Monosaccharides conversion

Pathways in the formation of NDP-sugars. A seiection of monosaccharide conversions occurring at the phosphate ester and nucieotide-monosaccharide ievei in animais, piants and bacteria are shown all pathways radiate from fructose-6-phosphate, indicating the central role of this metabolite. The dTDP, GDP and UDP-yV-acetylmu-ramic pathways are peculiar to bacteria, whereas ADP-o-glucose, UDP-o-apiose and UDP-L-arabinose are found in plants. For reasons of simplicity, other pathways, e. g., to UDP-L-rhamnose in plants, GDP-o-rhamnose in Pseudomonas aeroginosa and GDP-o-arabinose in trypanosomatids are not included. The figure is reproduced from Chap. 6.4 of the first edition of this book... 

Fructose—Dextrose Separation. Emctose—dextrose separation is an example of the appHcation of adsorption to nonhydrocarbon systems. An aqueous solution of the isomeric monosaccharide sugars, C H 2Dg, fmctose and dextrose (glucose), accompanied by minor quantities of polysaccharides, is produced commercially under the designation of "high" fmctose com symp by the enzymatic conversion of cornstarch. Because fmctose has about double the sweetness index of dextrose, the separation of fmctose from this mixture and the recycling of dextrose for further enzymatic conversion to fmctose is of commercial interest (see Sugar Sweeteners). 

All the essential monosaccharides arise from glucose, by the conversions summarized in Figure 25.10. We ll not look specifically at these conversions, but might note that end-of-chapter Problems 25.55 through 25.57 lead you through several of the biosynthetic pathways. 

Methanolysis of standard uronic acids has been studied by Inoue and Miyawaki in regard to the depolymerization of chondroitin sulfate and dermatan sulfate. These workers found the glucosiduronic linkage to ga-lactosamine to be rather resistant to methanolysis, but that it is more efficiently cleaved after deamination of the amino galactoside, with its conversion into 2,5-anhydrotalose. For iduronic, glucuronic, and man-nuronic acids released from a polymer, it was found that the peaks monitored for these acids, relative to an internal standard, increase during the first 8 h of methanolysis (M hydrogen chloride, 100°) and remain constant for up to 20 h of methanolysis. This indicated that 8 h is required for complete methanolysis, and that the monosaccharides liberated are stable to the conditions of methanolysis. 

The results of such studies are obtained in ( ), f space and a routine calculates the n and h values as functions of ( ) and f. This conversion depends on the exact coordinates of the residue and a precise glycosidic bond angle. However, most monosaccharides are... 

The sugars (monosaccharides) occur in the metabolism in many forms (derivatives). Only a few important conversion reactions are discussed here, using D-glucose as an example. 

Abstract Polyfunctionality of carbohydrates and their low solubility in conventional organic solvents make rather complex their conversion to higher value added chemicals. Therefore, innovative processes are now strongly needed in order to increase the selectivity of these reactions. Here, we report an overview of the different heterogeneously-catalyzed processes described in the literature. In particular, hydrolysis, dehydration, oxidation, esterification, and etherification of carbohydrates are presented. We shall discuss the main structural parameters that need to be controlled and that permit the conversion of carbohydrates to bioproducts with good selectivity. The conversion of monosaccharides and disaccharides over solid catalysts, as well as recent advances in the heterogeneously-catalyzed conversion of cellulose, will be presented. 

Here we report an overview of the different heterogeneously-catalyzed pathways designed for the selective conversion of carbohydrates. On the basis of these results, we shall try to determine the key parameters allowing a better control of the reaction selectivity. Water being commonly used as solvent in carbohydrate chemistry, we will also discuss the stability of solid catalysts in the aqueous phase. In this review, heterogeneously-catalyzed hydrolysis, dehydration, oxidation, esterification, and etherification of monosaccharides and polysaccharides are reported. 

Oxidation of carbohydrates is probably the most efficient heterogeneously-catalyzed process since very high yield and selectivity are reported for reactions over solid catalysts. Despite important recent advances, the conversion of carbohydrates to HMF still requires further investigations. For reactions, in water, the yield of HMF is still too low due to the significant formation of side products. Today, several procedures for the conversion of monosaccharides, disaccharides, oligosaccharides, and starch in water into high value added materials are available. With cellulose, its heterogeneously-catalyzed conversion into useful products... 

The fact that each monosaccharide may give more than one peak owing to the formation of anomeric derivatives has led to a search for means to eliminate this complication. The anomeric center may be removed either by conversion into the oxime5 or the nitrile,394,3943 by oxidation followed by formation of the lactone (see Section IX, p. 71), or by reduction to the alditol. The last method is simpler than oxidation, and the separation of alditols and of aldononitriles will be discussed here additional examples are given in Table V (see p. 119). The early work on the separation of alditols has been discussed by Bishop.4 The necessity of decomposing borate complexes... 

Another approach for determination of the absolute configuration of the monosaccharide components69 involves their interaction with radioactive potassium cyanide and conversion of the products into a mixture of heptonamides. Isotopic-dilution experiments showed the presence of D-gfi/cero-L-manno-heptonamide, thus establishing the D-galacto configuration of the starting hexose. 

From among the variety of non-carbohydrate precursors, acetylenes and alkenes have found wide application as substrates for the synthesis of monosaccharides. Although introduction of more than three chiral centers having the desired, relative stereochemistry into acyclic compounds containing multiple bonds is usually difficult, the availability of such compounds, as well as the choice of methods accessible for their functionalization, make them convenient starting-substances for the synthesis. In this Section is given an outline of all of the synthetic methods that have been utilized for the conversion of acetylenic and olefinic precursors into carbohydrates. Only reactions leading from dialkenes to hexitols are omitted, as they have already been described in this Series.7... 

This conversion of readily available 2-furyl alcohols into unsaturated pyranosuloses proved a very effective route to racemic monosaccharides, through stepwise, selective functionalization of the enone grouping in 325. The shortest synthesis of a natural compound by following this scheme involves palladium-catalyzed hydrogenation of the aldosulose (325, R = Me) obtained from l-(2-furyl)ethanol, resulting209 in cinerulose A, the sugar component of the antibiotic cine-rubin. 

Acarbose, miglitol Inhibit intestinal cx-glucosidases Reduce conversion of starch and disaccharides to monosaccharides reduce postprandial hyperglycemia Type 2 diabetes Oral rapid onset Toxicity Gastrointestinal symptoms cannot use if impaired renal/hepatic function, intestinal disorders... 

---