[NH2:1][C@@H:2]([CH:8]([CH3:10])[CH3:9])[CH:3]([OH:7])[C:4]([OH:6])=[O:5].[OH-].[Na+].O1CCOCC1.Cl[C:20]([O:22][CH2:23][C:24]1[CH:29]=[CH:28][CH:27]=[CH:26][CH:25]=1)=[O:21]>O>[CH2:23]([O:22][C:20]([NH:1][C@@H:2]([CH:8]([CH3:10])[CH3:9])[CH:3]([OH:7])[C:4]([OH:6])=[O:5])=[O:21])[C:24]1[CH:29]=[CH:28][CH:27]=[CH:26][CH:25]=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 1 N 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 1 N 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 1 N 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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