Structure of cucumariosides H5, H6, H7 and H8, triterpene glycosides from the sea cucumber Eupentacta fraudatrix and unprecedented aglycone with 16,22-epoxy-group.

Four new triterpene glycosides cucumariosides H5 (1), H6 (2), H7 (3) and H8 (4) along with the known cucumarioside H (5) have been isolated from the Far Eastern sea cucumber Eupentacta fraudatrix. The structures of glycosides 1-4 were elucidated on the basis of spectral data (2D NMR and MS). Glycosides 1-4 belong to the group o f cucumariosides H having branched rare pentasaccharidecarbohydrate moieties with one sulfate group and 3-O-methyl-D-xylose as a terminal monosaccharide unit. Glycosides 1-3 and 5 differ from each other in structures of side chains of the aglycones, while cucumarioside H8 (4) has a novel aglycone with unprecedented 16(22)-epoxy-group, never found in the sea cucumbers glycosides. Glycosides 1-3, and 5 were cytotoxic against mouse lymphocytes and hemolytic against mouse erythrocytes. Glycoside 2 was less active in comparison with others.