A suspension of carbonic acid 2-{3-[(4-cyanophenylimino)-(5-oxo-1-pyrimidin-2-yl-4,5-dihydro-1H-[1,2,4]-triazol-3-yl)methyl]-2-fluoro-5-methoxyphenoxy}ethyl ester methyl ester (25.0 g, 47.1 mmol) and methanol (90 mL) was cooled to 15° C. Sodium cyanoborohydride (5.45 g, 87 mmol) was added thereto, and was rinsed with methanol (10 mL). Acetic acid (21.5 mL, 375 mmol) was added dropwise thereto, and the resulting mixture was stirred at room temperature for 28 hours. The mixture was cooled in an ice-water bath, and tetrahydrofuran (100 mL) and a 5 N aqueous sodium hydroxide solution (113 mL, 565 mmol) were added thereto. After stirring the resulting mixture for 18 hours, the mixture was cooled to 15° C. or below, and acetic acid (81 mL, 1.410 mol) was added thereto. To the solution obtained, a seed crystal (5.0 mg) of the captioned compound was added at room temperature, and water (250 mL) was added dropwise to the resulting mixture, after which the resulting mixture was stirred at 4° C. for 21.5 hours. The suspension obtained was filtered and was washed with 25% aqueous methanol (100 mL) and dried at 40° C. under reduced pressure to obtain the captioned compound (21.1 g) as a white solid.
