Campesterol, structure

The beauty of the microbiological method lies in its ability to oxidize the structurally similar C-17 side chains of other steroids which contaminate sitosterol (e.g., campesterol, dihydrobrassicasterol, and stigmasterol—all of which carry the 3 3-hydroxy-5-ene structure) at both C-17 and 9a sites to compound XXXVIII. 

Figure 9.15 Chemical structures of some of the important sterols used as biomarkers in estuaries (e.g., /3-sistosterol, stigmasterol, campesterol, brassicasterol, and cholesterol).

Phytosterols are structurally very similar to cholesterol and the major phytosterols (campesterol, sitosterol and stigmasterol) have the same kind of membrane viscosity modulating function in plants that cholesterol (C27 3-OH-C6 C6 G61 C5—C8) has in animals. Campesterol (24-methylcholesterol), sitosterol (24-ethylcholesterol) and stigmasterol (A22, 24-ethylcholesterol) are widespread phytosterols. The animal sterols lanosterol and cholesterol are present in particular plants. Phytosterol esters reduce cholesterol absorption and lower LDL-cholesterol. 

Phytosterols are partially absorbed in the small intestine. Human absorption efficiency is estimated to be approximately 10% for campesterol and campestanol, 4 to 5% for sitosterol and stigmasterol, and negligible for sitostanol. The absorption of cholesterol ranges from 33 to 60%. Structural features, including the length and configuration of the aliphatic side chain of phytosterols, are thought to contribute to the differences in the absorption efficiency between phytosterols and cholesterol. " Phytosterols apparently displace cholesterol by mass action and... 

Figure 1. Structures of the common sterols (phytosterols) In corn and their comparison with cholesterol, the main sterol In animals. Note that cholesterol has 27 carbons, campesterol has 28 carbons, and all of the other phytosterols shown have 29 carbons.

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. 

Generally the most abundant sterol in higher plants is sitosterol which has a 24a-ethyl (Table 1), which accounts for about 50 to 80% of the total amount of plant sterols [16]. However, only seven species of 39 plants hitherto examined have been known to contain BRs with a 24a-ethyl and these are not major BRs except in the green alga Hydrodictyon reticulatum [18] (Tables 1 and 2). Furthermore, immature seed of Phaseolus vulgaris contains sitosterol as the major sterol (56% of the total sterol), however, corresponding BRs (28-homocastasterone and related BRs) were detected at very low levels [19]. On the other hand, campesterol and 24-methylene-25-methylenecholesterol each accounts for only about 3% of the total sterols. However, castasterone and 25-methyldolichosterone (and related BRs), which structurally correspond to these sterols, respectively, are major... 

Phytosterols are nonnutrient bioactive substances and act as a structural component in the cell membranes, a role which in mammalian cells is played by cholesterol. The methyl or ethyl group at C-24 location makes them different from cholesterol [58]. They include plant sterols (unsaturated form) and plant stanols (saturated form). Both sterols and stanols are effective in lowering plasma total and LDL cholesterols and inhibit the absorption of cholesterol from the small intestine [59]. A wide spectrum of other biological activities in animals and humans has been reported, including anti-inflammatory [60], antibacterial [61], antioxidative [62], and anticancer activities [63]. P-Sitosterol, campesterol, stigmasterol, A -avenasterol, sitostanol, and campestanol are the most common representative members in this series. P-Sitosterol, campesterol, and stigmasterol are the major identified phytosterols in Brazil nut, with sitostanol, campestanol, and A -avenasterol present in trace amounts. 

Numerous phytosterols have been isolated from the unsaponifiable fraction of VOO the most important are 3-sitosterol, A5-avenasterol, and campesterol. Several other minor compounds, such as cholesterol, stigmasterol, clerosterol, A7-stigmastenol, and A7-avenasterol have also been found in VOOs [73,74]. Their structures can be seen in Figure 9.6. 

Figure 4. Molecular structures of campesterol (a 4-desmethyl sterol) and a-amyrin (a triterpene...

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