C[O:2][C:3](=[O:20])[CH2:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[CH2:11][NH:12][C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14].O.[OH-].[Li+]>O1CCCC1.O>[C:16]([O:15][C:13]([NH:12][CH2:11][C:6]1[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=1[CH2:4][C:3]([OH:20])=[O:2])=[O:14])([CH3:19])([CH3:17])[CH3:18]To a stirring solution of 5a in tetrahydrofuran (0.3 M) at room temperature was added a solution of lithium hydroxide monohydrate (1.2 M) in H2O (0.4 M). The reaction was stirred at room temperature overnight. The tetrahydrofuran was removed under reduced pressure. The remaining aqueous phase was acidified with concentrated hydrochloric acid. The precipitated product was filtered off and dried to afford a white solid. (98%) 1H NMR (400 MHz, DMSO-d6) δ 12.34 (br s, 1H), 7.29 (m, 1H), 7.19 (m, 4H), 4.12 (m, 2H), 3.65 (s, 2H), 1.38 (s, 9H).
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