A solution of the compound 13 (198 mg, 0.500 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (115 mg, 0.600 mmol) and 1-hydroxybenzotriazole (81 mg, 0.600 mmol) in dimethylformamide (3 ml) was stirred at room temperature for 1.5 hours. Then, methanol (3 ml) and triethylamine (153 ul, 1.10 mmol) were added, and the mixture was heated to reflux for 1.5 hours. The reaction solution was diluted with ethyl acetate, washed with an aqueous saturated sodium bicarbonate solution, a 10% aqueous citric acid solution, and an aqueous saturated sodium chloride solution, and dried with anhydrous sodium sulfate. The solvent was distilled off under reduced pressure, and the residue was washed with diethyl ether to obtain 3-benzyloxy-5-(4-fluoro-benzylcarbamoyl)-4-hydroxy-pyridine-2-carboxylic acid methyl ester 14 (141 mg, 60%) as a colorless crystal.
