Cl.[CH3:2][O:3][C:4](=[O:11])[C@H:5]([CH2:7][CH:8]([CH3:10])[CH3:9])[NH2:6].C([O-])([O-])=O.[Na+].[Na+].[CH2:18]([O:25][C:26](Cl)=[O:27])[C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1>O1CCOCC1>[CH3:2][O:3][C:4](=[O:11])[C@H:5]([CH2:7][CH:8]([CH3:10])[CH3:9])[NH:6][C:26]([O:25][CH2:18][C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)=[O:27]To a stirring solution of L-leucine methyl ester hydrochloride (2.0 g, 11.0 mmol) in 1,4-dioxane (20 mL) was added Na2CO3 (12.1 ml, 2M in water) followed by benzylchloroformate (1.96 g, 11.5 mmol). The mixture was stirred at room temperature for 4 h then partitioned between ethyl acetate and water. The organic layer was washed with brine, dried (MgSO4), filtered and concentrated to yield the title compound as a colorless oil (3.1 g, 100%). 1H NMR (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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