[CH3:1][O-:2].[Na+].O.[OH-].[Na+].[Br-].[C:8]([C:11]1[CH:12]=[C:13]([CH2:20][N+](C)(C)C)[CH:14]=[N:15][C:16]=1[C:17]([OH:19])=[O:18])([OH:10])=[O:9]>CO>[CH3:1][O:2][CH2:20][C:13]1[CH:12]=[C:11]([C:8]([OH:10])=[O:9])[C:16]([C:17]([OH:19])=[O:18])=[N:15][CH:14]=1A mixture of 25% sodium methoxide in methanol (270 g, 1.25 mol) and [(5,6-dicarboxy-3-pyridyl)-methyl]trimethylammonium bromide, dimethyl ester (347 g, 1.00 mol) in methanol (650 mL) is heated at reflux for I hour under nitrogen. Water (1 L) and sodium hydroxide (80.0 g, 2.0 mol) are added and the reaction mixture is distilled until the pot is 100°-105° C. The reaction mixture is cooled to room temperature, treated with sulfuric acid to adjust the pH to a value from 1.5 to 2 and filtered to obtain a solid. The solid is washed with water and dried in a vacuum oven to obtain the title product as a white solid (mp 161°-162° C.) which is greater than 99% pure by HPLC analysis.
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