C[O:2][C:3]([CH:5]1[CH2:9][N:8]([S:10]([CH3:13])(=[O:12])=[O:11])[CH:7]2[CH2:14][CH2:15][N:16]([C:17](=[O:33])[CH:18]([NH:25][C:26]([O:28][C:29]([CH3:32])([CH3:31])[CH3:30])=[O:27])[CH:19]3[CH2:24][CH2:23][CH2:22][CH2:21][CH2:20]3)[CH:6]12)=[O:4].[OH-].[Na+]>CO>[C:29]([O:28][C:26]([NH:25][CH:18]([CH:19]1[CH2:20][CH2:21][CH2:22][CH2:23][CH2:24]1)[C:17]([N:16]1[CH:6]2[CH:7]([N:8]([S:10]([CH3:13])(=[O:12])=[O:11])[CH2:9][CH:5]2[C:3]([OH:4])=[O:2])[CH2:14][CH2:15]1)=[O:33])=[O:27])([CH3:32])([CH3:30])[CH3:31]A solution of 28 (1.1 g, 2.3 mmol) in MeOH (20 mL) was treated with 1M NaOH (10 mL) at ambient temperature. After 40 min, the solution was concentrated, acidified with 1M HCl until pH˜2, and extracted with EtOAc. The organic extracts were washed with brine, dried over anhydrous Na2SO4, filtered and concentrated to afford 29 (1.0 g) as a light yellow-colored foam which was used without further purification. 1H NMR (CDCl3, 300 MHz): δ5.23 (d, J=9.0 Hz, 1H), 4.71 (d, J=6.3 Hz, 1H), 4.33-4.16 (m, 2H), 4.16-4.06 (m, 2H), 3.82-3.78 (m, 1H), 3.73-3.66 (m, 2H), 3.17 (m, 1H), 2.92 (s, 3H), 2.66 (dd, J=5.1, 13.5 Hz, 1H), 2.13 (m, 1H), 1.77-1.55 (m, 6H), 1.43 (s, 9H), 1.29-1.01 (m, 6H) ppm.
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