[C:1]([O:5][C:6]([NH:8][C:9]12[CH2:15][C:12]([C:16]([O:18]C)=[O:17])([CH2:13][CH2:14]1)[CH2:11][CH2:10]2)=[O:7])([CH3:4])([CH3:3])[CH3:2].[OH-].[Na+]>C1COCC1.CO>[C:1]([O:5][C:6]([NH:8][C:9]12[CH2:15][C:12]([C:16]([OH:18])=[O:17])([CH2:11][CH2:10]1)[CH2:13][CH2:14]2)=[O:7])([CH3:4])([CH3:2])[CH3:3]To a solution of methyl 4-(tert-butoxycarbonylamino)bicyclo[2.2.1]heptane-1-carboxylate (2.21 g, 8.20 mmol) in THF (27 mL) and MeOH (14 mL) was added aqueous NaOH (1 N, 20.0 mL, 20.0 mmol). The mixture was stirred at room temperature for about 16 h and concentrated to dryness under reduced pressure. Water (25 mL) was added to the remaining residue and the mixture was extracted with Et2O (2×25 mL) and the Et2O extracts were discarded. The aqueous layer was acidified to about pH 4 using aqueous 6 N HCl and extracted with Et2O (3×10 mL). The combined organic layers were dried over anhydrous MgSO4, filtered, and concentrated to dryness under reduced pressure to provide 4-(tert-butoxycarbonylamino)bicyclo[2.2.1]heptane-1-carboxylic acid as an off-white solid (1.69 g, 81%): 1H NMR (400 MHz, DMSO-d6) δ 12.07 (s, 1H), 7.00 (s, 1H), 2.00-1.69 (m, 6H), 1.67-1.45 (m, 4H), 1.37 (s, 9H).
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