[CH2:1]([C@H:8]1[C@H:12]([C:13]([OH:15])=[O:14])[O:11][C:10](=[O:16])[NH:9]1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.O=[C:18]1NCC(C(O)=O)O1.[OH-].[K+].Cl.[CH3:29][CH:30]([OH:32])[CH3:31]>ClCCl>[C:30]([O:32][C:10]([NH:9][C@@H:8]([CH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1)[C@@H:12]([OH:11])[C:13]([OH:15])=[O:14])=[O:16])([CH3:18])([CH3:31])[CH3:29]To (4S,5R)-4-benzyl-2-oxo-5-oxazolidinecarboxylic acid obtained in the same manner as in Example 4 (2.39 g) were added 2-propanol (6.7 ml) and 8N aqueous potassium hydroxide solution (6.7 ml), and the mixture was stirred at 90° C. for 3 hr. The mixture was cooled to room temperature and adjusted to pH=8 with 6N aqueous hydrochloric acid solution. To the reaction mixture was added di-tert-butoxycarbonate (2.83 g) dissolved in 2-propanol (6.7 ml) and the mixture was stirred at room temperature for 12 hr. After adjusting the mixture to pH=3, dichloromethane (20 ml) was added to extract the mixture. The solvent of the organic layer was removed under reduced pressure to give crude crystals of (2R,3S)-3-tert-butoxycarbonylamino-2-hydroxy-4-phenylbutyric acid (2.88 g). The crude crystals were analyzed by HPLC to confirm that (2R,3S)-3-tert-butoxycarbonylamino-2-hydroxy-4-phenylbutyric acid (2.55 g, yield 80%) was obtained.
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