C([CH2:4][CH2:5][NH:6][C:7]1[CH:12]=[CH:11][CH:10]=[CH:9][C:8]=1[N+:13]([O-])=O)(O)=O.Cl.[OH2:17].O.[C:19]([OH:24])(=O)[C:20](O)=[O:21].[CH2:25]([OH:27])C>[Pd]>[C:25]([CH:5]([N:6]1[C:7]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[NH:13][C:20](=[O:21])[C:19]1=[O:24])[CH3:4])([OH:27])=[O:17]1.5 g (7.1 mmol) N-carboxyethyl-2-nitroaniline was dissolved in 50 ml ethanol and the solution was hydrogenated at atm. pressure by using 5% Pd/C (100 mg) as a catalyst. The reaction mixture was filtered and evaporated. 50 ml 4N hydrochloric acid and 1.6 g (13 mmol) oxalic acid dihydrate was added, and the reaction mixture was refluxed for 2 h. After cooling to 25° C. the precipitate was filtered off, washed with water and ethanol to give 0,4 g (24%) 1-carboxyethyl-quinoxaline-2,3(1H,4H)-dione. M.p. >300° C. 1H-NMR (DMSO-d6): 12.0 (1H, broad s), 7.2 (4H, m), 4.3 (2H, t), 2.6 (2H, t).
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