First total synthesis of capsicoside C2 through regio - and stereoselective linear glycan assembly.

The first total synthesis of capsicoside C2, a tigogenin-based spirostanol saponin bearing a β-d-xylopyranosyl-(1 → 3)-β-d-glucopyranosyl-(1 → 4)-β-d-galactopyranosyl trisaccharide, has been achieved through a linear glycosylation strategy. A selectively protected tigogenin galactoside served as the key acceptor for sequential installation of the glucosyl and xylosyl residues using trichloroacetimidate donors. C2-ester protecting groups in donors ensured β-selective glycosylation, while regioselective xylosylation occurred at C3 of the glucosyl unit. The structure and stereochemistry of capsicoside C2 were confirmed by detailed 1D and 2D NMR analyses, including comprehensive characterization of its peracetylated derivative. To the best of our knowledge, this work represents the first chemical synthesis of capsicoside C2.