Hydrocarbons squalene

Triterpenes. The triterpenes (30 carbon atoms) are widely found in nature, especially plants, both in the free state and as esters or glycosides. A smaller but important group, including lanosterol [79-63-0] (114), occurs in animals. The triterpene hydrocarbon, squalene [111-02-4] (115), occurs in the hver oils of certain fish, especially those of sharks. 

Steroids are heavily modified triterpenoids that are biosynthesized in living organisms from farnesyl diphosphate (Cl5) by a reductive dimerization to the acyclic hydrocarbon squalene (C30), which is converted into lanosterol (Figure 27.12). Further rearrangements and degradations then take place to yield various steroids. The conversion of squalene to lanosterol is among the most... 

Steroids are plant and animal lipids with a characteristic tetracyclic carbon skeleton. Like the eicosanoids, steroids occur widely in body tissues and have a large variety of physiological activities. Steroids are closely related to terpenoids and arise biosynthetically from the triterpene lanosterol. Lanosterol, in turn, arises from cationic cyclization of the acyclic hydrocarbon squalene. 

Arabica/Robusta beans used in different countries ranges from 1.5 1 in Italy, 4 1 to 3 1 in the U.S., and 20 1 in Sweden and Norway.2 As described in Chapter 6, coffee contains a number of physiologically active components, including caffeine, diterpene alcohols, sterols, hydrocarbons, squalene, and others. 

Steroids are important lipids whose structures are based on a tetracyclic system. Most steroids function as hormone chemical messengers, and thus these molecules have been discussed in detail in chapter 5. Structurally, steroids are heavily modified triterpenes that are biosynthesized starting from the acyclic hydrocarbon squalene and progressing through cholesterol to the final steroid product Bloch and Cornforth, who were awarded Nobel Prizes in medicine (1964), contributed greatly to the elucidation of this remarkable biosynthetic transformation. 

Triterpenes are not formed by an extension of the now familiar process of adding IPP to the growing chain. Instead, two molecules of farnesyl PP are joined tail to tail to yield the hydrocarbon squalene (Figure 5.54), originally isolated from the liver oil of shark (Squalus sp.). Squalene was subsequently found in rat liver and yeast, and these systems were used to study its biosynthetic role... 

Most oils contain low levels of saturated and unsaturated hydrocarbons. In olive oil, the unsaturated hydrocarbon squalene can constitute up to 40% of the unsaponifiable fraction (Boskou, 1996). Other hydrocarbons commonly present in olive oil are straight chain alkanes and alkenes with 13 to 35 carbon atoms, along with very low amounts of branched chain hydrocarbons. Variations are found between different olive varieties but the main hydrocarbons are those with 23, 25, 27 and 29 carbon atoms (Guinda et al., 1996). Olive oil can clearly be differentiated from other vegetable oils on the basis of hydrocarbon components, and levels of 2.6% crude rapeseed oil or crude sunflower oil can be detected by hydrocarbon analysis (Webster et al., 1999). Terpenes have been identified in the volatile fraction of crude sunflower oil (Bocci and Frega, 1996). 

Oils Hydrocarbons Squalene Aliphatic Alcohols Terpenic Alcohols Sterols... 

Hydrocarbons are very minor components of oils and fats but are of dietary and legislative interest. They include alkanes, alkenes such as squalene and carotenes, and polycyclicaromatic hydrocarbons. Squalene (C30H50) is a highly unsaturated open-chain triterpene. It is used in the cosmetic industry after hydrogenation to squalane (C30H62). The most abundant source of squalene is the liver oil of the deep-sea dogfish (Squalus acanthus—hence the name squalene) and some other marine species. Vegetable sources of potential interest include olive oil and amar-anthus (Section 6). 

Hydrocarbons. Both even- and odd-chain w-paraffins, including branched-chain (iso and anteiso) compounds, which are minor components of the hydrocarbon fraction, are present in virgin olive oil. The polyunsaturated triterpenic hydrocarbon squalene, and biochemical precursor of sterols, is the main component of the hydro carbon fraction. The squalene content of olive oil ranges from 150 to 700 mg per 100 g (27-30). p-Carotene is also present in olive oil as are aromatic hydrocarbons, including benzenoid, napthalenic, and more complex aromatic hydrocarbons (30-37). 

First, we will take up cyclopropyl group formation by the rearrangement of carbon skeletons via cationic intermediates encountered in various mono- and sesquiterpenes, and also examine the illudin biosynthesis where contraction of a cyclobutyl cation to a cyclopropane has been invoked. We will then discuss the head-to-head condensation of isoprenoid alcohols at the C15 or C20 level to generate the cyclopropyl intermediates, presqualene pyrophosphate and prephytoene pyrophosphate, on the way to the C30 and C40 polyene hydrocarbons, squalene and phytoene respectively. Conversion of 2,3-oxidosqualene via common intermediate protosterol cation to cycloartenol or lanosterol represents an important pathway in which the angular methyl group participates in the three-membered ring formation. The cyclopropanation outcome of this process has been carefully studied. 

Sfiica impregnated with saturated and unsaturated hydrocarbons (squalene, paraffin oil), silicone and plant oils, complexing agents (silver ions, boric add and borates, unsaturated and aromatic compounds), tigands (EDTA, digitonin), and transition metal salts silanized silica gel impregnated with anionic and cationic surfactants Cross-linked, polymeric dextran gels (Sephadex)... 

Steroids arc heavily modified triterpenes that are hiosynthesized in living organisms from the acyclic hydrocarbon squalene (Section 27.6). The exact pathw ay by which this remarkable transformation is accomplished is lengthy and complex, but the key steps have now been worked out, with notable contributions made by Konrad Bloch and John Cornforth, who received Nobel Prizes for their efforts. 

The C30 hydrocarbon squalene is present at about 200-500 ppm in crude palm oil sesquiterpene (C15) and diterpene (C20) hydrocarbons are present at lower levels. Abdul Gapor and Hazrina (2000) reported squalene as high as 979 ppm in some crude oils and 791 ppm in refined oils. These levels are generally higher than that of other vegetable oils, with the exception of olive oil. Palm fatty acid distillate has 5000 ppm to 8000 ppm of squalene. Crude palm oil also has 10-80 ppm of ubiquinone 10 (Hazura et al. 1996). 

A schematic of fungal ergosterol biosynthesis starting from squalene is shown in Figure 40.1. The biosynthetic pathway has been simplified to emphasize steps important to the action of currently employed antifungal drugs. The last nonsteroidal precursor to both ergosterol and cholesterol is the hydrocarbon squalene. Squalene is converted to squalene epoxide by the enzyme squalene epoxidase. Squalene epoxide is then cyclized to lanosterol, the first steroid in the biosynthetic pathway. The... 

Cholesterol, which is present in brain and in almost all tissues, is synthesised from isopentenyl pyrophosphate via squalene, farnesyl and geranyl pyrophosphates. The synthesis of squalene commences with the isomerisation of isopentenyl pyrophosphate to dimethylallyl pyrophosphate, after which successive condensations take place according to Equation 11.118. The hydrocarbon squalene is then transformed into the tetracyclic steroidal configuration of lanosterol by appropriate enzymes, and this is followed by conversion into cholesterol. Cholesterol is the precursor to most other steroids in the body. 

The green microalga B. braunii grows as colonies of individual cells held together by a colony matrix that contains a large mixture of liquid hydrocarbons. B. braunii is further classified into four races namely races A, B, L, and S, depending on the type of hydrocarbons synthesized. The B race produces triterpenoid hydrocarbons, squalene (Figure 2.7) and botryococcene, both of which are putative condensation products of farnesyl diphosphate as the major matrix components. ... 

Sharks and related cartilaginous fishes lack swim bladders and may adjust their buoyancy with large and fatty livers (>25% of body mass). The hydrocarbon squalene (C30H50) has a density of 0.866 at 5 C and is often... 

Channon, H. j. The biological significance of the unsaponifiable matter of oils. I. Experiments with the unsaturated hydrocarbon squalene. Biochem. J. 20, 400 (1926). 

A variation on the amplitude modulation technique was also used to measure oscillatory surface forces with increased sensitivity in a branched hydrocarbon, squalene. In this technique, the sample was oscillated with low amplitude (c. 1 A), and both the cantilever static and dynamic (induced oscillation from a change in the tip-sample force gradient) deflection was measured. Figure 1.13 shows the static force measurement and Fig. 1.14 the dynamic measurement, shown as an interaction stiffness. The sensitivity of the dynamic force measurement is such that the interdigitation of the branched methyl groups can be detected (indicated by arrows in Fig. 1.14). 

In addition to the above mentioned hydrocarbons, oils also contain alkenes and monoterpenic and sesquiterpenic hydrocarbons. For example, the amount of alkenes in olive oils range from 0.5 to 2 mg/kg and includes a series of alk-9-enes from C22 to C27, heptadec-8-ene and 6,10-dimethyl-undec-l-ene. An important compound is the linear triterpenic (C39) hydrocarbon squalene (3-81), aIl-tra s-2,6,10,15,19,23-hexamethyltetracosa-2, 6,10,14,18,22-hexaene, which is the universal precursor of all triterpenoids and steroids. It was given this name because it was discovered in the Hver of sharks (Squalidae). Shark Hver oil contains about 30% squalene, about 7% pristane (2,6,10,14-tetramethylpentadecane) and smaller amounts of phytane (2,6,10,14-tetramethylhexadecane). Squalene occurs in small amounts in edible oils and especially in oHve oil, where its content is in the tenths of a percent (1-7 g/kg). 

Steroids are synthesised in organisms via complex mechanisms from isoprene units, isopentenyl diphosphate and dimethylaUyl diphosphate, which first yield geranyl diphosphate. Reaction with another molecule of isopentenyl diphosphate gives an important intermediate, farnesyl diphosphate (Figure 3.10). Two molecules of farnesyl phosphate give rise to triterpenic hydrocarbon squalene (3-81), which in the body of animals yields triterpenic alcohol lanosterol (3-92) and the triterpenic alcohol cycloartenol (3-93) in plants. 

In animals, six molecules of isoprenyl pyrophosphate are used to construct the hydrocarbon squalene, which contains a 24-carbon chain and six methyl substituents. Squalene, in... 

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