To a suspension of 3-hydroxy-7beta-phenylacetylaminocepham-4-carboxylic acid diphenylmethyl ester (2) in dichloromethane (18 parts) cooling at -30° C. are dropwise added methanesulfonyl chloride (6 equivalents) and then pyridine (6 equivalents). The mixture is let stand at 0° to 5° C. for 17 hours. The reaction mixture is diluted with ice-water, the organic layer is taken, washed with hydrochloric acid and water, dried, and concentrated. The residue is crystallized from a mixtue of ethyl acetate and hexane to give 3-methanesulfonyloxy-7beta-phenylacetylaminocepham-4-carboxylic acid diphenylmethyl ester (3c). Yield: 96.5%. mp. 151°-152° C. (decomposition).
