Octadecenoic acid, isomers

Figure 3. Surface pressure vs. area per molecule for some trans-octadecenoic acid isomers at 25° C...

Emken, E.A., Adlof, R.O., Rohwedder, W.K. and Gulley, R.M. (1989) Incorporation of trans-8- and ds-8-octadecenoic acid isomers in human plasma and lipoprotein lipids. Lipids, 24, 61-69. 

Wolff, R.L., D. Precht, B. Nasser, and M.S. El Kebbaj. Trans- and CA-Octadecenoic Acid Isomers in the Hump and Milk Lipids from Camelus dromedarius, Lipi 36 1175-1178 (2001). 

Emken, E.A., WK. Rohwedder, R.O. Adlof, W.J. Dejarlais, and R.M. Gulley, In Vivo Distribution and Turnover of trans- and m-lO-Octadecenoic Acid Isomers in Human... 

Selberg, K.T., Staples, C.R., and Badinga, L. (2002) Production and Metabolic Responses to Dietary Conjugated Linoleic Acid (CLA) and frani -Octadecenoic Acid Isomers in Periparturient Holstein Cows, J. Dairy Sci. 85 (Suppl. 1), 19-20 (Abstr.). 

The pyrrolidides of the remaining octadecenoic acid isomers also have distinctive spectra, but they do not fit the rule. The technique has been utilised with vicinal di-deuteriated monoethylenic compounds [49]. 

Odd numbered carbon branched and straight chain fatty acids (Q5, C17 and Qg), positional isomers of octadecenoic acid Fat from ruminant animals [5]... 

The methyl esters obtained are readily analysed qualitatively and quantitatively by gas chromatography, and the data obtained allow detection of sophistication. In the literature there is a wealth of fatty acid analysis data on virgin olive oils, all constantly reporting almost the same qualitative composition. However, what is surprising is the systematic attitude of so many researchers not reporting the presence of vaccenic acid, 11 -ds-octadecenoic acid, an isomer of oleic acid. The presence of this positional isomer of oleic acids was first described in olive oil by Tulloch and Craig (1964). 

The presence of Qg tram-fatty acids in milk fat is the result of incomplete biohydrogenation of the unsaturated dietary lipids in the rumen. These fatty acids have attracted attention because of their adverse nutritional affects. Clinical trials have shown that traus-octadecenoic acids, relative to the cis isomer, can increase the LDL-cholesterol and decrease the HDL-cholesterol, thus, producing an unfavourable affect on the LDL HDL ratio (Mensink and Katan, 1993). 

Piperova, L.S., Sampugna, J., Teter, B.B., Kalscheur, K.F., Yurawecz, M.P., Ku, Y., Morehouse, K.M., Erdman, R.A. 2002. Duodenal and milk trans octadecenoic acid and conjugated linoleic acid (CLA) isomers indicate that postabsorptive synthesis is the predominant source of cis-9-containing CLA in lactating dairy cows. J. Nutr. 132, 1235-1241. 

Body temperatures are approximately 37°C/ 98.6°F for humans 38.5-39.5°C/101-103°F) for domestic animals and 40.5-41.5°C/ 105—107°F) for poultry. As shown in Table 34.1, the longest saturated fatty acid that is fluid at these temperatures is caproic (Cl0 0). All longer saturated fatty acids must be accompanied by lower melting unsaturated fatty acids as in a TAG structure to be fluid. The C18 oleic acid (c-9-octadecenoic acid) has a melting point of 16.3°C, the trans isomer elaidic acid (t-9-octadecenoic acid) melts at 43.7°C, and the biohydrogenated product trans-vaccenic acid (t- 1-octacedenoic acid) melts at 44°C.40... 

The great variety of fatty acids in butter fat cannot be treated in detail here reference will be made to only a few of the many available reports. Octadecadienoic acids are present in significant amounts there are traces of hexadecadienoic acid, octadecatrienoic acids, and highly unsaturated C20 and C22 acids. Traces of dUiy-droxystearic acid and hydroxypalmitic acid have been detected (8, 9). A small proportion of the octadecenoic acid consists, not of oleic acid, but of trans-l 1,12 isomer, vaccenic acid (8, 9). One report states that about 66% of one octadecienoic... 

As is outlined in the following section, it is now apparent that endogenous synthesis of RA occurs in most, if not all, animal species. The classic studies of Mahfouz et al. (1980) and Pollard et al. (1980) showed independently that positional isomers of trans-octadecenoic acids are desaturated by the enzyme A-9 desaturase in rat liver microsomal systems. All tram monoenes, A-4 to A-13, except A-8, 9, and 10, were substrates, with products being trans-A-x, cis-9 dienes. The rate of A-9 desaturation increased as the trans bond was removed further from the A-9 position, so that trans-A-4 and A-13 monoenes were most rapidly desaturated (Mahfouz et al., 1980). The trans-5, cis-9 18 2 was isomerized rapidly to the cis, cis diene without changing bond positions tram-4, cis-9 18 2 was isomerized similarly, but at a slower rate (Mahfouz et al., 1980). Significant amounts of some of the cis/trans dienes were desaturated further at A-6, to yield cis, tram, cis trienes (Pollard et al., 1980). 

Two rather interesting racemic syntheses for allylic methylated fatty acids have been recently accomplished [15]. One of these corresponds to the intriguing (12 )-11-methyl-12-octadecenoic acid (6), a marine bacterial fatty acid that in most reported identifications from natural sources has been shown to have the E double bond stereochemistry, but both Z,E isomers have been synthesized [15]. This mainly bacterial fatty acid was initially isolated from Byrsocarpus coccineus seed oil [16], but later it was reported in a bacterium associated with cat scratch disease [17], in Mycobacterium fallax [18], and most recently in a Pseudomonas sp. (.Alteromonas) associated with both the toxic dinoflagellate Ostreopsis lenticularis and several Caribbean Palythoa species [15]. More recently, acid 6 has been identified as an intermediate in the biosynthesis of the bacterial acid 10,13-epoxy-l l-methyloctadeca-10,12-dienoic acid, a furan fatty acid identified in several marine bacteria such as Shewanella putrefaciens [19-20]. 

A novel two carbon analog of 8, namely the 7-methyl-6(Z)-octadecenoic acid was recently identified in the holothurian Holothuria mexicana [27]. However, both Z and E stereoisomers were later shown to originate from the bacterium Vibrio alginolyticus [27]. Therefore, the real source of 7-methyl-6-octadecenoic acid is also bacterial. Both Z and E isomers of 7-methyl-6-octadecenoic acid were synthesized as shown in Fig. (9). In this short synthesis (little more than one step) a Wittig coupling of (6-carboxyhexyl)triphenylphosphonium bromide with 2-tridecanone readily afforded a 1 1 mixture of 7-methyl-6(Z)-octadecenoic... 

The production requires 2 fermentations. In the first fermentation, lipase enzymes liberate the unsaturated fatty acids of flaxseed oil. During the first feraientation, the hydrolyzed fatty acids, linolenic acid, linoleic acid and oleic acid, are converted to (respectively) 10-hydroxy-12(Z),15(Z)-octadecadienoic acid, 10-hydroxy-12(Z)-octadecenoic acid and 10-hydroxydecanoic acid by Pseudomonas sp. NRRL-2994. Pseudomonas sp. produced stereochemically pure d (R)-isomers of each of the hydroxy fatty acids (>95.8%) 23) at a concentration of >12 g/L in the fermentation broth. The resulting hydroxy fatty acids were recovered by phase separation technique, and used for the second fermentation. 

The average monoenoic acid content of milk fat is around 30%. Oleic acid (cis-9-18 1) is the predominant monoenoic acid. It constitutes 95.8% of the positional cis isomers of octadecenoic acid. Monoenoic FA also comprise trans isomers, mainly trani-octadecenoic acids. Cow s milk fat contains 1.3 to 7.3% tra y-18 l acids, with an average of 3.7%. The relative proportions of trans-l8 l positional isomers in milk fat are given in Table 13.4. Trans-I6 l isomers occur in amounts of approximately 0.13% (Precht and Molkentin, 2000). 

Precht, D. and Molkentin, J. 1996. Rapid analysis of the isomers of frara-octadecenoic acid in milk fat, Int. Dairy J., 6, 791-809. 

Bore et al. [154] found that the structures of the Qg fatty acids of oily and dry hair differ. For subjects with dry hair, the predominant isomer is octadecenoic acid (oleic acid), whereas for subjects with oily hair 8-octadecenoic acid was the predominant isomer. Thus, oily hair is different from dry hair in its chemical composition and in its rheological character. 

The trans isomers of octadecenoic acid such as elaidic acid are known inhibitors of A6 desaturase. Elaidic acid is usually formed during the hardening process of vegetable oils. Unfortunately, this acid is considered to be a hypercho-lesterolemic fatty acid (14). Conjugated linoleic acid (CLA), found in dairy products, is a trans-cis isomer of octadeca-dienoic acid. CLA has been shown to downregulate the metabolism of LA (15,16). CLA also reduces production of eicosanoids in several tissues (Fig. 3). The 9c,lU-isomer of conjugated linoleic acid appears to inhibit, whereas the 10Ll2c-isomer stimulates eicosanoid production in human saphenous vein endothelial cells (16). 

Infrared analysis for trans-octadecenoic acid is a standard method (Report of the Spectroscopy Committee, 1959). Good quantitative results for the trans-isomers are possible by infrared analyses, and such analyses are done routinely by many laboratories. Kauffman and Lee (1960) found good agreement between the infrared analysis and the gas-liquid partition chromatographic analysis of methyl elaidate in hydrogenated vegetable oil... 

Autoxidation of linoleic acid gives rise to three isomers of trihydroxy-octadecenoic acid. The concentrations found in beer (Table 22.7) are higher than those found for linoleic acid itself [47]. All three acids are potential precursors of 2-trans-nonmdX which is an important component of the cardboard or paper flavour of stale beer. 

Ruminant depot and milk fats are characterized by their low level of unsaturation and by the presence of small amounts of trans acids resulting from rumen biohydrogenation (Section 10.1.3). The most common acid appears to be vaccenic (18 lilt) but other trans acids are also present. For example, butterfat contains ten octadecenoic acids (It through 16t) with the All isomer accounting for 72% of this group. Trans acids have been identified in human milk fat (2-4%), presumably arising from dietary trans acids (Section 3.4). 

As with lard, beef tallow contains significant levels of branched and odd-chain acids and also trans acids (Hoffman and Meijboom, 1969). Tabulated data presented here do not reflect the complexity of the fatty acids present in tallow. Trans-9, 10- and 11-octadecenoic acids (5% total) have been reported. Similarly trans isomers occur in the dienoic series of... 

A number of specific tmns and cis octadecenoic acids and/or their methyl esters are available from Sigma Inc. (St. Louis, MO). A complete mixture of all the trans and cis isomers of 16 1, 18 1 and 20 1 can be obtained by isolating larger amounts of the trans and cis fractions from total milk fats by Ag -TLC as described below. We generally use these mixtures as qualitative standards for the identification of mono cis and trans isomers. 

Piperova, L.S., J. Sampugna, B.B. Teter, K.F. Kalscheur, M.P Yurawecz, Y. Ku, K.M. Morehouse, and R.A. Erdman. Duodenal and Milk Trans Octadecenoic Acid and Conjugated Linoleic Acid (CLA) Isomers Indicate that Postabsorptive Synthesis is the Predominant Source of Cw-9-Containing CLA in Lactating Dairy Cows. J. Nutr. 132 1235-1241 (2002). 

Precht, D. and J. Molkentin. Rapid Analysis of the Isomers of Thrw-Octadecenoic Acid in... 

Precht, D. andj. Molkentin. Effect of Feeding on 7)a rPositional Isomers of Octadecenoic Acid in Milk Fats, Milchwissenschaft 52 564—568 (1997). 

Katz and Keeney (8) identified an array of trans octadecenoic acids in cows milk with the trans- - being the most abundant isomer and all the isomers from positions 4 to 16 being observed. Parodi (9) identified cis-9, 1-18 2 in milk fat... 

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