C[O:2][C:3](=O)[C@H:4]([OH:21])[C@@H:5]([NH:13][C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[CH2:6][C:7]1[CH:12]=[CH:11][CH:10]=[CH:9][CH:8]=1.[BH4-].[Na+].Cl>C(O)C>[C:17]([O:16][C:14]([NH:13][C@@H:5]([CH2:6][C:7]1[CH:8]=[CH:9][CH:10]=[CH:11][CH:12]=1)[C@@H:4]([OH:21])[CH2:3][OH:2])=[O:15])([CH3:20])([CH3:18])[CH3:19]A solution of N-tert-butoxycarbonyl-3(S)-amino-2(R)-hydroxy-4-phenylbutyric acid methyl ester 85.1 kg dissolved in ethanol 220 kg was kept at 10-20° C. and mixed with sodium borohydride 13.5 kg and stirred at 15-45° C. for 3 hrs. The reaction solution was cooled, adjusted with 3N-HCl to pH 2.5-3.5, concentrated under a reduced pressure, and washed with ethyl acetate and water to separate an organic phase, which was washed with aqueous 10% sodium chloride solution and concentrated under an reduced pressure to obtain the crude N-tert-butoxycarbonyl-3(S)-amino-2(R)-hydroxy-4-phenyl-1-butanol.
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