Terpenoids phytosterols

Subsequent studies indicated the major precursors in tobacco of PAHs in its smoke were not cellulose and lignin but were the lipophilic tobacco components. Rodgman and Cook (3269, 3286, 3291) and Severson et al. (3616) reported that terpenoids, phytosterols, and saturated hydrocarbons were PAH precursors... 

The biosynthesis of cholesterol, related steroids, and phytosterols is dealt with in this section whereas the further metabolism of these classes and the remaining nonsteroidal triterpenoids are covered in the following two sections. Reviews have appeared on the biosynthesis of sterols and higher terpenoids, the in vivo metabolism of steroids in primates" and in plant tissue culture," and dietary feedback control of cholesterol synthesis." The latter contains a reasoned defence of the hypothesis that HMG-CoA reductase is controlled by alterations to its supporting microsomal membrane. Abstracts of a symposium on all aspects of steroid biosynthesis have appeared." ... 

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. ... 

From the results of studies on the pyrolysis of the tobacco paraffins, which comprise the n-, iso-, and anteiso-alkmes, it was suggested by Lam (2255-2258), Wynder et al. (4356), Wynder and Hoffmann (4319, 4332), and Hoffmann and Wynder (1798) that these components were the major precursors in tobacco of the PAHs in tobacco smoke. However, in 1958, Rayburn and his colleagues (3091, 3092) challenged the proposal that the tobacco alkanes were the major precursors of the smoke PAHs, but their experimental data were not overly conclusive in support of their challenge. Nevertheless, it should be realized that in one sense Rayburn et al. were partly correct as PAH precursors, the tobacco alkanes do contribute to the PAHs in tobacco smoke but their contribution is much less significant than other precursors (the phytosterols and terpenoids such as solanesol) in tobacco [cf. Wright (4282), Rodgman and Cook, (3269, 3286), Severson et al. (3616)]. 

Organic solvent-soluble components long-chained aliphatic saturated and unsaturated hydrocarbons terpenoid alcohols such as the duvanediols, phytosterols, phytol, and solanesol normal long-chained aliphatic alcohols esters of these groups of alcohols with long-chained aliphatic acids (palmitic, stearic, oleic, etc.)... 

The structure of the unsaturated C45 polyisoprenoid alcohol, solanesol, was established in 1956 by Rowland et al. (3359). Despite the fact that solanesol was one of the major individnal components of the extractable waxes from tobacco, its pyrolysis was not reported until 1962. While Lam (2255) favored the satnrated hydrocarbons as the major precursors in tobacco of PAHs in smoke, Wynder (4294) considered both the satnrated hydrocarbons and the phytosterols to be the major precnrsors. Wright (4282) proposed that the phytosterols and other terpenoids snch as solanesol were the major precursors in tobacco of PAHs in smoke. In spite of their differences of opinion on the relative importance of these tobacco components in their contribntion to smoke PAHs, they collaborated on several stndies in the late 1950s (4355, 4356). Snbseqnently, the satnrated hydrocarbons, the phytosterols, and other terpenoids snch as solanesol were shown to be important in the formation of PAHs in tobacco smoke (3251, 3269, 3291, 3616). 

Tree nuts are highly nutritious and provide macronutrients (fat, protein, and carbohydrate)[l,8], micronutrients (minerals and vitamins)[l], fat-soluble bioactives (monounsaturated fatty adds [MUFA], polyunsaturated fatty acids [PUFA], monoacylglycerols [MAG], diacylglycerols [DAG], tria-cylglycerols [TAG], phospholipids, sterol esters, tocopherols, tocotrienols, phytosterols, phytostanols, squalene, terpenoids, sphingolipids, and essential oils, among others) [1,4-6,9-12] (Table 1.2), and phy-... 

Terpenoids such as some triterpenoids and phytosterols are also present in almond and contribute to the bioactivity and functional properties of almond. Triterpenoids are believed to possess antiinflammatory, anti-human immunodeficiency virus (HIV), and anticancer activities [2] phytosterols are able to reduce total cholesterol and LDL cholesterol concentrations [52,53], Triterpenoids... 

Squalene is a 30-carbon, straight-chain terpenoid hydrocarbon that serves as a precursor of steroids, both in plant cells and animals. In plant cells, squalene can be converted to phytosterols. It has been reported that squalene significantly decreases total cholesterol, LDL cholesterol, and TAG levels in hypercholesterolemic patients [161,162]. There has been growing interest in squalene as a potential chemopreventative agent [163-165]. In addition, the possible protective effect of squalene maybe attributed to its antioxidant function [166-168]. 

The edible uses of pistachio also include its oil, which is obtained from the seed but not produced commercially because of the high price of the seed. The seed yields up to 40% of this nondrying oil, which has a pleasant mild flavor and contains a number of terpenoids [15] (Table 18.2). The chemical structure of phytosterols and phytostanols found in pistachio nuts are shown in Figure 18.2. 

Limonene as a by-product of orange juice production can be used for polymer production together with CO2 to form a polystyrol-like foam. Menthon can be used as a precursor for branched dicarbonic acids and alpha-pinen (a by-product of the forest industry) as precursor for cymol production or for enzymatic verbenone production. Other important terpenoids are phytosterols. They are used in the production of steroid hormones such as cortison or progesteron by Bayer Sobering Pharma. Probably the most important example where plant secondary metabolism and microbial fermentation are synergistically combined, steroid hormones, are produced from phytosterols. A fermentation process by Bayer Schering Pharma uses a plant metaboUte and converts it by a single-step microbial fermentation into the desired end product. 

Goad, L. J., Inhibition of phytosterol biosynthesis and the consequences for plant growth, in Ecological Chemistry Biochemistry of Plant Terpenoids (J. B. Harbome and F. A. Tomas-Barber, eds.). Phytochemistry Society of Europe Vol. 31, 209-229, Clarendon, Oxford, 1991b. 

As artemisinin has a terpenic structure, its biosynthesis starts in the formation of isopentenyl diphosphate GPP)> as in all the natural terpenoids. In plants, IPP is synthesized either via the mevalonate pathway in the cytosol or via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in the plastid. The IPP derived from the mevalonate pathway is generally used in the biosynthesis of sesquiterpenes (such as artemisinin), phytosterols, and triterpenes, and the IPP derived from the non-mevalonate pathway is employed in the biosynthesis of monoterpenes, diterpenes, and tetraterpenes (Fig. 89.15). 

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