Structure of Acrosome Reaction-Inducing Steroidal Saponins from the Egg Jelly of the Starfish, Asterias amurensis

Three steroidal saponins (designated as Co-ARIS I, II, III) which are essential for inducing the acrosome reaction, were isolated from the egg jelly of the starfish, Asterias amurensis, and their structures were elucidated by chemical and spectral means. The structure of Co-ARIS II was determined to be 6α-O-{O-β-D-fucopyranosyl-(1→2)-O-β-D-fucopyranosyl-(l→ 4)-[O-β-d-quinovopyranosyl-(1→ 2)]-O-β-D-quinovopyranosyl-(l→3)-6-deoxy-β-D-xylo-hexos-4-ulopyranos-l-yl}-3β-hydroxysulfonyloxy-5α-cholesta-9(l 1), 17(20),24-trien-23-one (2), whereas Co-ARIS I (1) and Co-ARIS III (3) were identical with ovarian asterosaponin-1 (OA-1) and OA-4 previously isolated from the same species of starfish.