Oxidation carbohydrates

At one stage in our project we were surprised to learn that some workers had found difficulties in preparing the tetroxide from the dioxide, until we experienced the same trouble. This problem has now been resolved (3). Ruthenium dioxide is available commercially in both anhydrous and hydrated forms, the former being obtained by direct oxidation of ruthenium metal and the latter by a precipitation process. Only the hydrated form is oxidizable under the mild conditions (2,3) that we use and this form must be specified when purchasing the dioxide. It is noteworthy that the dioxide recovered from carbohydrate oxidations is always easily re-oxidized to the tetroxide. The stoichiometry has been determined of both the oxidation of the dioxide by periodate and reduction of the tetroxide which results on oxidation of an alcohol. 

Dissolve the glycoprotein(s) to be labeled in ice-cold ImM sodium periodate, lOmM sodium phosphate, 0.15 M NaCl, pH 7.4, for the exclusive oxidation of sialic acid residues. For general carbohydrate oxidation, increase the periodate concentration to 10 mM in PBS at room temperature. 

Dissolve a glycoprotein to be oxidized in 0.1 M sodium acetate, pH 5.5 (oxidation buffer), at a concentration of 2-10mg/ml. PBS at physiological pH may be used for this reaction, as well. The use of cold buffers for the oxidation step will limit the extent of carbohydrate oxidation and the potential for protein oxidation. 

Evans, Nicoll, Strause and Waring46 oxidized D-glucose and D-fructose in aqueous solution with excess cupric acetate at 50° for the purpose of ascertaining whether the general principles underlying the mechanism of carbohydrate oxidation in alkaline solutions are sufficient to explain the course of such oxidations in acid solutions. D-Glucosone was claimed to be one of the first products of oxidation the osone was not isolated, and,... 

ASPECTS OF CARBOHYDRATE OXIDATION, ELECTRON TRANSFER, AND OXIDATIVE PHOSPHORYLATION... 

The first suggestion that substrates in carbohydrate oxidation might exert catalytic effects on the oxidation of other intermediates (cf.earlier demonstration of such action in the urea cycle by Krebs and Henseleit, 1932 see Chapter 6) arose from the work of Szent-Gyorgi (1936). He demonstrated that succinate and its 4C oxidation products catalytically stimulated the rate of respiration by muscle tissues. He also observed that reactions between the 4C intermediates were reversible and that if muscle was incubated with oxaloacetate, fumarate and malate made up 50-75% of the products, 2-oxoglutarate 10-25% and, significantly, 1-2% of the C was converted to citrate. These observations were... 

When his studies on carbohydrate oxidation restarted in Sheffield, Krebs experiments included studies on the anaerobic dismutation of pyruvate by bacteria and various animal tissues. Assuming the role for the dicarboxylic acids postulated by Szent-Gyorgi, the main question was the route by which the carbon atoms of pyruvate were converted to succinate. In May 1936 Krebs had observed that if 2-oxoglutarate was added to pyruvate, the yield of succinate was enormously increased. In his notebook written that year (Holmes, 1993) Krebs postulated ... 

Besides Szent-Gyorgi and Krebs, other groups were attacking the problem of carbohydrate oxidation. Weil-Malherbe suggested It is probable that the further oxidation of succinic acids passes through the stages of fumaric, malic, and oxaloacetic acid pyruvic acid is formed by the decarboxylation of the latter and the oxidative cycle starts again. K.A.C. Elliott, from the Cancer Research Laboratories at the University of Pennsylvania, also proposed a cycle via some 6C acid. 

It was appreciated by the beginning of the twentieth century that glucose was the major fuel of carbohydrate oxidation. However, it was not nntU 1956 that it was established that long-chain fatty acids were the major fuel by which fat is oxidised. 

Kinetic parameters for the oxidation by stoich. [Ru(H30)(bpy)(tpy)] Vwater pH 7 of a number of carbohydrates and nucleotides were measured and are consistent with carbohydrate oxidation at the T position [668]. Electrocatalytic oxidations of 2-propanol to acetone, ethanol and acetaldehyde to acetate, p-xylene and /i-phthalate to terephthalate, cyclohexene to 2-cyclohexen-l-one and toluene to benzoate with the couple [Ru(0)(bpy)(tpy)] V[Ru"(H30)(bpy)(tpy)] Vwater pH... 

Although these encompass primary and secondary alcohols they are considered here in a separate section since so much work has been done in the area, using RuO as the oxidant. In most cases it was used for oxidation of secondary alcohol groups in carbohydrates to ketones, but its first application, albeit stoicheiometrically as RuOy CCy was for the conversion of a secondary alcohol unit in l,2 5,6-di-0-isopropy-lidene-a-D-glucofuranose to the D-nfeo-hexofuranos-3-ulose (Fig. 2.13) [310]. There are early but illuminating reviews on carbohydrate oxidations by RuO [18, 311]. 

A typical list of secondary carbohydrate oxidations is given in Table 2.3 bnt we start with primary alcohol oxidations in furanoses. Work on nncleosides and nncleotides is included in this section. 

The reagent RuO /aq. Na(IO )/CCl (the first catalytic system for Ru-based carbohydrate oxidations) oxidised 1,2-0-isopropylidene-L-threose to D-glycew-1,2-0-isopropylidene-tetros-3-ulose, and a number of pyranoses were similarly oxidised [2]. Other furanoses were made with RuCl3/TCCA/( Bu N)Br (Table 2.3 Fig. 2.14) [25]... 

In general RuO - normally likely to be the active species in most Ru-assisted carbohydrate oxidations - is an excellent oxidant for aUcylidene and arylidene derivatives [311,317]. 

Formation of l,2 5,6-di-0-isopropylidene-a-D-n7i( -hexo-furanos-3-ulose (Fig. 2.13, 2.4.2.1 Table 2.3) was one of the first carbohydrate oxidations effected by stoich. RuOyCCl [310, 311]. The reagent was also used for oxidation of 1,6-anhydro-3,4-0-isopropylidene-P-D-galactopyranose to the -P-D-/yxo-hexopyranos-2--ulose, part of a route leading to 1,6-anhydro-P-D-talopyranose (Fig. 2.15) [321]. 

H. W. Arnold and W, L. Bvans, The mechanism of carbohydrate oxidation. Fait XXB. The preparation and reactions of glyceraldehyde diethyl mereaptal, J. Am. Chan. Soc. 58 1950... 

In a placebo-controlled study in six patients with type 2 diabetes mellitus thalidomide 150 mg/day for 3 weeks reduced insulin-stimulated glucose uptake by 31% and glycogen synthesis by 48% (1115). However, it had no effect on rates of glycolysis, carbohydrate oxidation, non-oxidative glycolysis, lipolysis, free fatty acid oxidation, or re-esterification. The authors concluded that thalidomide increases insulin resistance in obese patients with type 2 diabetes. 

CONTENTS Acknowledgments, Margery G. Ord and Lloyd A. Stocken. Introduction. Biochemistry Before 1900. Early Metabolic Studies Energy Needs and the Composition of the Diet. Carbohydrate Utilization Glycolysis and Related Activities. Aspects of Carbohydrate Oxidation, Electron Transfer, and Oxidative Phosphorylation. Amino Acid Catabolism in Animals. The Utilization of Fatty Acids. The Impact of Isotopes 1925-1965. Biochemistry and the Cell. Concepts of protein Structure and Function. Chronological Summary of Main Events Up to ca. 1960. Principal Metabolic Pathways. Index. 

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