Methylene interrupted double bond

The unsaturated fatty acids may have one double bond (monosatu-rated) or have more than one cis-methylene interrupted double bond (polyunsaturated) as illustrated in Fig. 4.1. 

In general, the migration order of any lipid class is determined by the overall number of double bonds in the molecule. Thus the retention of common fatty acids (chain lengths of 16-22 carbon atoms, methylene interrupted double bonds) increases with increasing number of double... 

Methylene interrupted double bonds Due to the fatty acid elongation process during their synthesis, the double bonds are separated by one methylene group (spaced by three carbons)... 

On the other hand, MDA has been measured in plasma and urine. Because of its relative ease of colorimetric measurement, it is the most widely investigated product of peroxidation (J9). It is largely a product of PUFA with more than two methylene-interrupted double bonds such as arachidonic acid and docosahexaenoic acid. These possess at least three double bonds (C=C—C—C=CCC=C) so that they can more easily be broken down into the small 3-carbon, dicarbonyl MDA than can linoleic acid, which contains only one activated double bond (J2, J9). 

The catalyst is compatible with a variety of functional groups including aldehydes, esters, nitriles, ketones, lactones, ethers, and methylene-interrupted double bonds. 

Prostaglandins are biosynthesised from certain Cjo straight chain fatty acids which have a system of methylene-interrupted double bonds. Thus PGEj, PGEj and PGEj are derived from all-cj5-8,ll,I4-eicosatrienoic (dihomo-y-linolenic) 5,8,1 l,14-eicosatetraenoic (arachidonic) and 5,8,11,14, 17-eicosapentaenoic acids respectively (Figure 7.3) [62, 73-75]. 

This reaction was initially reported by Grundmann in 1936. It is the conversion of acyl chloride into aldehyde with the exact same carbon skeleton via the following consecutive steps a) treatment of acyl chloride with diazomethane to form a ketone, (b) conversion of such a ketone into ketol acetate with acetic acid, (c) reduction of ketol acetate with aluminum isopropylate, and d) hydrolysis and oxidation with lead tetraacetate. This method is especially useful in the preparation of aliphatic aldehydes with methylene-interrupted double bond(s). Although polymers might form in the preparation of highly unsaturated aldehydes during the reduction with aluminum isopropylate, the reduction from lithium aluminum hydride can eliminate such drawbacks. ... 

Acetonitrile, when used as a reagent for chemical ionization in a bench top ion trap mass spectrometer, has been shown to provide complete information on double bond positions in homoallylic (i.e., methylene-interrupted double bonds) unsaturated fatty acid methyl esters (FAME) (4-6). The m/z 54 ion (l-methyleneimino)-l-ethenylium (MIE) is formed from acetonitrile in the ion trap (7) and covalently adds across C-C double bonds of FAME. Isolation and collisional dissociation (i.e., MS/ MS) of the resulting [M+54] " ion yields fragments that are indicative of the location of the added MIE in the parent, and allows unambiguous assignment of double bond position. As MIE adds to any of the C-C double bonds, more fragments are observed... 

The activity of the microbial isomerase or isomerases (Fig. 1.1.) is key to the production of CLA. An isomerase is solely responsible for movement of the methylene-interrupted double bonds in hnoleic and linolenic adds to conjugated positions. Subsequent action of a reductase reduces or eliminates double bonds, but serves no function in rearrangement of double bonds to conjugated positions. Thus, it is the study and regulation of the isomerases that is needed to maximize the quantity of specific CLA isomers. 

The metabohtes isolated from rats fed a fat-free diet and force-fed a commercial CLA containing a mixture of isomers were examined as the DMOX derivatives (79,80). The structures of 8,11,13-20 3 (derived from 9,11-18 2) (79), and 8,12,14-20 3 and 5,8,12,14-20 4 (derived from 10,12-18 2) (80) acids were readily determined by using the 12 amu rule. For example, the molecular ion for the DMOX derivative of 8,12,14-20 3 was at m/z 359, and gaps of 12 amu between tn/z 182 and 194, 236 and 248, and 262 and 274 located the double bonds at C-8, C-12 and C-14, respectively. The base peak at m/z 222 was due to cleavage between C-10 and C-11, i.e., at the center of the bw-methylene-interrupted double bond system. Analogous intense ions are characteristic of other fatty acids with similar systems (59)... 

The presence of conjugated double bond systems in the alkyl chain increases the retention time of an ester considerably over that of a similar compound with methylene-interrupted double bonds. Methyl 9-c/s,11-frans-octadecadienoate, for example, is a common minor constituent of ruminant and other tissues and has ECL values of 20.48 on EGSS-X and 20.24 on EGSS-Y , i.e. appreciably greater than the corresponding values for methyl linoleate [161]. In addition, the configuration of the double... 

An isolated triple bond has a similar effect on the retention characteristics of a fatty acid as three methylene-interrupted double bonds, and methyl stearolate (methyl octadec-9-ynoate) is eluted with or slightly after methyl linolenate on columns packed with DEGS [333] or PEGA [620]. Retention data on several different stationary phases have been published for the complete series of methyl octadecynoates (i.e. in positions 2 to 17) [85,323], The ECL values tend to be parallel to those of the corresponding frans-monoene isomers, but differing by 0.6 to 0.7 units on DEGS and 0.1 to 0.2 units on... 

The procedure can be scaled up for polyunsaturated fatty acids, but the proportion of water to terf-butanol should be kept as close to 2 1 (vA/) as possible. Malonic acid, formed by oxidation of methylene-interrupted double bonds, is oxidised further and is not detected. Ambiguity may result when polyunsaturated fatty acids with more than one methylene group between the double bonds are oxidised, as it is then not possible to state which dibasic fragment contained the original carboxyl group. However, this difficulty can be resolved by reducing the carboxyl group to an alcohol prior to the analysis [329]. 

With oxidative ozonolysis, standards are freely available for identification purposes. The procedure has been applied successfully to monoenoic fatty acids [12] and, with some modification, to polyunsaturated fatty acids with other than methylene-interrupted double bonds [26,756],... 

Fatty acids with two isolated double bonds separated by one methylene group (methylene interrupted double bonds) are very important in nutrition. Theoretically, there should be far more of these acids than of monoenoic fatty acids in natural lipids, but only a few are found in significant amounts (Table 3.3). The most important dienoic acid is linoleic acid (3-7). Again, positional as well as geometric isomers of polyenoic fatty acids exist. For example, linoleic acid is a 9cis, 12ds-isomer, that is, a 9-cis, 12-cis-isomer... 

Conjugated linoleic acid (CLA) is the collective name given to a group of Cj positional and geometric isomers containing two conjugated double bonds, rather than the more common methylene-interrupted double bond sequence. An example of one such isomer is shown in Figure 1. 

The essential fatty acids (EFA) are long-chain unsaturated lipids so named as they are essential to the diet of mammals and cannot be synthesized de novo as are all other lipids. There are two major EFAs, both of co-6 configuration (denoting the position of the first methylene-interrupted double bond, numbered from the methyl end of the chain) and their structures are shown in Figure 2.1. Linoleic acid is the most common EFA, and arachidonic acid is a chain elongation product of it. 

Chemically, PUFAs are fatty acids containing two or more methylene-interrupted double bonds in their structure. The configuration of the double bonds in many naturally occurring unsaturated fatty acids is Z. These compounds are also referred to as cw-fatty acids or all-cA fatty acids. PUFAs containing E-configured double bonds also occur naturally. These so-called trans-fmy acids have been isolated from bovine fat and the milk of cow, goat, and ewe [15], There are four families of PUFAs, namely, the (0-9, (0-7, (0-6, and (0-3 PUFAs. Oleic acid (2) is the precursor for the (0-9 family, and palmitoleic acid (3) is the precursor... 

PUFAs can be used in their own right as starting material for the semisynthesis of more complex members of the PUFA family. A particular advantage using this approach is the conservation of the methylene-interrupted double bonds throughout the synthesis and to be present in the final product. 

Joh, Y.-G., Elenkov, I.J., Stefanov, K.L., Popov, S.S., Dobson, G., and Christie, W.W. (1997) Novel di-, tri-, and tetraenoic fatty adds with is-methylene-interrupted double-bond systems from the sponge Halidona anerea. Lipids, 32,13—17. 

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