[OH-].[K+].[CH2:3]([O:10][CH2:11][C:12]([NH:14][N:15]1[C:19]([C:20]([NH2:22])=[O:21])=[CH:18][N:17]=[CH:16]1)=O)[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1>O.CCO>[CH2:3]([O:10][CH2:11][C:12]1[NH:22][C:20](=[O:21])[C:19]2=[CH:18][N:17]=[CH:16][N:15]2[N:14]=1)[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1A solution of KOH (4.4 g, 78.5 mmol) in water (50 mL) was added dropwise to a solution of compound 3 (7.3 g, 26.6 mmol) in EtOH (60 mL) at room temperature. The resulting solution was heated to 110° C. for 3 hours. After removal of the organic solvent, the mixture was poured into ice water and the pH was adjusted to 7.0 with 1M aqueous HCl solution. The suspension was filtered and the filtrate was dried to afford compound 4 (4.9 g, 71% yield) as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 12.05 (s, 1H), 8.45 (s, 1H), 7.74 (s, 1H), 7.39˜7.29 (m, 5H), 4.59 (s, 2H), 4.36 (s, 2H). LC-MS: m/z 257.2 [M+H]+.
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