To a solution of phenol (30 mg, 0.32 mmol) in acetone (2 ml) and 1 N NaOH (0.25 ml), (3S,4S)-3{N-benzyloxycarbonyl-β-(2-naphthyl)-L-alanyl}-amino-4-acetoxy-azetidin-2-one (95 mg, 0.2 mmol) in acetone (1 ml) and THF (2 ml) was added at 5° C. The mixture was stirred at 5° C. for 1 hr and then at room temperature for 1 hr. After removal of solvent, the residue was dissolved in ethyl acetate, washed with water, brine and dried over sodium sulfate. After removal of solvent, the residue was purified by silica gel column chromatography using ethyl acetate-hexane (1:2) as eluent and 45 mg of (3S,4S)-3-{N-benzyloxycarbonyl-β-(2-naphthyl)-L-alanyl}-amino-4-phenoxy-azetidin-2-one was obtained.
