Sterols in Porifera sponges

Porifera (sponges) were the first invertebrates found to contain sterols other than cholesterol. Clionasterol (12B), poriferasterol (14B), chondrillasterol (14C), and chalinasterol (lOB) were isolated by Bergmann. Minale et al. isolated sterols having an additional methyl group at C-26, aplysterol (18) and 24,28-dehydroaplysterol (19) as the principal sterols of Aplysia aerophoba [12]. They also found that the sterols of Axinella polypoides were a mixture of 19-nor-stanols (21) which have conventional side chains [13]. 

After the discovery of the C26-sterols in marine planktons, all the marine Cje-sterols were suggested to have originated from a phytoplankton. The occurrence of 19-nor-C26-sterol in A. polypoides, probably originating from C26-sterol in the diet, suggests that one of the processes involved in the biosynthesis of these 19-nor-sterols could be the removal of the Cjo-methyl group from the substrates [13]. The sterols in Axinella verrucosa were found to consist of a mixture of unique stanols containing a 3)8-hydroxymethyl-A-nor-5a-cholestane (22) nucleus with conventional side chains [14]. Cholest-4-en-3-one was found to be an intermediate in the bioconversion of cholesterol into 3)8-hydroxymethyl-A-nor-5a-cholestane [15]. 

Recently, 24- and 25-methylated sterols were isolated from sponges by Djerassi s group. GC/MS analysis of X. muta from Barbados showed that at least 18 sterols were present, the main sterol being 24(28)-dehydroaplysterol (19). In addition, 24-isopropenylcholesterol (29), verongulasterol (26), and a new sterol named mutasterol (30) were identified [21] (Fig. 3). 

Capillary GC analysis of the sterols of the Caribbean Xestospongia species, containing predominantly xestosterol (27), indicated a new sterol, xestospongesterol (31) which was separated by reversed-phase HPLC [22]. The structure was determined by mass spectrometry and NMR as a hitherto unprecedented quadruply biomethylated sterol. From the Indopacific sponge Strongylophora durissima, which has been reported to contain over 90% of strongylosterol, a new sterol named 

Another cyclopropane sterol, petrosterol (42) was isolated as the major sterol from Petrosia ficiformis and Halichondria sp. The structure was determined as 

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