Synthesis, biological evaluation and mechanism studies of C-3 substituted nitrogenous heterocyclic 23-Hydroxybetulinic acid derivatives as anticancer agents

A series of novel nitrogenous heterocycle substituted 23-Hydroxybetulinic acid (23-HBA) derivatives with amide linkages at the C-3 position were designed, synthesized and evaluated for their antitumor activities. The biological screening results showed that most of the derivatives exhibited more potent antiproliferative activities than 23-HBA. In particular compound II-9 exhibited the most potent activities with IC50 values ranging from 1.96 μM to 6.20 μM against five cancer cell lines (B16, HepG2, A2780, MCF-7 and A549). The preliminary mechanism study showed that compound II-9 caused cell cycle arrest at G1 phase, induced cell apoptosis and depolarized mitochondria of B16 cells in a dose dependent manner. Moreover, western blot analysis indicated that compound II-9 down-regulated the expression of anti-apoptotic protein Bcl-2, up-regulated the expression of pro-apoptotic protein Bad, and activated cytochrome C and caspase 3 to cause cell apoptosis. In summary, II-9 may serve as a promising lead for the development of new natural product-based antitumor agents and deserve further investigation.