Concise synthesis of two trisaccharides related to the cytotoxic triterpenoid saponin isolated from Pithecellobium lucidum

Convergent synthesis of two trisaccharides related to the cytotoxic triterpenoid saponin isolated from Pithecellobium lucidum is reported. The trisaccharides are synthesized in the form of their propargyl glycosides to leave the scope for further glycoconjugate formation through various multi-component reactions. A simple protecting group manipulation is followed using commercially available monosaccharides, d-glucose, d-xylose, d-fucose and l-rhamnose. H2SO4 immobilized on silica is used as the Brönsted acid source for the N-iodosuccinimide-mediated thioglycoside activation for stereoselective glycosylations and proved to be a better choice over traditional Lewis acid catalysts such as TMSOTf and TfOH.