Identification of Sterols

An illustration of the determination of configuration is as follows. Two configurational standards among others have been established. They are stigmasterol 

The spectra of the two 24-methyl epimers are, incidentally, also quite different in regions other than where the C-21 doublet resonates. In particular, the methyl (C-28) on C-24 is adjacent to C-25, which contains two further methyl groups. Inversion of C-24, therefore, causes marked differences in the signals from these methyls, and the differences are of diagnostic as well as of quantitative value (28, 29, 69, 70). In one of the epimers, a branch of one of the doublets occurs at the position of a minimum in the spectrum of the other epimer, and the intensity of the branch is especially useful for quantitation if no other sterol is present with a signal there. To avoid contamination in this region, the 24-methylsterols can be obtained as a separate fraction by reversed phase chromatography on lipophilic Sephadex or by preparative HPLC. 

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Langlais, J., Kan, F.W.K., Granger, L, Raymond, L., Bleau, G., and Roberts, K.D. (1988). Identification of sterol acceptors that stimulate cholesterol efflux from human spermatozoa during in vitro capacitation. Gamete Res. 20 185-201. 

Kfen, V., feezanka, T., Sajdl, P. and Rehacek, Z. (1986) Identification of sterols in submerged cultures of different Claviceps species. Biochem. Physiol. Pflanzen, 181, 505-510. 

Benveniste, Isolement, caracterisation et composition en sterols de fractions subcellulaires de feuilles etiolees de Haricot. Physiol. Veg. 11 209 (1973). b) R.D. Brandt and P. Benveniste, Isolation and Identification of sterols from subcellular fractions of bean leaves (Phaseolus vulgaris). Biochim. Biophys. Acta 282 ... 

Koch, P., Djerassi, C., Lakshmi, V., and Schmitz, F.J. (1983) Identification of sterols having an oxygeneated side chains in the sponge Hyrtios sp. Helv. Chim. Acta, 66, 2431—2436. 

Although many sterols and bile acids were isolated in the nineteenth century, it was not until the twentieth century that the stmcture of the steroid nucleus was first elucidated (5). X-ray crystallographic data first suggested that the steroid nucleus was a thin, lath-shaped stmcture (6). This perhydro-l,2-cyclopentenophenanthrene ring system was eventually confirmed by the identification of the Diels hydrocarbon [549-88-2] (4) and by the total synthesis of equilenin [517-09-9] (5) (7). 

Chloroform-methanol extracts of Borrelia burgdorferi were used for the identification of lipids and other related components that could help in the diagnosis of Lyme disease [58]. The provitamin D fraction of skin lipids of rats was purified by PTLC and further analyzed by UV, HPLC, GLC, and GC-MS. MS results indicated that this fraction contained a small amount of cholesterol, lathosterol, and two other unknown sterols in addition to 7-dehydrocholesterol [12]. Two fluorescent lipids extracted from bovine brain white matter were isolated by two-step PTLC using silica gel G plates [59]. PTLC has been used for the separation of sterols, free fatty acids, triacylglycerols, and sterol esters in lipids extracted from the pathogenic fungus Fusarium culmorum [60]. 

J.S. Mills, R. White, The identification of paint media from the analysis of their sterol composition, Studies in Conservation, 20, 176 182 (1975). 

Gas chromatography appears to give adequate separation and measurement of the various sterols to be found in the marine environment where it is less than satisfactory is in the identification of the substances being measured. With compounds whose structures can be so similar, only gas chromatography-mass spectrometry can be expected to provide reasonable identifications. 

The potential for the preservation of lipids is relatively high since by definition they are hydrophobic and not susceptible to hydrolysis by water, unlike most amino acids and DNA. A wide range of fatty acids, sterols, acylglycerols, and wax esters have been identified in visible surface debris on pottery fragments or as residues absorbed into the permeable ceramic matrix. Isolation of lipids from these matrices is achieved by solvent extraction of powdered samples and analysis is often by the powerful and sensitive technique of combined gas chromatography-mass spectrometry (GC-MS see Section 8.4). This approach has been successfully used for the identification of ancient lipid residues, contributing to the study of artifact... 

CA107 Duplatre, A., C. Tisse, and J. Estienne. CAl 19 Identification of Arabica and Robusta (coffee) species by studying the sterol fraction. Ann Falsif Expert Chim Toxicol 1984 77(828) 259-270. 

HPLC determination (Osada et al., 1999), and HPLC/MS (Redden and Huang, 1991). In general, enzymatic determination is superior to colorimetry to obtain true cholesterol content. When food such as shellfish contains sterols other than cholesterol, the GC determination is the most adequate method. Although GC/MS also accomplishes good separation between and identification of all sterol analogs, the instrument is too expensive to use for routine analyses of cholesterol. 

Full identification of isolated sterols from commercially consumable fats performed by GC/MS, and quantitative estimation of cholesterol content by capillary GC with flame ionization detection. 

Moon, Y. A., Shah, N. A., Mohapatra, S., Warrington, J. A. and Horton, J.D. (2001). Identification of a mammalian long chain fatty acyl elongase regulated by sterol regulatory element-binding proteins. J. Biol. Chem., 276,45358—45366. 

Guyot, A. (1969) Identification of fat mixtures by analysis of fatty acids and sterols. Bull. Rech. Agron. Gembloux, 4, 484—508. 

IUPAC (1987) Identification and determination of sterols by gas-liquid chromatography, in Standard Methods of Analysis of Oils, Fats and Derivatives (eds C. Paquot and A. Hautfenne), Oxford, Blackwell Scientific, pp. 165-169. 

It has been proposed that acrolein can be transformed metabolically into acrylic acid, which may be incorporated into amino acids, fatty acids, and sterol. Flowever, specific biomarkers of effect for acrolein have not been identified. Studies regarding identification of these biomarkers would be useful. 

A24(25)-COmp0und, which is then reduced to give the saturated sterol side-chain. This route is further supported by a recent identification of stigmasta-7,24-dien-3/3-ol in higher plants.167 A similar pathway of alkylation operates for the biosynthesis of clionasterol [(24S)-(95)] from cycloartenol in the yellow-green alga Monodus subter-raneus, with the exception that direct reduction of a A24(28)-sterol [cf. (98)], rather than isomerization and then reduction, appears to occur.168... 

Agrawal, P. K. Bishnoi, V. Studies on Indian medical plants. 42. Sterol and taraxastane derivatives from Artemisia annua and a rational approach based upon C-13 NMR for the identification of skeletal type of amorphane sesquiterpenoids. Indian J. Chem., 1996, 35B 86-88. 

J. Sakai, R. B. Rawson, P. J. Espenhade, D. Cheng, A. C. SeegmiDer, J. L. Goldstein, and M. S. Brown. Molecular identification of the sterol-regulated luminal protease that cleaves SREBP s and controls lipid composition of animal cells. Molecular Cell, 2, 505—514, 1998. 

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