[C:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:22][C:11]3=[N:12][C:13]([NH2:21])=[C:14]([C:16]([O:18]CC)=[O:17])[CH:15]=[C:10]3[C:9](=[O:23])[C:8]=2[CH:24]=1)(=[O:3])[CH3:2].[OH-].[Na+].Cl>C(O)C.O>[C:1]([C:4]1[CH:5]=[CH:6][C:7]2[O:22][C:11]3=[N:12][C:13]([NH2:21])=[C:14]([C:16]([OH:18])=[O:17])[CH:15]=[C:10]3[C:9](=[O:23])[C:8]=2[CH:24]=1)(=[O:3])[CH3:2]In ethanol (3 l) was suspended ethyl 7-acetyl-2-amino-5-oxo-5H-[1]benzopyrano[2,3-b]pyridine-3-carboxylate (46 g). To the suspension were added water (460 ml) and 1N sodium hydroxide (462 ml). The mixture was stirred at room temperature for 1.5 hour, then at 50°-55° C. for 2 hours. The precipitating crystals were collected by filtration, and washed with ethanol. The crystals thus obtained were suspended in warm water (about 2 l). To the suspension was added concentrated hydrochloric acid (20 ml), and the mixture was stirred for 20 minutes. Insoluble matter was collected by filtration, washed with water, followed by recrystallization from dimethylformamide-water to give 7-acetyl-2-amino-5-oxo-5H-[1]benzopyrano[2,3-b]pyridine-3-carboxylic acid as colorless crystals (39.3 g). Melting point: >300° C.
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