[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]2[CH2:13][NH:14][CH2:15][C@H:9]12)=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH2:16]([O:23][C:24](ON1C(=O)CCC1=O)=[O:25])[C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1>ClCCl>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@@H:10]2[CH2:13][N:14]([C:24]([O:23][CH2:16][C:17]3[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=3)=[O:25])[CH2:15][C@H:9]12)=[O:7])([CH3:4])([CH3:2])[CH3:3](3aR,6aR)-Hexahydro-pyrrolo[3,4-b]pyrrole-1-carboxylic acid tert-butyl ester (3.0 g, 12.5 mmole) and N-(benzyloxycarbonyloxy)-succinimide (3.42 g, 13.7 mmole) were mixed in 15 ml of dichloromethane. The mixture was stirred at room temperature overnight and then concentrated under vacuum to provide the crude product The residue was purified by flash chromatography (20% ethyl acetate in hexane) to provide the title compound. 1H NMR (CDCl3) δ ppm 7.29-7.43 (m, 5H) 5.13 (s, 2H) 4.15-4.33 (m, 1H) 3.39-3.74 (m, 5H) 3.20-3.37 (m, 1H) 2.84-2.96 (m, 1H) 1.92-2.03 (m, 1H) 1.66-1.82 (m, 1H) 1.46 (s, 9H). MS: (M+H)+=347.
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