Synthesis and Cytotoxicity of Monomethylated Betulinic Acid 3--α-l-Rhamnopyranosides.

Three original derivatives of the cytotoxic betulinic acid 3--α-l-rhamnopyranoside featuring a monomethylated rhamnoside residue were synthesized. An improved catalytic procedure was involved to functionalize the -3 position of the monosaccharide in a site-selective fashion. The cytotoxicity of the novel compounds was evaluated in vitro to highlight the moderate impact of carbohydrate monomethylation on the biological activity of betulinic acid 3--α-l-rhamnopyranoside.