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.O>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 154.7 g dissolved in ethanol 300 ml was kept at 5-15° C. and mixed with sodium borohydride 24.6 g and stirred at 15-45° C. for 3hrs. The reaction solution was cooled and adjusted with 3N-HCl to pH 2.5-3.5. Water was added to the resultant solution and then the obtained solution was cooled to 5° C. or lower to deposit crystals. The crystals were filtered, dissolved in ethyl acetate, and washed with aqueous 5% sodium bicarbonate solution 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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