[OH:1]O.[N+:3]1([O-:17])[C:8]2[CH:9]=[C:10]3[C:14](=[CH:15][C:7]=2[N:6]=[C:5]([NH2:16])[N:4]=1)[CH2:13][CH2:12][CH2:11]3.N>CC(O)=O>[N+:3]1([O-:17])[C:8]2[CH:9]=[C:10]3[C:14](=[CH:15][C:7]=2[N+:6]([O-:1])=[C:5]([NH2:16])[N:4]=1)[CH2:13][CH2:12][CH2:11]3H2O2 (70%, 5.0 mL, ca. 99.4 mmol) was added dropwise to a stirred solution of 1-oxide 19 (2.0 g, 9.9 mmol) in HOAc (30 mL) and the solution was stirred at 50° C. for 96 h. The mixture was cooled to 0° C., neutralised with dilute aqueous NH3 solution and the mixture stirred vigorously for 30 min, then extracted with CHCl3 (4×50 mL). The combined organic fraction was dried and the solvent evaporated. The residue was purified by chromatography, eluting with a gradient (0-5%) of MeOH/DCM, to give 1,4-dioxide 20 (317 mg, 15%) as a red solid: mp (MeOH/EtOAc) 190-195° C.; 1H NMR [(CD3)2SO] δ 8.01 (s, 1H, H-9), 7.98 (s, 1H, H-5), 7.87 (br s, 2H, NH2), 3.07 (br t, J=7.4 Hz, 2H, H-6), 3.01 (br t, J=7.4 Hz, 2H, H-8), 2.10 (p, J=7.4 Hz, 2H, H-7); 13C NMR [(CD3)2SO] δ 154.3, 150.8, 144.7, 137.8, 129.6, 115.1, 111.2, 32.6, 31.7, 25.1. Anal. calcd for C10H10N4O2.½CH3OH: C, 53.8; H, 5.2; N, 23.9. Found: C, 53.6; H, 5.2; N, 23.9%.
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