C[O:2][C:3](=[O:24])[CH:4]=[CH:5][C:6]1[CH:14]=[C:13]2[C:9]([C:10]([S:15]([C:18]3[CH:23]=[CH:22][CH:21]=[CH:20][CH:19]=3)(=[O:17])=[O:16])=[CH:11][NH:12]2)=[CH:8][CH:7]=1.[OH-].[Li+].Cl>CO.O>[C:18]1([S:15]([C:10]2[C:9]3[C:13](=[CH:14][C:6]([CH:5]=[CH:4][C:3]([OH:24])=[O:2])=[CH:7][CH:8]=3)[NH:12][CH:11]=2)(=[O:17])=[O:16])[CH:19]=[CH:20][CH:21]=[CH:22][CH:23]=1
To a solution of 23 (0.36 g, 1.05 mmol) in MeOH (10 mL) and water (2 ml), lithium hydroxide (0.05 g, 2.11 mmol) was added. The reaction mixture was refluxed for 6 h and was then concentrated under reduced pressure to provide a residue. The residue was dissolved in water. 3N HCl was added up to acidic pH and the mixture was extracted with EtOAc (20 mL×3). The combined organic layer was dried over anhydrous MgSO4 and concentrated under reduced pressure to give a brown residue, which was recrystallized by EtOH to afford 24 (0.2 g). 1H NMR (500 MHz, CD3OD): δ 6.46 (d, J=15.8 Hz, 1H), 7.62-7.69 (m, 4H), 7.81 (s, 1H), 7.81 (d, J=16.0 Hz, 1H), 7.95 (d, J=8.4 Hz, 1H), 8.12 (d, J=7.3 Hz, 2H), 8.21 (s, 1H).
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