Sterols, acetates

Other sorbents that have also been used for separating steroids in TLC are cellulose, kieselguhr, alumina, polyamide, magnesium oxide, and celite. An-drostanes can be analyzed using cellulose layers impregnated with 1,2 propanediol. Layers consisting of alumina and magnesium oxide can be used to separate some sterols and sterol acetates. 

An example of the capability of glass-capillary gas chromatography (GC ) in separating complex sterol mixtures is shown in Fig. 13 (courtesy Gagosian and Heinzer, 1979). Sixteen sterol acetates were identified with the aid of mass spectral data in a sample of Black Sea water. 5a-cholestane was used as internal standard. 

To determine sterols, a portion of the total lipid extract is saponified using methanolic potassium hydroxide, and sterols subsequently recovered in 2 1 hex-ane/chloroform. The sterols are converted to the corresponding trimethylsilyl (TMS) ethers using bis-N,0-(trimethylsilyl)trifluoroacetamide, BSTFA, and analyzed by capillary GC and GC with mass spectrometry. Reviews of relative retention times and mass spectra for sterol TMS ethers have been published [e.g. 73]. In some cases, sterol acetates, rather than TMS ethers, are the derivatives prepared for GC. SiHca column chromatography of the total lipid extract may also be used instead of saponification to isolate the sterol fraction [74], or even sterol subclasses such as 4,4-dimethyl, 4-monomethyl and 4-desmethyl sterols [75], prior to derivatization. However, this approach only includes free sterols in the analysis, whereas by saponifying the total extract, sterols present as steryl esters are also detected. 

Argentation chromatography using chloroform to elute a silver nitrate-loaded silica stationary phase has also been used to resolve the cis and trans isomers of sterol acetates, although column efficiencies were reported to be poor (Colin et al., 1979). 

Table 60. Bsrvciktea (St = ChoUsteryl acetate, Ef 0.28) of sterol acetates in the reversed phase system undecanelacetic add ocetonitrile (20 + 60) [43]...

Sterol Abbrevia- tion jB i-value of sterol in A Est-yahie of sterol acetate in B... 

In the case of the acetates, a very extensive study of the structure of the C—O band of a large number of sterol acetates has enabled Jones et al [ 1 ] to obtain evidence as to the stereochemical structure of C3 acetoxy-sterols in relation to the hydrogen atom at C5. 

The most extensive study of ester carbonyl absorptions is that made by Jones and co-workers [9—11, 28, 42, 43] who have investigated the carbonyl frequencies of over a hundred sterol acetates, propionates, etc. With certain exceptions which will be dealt with later, all the saturated materials absorbed in the range 1742— 1735 cm", regardless of where the ester group was situated in the steroid nucleus, although there were indications that similarly substituted materials each had an even narrower range of characteristic frequencies. 

If a low figure is obtained in the Bomer test a search for wo-oleic acid must be made and the melting-point of the sterol acetates determined. If these tests preclude the presence of hydrogenated oils and fats, the adulterant is beef fat (or mutton or horse fat), and an approximate measure of... 

Synonyms Sterols, soybean Uses Emulsifier, humectant in cosmetics Soy sterol. See Soybean (Glycine soja) sterol Soy sterol acetate... 

Sterols, soybean. See Soybean (Glycine soja) sterol Soy sterol Sterols, soybean, acetates. See Soy sterol acetate 2,2 -Stilbenedisulfonic acid, 4,4 -bis ((4-anilino-6-ethylamino-s-triazin-2-yl) amino)-, disodium saK. See Disodium bisethylphenyl triaminotriazine stil-benedisulfonate... 

Aoki, S., Yoshida, Y, Miyamoto, Y, Higuchi, K., Setiawan, A., Murakami, N., Chen, Z.S., Sumizawa, T., Akiyatna, S.-I., and Kobayashi, M. (1998) Agosterol A, a novel polyhydroxylated sterol acetate reversing multidrug resistance from a marine sponge of Spongia sp. Tetrahedron Lett., 39,6303-6306. 

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