[NH2:1][C@@H:2]([CH:8]([CH3:10])[CH3:9])[CH:3]([OH:7])[C:4]([OH:6])=[O:5].Cl[C:12]([O:14][CH2:15][C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1)=[O:13]>[OH-].[Na+].O1CCOCC1.O>[CH2:15]([O:14][C:12]([NH:1][C@@H:2]([CH:8]([CH3:10])[CH3:9])[CH:3]([OH:7])[C:4]([OH:6])=[O:5])=[O:13])[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1To a solution under an atmosphere of nitrogen containing 1.0 g (6.8 mmol) of 3-(S)-amino-2-(R,S)-hydroxy-4-methylpentanoic acid in 9.5 mL of 1N NaOH and 10 mL of dioxane was added 1.43 g (8.4 mmol) of benzyl chloroformate. The pH was maintained above pH 8 with 1N NaOH as needed. The reaction mixture was allowed to stir at room temperature overnight. The reaction was diluted with water and washed with ether. The aqueous layer was acidified with 1N HCl to pH=2 and extracted with ether (2×). The combined organic layers were dried over magnesium sulfate, filtered and evaporated in vacuo to afford 1.75 g (92%) of 3-(S)-[(benzyloxycarbonyl)amino]-2-(R,S)-hydroxy-4-methylpentanoic acid as a light yellow viscous oil. FAB MS [M+H] m/z; Calcd: 282, Found: 282.
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