Antifungal nortriterpene and triterpene glycosides from the sea cucumber Apostichopus japonicus Selenka

A nortriterpene glycoside, 26-nor-25-oxo-holotoxin A1 (1), four triterpene glycosides, including both holostane and non-holostane types analogues, holotoxins D–G (2–5), together with three known triterpene glycosides, holotoxins A1 and B (6, 7), and cladoloside B (8), were isolated from the warty sea cucumber Apostichopus japonicus Selenka, a traditional tonic with high economic value in China. The structures of the new compounds were elucidated by a combination of detailed spectroscopic analysis and chemical methods. This is the first report of a nortriterpene glycoside isolated from sea cucumbers. These compounds showed potent antifungal activities in the in vitro biotest. A preliminary structure–activity analysis suggests that the 18(20) lactone group and the Δ25 terminal double bond may increase the activity. The component of the carbohydrate chain seems play an important role whereas the double bond transformation from Δ9(11) to Δ7 in the aglycone moiety contributes little to the bioactivity.