[CH3:1][O:2][CH2:3][C:4]1[CH:5]=[C:6]([C:14]([O:16]C)=[O:15])[C:7]([C:10]([O:12]C)=[O:11])=[N:8][CH:9]=1.[OH-].[Na+]>O>[CH3:1][O:2][CH2:3][C:4]1[CH:5]=[C:6]([C:14]([OH:16])=[O:15])[C:7]([C:10]([OH:12])=[O:11])=[N:8][CH:9]=1A mixture of dimethyl 5-(methoxymethyl)-2,3-pyridinedicarboxylate (60.0 g, 0.25 mol) and 50% sodium hydroxide solution (50.0 g, 0.63 mol) in water is heated at 90-110° C. for 2 hours under nitrogen while distilling off methanol and water. The reaction mixture is cooled to 10° C., treated with sulfuric acid to adjust the pH to 2.0 and filtered to obtain a solid. The solid is washed with water and vacuum dried to give the title product as a white solid (44.3 g, mp 161-162° C.).
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