Triterpene glycosides from the sea cucumber Eupentacta fraudatrix. Structure and biological action of cucumariosides A1, A3, A4, A5, A6, A12 and A15, seven new minor non-sulfated tetraosides and unprecedented 25-keto, 27-norholostane aglycone

Abstract

Seven new minor triterpene glycosides, cucumariosides A1 (1), A3 (2), A4 (3), A5 (4), A6 (5), A12 (6) and A15 (7) have been isolated from the Far Eastern sea cucumber Eupentacta fraudatrix. Structures of the glycosides were elucidated by 2D NMR spectroscopy and MS. Glycosides 1-7 belong to the group of cucumariosides A, having linear tetrasaccharide carbohydrate moieties without any sulfate group and possessing 3-O-methyl-D-xylose as a terminal monosaccharide unit. The latter peculiarity is rare in sea cucumber glycosides, but typical for the glycosides from E. fraudatrix. Glycosides 1-7 differ from each other by side chain structures in the aglycone moieties; three of them have unique structural features. The first is the presence of a 25-butoxy-group in the side chain of cucumarioside A3 (2), the second is a 23E,25-diene system in cucumarioside A6 (5) and the third is a 25-keto-27-nor-holostane aglycone in cucumarioside A12 (6); these were never previously found in sea cucumber glycosides. Cytotoxic activity of glycosides 1-7 against mouse spleen lymphocytes and the cells of the ascite form of mouse Ehrlich carcinoma, along with hemolytic activity against mouse erythrocytes and antifungal activity were studied. Glycosides 1 and 5 were the most active in all the tests.