Monosaccharides oxidation-reduction reactions

MUTAROTATION The a- and /T forms of monosaccharides are readily interconverted when dissolved in water. This spontaneous process, called mutarotation, produces an equilibrium mixture of a- and /1-forms in both furanose and pyranose ring structures. The proportion of each form differs with each sugar type. Glucose, for example, exists primarily as a mixture of a- (38%) and j8- (62%) pyranose forms (Figure 7.11). Fructose is predominantly found in the a-and /J-furanose forms. The open chain formed during mutarotation can participate in oxidation-reduction reactions. 

OXIDATION-REDUCTION REACTIONS In the presence of oxidizing agents, metal ions such as Cu2+, and certain enzymes, monosaccharides readily undergo... 

What are some oxidation-reduction reactions of sugars Monosaccharides can undergo various reactions. Oxidation reactions make up one important group. 

The presence of alcohol and, in some cases, an aldehyde group makes monosaccharides susceptible to oxidation, whereas the presence of a carbonyl group makes monosaccharides susceptible to reduction. Because monosaccharides are the fundamental carbohydrate, you need to know what happens in the many reactions in which they re involved. The following sections are here to help you out with that. Welcome to the nitty-gritty of monosaccharide oxidation and reduction ... 

Oxidation and reduction reactions occur at the carbonyl group of monosaccharides, so they all begin with the monosaccharide drawn in the acyclic form. We will confine our discussion to aldoses as starting materials. 

In this chapter, methods for oxidation, reduction, and deoxygenation of carbohydrates are presented. In most cases, the reactions have been used on aldoses and their derivatives including glycosides, uronic acids, glycals, and other unsaturated monosaccharides. A number of reactions have also been applied to aldonolactones. The methods include both chemical and enzymatic procedures and some of these can be applied for regioselective transformation of unprotected or partially protected carbohydrates. 

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. 

Show the products of the common reactions of monosaccharides that were presented in this chapter oxidation with nitric acid, oxidation with bromine, reduction with... 

Besides being useful for selective protection of monosaccharides, cyclic acetals can display a number of interesting reactions, such as reductive or oxidative ring opening, that amplify the synthetic interest of these protecting groups [125]. 

Complexes of Cr111 with ascorbate, which are likely to form during the reactions of Crvl with this major intracellular reductant, have been studied (mainly by Cieslak-Golonka and co-workers),1062-1064 but no definitive structural information has been obtained to date. Partially characterized Crm complexes with monosaccharides or their oxidized derivatives (e.g., aldonic acid) have been isolated from the reactions with either Cr1111092 or CrVI.1093,1094... 

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