Facile Synthesis of Saponins Containing 2,3-Branched Oligosaccharides by Using Partially Protected Glycosyl Donors

Two natural saponins 1 and 2, isolated from Solanum indicum L., and containing 2,3-branched sugar moieties, have been efficiently synthesized. Partially protected monosaccharide and disaccharide donors were used to facilitate target synthesis. Stereo factors were critical in incorporating 2,3-branched sugars on steroid aglycones. Saponin 1 was synthesized in five steps and 30% overall yield, while saponin 2 was obtained using six straightforward sequential reactions in 31% overall yield. Saponin 2 shows promising cytotoxic activity toward human hepatocellular carcinoma BEL-7402 with an IC50 of <6 microg/mL.