Acylate, fatty acid salt

Abstract New acylation techniques were developed for the fabrication of fatty estos of cellulose and starch. They exclude the use of organic solvents and are readily achieved. Emulsification of the fatty acid in water allowed die intimate contact between the tty recent and die polysaccharide. Fatty acid salts (soap) were used as both catalyst and emulsifying agent. Reaction conditions were optimized using an experimental design. Starch and cellulose octanoates were obtained having a DS of 0.52 and 0.23 with a recuperation yield of 70 and 85 %, respectively. Both polysaccharide esters showed a marked hydrophobic character. 

In this procedure, a-glycerol phosphate is acylated directly using acyl anhydrides (Lapidot et aL, 1969). The acyl anhydrides are prepared with dicyclohexyl-carbodi-imide (Rosenthal, 1975). Optically active or racemic phosphatidic acids can be prepared and either saturated or unsaturated acyl residues added. The method depends on the ability of the fatty acid salt to suppress the formation of mixed phosphoric-carboxylic anhydrides with the consequent phosphorylation of adjacent hydroxy groups. The use of acyl anhydrides rather then acyl chlorides probably prevents the formation of glycerol chlorhydrin esters (Aneja and Chadha, 1971a). 

An amine-terminated polyoxyalkylene having an average molecular weight from about 600 to about 10,000 can be acylated with a succinic acylating agent (e.g., hexadecenyl succinic anhydride or a Diels-Alder diacid) obtained from an unsaturated fatty acid [628,629] similarly, alkyl-aryl sulfonate salts [1319] can be used in lubrication. 

Lynen had studied chemistry in Munich under Wieland his skill as a chemist led to the successful synthesis of a number of fatty acyl CoA derivatives which proved to be substrates in the catabolic pathway. Many of these C=0 or C=C compounds had characteristic UV absorption spectra so that enzyme reactions utilizing them could be followed spectrophotometrically. This technique was also used to identify and monitor the flavoprotein and pyridine nucleotide-dependent steps. Independent evidence for the pathway was provided by Barker, Stadtman and their colleagues using Clostridium kluyveri. Once the outline of the degradation had been proposed the individual steps of the reactions were analyzed very rapidly by Lynen, Green, and Ochoa s groups using in the main acetone-dried powders from mitochondria, which, when extracted with dilute salt solutions, contained all the enzymes of the fatty acid oxidation system. 

Much of the cholesterol synthesis in vertebrates takes place in the liver. A small fraction of the cholesterol made there is incorporated into the membranes of he-patocytes, but most of it is exported in one of three forms biliary cholesterol, bile acids, or cholesteryl esters. Bile acids and their salts are relatively hydrophilic cholesterol derivatives that are synthesized in the liver and aid in lipid digestion (see Fig. 17-1). Cholesteryl esters are formed in the liver through the action of acyl-CoA-cholesterol acyl transferase (ACAT). This enzyme catalyzes the transfer of a fatty acid from coenzyme A to the hydroxyl group of cholesterol (Fig. 21-38), converting the cholesterol to a more hydrophobic form. Cholesteryl esters are transported in secreted lipoprotein particles to other tissues that use cholesterol, or they are stored in the liver. 

An essentially neutral process for C-acylation relies on the reaction of imidazolides (542) with the magnesium salt (543) of a malonic acid half thiol ester (Scheme 119) (79AG(E)72>. The method requires slight modification when applied to an w-hydroxycarboxylic acid since a primary hydroxyl reacts with carbonyldiimidazole. The use of malonic acid half thiol esters in this fashion patterns the scheme proposed for carbon-carbon bond formation in the biosynthesis of fatty acids. 

Chemistry and general properties. Sodium isethionate is 2-hydroxyethane sulphonate, sodium salt and will form an ester with a fatty acid halide, normally an acyl chloride (Figure 4.26). 

Both IDL and LDL can be removed from the circulation by the liver, which contains receptors for ApoE (IDL) and ApoB-100 (IDL and LDL). After IDL or LDL interacts with these receptors, they are internalized by the process of receptor-mediated endocytosis. Receptors for ApoB-100 are also present in peripheral tissues, so that clearance of LDL occurs one-half by the liver and one-half by other tissues. In the liver or other cells, LDL is degraded to cholesterol esters and its other component parts. Cholesterol esters are hydrolyzed by an acid lipase and may be used for cellular needs, such as the building of plasma membranes or bile salt synthesis, or they may be stored as such. Esterification of intracellular cholesterol by fatty acids is carried out by acyl-CoA-cholesterol acyltransferase (ACAT). Free cholesterol derived from LDL inhibits the biosynthesis of endogenous cholesterol. B-100 receptors are regulated by endogenous cholesterol levels. The higher the latter, the fewer ApoB-100 receptors are on the cell surface, and the less LDL uptake by cells takes place. 

Acylate ions are amphiphilic, and the hydrocarbon chains are able to penetrate fatty (hydrophobic) particles, leaving the surface of the particle ionic. (See Fig. 6-26.) Thus, the particle behaves as a micelle and is readily soluble in water. The sodium and potassium salts of fatty acids are soaps. Soaps have poor detergent properties in hard water because the calcium present in such water causes the micelles to aggregate and precipitate. The divalent calcium ion can act as a bridge between two micelles, but since a micelle is polyvalent, a small amount of calcium relative to the amount of the soap can cause all the micelles to aggregate. 

C-Acylation. C-Acylation of active methylene compounds is usually conducted under basic conditions. Masamune et al. have developed a new method for conducting this reaction under neutral conditions that is patterned on the enzymic synthesis of fatty acids. The acylating reagent is the imidazolide of a carboxylic acid (1) prepared in situ. The substrate is the neutral magnesium salt of a mono ester or thioester of a malonic acid (2), prepared with magnesium ethoxide. The reaction of 2 with 1 is conducted in THF at 25-35° for 18-24 hours the yield of products (3) is generally >85%. ... 

The favored structure for most phospholipids and glycolipids in aqueous media is a bimolecular sheet rather than a micelle. The reason is that the two fatty acyl chains of a phospholipid or a glycolipid are too bulky to fit into the interior of a micelle. In contrast, salts of fatty acids (such as sodium palmitate, a constituent of soap), which contain only one chain, readily form micelles. The formation of bilayers instead of micelles by phospholipids is of critical biological importance. A micelle is a limited structure, usually less than 20 nm (200 A) in diameter. In contrast, a bimolecular sheet can have macroscopic dimensions, such as a millimeter (10 nm, or 10 A). Phospholipids and related molecules are important membrane constituents because they readily form extensive bimolecular sheets (Figure 1211). 

It would be of interest to test these hypotheses by examining the methanogens and thermophiles for the presence of FAS and acyl transferases and studying the effect of salt concentration, low pH and high temperature on their activities and on those of the mevalonate enzyme system. It may be noted that preliminary studies with M. thermo-autotrophicum have revealed the presence of a functional FAS producing fatty acids for acylation only of membrane proteins (Pugh and Kates, unpublished data). 

I he average daily intake of total dietary cholesterol is 400-500 mg. Cholesterol also enters the gastrointestinal tract via the bile. Between fiOO and 1200 mg of free cholesterol is secreted in the bile per day. By weight, bile consists of 92% water, 6% bile salts, 0,3% cholesterol, and small amounts of bilirubin, fatty acids, phosphatidylcholine, and sails. The cholesteryl esters of the diet are hydmlyzed to free cholesterol and a fatty add by pancreatic cholesterol esterase. After entry into the enterocyte, the free cholesterol is nmverted back to cholesteryl esters by acyl CoA cholesterol acyl transferase. Some evidence suggests that the absorption of dietary cholesterol (from the bile salt micelles) is mediated by a membrane-bound transport protein of the brush border (1 humhofer and Hauser, 1990),... 

Although fatty acyl residues are present in all lipids, the analysis of free fatty acids by MALDI-TOF MS is rather difficult as they show-due to their relatively low molecular weights-a significant overlap with the matrix. This particularly holds if fatty acids at low concentrations have to be analyzed. One possibility to overcome this problem is the use of mesotetrakis(pentafiuorophe-nyl)porphyrin (Ayorinde et al. 1999) as matrix It could be shown that the analysis of free fatty acids obtained by alkaline saponification of different plant oils is possible by this matrix (Ayorinde et al. 2000). As an excess of sodium acetate was added, exclusively the Na adducts of the sodium salts of the fatty acids were detected by positive ion MALDI-TOF MS. Therefore, problems with peak assignments did not occur. Unfortunately, this approach... 

Preparation of Acyl Chlorides.—Acetyl chloride and its homologues may be prepared by the action of phosphorus pentachloride on the fatty acids or their salts —... 

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