[C:1]([O:5][C:6](=[O:13])[NH:7][C@@H:8]([CH2:11][CH3:12])[CH2:9][NH2:10])([CH3:4])([CH3:3])[CH3:2].C(N(CC)CC)C.Cl[C:22](=[O:27])[C:23]([O:25][CH3:26])=[O:24]>C(Cl)Cl.[Cl-].[Na+].O>[C:1]([O:5][C:6]([NH:7][C@@H:8]([CH2:11][CH3:12])[CH2:9][NH:10][C:22](=[O:27])[C:23]([O:25][CH3:26])=[O:24])=[O:13])([CH3:4])([CH3:3])[CH3:2]To an ice cold solution of (S)-tert-butyl(1-aminobutan-2-yl)carbamate (1.0 g, 5.4 mmol) and triethylamine (0.78 mL, 5.6 mmol) in DCM (33 mL) was added methyl chlorooxoacetate (0.52 mL, 5.6 mmol) dropwise. Following the addition, the reaction was allowed to warm to rt and stirred overnight. Brine was added, the layers were separated, and the aqueous layer was washed with DCM. The combined organic extracts were dried (Na2SO4), filtered, and concentrated to provide a yellow oil (1.4 g, 96%), which was used without further purification. 1H NMR (500 MHz, CDCl3) δ 7.78 (s, 1H), 4.59 (d, J=7.6 Hz, 1H), 3.92-3.81 (m, 3H), 3.69 (s, 1H) 3.45 (dt, J=13.5, 4.2 Hz, 1H), 3.39-3.22 (m, 1H), 1.47-1.38 (m, 11H), 0.98 (t, J=7.5 Hz, 3H).
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