[OH:1][CH:2]([C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)[CH2:3][N:4]1[C:8]2[NH:9][C:10](=[S:14])[NH:11][C:12](=[O:13])[C:7]=2[CH:6]=[N:5]1.[CH3:21]I>C1COCC1>[OH:1][CH:2]([C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)[CH2:3][N:4]1[C:8]2[N:9]=[C:10]([S:14][CH3:21])[NH:11][C:12](=[O:13])[C:7]=2[CH:6]=[N:5]1A solution of 7 (2.88 g, 10 mmol) and methyl iodide (7.10 g, 50 mmol) in anhydrous THF (20 mL) was refluxed for 12 h. The solvent and the excess of methyl iodide were removed by distillation under reduced pressure; the oil residue crystallized by adding CHCl3 (10 mL) and was purified by recrystallization with absolute ethanol to give 8a (2.17 g, 72%) as a white solid; mp 208-209° C. 1H NMR: δ 2.51 (s, 3H, CH3), 4.27-4.50 (m, 2H, CH2N), 5.04-5.18 (m, 1H, CHO), 5.68 (d, 1H, OH, disappears with D2O), 7.20-7.42 (m, 5H Ar), 7.97 (s, 1H, H-3). IR cm−1: 3544 (NH), 3450-3350 (OH), 1678 (CO). Anal. (C14H14N4O2S) C, H, N, S.
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