C[O:2][C:3](=[O:19])[CH2:4][C:5]([NH:8][C:9]([O:11][CH2:12][C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][CH:14]=1)=[O:10])([CH3:7])[CH3:6].[OH-].[Na+]>CO>[CH2:12]([O:11][C:9]([NH:8][C:5]([CH3:7])([CH3:6])[CH2:4][C:3]([OH:19])=[O:2])=[O:10])[C:13]1[CH:14]=[CH:15][CH:16]=[CH:17][CH:18]=1A solution of 18.27 g (68.9 mmol) of 3-benzyloxycarbonylamino-3-methylbutanoic acid methyl ester in 20 mL of methanol at room temperature was treated dropwise with 51 mL of 2N NaOH (102 mmol). The mixture was stirred at room temperature for 16 hours then transferred to a separatory funnel and washed with hexane (3×). The aqueous layer was removed, cooled to 0° C. and slowly acidified to pH 2 (paper) by dropwise addition of 6N HCl. This mixture was extracted with ether (6×); combined extracts were washed with 1N HCl and brine, then dried over magnesium sulfate, filtered and solvent removed under vacuum to afford 17.26 g (68.7 mmol, 99%) of the product.
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