[NH2:1][C@H:2]([C:7]([OH:9])=[O:8])[C:3]([CH3:6])([CH3:5])[CH3:4].C([O-])(O)=O.[Na+].Cl[C:16]([O:18][CH2:19][C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1)=[O:17].C([O-])([O-])=O.[Na+].[Na+]>O>[CH2:19]([O:18][C:16]([NH:1][CH:2]([C:3]([CH3:6])([CH3:5])[CH3:4])[C:7]([OH:9])=[O:8])=[O:17])[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1To a solution of L-tert-leucine (1) (50.0 g, 38.0 mmol) and NaHCO3 (96.0 g, 114 mmol) in ice (500 g) and water (500 ml) was added benzyl chloroformate (65.0 ml, 74.0 mmol) and the reaction stirred at 0° C. for 3 hours then at room temperature for 18 hours. 0.1N Na2CO3 was added until the oily layer dissolved and the solution was washed with 10% EtOAc in hexanes (2×500 ml). The iced aqueous phase was acidified to pH 1 using 12N HCl then extracted using EtOAc (3×350 ml). The combined organic extracts were dried over Na2SO4, filtered and evaporated to give the title compound as a colorless oil (82.4 g, 81.5% yield):
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