Branched-chain acids cyclopropane

Familial adenomatous polyposis 574 Faraday, numerical value of 283 Farnesyl group 402, 559 Fat(s). See also Triacylglycerol (triglyceride) composition of 380 hydrolysis of 507 Fatty acid(s) 380-382 activation of 512 acyl CoA, derivatives of 507 biosynthesis of 722 branched chain 381 cyclopropane-containing 399 essential 721 in lipids 380 names of, table 380 oxidation 511 pKa values of 380 stability of 589... 

NMR evidence indicates that the electroactive species is the protonated carboxylic acid. With branched chain acids the carbocation, formed similarly to that obtained in the alkane oxidation, will be a tertiary one and a single product is obtained. With straight-chain carboxylic acids the carbocation is formed at several positions of the carbon skeleton, and it will rearrange possibly by cyclopropane formation to form a stable tertiary carbocation (equation 18). The a,j5-unsaturated ketone will be formed by slow loss of the HSO3F group with the formation of a double bond and subsequent cyclization of the protonated acid. 

With the advent of gas chromatography the analysis of fatty acids has become a relatively routine task. As a consequence, the fatty adds of a wide variety of bacteria have been analyzed and some correlations with taxonomic classification have become clear. It should be pointed out that fatty acids, as free fatty acids, constitute only a small proportion of the lipids of both the Gram-negative and Gram-positive eubac-teria. For instance, in E. coU, Azotobacter agilis, and Agrobacterium tumefaciens, the free fatty acid content is less than 10% of the total lipid (Kaneshiro and Marr, 1961), while in Sarcina lutea it is 2.1% (Huston et al., 1965). Most analyses of die bacterial fatty adds have been performed on the total fatty adds obtained by hydrolysis of flie total hpid. Four general classes of fatty acid have been found in the eubacteria saturated and unsaturated fatty acids, and branched-chain and cyclopropane fatty adds. 

In addition to unsaturated fatty acids, several other modified fatty acids are found in nature. Microorganisms, for example, often contain branched-chain fatty acids, such as tuberculostearic acid (Figure 8.2). When these fatty acids are incorporated in membranes, the methyl group constitutes a local structural perturbation in a manner similar to the double bonds in unsaturated fatty acids (see Chapter 9). Some bacteria also synthesize fatty acids containing cyclic structures such as cyclopropane, cyclopropene, and even cyclopentane rings. 

A genus of bacteria, termed the Sphingobacterium, produces sphingolipids by a pathway similar to that in mammals. Clostridia produce plasmalogens (l-alk-l -enyl lipids) by an anaerobic pathway clearly different from the Oj-dependent pathway in mammals (Chapter 9). Branched-chain fatty acids are also found in which the methyl group is inserted post-synthetically into the middle of the chain, in a manner analogous to cyclopropane fatty acid synthesis (Section 5.5). S-adenosylmethionine is also the methyl donor for these reactions. The biochemistry surrounding the formation of these and many other bacterial phospholipids remains to be elucidated. 

Oxirans - The use of pyranose epoxides in the preparation of sugar amino acids and peptides, aminodeoxy, halodeoxy, branched-chain, cyclopropanated and aziridino sugars has been reviewed. ... 

Last, it should be pointed out that no information exists on the influence of fatty acid structure on its micellar solubility in bile acid solutions. It would be of interest to compare branched-chain fatty acids, cyclopropane fatty acids, hydroxy fatty acids, etc. 

Fatty acids in the 12-20 carbon chain-length range account for the majority of bacterial fatty acids. These are usually saturated or monounsaturated polyunsaturated fatty acids only occur in a few species, such as the gliding bacteria which accumulate large amounts of arachidonate (Fautz et al., 1979) or cyanobacteria which contain linoleate and linolenate. Reports of polyunsaturated fatty acids in bacteria should be treated with scepticism because of the ease with which bacteria can take up growth constituents which can include polyunsaturates. Besides the ubiquitous even-chain saturated and unsaturated fatty acids bacteria characteristically contain odd-chain and branched fatty acids as well as 3-hydroxy-and cyclopropane derivatives. These fatty acids are present in lipopolysaccharide, cell wall lipoprotein and lippteichoic acid as well as membrane glycerolipids (Table 3.209). 

Abel et al. (1963) have suggested that the fatty acid composition of a particular microorganism might be a useful tool to aid in the classification of the organism. While there is no doubt that there may be some merit to this idea, their study aptly points out the complications to such an approach. First, it is quite clear that a number of their tentative assignments of fatty acid structures are incorrect. For example, the presence of major amounts of cyclopropane fatty acids in E. coli reported by a number of workers (Dauchy and Asselineau, 1960 Kaneshiro and Marr, 1961) is completely overlooked. Branched-chain fatty acids in various species of Bacillus and Micrococcus are also ignored. These errors illustrate the fact that fatty acid identification by gas-liquid chromatography, without ancillary analysis by independent... 

Various amino acids containing a cyclopropyl residue have been found in members of the Sapindaceae, Hippocastanaceae and Aceraceae. The same plants often contain a range of Q- and Cz-amino acids, with a non-cyclic branched carbon skeleton. The position of branching suggests possible bio-genetic relationships to cyclopropane-containing amino acids. Variation of the basic structures mentioned in Fig. 3.22 is achieved by different chain lengths and by the introduction of double and triple bonds (Fowden, 1981). 

The profiles of cellular FA also appear to be valuable in taxonomic studies on microorganisms [370,371]. In the method of Moss and Dees [371], the whole cells are saponified, with a subsequent derivatization and GC to determine more or less characteristic profiles of the straight-chain, branched, cyclopropane and hydroxy acids. Numerous applications of GC in clinical microbiology have been reviewed in a book by Mitruka [372]. 

Secondary fatty acids may differ from common fatty acids in chain length, additional fimctional groups, e.g., hydroxy and hydroperoxy groups, or other structural elements (branches in the carbon chain, presence of cyclopropane or cyclopentene rings, etc.) (D 3.2). 

Witten et al. (1973) identified adipic and 3-methyladipic acids and also reported the presence in urine, using GC-MS, of aconitic and isocitric acids in addition to citrate. Mamer et al, (1971) reported the occurrence of several hydroxyaliphatic acids in addition to those already identified by other workers, and Mamer and Tjoa have identified 2-ethylhydracrylic acid in urine derived from isoleucine metabolism (Mamer and Tjoa, 1974). Urine from healthy children and adults may contain low amounts of aliphatic dicarboxylic acids of chain length C4-C8 (Lawson et ai, 1976). Pettersen and Stokke (1973) reported a series of 3-methyl-branched C4-C8 dicarboxylic acids in urine from normal subjects, and Lindstedt and co-workers have identified other dicarboxylic acids with cyclopropane rings and acetylenic bonds as well as a series of cis and trans mono-unsaturated aliphatic dicarboxylic acids (Lindstedt et al., 1974,1976 Lindstedt and Steen, 1975). 

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