Fatty-acid derived substances

There is no rigid scheme for classifying natural products—their immense diversity in structure, function, and biosynthesis is too great to allow them to fit neatly into a few simple categories. In practice, however, workers in the field often speak of five main classes of natural products terpenoids and steroids, fatty acid-derived substances and polyketides, alkaloids, nonribosomal polypeptides, and enzyme cofactors. 

Fatty acid-derived substances and polyketides, of which more than 10,000 are known, are biosynthesized from simple acyl precursors such as acetyl CoA, propionyl CoA, and methylmalonyl CoA. Natural products derived from fatty acids generally have most of the oxygen atoms removed, but polyketides, sucb as tbe antibiotic erythromycin A, often have many oxygen substituents remaining. WeTl look at erythromycin biosynthesis in Section 25.4. 

Fatty acid-derived substance (Section 25.1) A natural... 

TEicosanoids are paracrine hormones, substances that act only on cells near the point of hormone synthesis instead of being transported in the blood to act on cells in other tissues or organs. These fatty acid derivatives have a variety of dramatic effects on vertebrate tissues. They are known to be involved in reproductive function in the inflammation, fever, and pain associated with injury or disease in the formation of blood clots and the regulation of blood pressure in gastric acid secretion and in a variety of other processes important in human health or disease. 

The special potential for constructing double bonds stereoselectively, often necessary in natural material syntheses, makes the Wittig reaction a valuable alternative compared to partial hydrogenation of acetylenes. It is used in the synthesis of carotenoids, fragrance and aroma compounds, terpenes, steroides, hormones, prostaglandins, pheromones, fatty acid derivatives, plant substances, and a variety of other olefinic naturally occurring compounds. Because of the considerable volume of this topic we would like to consider only selected paths of the synthesis of natural compounds in the following sections and to restrict it to reactions of phosphoranes (ylides) only. 

PG [Prostaglandin] A group of hormone-like substances found in virtually all tissues and organs that are derived from unsaturated fatty acids. These substances mediate a wide range of physiological functions, the most common of which are muscular constriction and the mediation of inflammation. Letters after PG in the abbreviation symbolize different substitutions made to the hydrocarbon backbone, whereas subscript numbers indicate tlae degree of unsaturation (i.e., the number of double bonds). 

AquaMephyton solution for s.c.fi.m. injection Active substance Solubilizer Preservative To adjust isotonicity Solvent phytomenadione poiyoxyethylated fatty acid derivative benzyl alcohol dextrose water in 1 ml 2 or 10 mg 70 mg 0.9% 37.5 mg to volume... 

While almost all insect pheromones are fatty-acid-derived hydrocarbons (Baker, Chap. 27), crustacean pheromones are more diverse. They belong to various substance classes such as peptides (Rittschof and Cohen 2004), nucleotides (Hardege and Terschak, Chap. 19) or other small polar molecules (Kamio and Derby, Chap. 20), small nonpolar molecules (Ingvarsdottir et al. 2002), and possibly to ceramids (Asai et al. 2000). The higher diversity of waterborne pheromones again reflects the physical differences between the two media, with solubility in water being much less restrictive for the evolution of signal molecules than volatility in air. 

Emulsions of fatty- and petroleum-based substances, both oils and waxes, of the o/w type are made by using blends of sorbitan fatty esters and their poly(oxyethylene) derivatives. Mixtures of poly(oxyethylene(20)) sorbitan monostearate (Polysorbate 60) and sorbitan monostearate are typical examples of blends used for lotions and creams. Both sorbitan fatty acid esters and their poly(oxyethylene) derivatives are particularly advantageous in cosmetic uses because of their very low skin irritant properties. Sorbitan fatty ester emulsifiers for w/o emulsions of mineral oil are used in hair preparations of both the lotion and cream type. Poly(oxyethylene(20)) sorbitan monolaurate is useflil in shampoo formulations (see Hairpreparations). Poly(oxyethylene) sorbitan surfactants are also used for solubilization of essential oils in the preparation of colognes and after-shave lotions. 

Whereas catabolism is fundamentally an oxidative process, anabolism is, by its contrasting nature, reductive. The biosynthesis of the complex constituents of the cell begins at the level of intermediates derived from the degradative pathways of catabolism or, less commonly, biosynthesis begins with oxidized substances available in the inanimate environment, such as carbon dioxide. When the hydrocarbon chains of fatty acids are assembled from acetyl-CoA units, activated hydrogens are needed to reduce the carbonyl (C=0) carbon of acetyl-CoA into a —CHg— at every other position along the chain. When glucose is... 

From both economic and ecological points of view, substances derived from esters of monocarboxylic acids sulfonated in the a position form an interesting class of surfactants [1]. The general formula of these a-sulfomonocarboxylic esters, also called a-sulfo fatty acid esters or, in short, a-ester sulfonates, is Rj-CH(S03Me)-C00-R2 (with Rj and R2 = alkyl groups, Me = alkali metal). 

The major fatty acids present in plant-derived fatty substances are oleic acid (9-octadecenoic, C18 l), linoleic acid (9,12-octadecadienoic, C18 2) and the conjugated isomers thereof and linolenic acid (9,12,15-octadecatrienoic, C18 3) (Scheme 31.1). Their rates of oxygen absorption are 100 40 1, respectively, hence partial hydrogenation with consequent lowering of the iodine number would lead to a significant increase in oxidative stabihty, particularly when C18 3 is reduced. 

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