Steroids from the starfish Euretaster insignis: a novel group of sulphated 3β,21-dihydroxysteroids

Abstract

The aqueous extracts of the starfish Euretaster insignis contain two groups of sterol sulphates. The more polar compounds are sulphated 3β,21-dihydroxysteroids; after solvolysis to remove the sulphate groups they were identified as (20R)-24-methylenecholestane-3β,21-diol (3a)(major), (20R)-24-methylenecholest-5-ene-3β,21-diol (3b)(minor), (20R,22E)-24-methylcholest-22-ene-3β,21-diol (4a)(major), (20R)-cholestane-3β,21-diol (1a)(minor), (20R,22E)-cholest-22-ene-3β,21-diol (2a)(minor), and (20R)-cholest-5-ene-3β,21-diol (1b)(minor). The less polar compounds are sterol sulphates which are ‘normal’ constituents of starfishes. Analysis of the free sterols mixture has revealed that it contains a low level of cholest-7-en-3β-ol (3% of the total sterol mixtures) and C₂₆, C₂₇, C₂₈, and C₂₉ 5α-steroidal alcohols. This finding, in contrast with previous results indicating the preponderance of Δ⁷-sterols in starfishes, could be related to the apparent absence of asterosaponins in this species.