[CH3:1][O:2][C:3](=[O:10])[C@H:4]([CH2:6][CH:7]([CH3:9])[CH3:8])[NH2:5].C([O-])([O-])=O.[Na+].[Na+].[CH2:17]([O:24][C:25](Cl)=[O:26])[C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1>O1CCOCC1>[CH3:1][O:2][C:3](=[O:10])[C@H:4]([CH2:6][CH:7]([CH3:9])[CH3:8])[NH:5][C:25]([O:24][CH2:17][C:18]1[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=1)=[O:26]To a stirring solution of L-leucine methyl ester (2.0 g, 11.0 mmol) in 1,4-dioxane (20 mL) was added aqueous Na2CO3 solution (12.1 mL, 2M in H2O) followed by benzylchloroformate (1.96 g, 11.5 mmol). The mixture stirred at room temperature for 4 h then partitioned between ethyl acetate and water. The organic layer was washed with saturated brine, dried (MgSO4), filtered and concentrated to yield the title compound as a colorless oil (3.1 g, 100%). 1HNMR (400 MHz, CDCl3) δ 7.34 (m, 5H), 5.27 (d, 1H), 5.12 (s, 2H), 4.41 (s, 2H), 3.75 (s, 3H), 1.65 (m, 3H), 0.96 (m, 6H).
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