Sterols marine invertebrates

Steroid chemistry, the glamor area of natural product research in the years following World War II, was replaced by macrolides, alkaloids, and prostanoids. Sterol chemistry again became exciting when an unanticipated rich diversity of marine invertebrate sterols were isolated, notably from sponges. After pioneering research in Italy, the field was reborn in Carl Djerassi s laboratory at Stanford. As a result, we now have a better and more detailed knowledge of sterol biosynthesis than of any other class of marine natural products. The authors of Chapter 1 are Stanford alumni. 

Since then, progress on sponge sterol research has been reported by Bergmann who reviewed the subject up to about 1960 (77). An earlier review on marine invertebrate sterols was written by the same author in 1949 16). 

The surge of interest in marine sterols, stimulated by some several hundred new and unique sterol structures found in marine invertebrates over the last two... 

Marine organisms frequently contain a complex mixture of sterols. The biosynthetic origin of these compounds is complicated by the fact that there are four possible sources. The sources by which marine invertebrates may obtain sterols, first described by Goad [3], are (1) de novo biosynthesis, (2) assimilation from diet, (3) modification of dietary sterols and (4) assimilation of symbiont-produced sterols or sterol precursors. In any examination of the biosynthetic origin(s) of sterols one must consider all of these factors needless to say, a complex picture is emerging. 

Goad LJ (1978) The sterols of marine invertebrates. In Scheuer PJ (ed) Marine natural products, vol II. Academic, New York, p 76... 

Marine Sterols. Several hundred unique sterol structures have been elucidated from a variety of marine invertebrates. A single nucleus can be used to describe most terrestrial sterols, but no single template suffices for marine sterols, Similar to cholesterol, marine sterols play a critical role in both the physiology and biochemistry of biological systems. 

Bergmann, W. (1949) Comparative biochemical studies on the lipids of marine invertebrates with special reference to the sterols. J. Mar. Res. 8, 137-176. 

Recent studies in marine sterols were reviewed144 and related to this is a review of sterol biosynthesis and metabolism in marine invertebrates.148 Mutasterol (171), a... 

Sterols of marine invertebrates have been found to comprise most complex mixtures more than 120 sterols have been isolated and their structures determined [1]. Analysis of these sterols has been performed largely by GC, GC/MS and HPLC. Stereochemical details were determined by NMR or by synthetic work. Fig. 1 demonstrates the effectivity of a capillary colunrn a and b showing the GC analysis of a sterol fraction obtained from the sponge, Hymeniacidon perleve using a packed and a capillary column, respectively [2]. 

Sterol patterns in marine invertebrates reflect the complexity of mixtures of sterols arising through food chains. Even in the same species, the sterol fractions show different patterns depending upon the location where the organisms have been collected. The capability of further biochemical modification of the dietary sterols makes the sterol mixtures even more complex. The symbiotic relationship between organisms also complicates the sterol compositions. These conditions are quite different from those affecting sterols of terrestrial organisms. Many sterols of unprecedented structures have now been isolated from marine sources. 

Several excellent comprehensive reviews [1-11] on the structures and biosynthesis of marine sterols are available. This chapter focuses mainly on recent advances. Sterols widely distributed in marine invertebrates are shown in Fig. 2, which shows... 

Djerassi et al. have found a group of characteristic sterols in marine organisms which have side chains ranging from 0 to 6 carbon atoms. They occur as minor components in various species of Porifera and Coelenterata [78] and may be formed by in vivo auto-oxidation, or be of dietary origin. Accumulation of auto-oxidation products may be more prevalent in marine invertebrates than in mammals, since many marine organisms are known to store excretion products. The side chains are apparently too short for the sterols to be functional membrane constituents, but if these sterols are shown to arise by in vivo or environmental auto-oxidation in the oceans, it will have important imphcations in marine biochemistry and ecology. 

Side chain modification of sterols in marine invertebrates... 

Biosynthesis of branched and highly alkylated sterols in marine invertebrates has been the subject of speculation. Tris- or quadruple-methylation would produce branched sterols in Porifera. Epi-codisterol (C-24-Epi-9B) can be assumed to be a precursor of 25(26)-dehydroaplysterol (20) which is biomethylated again to give... 

The evidence that the Cjv-nor-sterol, occelasterol (85), has the same 24a-config-uration as 24a-methylcholesta-5,22-dien-3i8-ol (7B) which was identified in a scallop, indicates the demethylation pathway from Cjv-sterol to 27-nor-sterol. The C26-sterol (83) may be formed from C27-nor-sterol (85) (Fig. 14). Since C26-sterol is widely distributed in marine invertebrates, it seems likely that this sterol may be produced in a rather early stage of the marine food chain. 

Another metabolite extracted and isolated from extracts of Pseudopterogorgia acerosa is acerosterol, 90. This tetrahydroxy sterol was first isolated by John et al. [57] (see also references within). It should be noted that dinosterol 55, and other similar derivatives having a-methyl substituents have been isolated from marine invertebrates containing a symbiotic zooxanthellae. Thus, it is speculated that acerosterol, 90, may... 

Walters JM, Cain RB, Higgins IJ, Corner EDS (1979b) Cell-free benzo[a]pyrene hydroxylase activity in marine zooplankton. J Mar Biol Assoc UK 59 553-563 Walton MJ, Pennock JF (1972) Some studies on the biosynthesis of ubiquinone, isoprenoid alcohols, squalene and sterols by marine invertebrates. Biochem J 127 471-479... 

Lipids are involved in a number of essential processes in the growth and reproduction of marine invertebrates. Membrane lipids, primarily phospholipids and sterols, combine with membrane proteins to form insoluble complexes that are important in membrane structure. Many marine invertebrates have oil droplets within cells of hepatic-type tissues. These droplets are primarily triacylglycerols or wax esters and serve as energy stores. Finally, lipids occur in water-soluble lipoproteins where phospholipids, triacylglycerols, and sterols are combined with various apoproteins. Lipids are transported between various tissues via hemolymph lipoproteins. Female-specific lipoproteins occur in the hemolymph and eggs of adult females of many marine invertebrates. These egg lipoproteins provide protein and lipid for the development of larvae after they hatch from the... 

High density lipoproteins (HDL) are the predominant class of hemolymph lipoproteins in marine invertebrates. Very low density and low density lipoproteins are absent. These HDL are characterized by high molecular peptide(s) and phosphatidyl choline as the predominant lipid. Sterol esters are absent or in trace amounts. 

Isolation, biosynthesis, and metabolism of sterols in marine invertebrates constitutes an active field of reseach (21-26) the discovery of... 

Goad, L.J. Sterol Biosynthesis and Metabolism in Marine Invertebrates. Pure and Appl. Chem. 51, 837 (1981). 

Withers, N.W., W.C.M.C. Kokke, W. Fenical, and C. Djerassi Sterol Patterns of Cultured Zooxanthellae Isolated from Marine Invertebrates Synthesis of Gorgo-sterol and 23-Desmethylgorgosterol by Aposx mbiotic Algae. Proc. Natl. Acad. Sci. U.S.A. 79, 3764(1982). 

Bohlin, L., H.P. Gehrken, P.J. Scheuer, and C. Djerassi Minor and Trace Sterols in Marine Invertebrates XVI. 3 -Hydroxymethyl-A- or-5a-gorgostane, a Novel Sponge Sterol. Steroids 35, 295 (1980). 

Li, L.N., U. Sjostrand, and C. Djerassi Minor and Trace Sterols in Marine Invertebrates. 19. Isolation, Structure Elucidation, and Partial Synthesis of 24-Methylene-25-ethylcholesterol (Mutasterol) First Example of Sterol Side-Chain Bioalkylation at Position 25. J. Am. Chem. Soc. 103,115 (1981). 

Bohlin, L., U. Sjostrand, C. Djerassi, and B.W. Sullivan Minor and Trace Sterols in Marine Invertebrates. Part 20. 3 -Hydroxymethyl-A-/iur-patinosterol and 3 -Hydroxymethyl-A-nur-dinosterol. Two New Sterols with Modified Nucleus and Side-chain from the Sponge Teichaxinella morchella. J. Chem. Soc., Perkin Trans. I 1981,1023. 

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