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, β-D-xylopyranosyl-(1→3)-β-D-fucopyranosyl-(1→2)-β-D-quinovopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-xylopyranosyl-(1→3)-β-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.