[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[CH:16]=[CH:15][C:11]([C:12]([OH:14])=[O:13])=[CH:10][CH:9]=2)=[CH:4][N:3]=1.S(=O)(=O)(O)O.[C:22](=O)(O)[O-].[Na+].O>CO.C(OCC)(=O)C>[NH2:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[CH:16]=[CH:15][C:11]([C:12]([O:14][CH3:22])=[O:13])=[CH:10][CH:9]=2)=[CH:4][N:3]=1The resulting 4-(2-aminopyridin-5-yl)benzoic acid (684 mg) was dissolved in methanol (50 ml) at room temperature, followed by the addition of concentrated sulfuric acid (1 ml). After heating under reflux for 2 hours, the reaction mixture was made weakly alkaline with an aqueous solution of sodium bicarbonate. Water and ethyl acetate were added to the resulting mixture to separate the organic layer. The organic layer was then dried over anhydrous magnesium sulfate. The solvent was distilled off. Hexane was added to the residue for crystallization, whereby the title compound (243 mg, 23%) was obtained.
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