Minor sterols of marine invertebrates 37. Isolation of novel coprostanols and 4 alpha-methyl sterols from the tunicate Ascidia nigra

Phallusiasterols A and B: two new sulfated sterols from the Mediterranean tunicate Phallusia fumigata and their effects as modulators of the PXR receptor

Purification of the apolar extracts of the marine ascidian Phallusia fumigata, afforded two new sulfated sterols, phallusiasterols A (1) and B (2). The structures of the new compounds have been elucidated using mass spectrometry and NMR experiments. The effects of phallusiasterols A and B as modulators of pregnane-X-receptor (PXR) have been investigated. These studies revealed that phallusiasterol A induces PXR transactivation in HepG2 cells and stimulates the expression of the PXR target genes CYP3A4 and MDR1 in the same cell line. Molecular docking calculations suggested the theoretical binding mode of phallusiasterol A with hPXR and revealed that phallusiasterol A fitted well in the LBD of PXR.

Structure determination of new steroids from Abutilon pakistanicum by NMR techniques

Two new steroids provisionally named as pakisteroid-A (1) and pakisteroid-B (2) have been isolated in crystalline form from Abutilon pakistanicum. Their structures have been assigned as 3-O-beta-D-glucopyranosyl-stigmasta-5,11(12)-diene (1) and 24beta-ethylcholesta-5, 9(11), 22E-trien-3beta-benzoate (2), respectively through extensive NMR studies.

A new dihydroxysterol from the marine phytoplankton Diacronema sp

Diacronema sp. was cultured and its sterols were separated by column chromatography on silica gel. The new sterol 24-ethyl-4alpha-methyl-cholestane-3,20-diol (1) was characterised by NMR and MS spectrometry, as well as (22E)-24-ethyl-4alpha-methyl-5alpha-cholest-22-en-3beta-ol (2) and beta-sitosterol, the major components of the sterol fractions. Neither the biosynthetic origin of the new dihydroxysterol nor its role in the biochemistry of Diacronema is known.

4alpha-methyl-24beta-ethyl-5alpha-cholesta-14,25-dien-3beta-ol and 24beta-ethylcholesta-5, 9(11), 22E-trien-3beta-ol, sterols from Clerodendrum inerme

From the aerial parts of Clerodendrum inerme, two new sterols (4alpha-methyl-24beta-ethyl-5alpha-cholesta-14, 25-dien-3beta-ol and 24beta-ethylcholesta-5, 9(11), 22E-trien-3beta-ol) and a new aliphatic ketone (11-pentacosanone) were isolated together with another known aliphatic ketone (6-nonacosanone) and a diterpene (clerodermic acid). The structure elucidations were based on analyses of physical and spectroscopic data.

26-Nor-25-isopropyl-ergosta-5,7,22E-trien-3beta-ol: a new C(29) sterol from the sponge Agelas sceptrum from Jamaica

In addition to several known sterols, a new C(29) marine sterol with a normal ergosterol nucleus but a modified side chain, named 26-nor-25-isopropyl-ergosta-5,7,22E-trien-3beta-ol, was isolated from the Jamaican sponge Agelas sceptrum. The structures were assigned by spectroscopic methods including high-resolution 2D NMR techniques.

The lipid geochemistry of a Recent sapropel and associated sediments from the Hellenic Outer Ridge, eastern Mediterranean Sea

Five sections (0-7, 29-36, 53-60, 78-85 and 104-111 cm), of a 0-2 m sediment core from the Hellenic Outer Ridge, in the eastern Mediterranean Sea, have been examined for lipids. Three of these sections were from a 73 cm thick S 1 ( ca . 6000—9000 years b.p.) sapropel layer, one from an upper ooze layer and one from a lower marl. The lipids were extracted and the major classes analysed in detail by gas chromatography and computerized gas chromatography—mass spectrometry. In all sections, the n -alkanes were dominated by C 25 —C 31 components, showing a high odd-over-even predominance, with smaller amounts of lower chain-length components. The acyclic ketone fraction consisted mainly of C 37 —C 39 di- and triunsaturated alken-2-ones and alken-3-ones. Alkanols, ranging from C 12 —C 32 with a high even-odd preponderance, were present in all sections, maximizing at n -C 22 or n -C 26 . The sapropel contained abundant phytol (up to 7000 ng g -1 dry sediment), and considerable amounts of 22 :1, 24:1 and 26 :1 n -alkenols; in the non-sapropelic sediment, phytol was only a minor com ponent, and no n -alkenols were detected. In addition to these alcohols, the sapropel also contained C 28 —C 32 1,13-, 1,14- and 1,15- diols and 15-keto-alkan-l-ols, the 30 :0 compound predominating in both series. In all sections, fatty acids were the most abundant lipid class. These were mainly C 12 —C 30 straight-chain compounds, maximizing at 16:0 with a high even—odd predominance; most were saturated, but C 16 , C 18 , C 20 , C 22 and C 24 monoenoic acids and small amounts of C 16 , C 18 , C 20 , C 22 and C 24 polyenoic acids were present. A range of branched and cyclic acids were also identified. The non-sapropelic upper and lower sediments differed from the sapropel in containing higher levels of branched acids (especially C 15 and C 17 iso- and anteiso-compounds) and C 18 monoenoic acids: these differences could be related to differing inputs, especially in terms of microbial communities. The sterol distributions of the sapropel displayed a wide range of structures (C 26 —C 31 ), totalling over sixty different components. These included both 4-methyland 4-desmethylnuclei, a variety of C 8 —C 11 side-chains, and encompassed Δ 5 , Δ 5,22 , Δ 5,24 , Δ 5,24(28) , Δ 22 , Δ 24(28) , Δ 7 and Δ 8(14) unsaturation plus a range of fully saturated stands. Major components were 4α, 23, 24-trimethyl-5α-cholest-22-en-3β-ol (dinosterol), cholest-5-en-3|I-ol (cholesterol), 24-methylcholesta-5,22-dien-3β-ol and 24-ethylcholest-5-en-3β-ol. In contrast, the non-sapropelic sediments contained very low levels of only a few sterols, chiefly cholesterol and dinosterol, probably due to input differences. In addition to sterols, the sapropel also contained small amounts of stanones and sterenes. A significant terrigenous input of lipids is evident throughout the core (especially from the n -alkane data), but the sapropel lipid composition appears to be predominantly of marine origin. Individual ‘biological marker’ lipids suggest inputs from Dinophycean and Haptophycean algae to the sapropel. Potential contributions of lipids from organisms such as foraminifera and pteropods, remains of which were observed in the sediment, are difficult to assess due to a paucity of data on the lipid compositions of such organisms. The lipids of the non-sapropelic sediments showed a much less prominent marine signal, especially in terms of the lower levels of phytol and sterols and the higher relative abundance of terrestrial n -alkanes. Two main models have been proposed to explain the formation of organic-rich sapropel facies; (i) stagnation of the water column and the establishment of anoxic conditions in bottom water and sediments, resulting in enhanced preservation of sedimentary organic matter, and (ii) increased biological production providing an increased input of organic matter to the sediments. The lipid composition strongly suggests that this sapropel received a large marine-derived input of organic matter. Since this was less evident in the overlying and underlying sediments, sapropel deposition appears to have been associated with an increased autochthonous input. The anoxic nature of the sapropel, by restricting degradation to anaerobic processes, will also have contributed to the differences in lipid composition between the sediment types. Little diagenesis of lipids in the sapropel was evident. Small amounts of sterenes and 5β(H)-stands were present, probably formed by dehydration and reduction, respectively, of precursor sterols. Diagenetic dehydration of phytol may have contributed to the presence of minor amounts of certain other isoprenoid lipids.

Short side chain sterols from the tunicate Polizoa opuntia

The sterol composition of the Patagonian tunicate Polizoa opuntia was examined, and twenty-four compounds were identified as having either a delta 5, delta 7, or delta 0 nucleus. Two of them, the rare 20-methylpregn-5-en-3 beta-ol and 20-ethylpregn-5-en-3 beta-ol, were previously unreported as natural products from tunicates. These compounds were present only as trace components; therefore, their structures were confirmed by synthesis from suitable precursors and by comparison of the spectral and chromatographic constants of the synthetic and natural compounds.

Minor and trace sterols in marine invertebrates. 62. Novel coprostanols with unusual side chains from the marine sponge Calyx nicaeensis

Seventeen stanols with a variety of unusual side chains and possessing the rare 5 beta-dihydro nucleus have been isolated from the sponge Calyx nicaeensis. These stanols probably result from bacterial metabolism of the endogenous sponge sterols.

Minor and trace sterols from marine invertebrates 56. Novel coprostanols from the marine sponge Petrosia ficiformis

Twelve stanols possessing the rare 5 beta-dihydro nucleus have been isolated from the marine sponge Petrosia ficiformis. These stanols have not previously been encountered in any samples of P. ficiformis which we have examined and appear to be the result of bacterial metabolism of the endogenous sponge sterols.

Novel nuclear methylation of sterols by the nematode Caenorhabditis elegans

Caenorhabditis elegans possesses a unique sterol methylation pathway not reported to occur in any other organism and also removes the C-24 ethyl group of sitosterol (a plant sterol). This nematode produced substantial quantities of 4 alpha-methyl-5 alpha-cholest-8(14)-en-3 beta-ol and smaller amounts of lophenol from dietary cholesterol, desmosterol or sitosterol. When C. elegans was propagated in media containing sitosterol plus 25-azacoprostane hydrochloride (25-aza-5 beta-cholestane hydrochloride), an inhibitor of delta 24-sterol reductase in insects, its 4 alpha-methylsterol fraction largely consisted of equal amounts of 4 alpha-methyl-5 alpha-cholesta-7,24-dien-3 beta-ol and 4 alpha-methyl-5 alpha-cholesta-8(14),24-dien-3 beta-ol. Thus 25-azacoprostane hydrochloride inhibited both a delta 24-sterol reductase and a delta 7-sterol isomerase in C. elegans.

Marine 4-methyl sterols: synthesis of C-24 epimers of 4 alpha, 24-dimethyl-5 alpha-cholestan-3 beta-ol and 360 MHz 1HNMR comparisons to the natural product from Plexaura homomalla

Comparison of the highfield 1HNMR spectrum of 4 alpha, 24-dimethyl-5 alpha-cholestan-3 beta-o1 isolated by open column adsorptive chromatography and reversed-phase HPLC from P. homomalla with those of the corresponding synthetic 24 alpha and 24 beta compounds demonstrate that the gorgonian natural product is purely 24 beta, the same C-24 configuration found in sterols related to dinosterol and gorgosterol. 360 MHz 1HNMR data are also reported for synthetic 4 alpha, 24 beta-dimethyl-5 alpha-cholest-22E-en-3 beta-o1 (another P. homomalla natural product). The use of 1HNMR correlations in assigning C-24 configurations of 24-methyl marine sterols possessing various nuclei is examined and discussed. Analyses of the methyl sterol components of P. homomalla are tabulated and discussed with regard to origin and plausible biosynthetic interrelationships in light of the C-24 configurational findings.