Anteiso-acids

Many substituted, ie, branched, fatty acids, particularly methacryUc, 2-ethylhexanoic, and ricinoleic acids, are commercially significant. Several substituted fatty acids exist naturally (Table 5). Fatty acids with a methyl group in the penultimate position are called iso acids, and those with a methyl group in the antepenultimate position are called anteiso acids (1) (see Carboxylic acids, branched-CHAIN acids). However, the term iso is often used in a broader sense to mean branched or mixtures of branched-chain industrial acids. 

Antarctic polar stratospheric clouds, effect on ozone depletion, 17 788-789 Anteiso acids, 5 28 Antenna effect, 8 263... 

Wool (anhydrous lanolin) 36-42 Cholesteryl estolidic esters, alcohol esters of iso- and anteiso acids... 

Anteiso acids are branched at the (co - 2) position, e.g., anteisopalmitic acid = H3CCH2CH(CH3) (CH2) C00H. 

These branched acids can be source-specific and they are rarely unsaturated. They are formed by the incorporation of branched amino acids into the biosynthetic pathway, yielding iso and anteiso acids, as noted in Section 5.1.3. Iso and anteiso saturated fatty acids are found in fungi, molluscs and phytoplankton, but they are generally in higher levels in bacteria and are often observed in the C13—C17 range (Harwood Russell 1984).The C15 isomers (Fig. 5.1) are usually particularly abundant in bacteria and the ratio (iso + anteiso)/normal derived from C15 components can be used as an indication of relative bacterial contributions (Parkes Taylor 1983). Similarly, the (08 isomers of /. >- 5 1 and iso-17 1 are bacterial markers (Perry et al. 1979), and iso-17 1(07 is characteristically a major fatty acid in the sulphate-reducing bacteria Desulfovibrio desulfuricans (Taylor Parkes 1983). 

PCA of fatty acid and lipid class data for net-tows and traps from various stations consistently showed total lipids and 16 0 grouping together reflecting the ubiquity of this acid in acyl lipids. 15 0 and iso + anteiso acids always grouped... 

Iso and anteiso acids occur widely in animal fats and waxes (where they are sometimes major components) and in the lipids of some micro-organisms. The iso and anteiso acids usually have a total number of even and odd carbon atoms respectively and the anteiso acids are generally dextrorotatory with absolute configuration l(5). They are thought to result from a modification of the normal de novo pathway in which the usual starter acetate molecule is replaced by 2-methylpropanoate or 2-methylbutanoate ... 

New acids identified among the polyene acids in Norwegian spruce include three unsaturated anteiso acids (5,9 9,12 5,9,12)... 

Recent investigations have shown that these iso- and anteiso acids also occur in yellow-white leaves of the plastome mutant "Xanthi" of Nicotiana tabacum. The fatty acids were detected in the phosphatides of both plants and make up for 16-24 per cent of the fatty acids of the phospholipids. Phospholipids are known to be functional components of the lipid matrix of the cell membrane as well as of membranes of various cell organelles which allow biological activity in cooperation with other membrane components. ... 

The fatty acid content is given as per cent of the total fatty acid content of the respective phospholipids. The iso-acids were identified by their retentions times in GLC to have the following chain lengths lO-methyl-undecanoic acid (iso-lauric) 12-methyl-tridecanoic acid (iso-iayristic)j 14-methyl-pentadecanoic acid (iso-palmitic) 16-methyl-heptadecanoic acid (iso-stearic) 20-methyl-heneicosanoic acid (iso-behenic). The anteiso-acids were 12-me-thyl-tetradecanoic acid 14-methyl-hexadecanoic-acid 16-methyl-octadecanoic acid 19-methyl-heneicosanoic acid. 

Q acids respectively. Iso-acids have an even number of carbon atoms, anteiso-acids have an odd number. The two unsaturated anteiso-compounds are part of the sex pheromone of some Trogoderma species... 

Branched fatty acids, known as iso-acids and anteiso-acids, occur normally in small quantities in fats. Their synthesis begins with the amino-acids valine and isoleucine (Figure 3.12). This has been demonstrated with radio-labelled isotopes, by radio-active monitoring and with stable isotopes by C nuclear magnetic resonance spectroscopy or mass spectrometry. Both isobutyric acid and 2-methylbutyric acid are common defensive compounds among insects. Note that a chiral centre is introduced in 2-methylbutyric acid and anteiso acids. 

Figure 3.17 The formation of 2-methylalkanes and 3-methylalkanes. The latter can be formed in two alternative ways, starting from an anteiso-acid, or from a straight chain acid by insertion of a propionic acid unit later...

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