Unusual Sterols

A further structural variant is now represented by aplysterol (179) and 24,28-didehydroaplysterol (180), the principal sterol components of the sponges of the family Verongidae (Table 2), in which an extra carbon atom is attached at C-26 70). 

Order Dictioceratida Family Verongidae V. aerophoba V. archeri (hard) V. archeri (soft) V.fistularis V. thiona 

A new remarkable side chain alkylation pattern has been found in calysterol, the principal sterol component of the sponge Calyx nicaensis 75a). Structure (181), reminiscent of those of gorgosterol (175) and its relatives (176) and (177), has been proposed for this unique sterol on the basis of spectral data (m.s. and n.m.r.) of the acetate, m.p. 105—106°, [a]o-34.3°, and Lemieux oxidation of the corresponding stanol to a p-diketone (182). Interestingly, calysterol (181) completely decomposes on an alumina-silver nitrate column to give four compounds the major one has been characterized as (182 a). 

Modifications of the sterol nucleus have also been found in sponges. 

The total sterol content of Axinella polypoides is a mixture of stanols having a 19-norcholestanol nucleus carrying conventional saturated and mono-unsaturated C7 (24-nor), Cs, C9 and Cio side-chains 140). The 

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It has been suggested [6] that these unusual sterols, especially in those cases where these unusual sterols comprise the entire sterol content of the organisms, likely replace conventional sterols as cell-membrane components. Evidence for this comes from subcellular fractionation and subsequent analysis of two marine sponges [10]. The sterol composition of the membrane isolates was found to be identical to that of the intact sponge. Most common variation of the marine sterol is in the side-chain, situated deep in the lipophylic environment of the phospholipid bilayer. This suggests that unusual fatty acids might accompany the sterols, and indeed this is often the case [8]. 

Sitosterol Campesterol Stigmasterol Unusual sterols Cycloartenol Cholesterol, minute quantities... 

Extract from Bahamas inhibits the sea urchin A punctulata (Bolser and Hay 1996). An unusual sterol from Brazilian specimens inhibits feeding by P. transversus (Teixeira et al. 2006)... 

Chlorophylls are produced by all photosynthetic organisms — and even by some nonphotosynthetic bacteria — and details of their structures depend on their source. Collectively they represent a considerable reserve of organic carbon and nitrogen, although little seems to have been established on their persistence. A wide range of transformation products of chlorophylls has been recovered from the sediments of a freshwater eutrophic lake, and these included the unusual sterol esters of pyrophaeophorbides (Eckardt et al. 1995). It is also presumable that such chlorophyll transformation products produce the pyrroles and indoles that have been described in sediment pyrolysates noted above. 

The pioneering paper on metabolites from sponges of Theonella genus appeared in literature in 1981 dealing with the isolation of two new and unusual sterols with the unprecedented 4-methylene nucleus, conicasterol (2) and theonellasterol (3) [3]. Subsequently, the 3-keto derivatives, conicasterone (4) and theonellasterone (5), together with a Diels Alder type dimeric steroid, named bistheonellasterone (6), were reported from the Okinawan marine sponge Theonella swinhoei [4], It is noteworthy that... 

Lastly, it is worth mentioning several Halichondrid sponges for which one unusual sterol occurs at very high percentage, suggesting an important function in the cell membrane (Castellanos et al, 2003). 

Barnathan, G., Miralles, J., Kornprobst, J.M., Mangoni, A., Fattorusso, E., and Boury-Esnault, N. (2000) Unusual sterol composition and classification of two marine sponge families, in Marine Lipids (eds G. Baudimant, J. Guezennec, P. Roy, and J.-F. Samain), Editions de ITfremer, Plouzan, actes de colloques 17, pp. 87-94. 

Do, H.Q., Van Landeghem, L., Wielgosz-Collin, G Takoudju, M Huvelin, J.-M., Kornprobst, J.-M., Bard, J.-M., Bamathan, G and Nazih, H. (2009) Unusual sterolic mixture, and 24-isopropylcholesterol from the sponge Ciocalypta sp., reduce cholesterol uptake and basolateral secretion in Caco-2 cells. J. Cell Biochem., 106, 659-665,... 

Mandeau, A., Masson, V., Menou, J.-L., and Debitus, C. (2006) 24-methylstigmasterol, an unusual sterol from the marine sponge Psammocinia bulbosa BergquisL 1995. Biochem. Syst. Ecol., 34, 92-95. 

Fattorusso and co-workers (79 ) have discovered two further unusual sterols (245) and (246) in Calyx nicaensis. This sponge also... 

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