Synthesis of Novel Heterocyclic Ring-Fused 18β-Glycyrrhetinic Acid Derivatives with Antitumor and Antimetastatic Activity

Glycyrrhetinic acid (GA) is one of the most important triterpenoic acids shows many pharmacological effects, especially antitumor activity. GA triggers apoptosis in various tumor cell lines. However, the antitumor activity of GA is weak, thus the synthesis of new synthetic analogs with enhanced potency is needed. By introducing various five-member fused heterocyclic rings at C-2 and C-3 positions, 18 novel GA derivatives were obtained. These compounds were evaluated for their inhibitory activity against the growth of eight different tumor cell lines using a SRB assay. The most active compound 37 showed IC50 between 5.19 and 11.72 mu M, which was about 11-fold more potent than the lead compound GA. An apoptotic effect of GA and 37 was determined using flow cytometry and trypan blue exclusion assays. We also demonstrated here for the first time that GA and the synthetic derivatives exhibited inhibitory effect on migration of the tested tumor cells, especially 37 which was about 20-fold more potent than GA on antimetastatic activity.