Hopanes methylated

Summons R. E. and Jahnke E. E. (1992) Hopenes and hopanes methylated in ring-A correlation of the hopanoids from extant methylotrophic bacteria with their fossil analogues. In Biological Markers in Sediments and Petroleum (eds. J. M. Moldowan, P. Albrecht, and R. P. Philp). Prentice Hall, Englewood Cliffs, NJ, pp. 182-200. 

Two new hopanes, methyl pyxinate (172) and the corresponding acetate (173), occurin the lichen Pyxine endochrysina along with several dammaranes. Full papers have appeared on the structure of leucotylic acid (174) and on the correlation of zeorin (175) with leucotylin (176). On treatment with acid, methyl leucotylate (177) and leucotylin (176) afford methyl isoleucotylate (178) and isoleucotylin (179), respectively. 

Fatty acids (methyl esters) FAMES TMS fragment Hopanes and hopenes Sterols (TMS)... 

A number of selected molecular parameters obtained from analysis of immature crude oils and sediment extracts are evaluated as indicators of palaeosalinity. The nature of these parameters is discussed taking into account the role of intermolecular and intramolecular incorporation of sulfur into specific functionalized lipids. Specific distribution patterns of methylated chromans and C20 isoprenoid thiophenes and the relative abundance of gammacerane are excellent indicators for palaeosalinity, whilst other parameters such as 14< (H),17a(H)/140(H),170(H) -sterane ratios, the pristane/phytane ratio, the even-over-odd carbon number predominance of n-alkanes and the relative abundance of C35 hopanes and/or hopenes may indicate palaeohypersalinity but are affected by environmental factors other than hypersalinity and by diagenesis. 

A more critical evaluation of the above mentioned ratios and phenomena reveals the usefulness of the various palaeosalinity indicators. Distribution patterns of methylated chromans and the relative abundance of gammacerane are not influenced by sulfur incorporation reactions and may directly reflect species distributions in the palaeoenvironment. To some extent this holds for 14a(H),17a(H)/140(H),170(H)-steraneratios as well, although incorporation of sulfur may influence this ratio and original A7/A5-sterol ratios do not always correlate with hypersaline environments. The isoprenoid thiophene ratio is highly useful as a palaeosalinity indicator since the distribution of the C20 isoprenoid thiophenes directly reflects the distribution of their substrates. The other parameters (pristane/phytane ratio, odd-over-even carbon number predominance of n-alkanes, relative abundance of C35 hopanes and/or hopenes) should be used with caution because they obviously depend on the quenching by sulfur of specific lipids, a process which is not restricted to hypersaline environments. 

Lead tetra-acetate-iodine oxidation of hopan-7a-ol, hopan-15/3-ol, and the corresponding 21 aH epimers resulted in functionalization of the 80, 14a, and 18a methyl groups.129 The details of the chemical investigation of spergulagenin A (169), from Mollugo spergula, whose structure was established by X-ray analysis, have been published.130... 

They are 6a,7a,22-trihydroxyhopane (129), 6a-acetoxy-7a,22-dihydroxyhopane (130), 7a-acetoxy-6a,22-dihydroxyhopane (131), and ll)S,22-dihydroxyhopane (132). 17ai7-Hopane and 17ai7-moretane have been prepared from 22,29,30-trisnor-21-oxo-17aff-hopane. The methyl resonances of these compounds and a number of derivatives have been assigned. 

It also appears that further clues about hopanoid origins can be drawn from the polar side-chains which carry different numbers and types of substituents. This, in turn, affects their subsequent diagenesis and the types of hopane hydrocarbon, ketone, and other products that are recorded in sediments. In addition to the diagnostic 3j8-methyl substituents, hexafunctionalized side-chains are prevalent in Type 1 methanotrophic bacteria (Neunlist and Rohmer, 1985 Zundel and Rohmer, 1985a). The hydroxy substituent at C-31 of these compounds appears to assist oxidative loss of this carbon or the one at C-30, resulting in a predominance of C30 hopane and 30-norhopane products where methanotrophs are prevalent or even dominant (e.g., Burhan et aL, 2002 Rohmer et ai, 1992). Anomalous C-depletion of these hopanoids often observed in sediments and oils is quite consistent with this interpretation (e.g.. Summons et ai, 2002). 

Cyclic Alkanes. In the cyclic fraction the following polycyclic isoprenoid compounds were identified (4) 27 29 steranes> methyl-C2g sterane> C 7 32 Pentacyclic triterpanes of hopane type (except C ft), anathe bicyclic tetraterpane perhydro-8-caro-tane (Table IIJ. 

Most of the alphatic fractions were separated into normal and branched alkane fractions after the removal of unsaturated hydrocarbon. Most of these subfractions were analysed by GO to give fingerprint chromatograms. These analyses were used to provide data that allowed carbon preference indices, pristane/phytane ratios etc. to be measured. Also, the relative amounts of (17 H, 21/ H 17/3 H, 21 oCH and 17 H, 21(3 H) hopanes, steranes, 4-methyl steranes, carotenoid and other related compounds were assessed from gas chromatograms and reconstructed ion chromatograms. A large number of Kovats Retention Indices (0V-101) were measured and tabulated for these compounds also (10). 

Fig. 2.20 (a) Ring numbering conventions for steroids and hopanoids (b) examples of all-chair conformations (with trans ring junctions) for steroids and hopanoids (c) examples of application of hopanoidal nomenclature system. (Ts may also be called 17-methyl-18,22,29,30-tetranor-17a,18a-hopane.)... 

Hopane and homohopane (180) have been identified in Messel oil shale. The structure of homohopane was confirmed by a partial synthesis from diplop-tene [hop-20(29)-ene]. It is suggested that homohopane arises by microbiological methylation and that a significant proportion of the triterpanes found in sediments and oils are of bacterial origin. Tetrahymanol (181) has been isolated from Green River Shale. 

Methyl shifts in hopane subsequently lead to neohopane (C-28 methyl from C-18 to C-17), femane (C-27-methyl from C-14 to C-13 C-26 methyl from C-8 to C-14), adianane (C-25 methyl from C-10 to C-9) and, finally, filieane (C-24 methyl from C-4 to C-5). In another pathway, the eyelopentane ring of hopane expands to a eyelohexane substmeture involving a shift of earbon atom C-17 from C-21 to C-22, thus generating gammaeerane. 

Homosecodaphniphyllic acid, methyl ester, K26 Homoterpenyl methyl ketone, Tl Homothujadicarboxylic acid, T7 Hopane, T4S Hopeaphenol, YIS Hopenone I, T4S Humulene dioxide, T30 Humulene epoxides, T30 Humulenols, T30 Hunteracine, K14 Hunterbumine, K8 Huratoxin, T39 Hydrastines, K3 Hydratropic acid, A41 3j8-hydroxyallocholanic acid, T49 Hydroxycitric acid, A30... 

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