4-Oxo-1,4-dihydro-2,6-pyridinedicarboxylic acid was synthesized from betulinic acid using a modified literature method. The specific operation was as follows: 425 mL of 30% ammonia solution (containing NH3 41.8 g, 0.21 mol) was slowly added dropwise to the reaction system at 0 °C, and the dropwise addition process was controlled to be completed within 1 hour. After the dropwise addition, the reaction mixture was stirred continuously at room temperature for 48 hours. Upon completion of the reaction, the excess ammonia solution was removed by distillation under reduced pressure. Subsequently, the residue was mixed with 50 mL of water, activated carbon was added and decolorized by refluxing for 15 minutes. After hot filtration, the filtrate was collected and, after being cooled to room temperature, the pH was adjusted with a 37% aqueous hydrochloric acid solution to 1. At this point, a white solid precipitated from the solution, which was collected by filtration, washed several times with cold water, and finally dried under vacuum for 16 h. The target compound, 4-oxo-1,4-dihydro-2,6-pyridinedicarboxylic acid (13), was obtained as a white solid in a yield of 42 g with 98% yield.
