[CH2:1]([O:8][CH2:9][C:10]1[NH:15][C:14](=[O:16])[C:13]2=[CH:17][N:18]=[CH:19][N:12]2[N:11]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Li]CCCC.[I:25]I>C1COCC1>[CH2:1]([O:8][CH2:9][C:10]1[NH:15][C:14](=[O:16])[C:13]2=[CH:17][N:18]=[C:19]([I:25])[N:12]2[N:11]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1To a solution of compound 4 (4.9 g, 19.1 mmol) in THF (120 mL) was added n-BuLi (23 mL) dropwise at −78° C. and the resulting reaction mixture was stirred below −70° C. for one hour, followed by dropwise addition of iodine (19.4 g, 76.3 mmol) in THF (60 mL) at the same temperature. The reaction was allowed to warm to room temperature slowly. The reaction was quenched with saturated aqueous Na2SO3 solution (60 mL), and it was then extracted with EtOAc (60 mL×3). The organic phases were combined and dried over Na2SO4. The solid was filtered and the filtrate was concentrated in vacuo to give the crude product, which was purified by chromatography on silica gel column (eluted with PE/EtOAc=10:1 to 2:1) to afford compound 5 (4.1 g, 56% yield) as a white solid. 1H NMR (400 MHz, DMSO-d6): δ 12.16 (s, 1H), 7.84 (s, 1H), 7.42˜7.29 (m, 5H), 4.62 (s, 2H), 4.40 (s, 2H). LC-MS: m/z 383.2 [M+H]+.
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