Glucose dehydrogenase (manufactured by Amano Enzyme) 1250 U, glucose 3 g, NADP 4 mg, (3S)-1-chloro-3-tert-butoxycarbonylamino-4-phenyl-2-butanone 0.25 g were added to 22.5 ml of a cell-free extract of E. coli HB101 (pNTOM4) prepared in Example 7, and the mixture was is stirred at 30° C. while adjusting to pH 6.5 by dropwise addition of 5 M sodium hydroxide. (3S)-1-chloro-3-tert-butoxycarbonylamino-4-phenyl-2-butanone (0.25 g) was added at 2 hr, 4 hr and 6 hr from the start of the reaction and 1.25 g thereof was added at 8 hr from the start of the reaction, and the mixture was reacted for 31 hr. After completion of the reaction, the reaction mixture was extracted with toluene, desolvated and the extract was analyzed in the same manner as in Example 8. As a result, (2R,3S)-1-chloro-3-tert-butoxycarbonylamino-4-phenyl-2-butanol (yield 99.0%, diastereomeric excess 99.8% d.e.) was obtained.
