To a solution of 5-[(2,5-difluorophenyl)[(4-fluorophenyl)sulfonyl]methyl]-4-methylpyridine-2-carboxylic acid (126 mg, 0.30 mmol) obtained in Example 12 in methylene chloride (3 ml), ethylamine hydrochloride (27 mg, 0.33 mmol), 1-hydroxybenzotriazole (45 mg, 0.33 mmol), 4-methylmorpholine (0.073 ml, 0.66 mmol), and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (63 mg, 0.33 mmol) were added at room temperature. After stirring for 7 days at room temperature, the reaction mixture was washed with saturated aqueous sodium hydrogencarbonate. The organic layer was dried over anhydrous sodium sulfate and filtered, then the filtrate was concentrated under reduced pressure, and the resulting residue was subjected to flash silica gel chromatography. The fraction obtained from an elution with hexane:ethyl acetate=7:3 was concentrated under reduced pressure, and the resulting residue was washed with a mixed solvent of ethanol and hexane, and was collected by filtration, to obtain the title compound (120 mg, 0.27 mmol, 89%) as a white solid.
