The general procedure for the synthesis of trimethyl pyridine-2,4,6-tricarboxylate from methanol and pyridine-2,4,6-tricarboxylic acid was as follows: the target compound pyridine-2,4,6-tricarboxylic acid trimethyl ester 2 was prepared according to the literature methodology [44].This was carried out as follows: pyridine-2,4,6-tricarboxylic acid 1 (10 g, 47 mmol) was dissolved in methanol (70 mL), added concentrated sulfuric acid ( 98%, 5 mL) and heated under reflux conditions for 6 h until the complete disappearance of raw material 1 was shown by thin layer chromatography (TLC) monitoring. Upon completion of the reaction, the reaction solution was neutralized with calcium carbonate (CaCO3), the insoluble material was removed by filtration and the filtrate was concentrated under reduced pressure to remove the solvent. The crude product was purified by recrystallization from toluene to give the white crystalline target product 2. Yield: 95%; melting point: 161 °C. Infrared spectrum (IR, KBr, cm?1): 3462, 3304 (NH stretching vibration), 2976, 1737 (C=O stretching vibration), 1644 (C=N stretching vibration), 1488 (C-N stretching vibration). Nuclear magnetic resonance hydrogen spectrum (1H NMR, DMSO-d6) δH: 8.54 (2H, apparent single peak), 3.95 (9H, apparent single peak).
