[O:1]=[C:2]1[NH:11][C:10]2[C:5](=[CH:6][CH:7]=[CH:8][CH:9]=2)[N:4]([CH2:12][C:13]([OH:15])=[O:14])[CH2:3]1.[Mn]([O-])(=O)(=O)=[O:17].[K+]>O.[OH-].[Na+]>[C:13]([CH2:12][N:4]1[C:5]2[C:10](=[CH:9][CH:8]=[CH:7][CH:6]=2)[NH:11][C:2](=[O:1])[C:3]1=[O:17])([OH:15])=[O:14]To a solution of 3.0 g (15 mmol) 1,2,3,4-tetrahydro-3-oxoquinoxaline-1-acetic acid in 50 ml water was added gradually a solution of 4. 0 g (25 mmol) potassium permanganate in aqueous sodium hydroxide (4%, w/v) and the mixture was refluxed for 4 h. The reaction mixture was cooled, filtered and the filtrate acidified with concentrated hydrochloric acid to pH 2.5. The precipitate was filtered off and washed with water to give 2.2 g (69%) 1-carboxymethylquinoxaline-2,3(1H,4H)- dione. M.p. >300° C. 1H-NMR (DMSO-d6): 12.0 (1H, broad s), 7.2 (4H, s), 7.0-5.0 (1H, broad s), 4.9 (2H, s).
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