Three new asterosaponins from the starfish Culcita novaeguineae and their bioactivity

Bioassay-guided fractionation of the active n-BuOH extract of the starfish Culcita novaeguineae resulted in the isolation of three new sulfated steroidal glycosides (asterosaponins) 1, 2 and 3, as active compounds causing morphological abnormality of Pyricularia oryzae mycelia. Compounds 1-3 possess the same pentasaccharide moiety, beta-D-fucopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1-->4)-[beta-D-quinovopyranosyl-(1-->2)]-beta-D-xylopyranosyl-(1-->3)-beta-D-quinovopyranosyl, linked to C-6 of 3beta-sulfated steroidal aglycones and differ from each other in the side chains. Their structures were elucidated by extensive spectral studies and chemical evidences. Saponins 1 and 3 showed significant cytotoxicity against two cancer cell lines (IC50 values for 1:3.57 microg/mL [K-562], 2.55 microg/mL [BEL-7402]; for 3:3.75 microg/mL [K-562], 1.89 microg/mL [BEL-7402]), as well as hemolytic activity to rabbit erythrocytes (ED50 values: 16 and 31 microg/mL, respectively), while 2 was inactive in these bioassays.