To a solution of 3-hydroxy-7beta-phenylacetylamino-3-cephem-4-carboxylic acid diphenylmethyl ester (1) in dimethylformamide (9.5 parts, dried over Molecular Sieves) at -50° C. under nitrogen is added sodium borohydride (4 equivalents) at -53° to -48° C. over 3 minutes. After 30 minutes at the same temperature, glacial acetic acid (1.4 parts) and then water (10 parts) are added to the mixture gradually, and extracted with ethyl acetate. The extract is washed with 5% aqueous sodium hydrogen carbonate and water, dried over sodium sulfate, and concentrated. The residue is crystallized from a mixture of dichloromethane (4 parts) and n-hexane (1.7 parts) to give 3-hydroxy-7beta-phenylacetylaminocepham-4-carboxylic acid diphenylmethyl ester (2). Yield: 76.3%. mp. 196°-198° C. (decomposition).
