(3S)-3-{[N-(tert-Butoxycarbonyl)-l-leucyl]amino}-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-Dichlorobenzoate (29)
Following the procedure described for the preparation of N2-(tert-butoxycarbonyl)-N1-((1S)-3-chloro-2-oxo-1-{[(3S)-2-oxopyrrolidin-3-yl]methyl}propyl)-l-leucinamide but substituting (3S)-3-[(tert-butoxycarbonyl)amino]-2-oxo-4-[(3S)-2-oxopyrrolidin-3-yl]butyl 2,6-dichlorobenzoate and making noncritical variations provided a brown foam. This material was purified by LC (50 g 230–400 SiO2, 2.5–3.5% methanol/chloroform) to afford 413 mg (61%) of the title compound as a light yellow foam. 1H NMR (DMSO-d6) δ 8.47 (d, J = 8 Hz, 1H), 7.60 (m, 4H), 7.05 (d, J = 8 Hz, 1H), 5.19 (d, J = 16 Hz, 1H), 5.13 (d, J = 16 Hz, 1H), 4.47 (m, 1H), 3.95 (m, 1H), 3.16 (m, 1H), 3.08 (m, 1H), 2.27 (m, 1H), 2.10 (m, 1H), 2.03 (m, 1H), 1.65 (m, 2H), 1.47–1.37 (m, 11 H), 0.89 (d, J = 4 Hz, 3H), 0.85 (d, J = 4 Hz, 3H); MS (ESI+) for C26H35Cl2N3O7m/z 572.1 (M + H)+. Anal. calcd for C26H35Cl2N3O7·0.5 H2O: C, 53.70; H, 6.24; N, 7.23. Found: C, 53.74; H, 6.31; N, 7.31; HRMS (ESI+) calcd for C26H35Cl2N3O7+Na 594.1744, found 594.1729.