Glycosidation of lupane-type triterpenoids as potent in vitro cytotoxic agents

The weak hydrosolubility of betulinic acid (3) hampers the clinical development of this natural anticancer agent. In order to circumvent this problem and to enhance the pharmacological properties of betulinic acid (3) and the lupane-type triterpenes lupeol (1), betulin (2), and methyl betulinate (7), glycosides (β-d-glucosides, α-l-rhamnosides, and α-d-arabinosides) were synthesized and in vitro tested for cytotoxicity against three cancerous (A-549, DLD-1, and B16-F1) and one healthy (WS1) cell lines. The addition of a sugar moiety at the C-3 or C-28 position of betulin (2) resulted in a loss of cytotoxicity. In contrast, the 3-O-β-d-glucosidation of lupeol (1) improved the activity by 7- to 12-fold (IC50 14–15.0 μM). Moreover, the results showed that cancer cell lines are 8- to 12-fold more sensitive to the 3-O-α-l-rhamnopyranoside derivative of betulinic acid (IC50 2.6–3.9 μM, 22) than the healthy cells (IC50 31 μM). Thus, this study indicates that 3-O-glycosides of lupane-type triterpenoids represent an interesting class of potent in vitro cytotoxic agents.

α-l-Rhamnopyranoside of betulinic acid (22) exerted the strongest in vitro cytotoxicity of tested glycosides with an activity of 8- to 12-fold more potent toward cancerous cells than on healthy cells.Figure optionsDownload as PowerPoint slide