Abstract
Six new triterpene tetra-, penta- and hexaosides, chitonoidosides A (1), A1 (2), B (3), C (4), D (5), and E (6), containing one or two sulfate groups, have been isolated from the Far-Eastern sea cucumber Psolus chitonoides, collected near Bering Island (Commander Islands) from the depth of 100–150 m. Three of the isolated compounds (1, 3 and 6) are characterized by the unusual aglycone of new type having 18(20)-ether bond and lacking a lactone in contrast with wide spread holostane derivatives. Another unexpected finding is 3-O-methylxylose residue as a terminal unit in the carbohydrate chains of chitonoidosides B (3), C (4), and E (6), which has never been found before in the glycosides from holothurians belonging to the Psolidae family. Moreover, this monosaccharide is sulfated in the compound 4 into unprecedented 3-O-methylxylose 4-O-sulfate residue. Chitonoidoside C (4) is characterized by tetrasaccharide moiety lacking a part of the bottom semi-chain, but having disaccharide fragment attached to C-4 of Xyl1. Such architecture is not common in sea cucumber glycosides. Cytotoxic activities of the compounds 1–5 against mouse and human erythrocytes and human cancer cell lines: adenocarcinoma HeLa, colorectal adenocarcinoma DLD-1, and leukemia promyeloblast HL-60 cells were studied. The cytotoxic effect of chitonoidoside d (5) was the most significant in this series due to the presence of pentasaccharide disulfated sugar chain in combination with holostane aglycone. Surprisingly, the glycosides 1 and 3, comprising the new aglycone without γ-lactone, demonstrated similar activity to the known compounds with holostane aglycones. Chitonoidoside C (4) was less cytotoxic due to the different architecture of the carbohydrate chain compared to the other glycosides and probably due to the presence of a sulfate group at C-4 in 3-O-MeXyl4.
Highlights
Triterpene glycosides, biosynthesized by the sea cucumbers, are natural compounds characterized by the diverse bioactivity [1,2,3,4,5]
The comparative structural analysis of a significant number of the isolated glycosides leads to the reconstruction of the sequences of biosynthetic transformations of their aglycones and carbohydrate chains during biosynthesis that can be reflected in the metabolic networks constructed for different species of the sea cucumbers [9,10]
Six unknown earlier triterpene glycosides were isolated from the sea cucumber Psolus chitonoides
Summary
Triterpene glycosides, biosynthesized by the sea cucumbers, are natural compounds characterized by the diverse bioactivity [1,2,3,4,5]. The isolation of glycosides from different sea cucumber species provides a unique opportunity to expand knowledge on their structural diversity and discover new unusual substances. The studies on biological activity of the glycosides reveal the peculiarities of «structure–activity relationships» demonstrating the significance. These data indicate the relevance of searching for new glycosides and studying their The genus Psolus comprises 58 species, and only three of them were chemically biological activities. As result of the studies on the fourth representative of the genus, P. chitonoides, six tigated up to the present time: P. fabricii [10,11,12,13,14], P. eximius [15], and P. patagonicus [16,17]. 13 Cas isolated and their chemical structuresHMBC, elucidated by the analyses of theas H, NMR, 1D mass spectra
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