Four New Asterosaponins, Hippasteriosides A-D, from the Far Eastern Starfish Hippasteria kurilensis

Four new sulfated steroidal glycosides (asterosaponins), hippasteriosides A-D (1-4, resp.), were isolated from the alcoholic extract of the Far Eastern starfish Hippasteria kurilensis, collected in the Sea of Okhotsk near Kuril Islands. Compounds 1-4 were determined to contain the same unprecedented hexasaccharide moiety, beta-D-xylopyranosyl-(1 -> 3)-beta-D-fucopyranosyl-(1 -> 2)-beta-D-quinovopyranosyl-(1 -> 4)-[beta-D-quinovopyranosyl-(1 -> 2)]-beta-D-xylopyranosyl-(1 -> 3)-beta-D-quinovopyranosyl, linked to C(6) of 3-O-sulfonylated steroidal aglycons, which differ from each other in their side-chain structures. Structures 1-4 were elucidated by extensive NMR and MS techniques, and chemical transformations. Not all the asterosaponins show a prominent cytotoxic activity against human colon tumor HT-29 cells, but some of them, especially compound 4 demonstrate a remarkable inhibition of the HT-29 colony formation in soft-agar clonogenic assay, suggesting its anticancerogenic properties.