[NH2:1][C@@H:2]([CH:6]1[CH2:10][CH2:9]CC1)[C:3]([OH:5])=[O:4].[OH-].[Na+].[CH:13](=O)[C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1.[BH4-].[Na+]>O>[CH2:13]([NH:1][C@@H:2]([CH:6]1[CH2:10][CH2:9]1)[C:3]([OH:5])=[O:4])[C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1(S)-2-amino-2-cyclopentylacetic acid (1) (66.0, 0.46 mol, 1.0 eq) was added in portions into 2N NaOH (230 mL, 0.46 mol, 1.0 eq) with stirring. After complete dissolution of the amino acid, benzaldehyde (49.0 g, 0.46 mol, 1.0 eq) was added all at once. The reaction mixture was allowed to stir at room temperature for 1 h. Sodium borohydride (17.5 g, 0.46 mol, 1.0 eq) was added slowly in portions at 0° C., and the reaction mixture was stirred at room temperature for 4 h. Then the reaction mixture was diluted with water (250 mL) and extracted twice with diethyl ether (250 mL). The clear aqueous layer was neutralized with 4N HCl (aq) to pH=7 and the white suspension were stirred at rt for 0.5 h. After filtration, the solid was washed with water (250 mL), the filter cake was dried to yield the product 2 (66 g, 59%) as a white solid.
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