[C:1]1([NH2:8])[CH:6]=[CH:5][CH:4]=[CH:3][C:2]=1[NH2:7].[C:9]1(=[O:15])[NH:13][C:12](=[O:14])[CH:11]=[CH:10]1>O.CO>[O:15]=[C:9]1[NH:8][C:1]2[C:2](=[CH:3][CH:4]=[CH:5][CH:6]=2)[NH:7][CH:10]1[CH2:11][C:12]([NH2:13])=[O:14]To a solution of 1,2-phenylenediamine (21.5 g, 0.2 mol) in water (450 mL) was added dropwise a solution of maleimide, (20.0 g, 0.2 mol) in methanol (180 mL) over 60 min. The mixture was then stirred at 95° C. for 2 hours followed at rt overnight. The precipitate was collected via filtration and was washed with small amount of water for a few times to yield the title compound as a pale gray solid (pure product): 1H NMR (DMSO-d6) δ=10.2 (bs, 1H), 7.37 (bs, 1H) 6.88 (bs, 1H), 6.74-6.68 (m, 3H), 6.31-6.57 (m, 1H), 5.78 (bs, 1H), 4.08-4.04 (m, 1H), 2.63 (dd, 1H, J=3.6, 15.5 Hz), 2.32 (dd, 1H, J=3.3, 15.5 Hz); HPLC (CH3CN—H2O-0.1% TFA): Rf=9.49 min.
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