Carbohydrates esters

1 How to Make Lipase-Catalysed Carbohydrate Ester Synthesis Efficient 

Most studies of enzymatic sugar ester synthesis have focused on the esterification of monosaccharides, since the problems with poor substrate miscibility increase significantly with increasing size of the carbohydrate. However, by careful choice of reaction conditions it has been shown possible to acylate several di- and trisaccharides efficiently. Solvent mixtures of 2-methyl-2-butanol and dimethylsulfoxide have thus been used in 

Ionic liquids are promising nonaqueous solvents for the dissolution of carbohydrates and they have been used in several studies on enzymatic sugar ester synthesis. Candida antarctica lipase B was the best enzyme for synthesis of glucose esters in a two-phase system containing an ionic liquid and rm-butanol [31]. Recently, the use of supersaturated sugar solutions [32] and ultrasonic treatment [33] has been reported to make sugar ester synthesis in ionic liquids even more efficient. 

Efficient enzymatic conversion can be achieved even though most of the reactants are present as solids, provided that there is a liquid phase in which the reaction can occur. This approach has been successfully used for carbohydrate ester synthesis with synthesis of glucose esters of fatty acids between C12 and C18 as typical examples [34]. It is important that the substrates dissolve during the reaction, and often the products precipitate as they are formed, which can be an advantage due to a favourable effect on the equilibrium position. Candida antarctica lipase B is an efficient catalyst in this system and solvents used (in moderate amounts) include ethyl methyl ketone, acetone or dioxane. In order to increase the ester yield, water formed in the reaction can be removed by azeotropic distillation and the solvent (e.g. ethyl metyl ketone) can after condensation be dried by pervaporation, giving a practically useful complete process [35]. 

Carbohydrate Acyl donor Main products Enzyme References 

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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],... 

Although organic substrates such as carboxylic acids are thermally stable and may be sterilized with the basal media, many others including, for example, carbohydrates, esters, or amides are better prepared as concentrated stock solutions, sterilized by filtration through 0.22 pm filters and added to the sterile basal medium. 

Polyethers, alkanolamides, alkyls, alkylethoxylates, amines, benzyls, carbohydrates, esters, perfluoroalkyls Alkyl-, amidoimidazoline- and carboxy-quaternary ammonium salts Betaines, phosphobetaines, sulfobetaines... 

Because carbohydrates are so frequently used as substrates in kinetic studies of enzymes and metabolic pathways, we refer the reader to the following topics in Ro-byt s excellent account of chemical reactions used to modify carbohydrates formation of carbohydrate esters, pp. 77-81 sulfonic acid esters, pp. 81-83 ethers [methyl, p. 83 trityl, pp. 83-84 benzyl, pp. 84-85 trialkyl silyl, p. 85] acetals and ketals, pp. 85-92 modifications at C-1 [reduction of aldehydes and ketones, pp. 92-93 reduction of thioacetals, p. 93 oxidation, pp. 93-94 chain elongation, pp. 94-98 chain length reduction, pp. 98-99 substitution at the reducing carbon atom, pp. 99-103 formation of gycosides, pp. 103-105 formation of glycosidic linkages between monosaccharide residues, 105-108] modifications at C-2, pp. 108-113 modifications at C-3, pp. 113-120 modifications at C-4, pp. 121-124 modifications at C-5, pp. 125-128 modifications at C-6 in hexopy-ranoses, pp. 128-134. 

Recently, Williams et al. have reported the ring-opening polymerization of carbohydrate lactones [43, 44] and the lactide polymerization coinitiated by carbohydrate esters and pyranoses [45] (Scheme 4). 

Bacteria also contain a very rich variety of glycolipids with unusual structures. Lipid A13 is the site of attachement of the 0-specific chain of Gram (-) bacteria, which constitutes the antigenic lipopolysaccharide [87]. Other members of this family can be quoted, for example glycosyl glycerophospholipids in which the carbohydrate and glycerol moieties are linked by a phosphodiester bond (e.g. GPI anchor 14) [88] or carbohydrate esters (e.g. cord-factor of mycobacteria 15). 

The first study1 on the reaction of a carbohydrate ester with ammonia was performed in 1893 by Wohl, who submitted 2,3,4,5,6-... 

The most important of the carbohydrate esters of nitric acid are the polysaccharide nitrates, particularly cellulose nitrate or nitrocellulose (NC) and starch nitrate ( nitrostarch ) which is much less used. Nitric esters prepared from other sugars such as saccharose and lactose are not of any importance as explosives. 

M. Abdel-Akher and F. Smith, The detection of carbohydrate esters and lactones after separation by paper chromatography, J. Am. Chem. Soc., 73 (1951) 5859-5861. 

Immobilized HRP on different cinnamic carbohydrate esters The thermostability of the immobilized HRP was greater than that of the free enzyme and also showed great [51,52]... 

Rojas-Melgarejo F, Rodrfguez-Lopez IN, Garcia-Canovas F et al (2004) Immobilization of horseradish peroxidase on cinnamic carbohydrate esters. Process Biochem 39 1455-1464... 

Conjugate-addition Reactions of Grignard Reagents with a,/3-Unsaturated Carbohydrate Esters [Type 2]... 

For many years, the carbohydrate esters of carbonic acid and thiocar-bonic acid have found important application as intermediates in the synthesis of otherwise difficultly accessible derivatives. A review of these esters is particularly opportune, because both their preparation and properties are considerably influenced by stereochemical factors which require interpretation in the light of modem concepts of reaction mechanisms and conformational analysis. Although the historical development of the chemistry of the carbonic and thiocarbonic esters of carbohydrates has been independent, it is appropriate to give a comparative treatment of their closely related structures and properties. 

FIGURE 6.3 Peptide, enzyme, and carbohydrate esters of cotton cellulose that form bioconjugates creating biologically active cotton textile surfaces. 

Hartley, R.D. Jones, E.C. 1976. Carbohydrates and carbohydrate esters of ferulic acid released from cell walls of Lolium multiflorum by treatment with celluotyic enzymes. Phytochem. 15 305-307. 

Liquid-liquid extraction (LLE), solid phase extraction (SPE), and solid phase micro-extraction (SPME) are frequently applied for sample pretreatment. The type of extraction is highly related to the type of metabolites selected for determination. In previous metabolomics studies, extraction was focused on compounds of adequate stability that could be extracted together (carbohydrates, esters, amino acids, or organic acids). 

A third wax subfraction (soluble in both ether and alcohol) was shown to be a mixture of glycerides, carbohydrate esters of fatty acids, and true waxes. Alkaline hydrolysis gave glycerol and the carbohydrate as the water-soluble constituents. The carbohydrate yielded only inositol and D-mannose on hydrolysis with dilute mineral acid. 

Non-polar column coatings include silicone oil, hydrocarbons, and esters of high molecular weight alcohols, and dibasic acids. Polyethylene glycols, polyesters, ethers, carbohydrate esters, and derivatives of ethylenediamine are widely used polar liquid phases. 

The precursor 265, derived from (—)-D-xylose, was transformed into the saturated ester 266 with a similar diastereoselectivity when TiCl4 was added (Scheme 10.86). After saponification of the carbohydrate ester 266, (5 )-( + )-indan acid 264 was isolated. 

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