Major saponins from the starfish Asteriasforbesi. Complete structures by nuclear magnetic resonance methods

Abstract

The structures of the two major saponins isolated from the starfish Asteriasforbesi have been deduced totally by nuclear magnetic resonance methods applied to the undegraded molecules. The structure of forbeside A, 6α-O-{β-D-galactopyranosyl-(1 → 3)-β-D-fucopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 4)-[β-D-quinovopyranosyl-(1 → 2)]-β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl}-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl sodium sulfate, was deduced principally from 1H 2D-COSY, J-resolved, nuclear Overhauser enhancement and selected decoupling experiments. The structure of forbeside B, 6α-O-{β-D-quinovopyranosyl-(1 → 2)-β-D-galactopyranosyl-(1 → 4)-[β-D-quinovopyranosyl-(1 → 2)]-β-D-xylopyranosyl-(1 → 3)-β-D-quinovopyranosyl}-20-hydroxy-23-oxo-5α-cholest-9(11)-en-3β-yl sodium sulfate, was deduced principally from 2D-COSY, HCORR, RECSY, and NOESY experiments.