Fatty acids chiral

Morigaki, K., Dallavalle, S., Walde, P, Colonna, S., and Luisi, P. L. (1997). Autopoietic self-reproduction of chiral fatty acid vesicles. /. Am. Chem. Soc., 119, 292-301. 

In nature one also finds chiral fatty acid or fatty alcohol derivatives with a hydroxyl or amino substituent at the alkyl chain. Common examples are given in Table 2.2.2 of the fatty acids in cheap commercial castor oil (a fat mixture) consist of ricinoleic acid (12-/ -hydroxy-9-Z-octadecene-carboxylic acid). The hydrogenation product (R)-12-hydroxy-stearic acid is the cheapest chiral fatty acid (about 100/g). Sphingosin (2-S-amino-4-E-octadecene-l,3-R-diol) is a chiral a--arnino-diol, which is found in large amounts in nerve tissue ( 5,000/g). Chirality is expensive, if it is localized within the hydrophobic chain. 

Figure 1. Chemical structures of lipid A-diphosphate (A) and two antagonistic lipid A-diphosphate molecules, (B and C). Lipid A-diphosphate from E. coli is a 1,4-di-phosphorylated P-1,6-linked D-glucosamine disaccharide with four residues of amide-and esterified R-(-)-3-hydroxy fatty acids ( denotes the chiral centers in the hydroxy fatty-acid esters, apart form the chiral and epimeric carbons in the disaccharide moieties which are not marked). The antagonistic lipid A-diphosphate molecules shown in (B) and (C) contain the same disaccharide as in (A) however, they differ in the number anchored carbohydrate positions and the number of chiral fatty-acid chains but the chain lengths is the same (C J. The corresponding monophosphate of lipid A is only phosphorylated at the reducing end of the disaccharide.

Both 2- and 3-D assemblies of lipid A-mono or diphosphate constructed from single or multiple chemical entities of known chemical composition ( coded subunits ) were quite complex. These assemblies were very unlikely to be loose or unordered combinations of lipid A molecules or of their analogs. The coded subunit addresses the chemical appearances of single or identical chemical stractures of lipid A-phosphate. However, they were non-identical and differed in chemical structure for example number of chiral fatty acid chains, length of the hydrocarbon chain (number of carbons), inserted double bonds in the hydrocarbon chain, and hexose compositions (Christ et al., 2003). The assemblies were characterized by being comprised of two phosphates residues one at the reducing end and the other one at the non-reducing end for the... 

Most naturally occurring lipids are not chiral (parafiins, oleic acid, palmitin, etc.) or are mixtures of compounds which are difficult to separate (lecithin, asymmetric glycerols). A few chiral fatty acids have been used, like methylated (Figure 4.4) [8] and alicylic (Figure 4.5) [9] adds. The chiral centers of fatty acids are often comformational flexible and they are not connected with large dipole moments. Also, the chemical modification of the chiral centers is more difficult than for amino acids and sugars. Thus, chiral lipids have only limited use in liquid crystal research. 

Morigaki et al. (25) have described the autopoietic self-reproduction of chiral fatty acids with the aim... 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Despite of the disadvantage, that at least one symmetrical dimer is formed as a major side product, mixed Kolbe electrolysis has turned out to be a powerful synthetic method. It enables the efficient synthesis of rare fatty acids, pheromones, chiral building blocks or non proteinogenic amino acids. The starting compounds are either accessible from the large pool of fatty acids or can be easily prepared via the potent methodologies for the construction of carboxylic acids. 

By the radical pathway l, -diesters, -diketones, -dienes or -dihalides, chiral intermediates for synthesis, pheromones and unusual hydrocarbons or fatty acids are accessible in one to few steps. The addition of the intermediate radicals to double bonds affords additive dimers, whereby four units can be coupled in one step. By way of intramolecular addition unsaturated carboxyhc acids can be converted into five raembered hetero- or carbocyclic compounds. These radical reactions are attractive for synthesis because they can tolerate polar functional groups without protection. 

Applications of peroxide formation are underrepresented in chiral synthetic chemistry, most likely owing to the limited stability of such intermediates. Lipoxygenases, as prototype biocatalysts for such reactions, display rather limited substrate specificity. However, interesting functionalizations at allylic positions of unsaturated fatty acids can be realized in high regio- and stereoselectivity, when the enzymatic oxidation is coupled to a chemical or enzymatic reduction process. While early work focused on derivatives of arachidonic acid chemical modifications to the carboxylate moiety are possible, provided that a sufficiently hydrophilic functionality remained. By means of this strategy, chiral diendiols are accessible after hydroperoxide reduction (Scheme 9.12) [103,104]. 

Unlike electron and scanning tunneling microscopy, the use of fluorescent dyes in monolayers at the air-water interface allows the use of contrast imaging to view the monolayer in situ during compression and expansion of the film. Under ideal circumstances, one may observe the changes in monolayer phase and the formation of specific aggregate domains as the film is compressed. This technique has been used to visualize phase changes in monolayers of chiral phospholipids (McConnell et al, 1984, 1986 Weis and McConnell, 1984 Keller et al., 1986 McConnell and Moy, 1988) and achiral fatty acids (Moore et al., 1986). 

Sulfated alkenes, 23 538 Sulfated carbohydrate products, 23 538 Sulfated cyclodextrin-based chiral stationary phase, 6 87 Sulfated fatty acids, 23 538 Sulfated fatty alcohol ethoxylates, 23 537 Sulfated fatty oils, 23 538 Sulfated products... 

We Umit this section to a discussion of stereochemical studies that sought to demonstrate discriminating enantiomeric interactions in monolayers of simple surfactants having one hydrophobic chain of methylenes and, generally, a single chiral center. Work in this area includes derivatives of long chain fatty acids, alcohols, or esters whose chiral center is included in the methylene chain. 

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