Development of betulinic acid triazole conjugates as potential anti-cancer agents

Betulin and betulinic acid are pentacyclic triterpenoid natural product isolated from the bark of birch trees. While betulin is abundantly available in the bark, betulinic acid is present in scarce quantities in nature. However, betulinic acid can be conveniently synthesized from betulin via simple redox manipulations. Betulinic acid shows selective cytotoxicity profile against cancer cells in vitro while being relatively safe for normal cells. One of the challenges for the clinical development of betulinic acid is its lack of aqueous solubility. The three key structural features of betulin/betulinic acid that have been routinely exploited for structural modifications to enhance their chemical and biological properties include C28 primary alcohol, C3 secondary alcohol, and a C20 alkene moiety. We have been working on the functionalization of betulin for potential development as anti-cancer agents. Previously, we had reported the synthesis of betulin conjugates via reactions such as Passerini, reductive amination, and aldol condensation. Herein, we report the synthesis of betulinic acid triazole conjugates employing Baylis-Hillman and click reaction protocols as the key steps in our synthesis. The cytotoxicity evaluation of these conjugates demonstrated promising anti-cancer activity against two cancer cell lines