To a solution of 4-acetylthiomethylthio-1,2,3-triazole (230 mg: 1.22 mMol.) in dimethylformamide (6 ml) is dropwise added a 1.26N-sodium methoxide in methanol (1.9 ml) at -60° C., and the mixture is stirred for 20 minutes, mixed with a solution of 7β-[(Z)-2-(2-t-butoxycarbonylaminothiazol-4-yl)-2-pentenoylamino]-3-methanesulfonyloxy-3-cephem-4-carboxylic acid diphenylmethyl ester (740 mg: 1 mMol.) in dimethylformamide (3 ml), and stirred at the same temperature for 40 minutes. The reaction mixture is diluted with 10% hydrochloric acid (2 ml) and water (30 ml) and extracted with ethyl acetate. The extract is washed with water, dried over sodium sulfate, and purified by silica gel chromatography (toluene: ethyl acetate=2:1) to give 7β-[(Z)-2-(2-t-butoxycarbonylaminothiazol-4-yl)-2-pentenoylamino]-3-(1,2,3-triazol-4-ylthiomethylthio)-3-cephem-4-carboxylic acid diphenylmethyl ester (553 mg) as colorless foam. Yield: 70%.
