Methanesulfonic acid (5.77 g, 60 mmol) was added dropwise to a solution of 7β-aminocephalosporanic acid (3.27 g, 12.0 mmol) and 1-acetamido-5-mercapto-1H-tetrazole (2.50 g, 15.7 mmol) in acetonitrile (15 ml). The mixture was stirred at room temperature for 30 minutes and at 50° C. for 4 hours. Water (20 ml) was added with cooling to the reaction mixture, which was then adjusted to pH 3.5 with 28% aqueous ammonium hydroxide. Precipitates formed were filtered, washed with water and acetone successively and dried to give pale brown powder of 7β-amino-3-[(1-acetamido-1H-tetrazol-5-yl)thiomethyl]-3-cephem-4-carboxylic acid (3.36 g, 75. 3%), mp~195° C. (decomposition).
