Esterification of Betulin 3-Acetate in Melts of the Maleic and Levulinic Acids

Objective: Esters of betulin containing residues of bioactive aromatic and aliphatic acids are of interest to the chemical and pharmaceutical industry as hepatoprotectors, anti-inflammatory, antiulcer and immunomodulatory substances. The development of new efficient, ecological and economical methods for the synthesis of betulin esters is an urgent task. Methods: The structure of the resulting betulin esters was determined using IR and NMR spectroscopy, and the composition was determined by elemental analysis. Results and Discussion: A new “green” method for the production of betulin 3-acetate-28-maleate and betulin 3-acetate-28-levulinate has been developed. For the first time, esterification of betulin 3-acetate with melts of maleic acid and levulinic acids was carried out at a temperature of 185–200°C for 5–7 min to obtain betulin 3-acetate-28-maleate and betulin 3-acetate-28-levulinate, respectively. Conclusions: The advantages of the developed method for the synthesis of 3-acetate-28-maleate and 3-acetate-28-levulinate of betulin in comparison with the known ones are: the synthesis is carried out in the absence of harmful and hazardous solvents (pyridine, methylene chloride, chloroform); the duration of synthesis is reduced from 15–40 h to 5–7 min. Maleic acid is used instead of maleic anhydride on the preparation of betulin 3-acetate-28-maleate.