To a solution of (2R)-2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(1R)-3-oxocyclopentyl]propionic acid (160 mg) in dichloromethane (5 mL) were added oxalyl chloride (0.04 mL) and a drop of DMF under ice-cooling, followed by stirring for 1 hour under ice-cooling. To the reaction mixture were sequentially added pyridine (0.04 mL) and tert-butyl 3-amino-1H-pyrazole-1-carboxylate (90 mg), followed by stirring at room temperature overnight. To the reaction mixture were added ethyl acetate (30 mL) and 1 M hydrochloric acid (30 mL), and the organic layer was sequentially washed with saturated aqueous sodium bicarbonate (30 mL) and saturated brine (30 mL). After drying over anhydrous magnesium sulfate, the solvent was then evaporated under reduced pressure to obtain tert-butyl 3-({(2R)-2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(1R)-3-oxocyclopentyl]propanoyl}amino)-1H-pyrazole-1-carboxylate (197 mg) as a pale yellow amorphous substance. To a solution of tert-butyl 3-({(2R)-2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(1R)-3-oxocyclopentyl]propanoyl}amino)-1H-pyrazole-1-carboxylate (190 mg) in ethyl acetate (5 mL) was added 4 M hydrogen chloride/ethyl acetate (5 mL) under ice-cooling, followed by stirring at room temperature overnight. The solvent was evaporated under reduced pressure, ethyl acetate (20 mL) and saturated aqueous sodium bicarbonate (20 mL) were added thereto, and the organic layer was washed with saturated brine (20 mL) and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure, and the residue was then purified by silica gel column chromatography (ethyl acetate) to obtain (2R)-2-[3-cyclopropyl-4-(cyclopropylsulfonyl)phenyl]-3-[(1R)-3-oxocyclopentyl]-N-1H-pyrazol-3-yl propanamide (62 mg) as a colorless amorphous substance.
