[CH2:1]([O:8][C:9]([NH:11][C:12]12[CH2:19][C:16]([C:20]([O:22]C)=[O:21])([CH2:17][CH2:18]1)[CH2:15][CH2:14][CH2:13]2)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[OH-].[Na+]>CO>[CH2:1]([O:8][C:9]([NH:11][C:12]12[CH2:19][C:16]([C:20]([OH:22])=[O:21])([CH2:17][CH2:18]1)[CH2:15][CH2:14][CH2:13]2)=[O:10])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1To a solution of methyl 5-(benzyloxycarbonylamino)bicyclo-[3.2.1]octane-1-carboxylate (25 g, crude product) in methanol (200 mL) was added NaOH (5N, 50 mL) and the reaction mixture was refluxed for two hours. After cooled to room temperature, the mixture was concentrated under reduced pressure. The residue was diluted with water (100 mL) and extracted with diethyl ether (3×100 mL) to remove the organic impurities. The aqueous phase was adjusted to pH 1˜2 with 2N aq. HCl, and extracted with dichloromethane (3×100 mL). The combined organic layer was washed with brine, dried over sodium sulfate and concentrated under reduced pressure to afford 8.5 g (49%, steps 5 and 6) of 5-(benzyloxycarbonylamino)bicyclo[3.2.1]octane-1-carboxylic acid as a yellow oil. ESI-MS m/z: 304 (M+H)+.
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