Stearic acid, synthesis

Biosynthesis of Unsaturated Fatty Acids. In the mammalian tissues, the forma-tion of monoene fatty acids is only possible. Oleic acid is derived from stearic acid, and palmitooleic acid, from palmitic acid. This synthesis is carried out in the endoplasmic reticulum of the liver cells via the monooxigenase oxidation chain. Any other unsaturated fatty acids are not produced in the human organism and must be supplied in vegetable food (plants are capable of generating polyene fatty acids). Polyene fatty acids are essential food factors for mammals. 

The hyperbranched polyesteramides described above can also easily be functionalized by esterification with various mono carboxylic acids like acetic acid, benzoic acid, 2-ethylhexanoic acid, stearic acid, (un)satuxated fatty acids, or (meth)acrylic acid. With the exception of the latter mentioned acids, which give highly temperature sensitive products, the synthesis of these functionalized hyperbranched polyesteramides can be performed in two different ways ... 

A 50% functionalization evokes the interesting question, bearing in mind facile transesterification, of how the fluoroalkyl chains will be distributed over the molecules and how they will be distributed on one particular molecule This question has been examined in detail for dendrimers of the poly(propyleneimine) type functionalized with stearic acid [33]. It was proven that the compositional heterogeneity (distribution of degree of substitution) is random, but the positional heterogeneity (spatial distribution of the substituents over the dendrimer molecule) is not random. However, due to flexibility, no particular effect of the spatial distribution can be observed. Unlike the dendrimers, we expect the hyperbranched polyesteramides to be stiffer, so that spatial distribution could lead to interesting effects if the molecule were composed of a functionalized side and a non-func-tionalized side (Fig. 28), as shown possible for dendrimers via a convergent synthesis [34]. 

PI is synthesized from free inositol and CDP-diacylglycerol as shown in Figure 17.5. PI is an unusual phospholipid in that it olten contains stearic acid on carbon 1 and arachidonic acid on carbon 2 of the glycerol. PI, therefore, serves as a reservoir of arachidonic j acid in membranes and, thus, provides the substrate fa-prostaglandin synthesis when required (see p. 211 for a discussion of these compounds). 

Figure 3.30 Synthesis route of PMO magnetic hollow spheres (a) hydrophobic, stearic acid-capped Fes04 nanoparticles in an organic phase are treated with CTAB to produce (b) water-dispersible nanoparticles, (c) Formation of FC4 vesicles leads to encapsulation of the CTAB-stabilized Fe304 nanoparticles, (d) Addition of BTME/CTAB forms the outer ethane-bridged PMO shell surrounding the vesicles. (See color insert.)...

The formation of a triglyceride (a fat), such as the biochemical synthesis of tristearin via the reaction of stearic acid with glycerol ... 

In the melanogaster subgroup, the same enzyme Desatl seems to be involved in the first desaturation step of pheromone synthesis (Figure 4.7), even if the specificity concerning the desaturation is somewhat modified (for example, in D. erecta, stearic acid is used for the first desaturation, instead of palmitic acid as in other species). In other Drosophila species, other enzymes could be involved Desat2 in D. ananassae and another yet unknown desaturase in D. virilis. The position of the double bond on carbon 11 in the latter species could indicate either that the desaturase acts on C20 saturated fatty acid, or that it has another unknown specificity, resembling the unusual specificities of some lepidopteran desaturases. 

Modern concepts of milk fat synthesis developed rapidly in the 1950s with the carefully-designed physiological studies in lactating goats by Popjak et al. (1951) which showed unequivocally the de novo synthesis of short-chain fatty acids from 14C-labelled acetate. Also, the incorporation of tritium-labelled stearic acid into milk fat was demonstrated by Glascock et al. (1956). From empirical calculations of the quantity of dietary fat and the recovery of label in milk fat, the latter authors estimated that dietary fat contributed a maximum 25% of the weight of milk fat. 

Fatty acids are the building blocks of TAG. More than 90 percent of fatty acids have an even number of carbon atoms, and are in aliphatic chains ranging from 4 to 22 carbons in length. The major fatty acid synthesis pathway is production of stearic acid (18 carbons) after which separate desaturase systems introduce 1, 2, or 3 unsaturated (double) bonds. Additional enzymes become active in elongating the chain as needed. Shorter fatty acids also are produced. Trace amounts of odd-number carbon fatty acids are found in most fats, and also have been synthesized for research purposes. Microorganisms frequently produce odd-number carbon fatty acids, with heptadecenoic (17 carbon) acid a major component of Candida tropicalis yeast fat. Up to 8 percent C17 fatty acids have been found in milk and meat fats of ruminants (cattle, sheep, goats) and are of rumen microbe origin. 

Fatty acids have been used previously in the development of polymers for biomedical applications as they are considered to be inert, inexpensive and biocompatible. The main fatty acids which are used as a base for synthesis of biomedical polymers (polyanhydrides) are stearic acid (/), erucic acid (C22 unsaturated fatty acid) dimer (2), bile acid dimer (i), ricinoleic acid 4) and other fatty acids (5), middle long carbon chain (C12 - 15) dibasic acids, such as dodecanedioic, brassylic acid, tetradecandioic acid and pentadecandioic acid (/). 

Fatty acids are especially important and ubiquitous lipids. Apart from their use as fuel, they may be used in the synthesis of many other kinds of molecules. A fatty acid is a hydrocarbon chain with a terminal —COOH group. Usually, fatty acids contain between 14 and 25 carbons, 16 and 18 being most common. Unsaturated fatty acids are those that contain double bonds between some carbon atoms. Saturated fatty acids contain only single bonds. Palmitic acid (16) and stearic acid (Cl8) are particularly common saturated fatty acids in humans. Linoleic acid (Cl8), linolenic acid (Cl8) and arachidonic acid (C20) are common polyunsaturated fatty acids ( poly meaning more than one double bond). The number of carbons typically is even, reflecting the fact that fatty acid chains are built up (and broken down) in units of 2 carbon atoms at a time. 

Glaessner, Austria, 1931), ammoniacal bleached shellac (Wruble, 1933), stearic acid, carnauba wax, petrolatum, elm bark, and agar (Miller, 1935, and Worton, 1938), and abietic, oleic, and benzoic acids with methyl abietate (Eldred, 1937). Since 1940, research on enteric coatings has focused on the synthesis of resinous polymers, which are insoluble in acids, such as cellulose acetate phthalate (Hiatt, 1940) and a glycerol-stearic acid-phthalic anhydride ester (Volweiler and Moore, 1940). 

Because the metabolism of trans-18 1 to stearic acid is thought to be the rate-limiting step in complete BH (Keeney, 1970), the effects of diet on lipid metabolism in the rumen tend to have a more pronounced effect on the amount and relative proportions of trans-18 1 leaving the rumen than on other BH intermediates including isomers of CLA. With respect to enhancing RA content of ruminant foods, it could be argued that the most important aspects of dietary effects on ruminal BH relate to those on VA and the factors that regulate its synthesis. 

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