Cytotoxic Triterpene Glycosides from Far‐Eastern Sea Cucumbers Belonging to the Genus Cucumaria

New cytotoxic triterpene oligoglycoside disulfates, cucumariosides A3 (1) and A6‐2 (2), have been isolated from the sea cucumber Cucumaria japonica. The trisulfated cucumarioside A7‐3 (4) was found to be the major component in the glycoside fraction of Cucumaria miniata. The structures were assigned on the basis of extensive spectral data (NMR and MS), selective solvolysis of desulfated derivative 3 and other chemical evidence. The presence or absence of a carbonyl group at C‐16 of the aglycone and of sulfate groups at C‐6 of the glucose and 3‐O‐methylglucose units are interpreted in terms of the functional evolution of sea cucumbers in order to improve their defensive system. Both (1) and (2) are cytotoxic in vitro at IC50 = 1 μg/ml against a selection of five human and mice tumoral cell lines.