To a solution of 3-hydroxy-7beta-phenylacetylaminocepham-4-carboxylic acid diphenylmethyl ester (2) in dimethylformamide (9.5 parts, dried over Molecular Sieves) cooling at -50° C. under nitrogen are added triethylamine (4 equivalents) and then methanesulfonyl chloride (2 equivalents) over 3 minutes at -52° to -45° C. After 2.5 hours at -55° to -45° C., the produced methanesulfonate (3) solution is stirred for 50 minutes at -15° to -12° C. diluted with ethyl acetate, washed with water, 5% hydrochloric acid, and water, dried over sodium sulfate, and concentrated. The residue is crystallized from methanol to give 7beta-phenylacetylamino-3-cephem-4-carboxylic acid diphenylmethyl ester (6). (Yield: 81.53%). mp. 166° C. (decomposition).
