To a suspension of 4-nitrobenzyl 7-(2-phenylacetamido)-3-mesyloxy-3-cephem-4-carboxylate (11 g.) in methylene chloride (100 ml.) were added pyridine (2.37 g.) at ambient temperature and then phosphorus pentachloride (5.4 g.) at 0° C. with stirring, whereafter the mixture was stirred at -3° to 3° C. for 2 hours. After adding methanol (5.2 g.) at -20° C., the stirring was continued at the same temperature for additional an hour. The reaction mixture was poured into water and adjusted to pH 7.5 with sodium bicarbonate, followed by extraction with ethyl acetate (500 ml.). The extract was washed with an aqueous solution of sodium chloride, dried over anhydrous magnesium sulfate, and then concentrated under reduced pressure. The residue was pulverized with diethyl ether to give 4-nitrobenzyl 7-amino-3-mesyloxy-3-cephem-4-carboxylate (8.8 g.).
