Starfish saponins. Part 5. Structure of sepositoside A, a novel steroidal cyclic glycoside from the starfish Echinaster sepositus

Abstract

The toxic major saponin from the starfish Echinaster sepositus, has been completely characterized. The structure is unique having as it does both a Δ⁷,3β,6β-dioxygenated-23-oxosteroidal moiety and a sugar moiety [β-D-glucopyranosyl-(1→2)-β-D-galactopyranosyl-(1→2)-β-D-glucuronopyranosyl] which bridges the C-3 and C-6 atoms of the steroid. The 3β-hydroxy-group of the steroid forms an O-acetal linkage with the glucuronate unit, while the HO–C(6‴) of the glucopyranosyl unit is attached to C-6 of the aglycone, forming a 6β-O-ethereal linkage.