Glycosides from the sea cucumber Cucumaria frondosa. IV. Structure of frondosides A2-4, A2-7, and A2-8, three new minor monosulfated triterpene glycosides

Frondosides A2-4 (1), A2-7 (2), and A2-8 (3) are new monosulfated triterpene glycosides isolated from the sea cucumber Cucumaria frondosa. Their structures have been elucidated on the basis of spectral data (2D NMR and MS). Frondosides A2-7 (2) and A2-8 (3) are isomers and differ from each other only by the position of a double bond in their non-holostane-type aglycones.