Polyenoic acid derivation

The polyenoic acids derived from linoleic or a-linolenic acid are prominent components of testicular tissue of various animals. 

Dietary factors affecting the fatty acid composition of and metabolism in rat testes include a fat-free diet, which results in testicular accumulation of 20 3n-9 and loss of 18 2, 20 4 and 22 5 (all n-6) and increased activity of acetyl CoA carboxylase various dietary oils, such as cod liver oil and rapeseed oil, which result in testicular accumulation of the n-3 polyenoic acid derivatives of a-linolenic acid feeding a vitamin E-deficient diet, which results in a decreased concentration of 22 5n-6 and increased concen-... 

Schnurr et al. [22] showed that rabbit 15-LOX oxidized beef heart submitochondrial particles to form phospholipid-bound hydroperoxy- and keto-polyenoic fatty acids and induced the oxidative modification of membrane proteins. It was also found that the total oxygen uptake significantly exceeded the formation of oxygenated polyenoic acids supposedly due to the formation of hydroxyl radicals by the reaction of ubiquinone with lipid 15-LOX-derived hydroperoxides. However, it is impossible to agree with this proposal because it is known for a long time [23] that quinones cannot catalyze the formation of hydroxyl radicals by the Fenton reaction. Oxidation of intracellular unsaturated acids (for example, linoleic and arachidonic acids) by lipoxygenases can be suppressed by fatty acid binding proteins [24]. 

Cw-polyenoic acids are present at low concentrations in milk fat, because of the biohydrogenation reactions that take place in the rumen. These acids are comprised almost exclusively of linoleic acid (9c, 12c-18 2), about 1.2 to 1.7% and a-linolenic acid (9c, 12c, 15c-18 3), about 0.9 to 1.2% (Table 1.2). These two fatty acids are essential fatty acids they cannot be synthesised within the body and must be supplied by the diet. In recent times, the usage of the term essential has been extended to include derivatives of these fatty acids, which are not synthesised in significant quantities (e.g., eicosapentaenoic acid, 20 5 and docosahexaenoic acid, 22 6). The proportion of a-linolenic acid appears to be affected by the cow s diet the concentration is higher in milk from pasture-fed cows than in milk from barn-fed cows (Hebeisen et al., 1993 Wolff et al., 1995). In the case of linoleic... 

Harvey, D.J. (1984) Picolinyl Derivatives for the Structural Determination of Fatty Acids by Mass Spectrometry Applications to Polyenoic Acids, Hydroxy Acids, Di-Acids and Related Compounds, Biomed. Mass Spectrom. 11,340-347. 

The adult brain contains high levels of polyenoic fatty acids deriving from linoleic (18 2 A9,12 n-6) and from linolenic acid... 

Similarly, epoxides are also formed during the reaction of olefins with hydrogen peroxide. Secondary reactions of oxidised polyenoic acids produce red-coloured cyclopentane derivatives (3-137) causing adverse colour changes to stored fish. 

Eicosanoids These compounds, derived from eicosa- (20-carbon) polyenoic fatty acids, comprise the prostanoids, leukotrienes (LTs), and lipoxins (LXs). Prostanoids include prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (TXs). 

Certain long-chain unsaturated fatty acids of metabolic significance in mammals are shown in Figure 23-1. Other C20, C22, and C24 polyenoic fatty acids may be derived from oleic, linoleic, and a-flnolenic acids by chain elongation. Palmitoleic and oleic acids are not essential in the diet because the tissues can introduce a double bond at the position of a saturated fatty acid. 

Normally, the method of choice for the analysis of complex mixtures of polyenoic fatty acids such as those derived from fish oils is capillary gas chromatography with prechromato-graphic derivatization and mass spectrometric detection. However, GC is impractical for the purification of the large amounts of polyenoic fatty acids required for biological and clinical studies. Moreover, the temperatures required in GC may cause degradation of oxidized long-chain polyunsaturated fatty acids that are present as minor components of the mixture. 

The preparation and handling of the fluorescent phospholipid derivatives is cumbersome, however. Special care has to be taken to prevent degradation of the polyenoic fatty acid. Furthermore, most spectroscopic techniques require calibration to equate the spectral changes with the amount of lipid transfer. It is also important to know whether the rate of transfer of this and other fluorescent and spin-labeled phospholipids is comparable to the transfer rate of more physiological phospholipid molecules. 

The C20- and C22-polyenoic fatty acids occurring in tissue phosphatides of higher animals are derived mainly from linoleic and linolenic acid by chain elongation and introduction of new double bonds (Fig. 1), main-... 

A wide choice of stationary phases is available for separation, such as reversed-phase or silver-ion impregnated phases. The separation of phenacyl derivatives of saturated, monoenoic, polyenoic, and monohydroxy fatty acids, and of the geometric isomers of fatty acids is possible. 

An accumulation of esterified hydro(pero)xy-polyenoic fatty acids in the storage lipids during germination has also been observed with some other oil-seeds (soybean, sunflower, anise, tobacco and rape [62,64]). Soybean seeds differ from the others in that lipoxygenase-derived oxygenated fatty acids are already present in the dry seeds [62]. 

The essentialness of a-linolenic acid and of its longer derivatives EPA or DHA is supported by experiments in animals and observations in young patients. In infant rhesus monkeys after a diet deficient in co-3 fatty acids a visual loss could be observed [21]. In 1982 Holman et al. [15] described the case of a 6-year-old girl with a-linolenic acid deficiency. She experienced distal numbness and paresthesias, weakness, periodic inability to walk, and blurring of vision. The authors suggest that a-linolenic acid respectively co-3-polyenoic fatty acids are required for normal nerve function, at least in growing individuals. Meanwhile co-3 fatty acid deficiency could be observed in five adults, documented by biochemical changes of fatty acid composition, but not by clinical symptoms [3,22]. In a 90-year-old female with a-linolenic acid deficiency, the effects of ethyl a-linolenate on biosynthesis of prostanoids could be demonstrated [4]. 

The developing brain accumulates long-chain (C20 and C22) polyenoic fatty acids, particularly during cell division (Crawford Sinclair, 1972 Sinclair Crawford, 1972). Vz novo synthesis of these acids does not occur in higher animals and they are derived either directly from food or by metabolism from the parent essential fatty acids, linoleate and a-linolenate. 

Retention data for all the Isomeric methyl oxostearates were recorded by Tulloch [926], and the elution pattern resembles that described above for the corresponding acetoxy derivatives. GC retention data for some conjugated polyenoic fatty acids with keto groups in position 4 have been recorded [334]. 

Hydroperoxides of polyenoic fatty acids with three or more double bonds in the molecule, which have a system of conjugated double bonds in position p to hydroperoxide group, are very unstable compounds. They tend to form more stable cyclic six-membered peroxides derived from 1,2-dioxane by 1,4-cyclisation, five-membered peroxides derived from 1,2-dioxolane by 1,3-cyclisation and endoperoxides. 

Dimerization.—Unsaturated acids, whether monoenoic or polyenoic, furnish dimers which are in demand because of the valuable surface-active properties of their various derivatives. Methods of dimerization have therefore been extensively examined, but understanding of the reaction and the structural identification of the products have lagged behind. Dimerization is effected in several ways but clay catalysts are the most widely employed, and it is now recognized that such catalysts operate in several ways. They may promote modification of monoenoic and dienoic acids to more reactive monomers in addition to assisting both the dimerization process and the subsequent changes in the dimer molecules. In particular, hydrogen transfer seems to be important monoenoic acids are thereby converted to more reactive dienoic acids and the dimer (probably a cyclohexene derivative resulting from Diels-Alder reaction) is converted to a substituted aromatic compound. ... 

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