Sugars esterification

Esterification.—Sugars can unite by means of their hydroxyl groups with acids, ketones, and other compounds to give a variety of esters, some of which occur naturally in the organism, while others have been of use in determining the constitution of the carbohydrates. 

Reaction with Organic Compounds. Many organic reactions are catalyzed by acids such as HCl. Typical examples of the use of HCl in these processes include conversion of HgnoceUulose to hexose and pentose, sucrose to inverted sugar, esterification of aromatic acids, transformation of acetaminochlorobenzene to chloroaruHdes, and inversion of methone [1074-95-9]. 

Esterification. The hydroxyl groups of sugars can react with organic and inorganic acids just as other alcohols do. Both natural and synthetic carbohydrate esters are important in various apphcations (1,13). Phosphate monoesters of sugars are important in metabohc reactions. An example is the enzyme-catalyzed, reversible aldol addition between dibydroxyacetone phosphate [57-04-51 and D-ylyceraldehyde 3-phosphate [591-57-1 / to form D-fmctose 1,6-bisphosphate [488-69-7],... 

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form ester derivatives. Esterification of carbohydrates by acetic anhydride, especially cellulose, is a major industrial application for this compound. In aqueous solutions, however, esterification may be a minor product, since the oxygen of water is about as strong a nucleophile as the hydroxyls of sugar residues. 

Fatty acid esters of sugars are also very important biodegradable and biocompatible surfactants that are prepared either by transesterification of methyl ester with sugar on basic catalysts or by esterification of fatty acids with sugar on acidic catalysts. Liquid acids and bases have been replaced by enzymatic catalysis with lipase, giving a higher yield of monoester [43, 44], but solid catalysts have not been used extensively so far. 

Sugar The hydrolysis of sucrose in the intestine produces both glucose and fructose, which are transported across the epithelial cells by specific carrier proteins. The fructose is taken up solely by the liver. Fructose is metabolised in the liver to the triose phosphates, dihydroxy-acetone and glycer-aldehyde phosphates. These can be converted either to glucose or to acetyl-CoA for lipid synthesis. In addition, they can be converted to glycerol 3-phosphate which is required for, and stimulates, esterification of fatty acids. The resulting triacylglycerol is incorporated into the VLDL which is then secreted. In this way, fructose increases the blood level of VLDL (Chapter 11). 

Incomplete carbonization of sugar, starch or cellulose followed by sulfonation produces stable and very active catalysts [25]. These materials, denoted sugar catalysts , not only show higher activity than other solid acids in the esterification of waste oils, but also maintain more than 90% of their original activity even after 50 cycles and they are stable up to 275 °C [26]. 

During his time at Reading, Richardson began his first successful incursions into the selective esterification of many common sugars, but it was at QEC that this work really took off, and the procedure was applied to many disaccharides, often with remarkable results. While space constraints prevent a complete discussion of all Richardson s work on the selective esterification of mono- and disaccharides, some highlights are recorded here. 

However, they varied in content of neutral sugars and extent of methyl-esterification. The presence of rham-nose in the backbone of pectin was believed to create kinks which probably disrupted helical stretches of the... 

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