Sea cucumbers release chemical repellents from their guts when they are in danger from predators or a hostile environment. To investigate the chemical structure of the repellent, we collected and chemically analyzed the viscera of stressed sea cucumbers (Apostichopus japonicus) in the Yellow Sea of China. Two undescribed triterpene glycosides (1 and 2), together with a known cladoloside A (3), were identified and elucidated as 3β-O-{2-O-[β-d-quinovopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (1), 3β-O-{2-O-[β-d-glucopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (2), 3β-O-{2-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (3) by spectroscopic analysis, including HR-ESI-MS and NMR spectra. Compounds 1, 2, and 3 display embryonic toxicity, as indicated by their 96-hour post-fertilization lethal concentration (96 hpf-LC50) values of 0.289, 0.536, and 0.091 μM, respectively. Our study discovered a class of triterpene glycoside compounds consisting of an oligosaccharide with four sugar units and a holostane aglycone. These compounds possess embryotoxicity and may serve as chemical defense molecules in marine benthic ecosystems.
Keywords: Saponin; acute toxicity; chemical defense; holostane; viscera.
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