H), 3.70 (s, 3H), 2.29-2.09 (m, 3H), 1.94-1.84 (m, 1H) ppm. 2-[5-(4′-{2-[1-(5,5,5-Trifluoro-2-methoxycarbonylamino-pentanoyl)-pyrrolidin-2-yl]-3H-imidazol-4-yl}-biphenyl-4-yl)-1H-imidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester: To a solution of 5,5,5-Trifluoro-2-methoxycarbonylamino-pentanoic acid methyl ester (194 mg, 0.80 mmol) in methanol (3 mL) was added an aqueous LiOH solution (1M, 2 mL, 2 mmol). The resulting solution was stirred at room temperature for 45 minutes and then washed with ethyl acetate. The ethyl acetate washing was discarded and the aqueous layer was acidified with concentrated HCl. The acidified aqueous layer was extracted twice with ethyl acetate. The combined organics were washed with brine, dried (MgSO4), and concentrated to give clean 5,5,5-Trifluoro-2-methoxy-carbonylamino-pentanoic acid. To a solution of the pentanoic acid in dimethylformamide (2 mL) was added HATU (300 mg, 0.79 mmol). After stirring for 5 minutes, a solution of 2-{5-[4′-(2-pyrrolidin-2-yl-3H-imidazol-4-yl)-biphenyl-4-yl]-1H-imidazol-2-yl}-pyrrolidine-1-carboxylic acid tert-butyl ester (412 mg, 0.79 mmol) in dimethylformamide (1.9 mL) was added to the reaction, followed immediately by diisopropylethylamine (275 μL, 1.58 mmol). The reaction was stirred for 1 hour at room temperature then diluted with ethyl acetate. The organic layer was washed with water and brine, dried (MgSO4), concentrated and purified by flash chromatography to yield 2-[5-(4′-{2-[1-(5,5,5-trifluoro-2-methoxycarbonylamino-pentanoyl)-pyrrolidin-2-yl]-3H-imidazol-4-yl]-biphenyl-4-yl)-1H-imidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (340 mg, 59%). LCMS-ESI+: calculated for C38H44F3N7O5: 735.34; observed [M+1]+ : 736.05. [4,4,4-Trifluoro-1-(2-{5-[4′-(2-pyrrolidin-2-yl-3H-imidazol-4-yl)-biphenyl-4-yl]-1H-imidazol-2-yl}-pyrrolidine-1-carbonyl)-butyl]-carbamic acid methyl ester: To a solution of 2-[5-(4′-{2-[1-(5,5,5-trifluoro-2-methoxycarbonylamino-pentanoyl)-pyrrolidin-2-yl]-3H-imidazol-4-yl}-biphenyl-4-yl)-1H-imidazol-2-yl]-pyrrolidine-1-carboxylic acid tert-butyl ester (340 mg, 0.46 mmol) in dichloromethane (5 mL) was added trifluoroacetic acid (1 mL). The reaction was stirred at room temperature for 3 hours and then thoroughly concentrated. The resulting residue was dissolved in dichloromethane and washed three times with saturated aqueous NaHCO3 solution. The organic layer was dried (MgSO4), and concentrated to give the crude free pyrrolidine (270 mg, 92%), which was clean enough to use without further purification. LCMS-ESI+: calculated for C33H36F3N7O3: 635.28; observed [M+1]+: 636.17. (4,4,4-Trifluoro-1-{2-[5-(4′-{2-[1-(2-methoxycarbonylamino-3-methyl-butyryl)-pyrrolidin-2-yl]-3H-imidazol-4-yl}-biphenyl-4-yl)-1H-imidazol-2-yl]-pyrrolidine-1-carbonyl}-butyl)-carbamic acid methyl ester: To a solution of crude [4,4,4-Trifluoro-1-(2-{5-[4′-(2-pyrrolidin-2-yl-3H-imidazol-4-yl)-biphenyl-4-yl]-1H-imidazol-2-yl}-pyrrolidine-1-carbonyl)-butyl]-carbamic acid methyl ester (125 mg, 0.20 mmol) in dimethylformamide (0.6 mL) was added a solution of 2-methoxycarbonylamino-3-methyl-butyric acid (38 mg, 0.22 mmol) and HATU (82 mg, 0.22 mmol) in dimethylformamide (0.6 mL). Diisopropylethylamine (70 μL, 0.40 mmol) was then added and the reaction was stirred at room temperature for 16 hours. The solution was concentrated and purified by preparative reverse phase HPLC (Gemini, 15 to 50% ACN/H2O+0.1% HCO2H) to yield (4,4,4-trifluoro-1-{2-[5-(4′-{2-[1-(2-methoxycarbonylamino-3-methyl-butyryl)-pyrrolidin-2-yl]-3H-imidazol-4-yl}-biphenyl-4-yl)-1H-imidazol-2-yl]-pyrrolidine-1-carbonyl]-butyl)-carbamic acid methyl ester (73 mg, 47%). LCMS-ESI+: calculated for C40H47F3N8O6: 792.85; observed [M+1]+ : 794.33. 1H-NMR: 400 MHz, (CD3OD) δ: 7.82-7.70 (m, 4H), 7.68-7.63 (m, 4H), 7.32-7.31 (m, 2H), 5.20-5.16 (m, 2H), 4.56-4.51 (m, 1H), 4.26-4.22 (m, 1H), 4.04-3.96 (m, 1H), 3.91-3.84 (m, 2H), 3.67 (s, 3H), 3.66 (s, 3H), 3.51-3.46 (m, 1H), 2.38-1.96 (m, 12H), 1.90-1.78 (m, 1H), 1.01-0.89 (m, 6H) ppm. The aqueous solution was washed once with ethyl acetate The aqueous layer was extracted twice with ethyl acetate The combined organics were washed with brine dried (MgSO4) concentrated