Sterol derivatives

FIGURE 8.20 The structures of several important sterols derived from cholesterol. 

Tomlinson, H., and S. Rich. Anti-senescent compounds reduce injury and steroid changes in ozonated leaves and their chloroplasts. Phytopathology 63 903-906. 1973. Tomlinson, H., and S. Rich. Effect of ozone on sterols and sterol derivatives in bean leaves. Phytopathology 61 1404-1405, 1971. 

Tomlinson, H., and S. Rich. Effect of ozone on sterols and sterol derivatives in bean leaves. Phytopathology 61 1404-1405, 1971. 

Lipid Metabolism. Next we explored changes in lipid metabolism in leaves exposed to ozone. Sterols and sterol derivatives were particularly interesting to us because they have been associated with membrane-containing fractions of leaves ( ). Changes produced in these compounds may be early events in the toxicity of ozone to plant cells. 

In another experiment (Table V), the free sterol content of ozonated chloroplasts from beans was found to be 32% less and the content of sterol derivatives 37% more than that of non-ozonated chloroplasts. What happens to the free sterols (FS), sterol glycosides (SG) and acetylated sterol glycosides (ASG) can be seen in Table VI, In these experiments ( ) with whole leaves of beans, FS in the ozonated leaves was 21% less, SG 32% more, and ASG 41% more than in non-ozonated leaves. 

Table V. Changes in free sterol and sterol derivative of chloroplasts in bean leaves exposed to ozone (50 pphm for 1 hr)...

Cholecalciferol is pure vitamin D3 derived from the ultraviolet conversion of 7-dehydrocholesterol to cholecalciferol. Ergocalciferol vitamin D2) is a sterol derived from yeast and fungal ergosterol. Calcitriol [Rocaltrol, 1,25-(0H)2D3] is the metabolically active vitamin D3 compound. Dihydrotachysterol is a synthetic compound that may act somewhat more quickly than either vitamin D2 or D3. 

Brand Name(s) DHT, DFIT Intensol, Hytakerol Chemical Class Sterol derivative... 

Bile acids are sterol derivatives derived from cholesterol that have two major functions. (l) The cholesterol delivered back to the liver by reverse cholesterol transport is converted into bile acids, which are excreted from the body via the intestine. (2) The bile acids secreted into the intestine are required for the solubilization of dietary lipids so that they can be degraded by lipases and absorbed into the intestinal wall (see fig. 18.2). 

Thus, the receptor-mediated, LDL-derived cholesterol meets cellular requirements for cholesterol and prevents its overaccumulation by inhibiting de novo cholesterol synthesis, suppressing further entry of LDL, and storing unused cholesterol as cholesteryl esters or exporting it from the liver as bile acids or other sterol-derived products. About 75% of high-affinity LDL uptake occurs in the liver. 

Practically all plant steroid molecules are sterols. The function of plant sterols is still relatively unclear. They undoubtedly play an important role in membrane structure and function. Certain sterol derivatives, such as the cardiac glycosides, are known to protect plants that produce them from predators. Most plant sterols... 

Squalene has been shown to assume the folding pattern of Woodward and Bloch in the cyclization process that forms sterols (Fig. 17). This was demonstrated by the labehng patterns of sterols derived from acetate and mevalonate [90,91]. There are several ways by which squalene can cyclize, consequently it is the precursor of several polycyclic terpenoids (Chapter 7). The product depends on the conformation squalene assumes in binding to the cyclase and the nature and position of the nucleophiles and bases on the enzyme. Mechanistically, squalene requires an electrophilic attack at C-3 for cyclization to occur. This can be accomplished by direct attack of a as in the cycUzation that produces tetrahymanol and femene or by... 

Numerous effectors (sterols, sterol derivatives, hormones, hormonal second messengers, lipoproteins, dietary components, drugs, lighting, conditioning and stress) produce quantitatively and temporally equivalent changes in HMG-CoA reductase activity and sterol biosynthesis in animals, tissue slices and primary and continuously cultured cells. 

The identity of the multiple signals which regulate HMG-CoA reductase levels has yet to be established. One of these appears to be a sterol or sterol derivative. The second appears to be mevalonate or one of its metabolites [141]. Leading candidates for the sterol signal(s) are oxygenated derivatives of cholesterol. These are present in the circulation and many are potent suppressors of HMG-CoA reductase levels [175-177]. A candidate for the regulatory metabolite of mevalonate is isopentenyl adenine. Compactin added to baby hamster kidney-21 cells completely inhibits both DNA synthesis and cell proliferation [178]. Added mevalonolactone relieved this inhibition, but added sterols did not. Isopentenyl adenine also relieved compactin inhibition, and did so 100-200 times more effectively than did mevalonolactone [178]. 

In a similar study of the metabolism of [24- C]12a-hydroxy-5)8-cholanic acid given intraperitoneally to male rats with bile fistulas [83], the identified biliary metabolites were 7a,12a-dihydroxy-5)8-cholanic acid (26%), deoxycholic acid (18%), cholic acid (15%), 6)8,12a-hydroxy-5)8-cholanic acid (0.8%), and 12% of unchanged 12a-hydroxy-5)8-cholanic acid. Thus, 5)8-cholanic acid and 12a-hydroxy-5)8-cholanic acids are hydroxylated in vivo preferentially in the order 7a, 3a, and 6)8. The preference for 7a-hydroxylation may be related to the concentration and properties of the active enzyme. Although no in vitro studies have been carried out, these studies infer the ability of hepatic tissue to provide characteristic 3a-hydroxy bile acids from derivatives devoid of a C-3 oxygen. How often this activity is required is questionable, because of the abundance of 3-hydroxylated sterol derivatives provided to and by the liver. 

Another example in which steric factors apparently override the overlap requirement is the reduction of sterol derivative 8 which also leads to the thermodynamically more stable cis-product 954. 

Branched long-chain alcohols (IV) obtained by condensation of lower alcohols (Guerbet synthesis) have some importance as lipophilic surfactants, emollients, and surfactant intermediates. Alcohols and sterols derived by saponification of wool wax, such as Amerchol 400 Amerchol), Argowax Westbrook Lanolin), Super Hartolan and Lanethyl Croda), sterols from vegetable waxes and oils, diols (such as 2,4,7,9-tetramethyl-decyne-5-diol-4,7 (V) that is known as wetting agent) as well as long-chain epoxy hydrolysates (1,2-diols) are also of some importance. 

Butenandt AH, Dannenberg H. Androsterone, a crystalline male sex hormone. III. Isolation of a new physiologically inert sterol derivative from male urine, its relationship to dehydroandrosterone and androsterone. Z Physiol Chem 1934 229 192-208. 

The known sterol derivative 61, containing a cyclopropane side chain was isolated in our lab (Adamczeski [8]) from Pseudopterogorgia sp. collection from Indonesia. This compound was first isolated from the soft coral... 

TRANSFORMATION TO STEROID DERIVATIVES. The conversion of solasodine to sterol derivatives was accomplished in two ways. The oxidation of acetylsolasodine with chromic acid in acetic acid resulted in a... 

The name cholesteric has a historical background since the first chemicals which showed the typical optical activity were esters of cholesterol. Cholesteric formulations comprised entirely of cholesterol and other sterol derived chemicals. 

Other metabolites like 5,7-dihydroxy-8-methoxychroman-4-one (37) and possibly a coumarin derivative (35) have also been found in the bulb wax of E. comosa. From the bulb tissue of different Eucomis spp. a series of sterol derivatives, dibenzo-a-pyrones and a dicarboxylic acid have been isolated (69, 82). 

There is a growing interest in sterols and their derivatives in plants. The subject has been reviewed by Grunwald (1975a) Mudd and Garcia (1975) and by Eichenbeiger (1977). Much has been done on identification and biosynthesis, but some aspects of these studies require further elucidation, such as the subcellular sites of biosynthesis. In other respects the study of sterol derivatives in plants is in its infancy very little is known about function and metabolic turnover. 

This chapter emphasizes the well-documented areas of research on sterol derivatives tissue analysis and biosynthesis. The subjects of function, and changes related to physiological phenomena, are introduced with the expectation that much progress will soon be made in these fields. 

In Chapter 15, the biosynthesis of phytosterols was described. Briefly some of the major sterols found in plants are shown in Fig. 1. Principal differences are in the side chain (C20-CJ7) which has different degrees of substitution and unsaturation. The sterol derivatives, also shown in Fig. 1, are (1) steryl esters (SEs), in which a long-chain fatty acid is esterified at the 3-OH of the sterol, (2) steryl glycosides (SGs) in which the 3-OH of the sterol forms a glycosidic linkage to the 1-position of a monosaccharide, usually glu-... 

The percentage composition of various sterol derivatives in plant tissue is indicated in Table I. Depending on the tissue, any one of the categories, sterol (S), SE, SG, or ASG can be dominant. In some cases sterol derivatives form a large percnetage of the total lipid. 

Most authors find sterols of all forms to be particularly abundant in ER (Table V). It should be realized that in animal tissue the cellular membranes richest in cholesterol are the plasma and lysosomal membranes. Further fractionation of plant membranes may reveal a high content of sterol derivatives in plasma membrane, tonoplast, and other membranes. Duperonet al. (1975) measured the sterol content of cauliflower mitochondria and found that the inner membrane contained 28 pg sterol per milligram of protein and the outer membrane 77 p,g sterol per milligram of protein. This enrichment in the outer membrane is also found in animal mitochondria. 

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