Natural steroid sitosterol

Crude fats and oils consist primarily of glycerides. However, they also contain many other hpids in minor quantitites. Com oil, for example, may contain glycerides plus phosphoUpids, glycolipids, many isomers of sitosterol and stigmasterol (plant steroids), several tocopherols (vitamins E), vitamin A, waxes, unsaturated hydrocarbons such as squalane and dozens of carotenoids and chlorophyll compounds, as well as many products of decomposition, hydrolysis, oxidation, and polymerization of any of the natural constituents. 

The structural relationship between phytosterols and BRs has been proposed from the biosynthetic points of view. All naturally occurring BRs possess carbon skeletons identical to those of common phytosterols (e.g., campesterol, 24-methylene-cholesterol, isofiicosterol, sitosterol, and cholesterol). Thus, BRs may be speculatively regarded as the enzymatic oxidation products of phytosterols with the corresponding carbon skeletons, as is the case of the biosynthesis of other steroid hormones (e.g., ecdysteroids (25) and 1,25-dihydroxyvitamin D3 (26)). Although BL has recently been proved to be biosynthesized from CS in crown gall cells of Catharanthus roseus (27), a major part of the biosynthesis of BRs is remained to be investigated. Experiments using radio-labeled precursors are required to clarify the biosynthesis of BRs in a suitable plant system. 

Arthropoda.—Steroid biosynthesis seems to be absent from all of this phylum. Examples of the class Arachnida, Diplopoda, Crustacea, and Insecta have been examined. Steroid metabolism in insects has been reviewed. " It should be borne in mind that insects can synthesise some terpenoids [e.g. (32) and (46)], but there is an absolute dietary requirement for steroids. Phytosterols such as -sitosterol are converted back into cholesterol derivatives apparently by the reverse of side chain alkylation (86 R = Et) (85 R = CHMe)—> (85 R = CHj)— (84)— (74). In addition a A -double bond is introduced. Parasites, and other organisms naturally present, may contribute to some of these reactions. ... 

It will be noted that stigmasterol also represents a commercial route to progesterone. This abundant plant sterol that is readily available from soybean with its C22-C23 double bond, easily converts to progesterone in four steps and has therefore become a preferred substrate for various steroidal drugs. Cholesterol itself, which is the natural substrate for all mammalian steroid hormones, and is readily available from various sources (e.g., wool grease), is now also convertible to desirable steroid intermediates utilizing biotransforma-tion chemistry. The same is true of P-sitosterol (Chapter 11), which is another plant sterol available from soybean. 

Steroids are widespread in nature, and those present in Aristolochia species are mostly derivatives of P-sitosterol and stigmasterol. P-Sitosterol (610) and its glucoside (611) were frequently encountered in several Aristolochia species (Table 22). P-Sitosterone (612), 3-one derivative of P-sitosterol was found in A. zollingeriana only [245], Stigmasterol (613) and its derivatives stigmast-4-en-3-one (614), 3P-... 

The bioconversion of steroids, the products of which are used in steroidal hormone pharmaceuticals, is carried out at a scale of more than 1(X)0 tons/year starting from natural phytosterols from soya, conifers and from rape seed (P-sitosterol, campesterol, stigmas-terol, brassicasterol, and P-sitostanol). 

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