Under nitrogen atmosphere, trifluoroacetic acid (4.0 ml) was added dropwise to a solution of diphenylmethyl 7β-[2-(2-amino-5-chlorothiazol-4-yl)-2-(Z)-(2-cyclopenten-1-yloxyimino)acetamido]-3-[(pyrazol-4-yl)methylthio]-3-cephem-4-carboxylate (1.71 g) in the mixture of dichloromethane (6.0 ml) and anisole (2.0 ml) at 0° C. Stirring was continued for 2 hours at the same temperature, the mixture was poured into isopropyl ether (200 ml). The resulting precipitate was collected by filtration, and then dissolved in the mixture of ethyl acetate and pH 6.86 buffer. The organic layer was removed, and the aqueous layer was adjusted pH 3.0 with 1N hydrochloric acid, concentrated in vacuo, then chlomatographed on a HP-20 column (eluent: water-methanol) to afford 7β-[2-(2-amino-5-chlorothiazol-4-yl)-2-(Z)-(hydroxyimino)acetamido]-3-[(pyrazol-4-yl)methylthio]-3-cephem-4-carboxylic acid (418.3 mg).
