Methyl-branched acids

The lipid moiety of the glycolipids under consideration is either composed of branched-chain fatty acids (for example, mycolic acids in cord factor and in wax D) or can be a wax formed by the union of a phenolic alcohol with branched-chain fatty acids of the mycocerosic acid type, as in mycosides A and B. In the phosphoglycolipids, simple normal fatty acids have been found, accompanied by some methyl branched acids. 

Dimer acid, trimer acid, and small amounts of higher polymers are formed when tall oil fatty acid is treated with an active clay (37). In the same process, part of the fatty acid is isomerized to methyl-branched acids. These can be hydrogenated to produce a mixture of isostearic and stearic acids, which can be separated by a solvent crystallization process. Dimer acids are separated from trimers by thin-film or molecular distillation. 

Several alkyl-branched fatty acids were found to be powerful and characteristic food flavors. 2-Methylbutyric acid is an important constituent of the aroma of cranberry Vaccinium vitis-idaea L.) (77). 3-Methyl-valeric acid and isovaleric acid were identified in tobacco leaves and found to contribute to the distinct sensory properties of Turkish tobacco smoke 590). Isovaleric acid, which has the lowest flavor threshold (0.7 ppm) 522) of all saturated fatty acids, is regarded as an essential flavor component of Limburger cheese (575). ( )-3-Methyl-2-hexenoic acid was recognized as the malodorous component of schizophrenics sweat (579). The undesirable odor of mutton can be attributed to branched-chain and unsaturated fatty acids having 8 to 10 carbon atoms. The 4-methyl-branched acids and in particular 4-methyloctanoic and 4-methyl-... 

Biosynthetic studies using acetate (Ac), propionate (Pr), and butyrate (Bu) revealed the polyketide nature of aurodox which has the composition Pr(Ac)g for the goldinamine skeleton C-7 to C-25 and the composition Bu(Ac) for the C-27 to C-39 carbon chain of goldinonic acid. In contrast to the methyl branch at C-8, those at C-19 and C-21 are methionine-derived as are all remaining methyl groups (52,53). The biogenetic origin of the pyridone moiety is not clear. 

Carbonylation, or the Koch reaction, can be represented by the same equation as for hydrocarboxylation. The catalyst is H2SO4. A mixture of C-19 dicarboxyhc acids results due to extensive isomerization of the double bond. Methyl-branched isomers are formed by rearrangement of the intermediate carbonium ions. Reaction of oleic acid with carbon monoxide at 4.6 MPa (45 atm) using 97% sulfuric acid gives an 83% yield of the C-19 dicarboxyhc acid (82). Further optimization of the reaction has been reported along with physical data of the various C-19 dibasic acids produced. The mixture of C-19 acids was found to contain approximately 25% secondary carboxyl and 75% tertiary carboxyl groups. As expected, the tertiary carboxyl was found to be very difficult to esterify (80,83). 

FIGURE 9.1 GC/MS of total methyl esters of fatty acids standards and single fractions after PLC. Abbreviations first number (18 or 20) = number of carbon atoms in the chain second number (0 to 5) = number of double bounds n = normal chain i =isoacid ai = anteisoacid m-br =multi-branched acid. (From Rezanka, T., J. Chromatogr. A, 727, 147-152, 1996. With permission.)... 

Duran, E., Komuniecki, R.W., Komuniecki, P.R., Wheelock, M.J., Klingbeil, M.M., Ma, Y.C. and Johnson, K.R. (1993) Characterization of cDNA clones for the 2-methyl branched-chain enoyl-CoA reductase. An enzyme involved in branched-chain fatty acid synthesis in anaerobic mitochondria of the parasitic nematode Ascaris suum. Journal of Biological Chemistry 268, 22391—22396. 

One of the sex pheromone components of the housefly, Musca domestica, is Z9-21 H that is found on the cuticular surface of the fly. This compound is formed by the elongation of Z9-18 CoA using malonyl-CoA and NADPH to Z15-24 CoA which is decarboxylated to form Z9-21 Hc (Fig. 3) [78-80]. Other pheromone components include an epoxide and ketone that are produced from Z9-21 Hc by a cytochrome P450 [81,82] and methyl-branched alkanes that are produced by the substitution of methylmalonyl-CoA in place of malonyl-CoA at specific points during chain elongation [83,84]. A novel microsomal fatty acid synthase is involved in production of methyl-branched alkanes in most insects [85-87]. This fatty acid synthase is different from the ubiquitous soluble fatty acid synthase that produces saturated straight chain fatty acids in that it is found in the microsomes and prefers methylmalonyl-CoA. The amino acids valine and isoleucine can provide the carbon skeletons for methylmalonyl-CoA as well as propionate [83]. 

Table I gives the compositions of alkylates produced with various acidic catalysts. The product distribution is similar for a variety of acidic catalysts, both solid and liquid, and over a wide range of process conditions. Typically, alkylate is a mixture of methyl-branched alkanes with a high content of isooctanes. Almost all the compounds have tertiary carbon atoms only very few have quaternary carbon atoms or are non-branched. Alkylate contains not only the primary products, trimethylpentanes, but also dimethylhexanes, sometimes methylheptanes, and a considerable amount of isopentane, isohexanes, isoheptanes and hydrocarbons with nine or more carbon atoms. The complexity of the product illustrates that no simple and straightforward single-step mechanism is operative rather, the reaction involves a set of parallel and consecutive reaction steps, with the importance of the individual steps differing markedly from one catalyst to another. To arrive at this complex product distribution from two simple molecules such as isobutane and butene, reaction steps such as isomerization, oligomerization, (3-scission, and hydride transfer have to be involved.

Given the absence of methyl branches and according to the suggestive positions of the double bonds within the two acyclic C1 hydrocarbons undeca-(l,3E,52)-triene and undeca-(l,3E,5Z,8Z)-tetraene, their origin from fatty acids is highly probable. In the case of higher plants, the... 

P. E. Sonnet, M. W. Baillargeon, Methyl-Branched Octanoic Acids as Substrates for Lipase-Catalyzed Reactions , Lipids 1991, 26, 295-300. 

Valine (Val or V) ((5)-2-amino-3-methyl-butanoic acid) is a nonpolar, neutral, aliphatic amino acid with the formula HOOCCH(NH2)CH(CH3)2. Along with Leu and He, Val is a branched-chain amino acid and is found in high concentrations in the muscles. Val is needed for muscle metabolism and coordination, tissue repair, and for the maintenance of proper nitrogen balance in the body. ° The steric hindrance present in Val and He (caused by branching) lowers the rate of coupling reactions, resulting in an increase in side reactions. ... 

Oxidation is used to break down methyl-branched fatty acids. It takes place through step-by-step removal of Ci residues, begins with a hydroxylation, does not require coenzyme A, and does not produce any ATP. 

Enzyme defects are also known to exist in the minor pathways of fatty acid degradation. In Refsum disease, the methyl-branched phytanic acid (obtained from vegetable foods) cannot be degraded by a-oxidation. In Zellweger syndrome, a peroxisomal defect means that long-chain fatty acids cannot be degraded. 

Another route to a methyl-branched derivative makes use of reductive cleavage of spiro epoxides ( ). The realization of this process was tested in the monosaccharide series. Hittig olefination of was used to form the exocyclic methylene compound 48. This sugar contains an inherent allyl alcohol fragmenC the chiral C-4 alcohol function of which should be idealy suited to determine the chirality of the epoxide to be formed by the Sharpless method. With tert-butvl hydroperoxide, titanium tetraisopropoxide and (-)-tartrate (for a "like mode" process) no reaction occured. After a number of attempts, the Sharpless method was abandoned and extended back to the well-established m-chloroperoxybenzoic acid epoxida-tion. The (3 )-epoxide was obtained stereospecifically in excellent yield (83%rT and this could be readily reduced to give the D-ribo compound 50. The exclusive formation of 49 is unexpected and may be associated with a strong ster chemical induction by the chiral centers at C-1, C-4, and C-5. 

The acyl-Co A dehydrogenases are a family of mitochondrial flavoenzymes involved in fatty acid and branched chain amino-acid metabolism. In addition to long chain acyl-Co A dehydrogenases (LCADs), there are short/ branched chain acyl-CoA dehydrogenase (SBCAD) that act on 2-methyl branched chain acyl-CoA substrates of varying chain lengths. 

Several F-labeled fatty acid derivatives have been successfully prepared and evaluated as potential FAO assessing tracers [19-24]. Methyl-branched-chain (w- F-fluorofatty acids, such as 3-methyl-(3-MFHA) and 5-methyl-17-[ F]fluoro-heptadecanoic acid (5-MFHA), have been reported [23]. In a comparative study, it was found that rw-[ F]fluoropalmitic acid (FPA) exhibits the highest myocardial uptake, followed by 5-MFHA and 3-MFHA. FPA possesses the fastest myocardial washout rate, and 3-MFHA the slowest. In lipid analysis studies, 5-MFHA... 

M.M. Goodman, F.F. Knapp Jr, Radiochemical synthesis of [ F]-3-methyl-branched omega fluorofatty acids, J. Label. Compd. Radiopharm. 26 (1989) 233-235. 

T. Takahashi, S. Nishimura, T. Ido, K. Ishiwata, R. Iwata, Biological evaluation of 5-methyl-branched-chain omega-[ F]-fluorofatty acid A potential myocardial imaging tracer for positron emission tomography, Nucl. Med. Biol. 23 (1996) 303-308. 

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