To a solution of 5-[(2,5-difluorophenyl)[[6-(trifluoromethyl)pyridin-3-yl]thio]methyl]-4-methylpyridine-2-carboxylic acid (176 mg, 0.40 mmol) obtained in Example 26 in N,N-dimethylformamide (4 ml), (benzotriazol-1-yloxy)tripyrrolidinophosphonium hexafluorophosphate (312 mg, 0.60 mmol), 1-hydroxybenzotriazole (81 mg, 0.60 mmol), ammonium chloride (43 mg, 0.80 mmol), and N-ethyldiisopropylamine (0.279 ml, 1.60 mmol) were added in an argon atmosphere at room temperature. After stirring for 5 hours at room temperature, ethyl acetate and water were added to the reaction mixture, and the resulting mixture was washed with saturated brine. 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=2:1 was concentrated under reduced pressure to obtain the title compound (168 mg, 0.38 mmol, 96%) as a white solid.
