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A total of 19 steroids, of which 13 steroidal oligoglycosides (nine new and four known) and six polyhydroxylated steroids (four new and two known), has been isolated from the Antarctic starfish Acodontaster conspicuus. The mixture is dominated by glycosides composed of steroidal aglycons having the hydroxyl groups typically disposed on one side of the tetracyclic nucleus, i.e., 3 beta,4 beta,6 alpha,8,15 beta-, with some having a sulfate at C-6, and differing in the side chains and/or in the disaccharide moieties that are usually attached at C-26, with some at C-28 and C-29. Those compounds are accompanied by minute amounts of glycosides with a delta 8(14)-double bond in the steroid, which is a structural feature not previously found among polyhydroxysteroids derived from starfish. Small amounts of six related unglycosidated polyhydroxysteroids and three higher-molecular-weight asterosaponins complete the composition of the mixture. The structures of the new compounds were determined by interpretation of their spectral data and by comparison with spectral data of known compounds. Eighteen of these compounds were evaluated for their ability to inhibit growth in Antarctic marine bacteria isolated from either the water column or the surfaces of benthic marine invertebrates. Of these compounds, 50% were active against at least one Antarctic marine bacterium. This suggests that these compounds may play an important role in deterring microbial fouling.

Nine polyhydroxy steroids and two steroid glycosides have been isolated from the starfish M. platyacanthum. The novel compds. possess the same 3β,5α,6β,15α-tetrol nucleus but differ in the side chains. Two levels of oxidn. (CH2OH and CO2H) at the side chain methyls were encountered in this class of steroids. The novel compd. I is an asterosaponin assigned as myxodermoside A, consisting of a Δ9(11)-3β,6α-dihydroxysteroidal moiety, a tetrasaccharide portion attached at C-6, and a sulfate group at C-3. The general structure of the novel compds. was detd. from spectral data (1H and 13C NMR and FAB MS), and the stereochem. of the side chains was detd. by correlating the resp. spectral data with those of synthetic models of known configuration. The stereoselective synthesis of the side chain of II is also described