To a stirred solution of acid N-carboxymethyl-1,4-dihydroquinoxaline-2,3-dione (200 mg, 0.910 mmol) and p-phenylenediamine (98 mg, 0.91 mmol) in DMF (2 mL) under N2 at 0° C., DCC (190 mg, 0.910 mmol) was added in one portion. The solution was allowed to warm to 28° C. and stirred at that temperature overnight. The precipitated solid was filtered and the clear filtrate was poured into water (10 mL). The solid thus obtained was filtered and dried under vacuum (water aspirator) to obtain 180 mg crude product as a brown powder. The product was purified by Soxhlet extraction in boiling ethanol (20 mL), keeping the oil bath temperature at 120° C., for 4 h. The insoluble material (in the thimble) was dried under vacuum to obtain 135 mg pure (1H NMR) N-(N'-(p-aminophenyl)carboxamidyl)methyl-1,4-dihydroquinoxaline-2,3-dione as a white powder. M.p.>300° C. (decomposes). 1H NMR: δ4.84 (s, 2H), 4.93 (s,2H), 6.5 (d, 2H, J=8.4 Hz), 7.15-7.25 (m, 6H), 9.83 (s, 1H), 12.15 (s, 1H). IR (KBr, cm-1): 3462, 3143, 1793, 1693, 1593, 1443. HRMS: Calculated for C16H14N4O3, 310.1066; Observed, 310.1071.
