Sugars oxidation products

The complex Ru(tpy)(bpy)02 [tpy = 2,2,2"-terpyridine, bpy = 2,2 -bypyridine] oxidizes organic substrates by hydride abstraction or oxo transfer. This complex, and its derivatives, cleave DNA by oxidation of the sugar at the V position and oxidation of guanine. Oxidation at the V position leads to the release of free bases and a furanone product. The kinetic parameters for the oxidation of D-ribose, 2-deoxy-D-ribose, and nucleotides by Ru(tpy)(bpy)02 were determined in phosphate buffer (pH 7). The increased reactivity of DNA as compared to RNA was rationalized on the basis of deactivation of the sugar oxidation product by the polar effect of the 2 -hydroxyl group.160... 

Spoilage of grapes by various parasites and bacteria may result in sugar oxidation products with one or more ketone functions. One of their properties is to combine with sulfur dioxide, making the wines difficult to store (Volume 1, Section 8.4.3.). 

Ofner Method. This method is for the determination of invert sugar in products with up to 10% invert in the presence of sucrose and is a copper-reduction method that uses Ofner s solution instead of Fehling s. The reduced cuprous oxide is treated with excess standardized iodine, which is black-titrated with thiosulfate using starch indicator. 

Although equation 9 is written as a total oxidation of sugar, this outcome is never realized. There are many iatermediate oxidation products possible. Also, the actual form of chromium produced is not as simple as that shown because of hydrolysis, polymerization, and anion penetration. Other reduciag agents are chosen to enhance the performance of the product. 

Like all hydrazones, osazones lose phenylhydrazine when heated with hydrochloric acid. Naturally, it is not the sugar originally taken which is thus recovered, but an oxidation product, a so-called osone. In the example chosen the osone is ... 

The kinetics and mechanisms of the oxidation of DNA, nucleic acid sugars, and nucleotides by [Ru(0)(tpy)(bpy)] and its derivatives have been reported. " The Ru =0 species is an efficient DNA cleavage agent it cleaves DNA by sugar oxidation at the 1 position, which is indicated by the termini formed with and without piperidine treatment and by the production of free bases and 5-methylene-2(5//)-furanone. Kinetic studies show that the I -C— activation is rate determining and a hydride transfer mechanism is proposed. The Ru =0 species also oxidizes guanine bases via an 0x0 transfer mechanism to produce piperidine-labile cleavages. 

From the yields of 5,6-dihydropyrimidine radicals, we predict reduction product yields of 0.04-0.06 pmol/J for 5,6-dihydrouracil and 0.03-0.05 pmol/J for 5,6-dihydro-thymine for B-form DNA hydrated to 9 waters per nucleotide. With respect to oxidation products, we predict strand-break yields —0.10 pmol/J. A very surprising prediction of this model is that the yield of damaged guanine is nil. Half the damage is oxidized sugar products and the other half is reduced pyrimidines. 

Structurally, these acids are cunsidered to be the oxidation products of polyhydric alcohols. However, a number of them can be formed from the oxidation of sugars. The careful oxidation of glycerol will yield a syrupy liquid, glyceric acid, an example of a dihydroxymonobasic carboxylic acid. 

When the structures of derivatives of the parent compounds depart more and more from those of the original sugars, the bridged-system nomenclature may be advantageously applied over the carbohydrate terms. This could be the case when one, or both, of the OH groups on C-4 and C-8 is (are) absent, as in the deoxy series (see Section V,3), and also in the oxidation products (see Section V,4), where sugar-derived names become complex. 

This section deals with acids, that are formally modified aldonic acids, such as keto, deoxy, and branched-chain acids (including the so-called saccharinic acids). The aminoaldonic acids, which are oxidation products of amino sugars, and, in particular, the important nonulosaminic acids (neuraminic acids) and muramic acid, are not discussed here. The formation of saccharinic acids by the treatment of sugars with alkali, and the mechanisms involved, are likewise outside the scope of this chapter. 

Kinetics of oxidation of four pentoses by bromamide-T were conducted in alkaline medium at different temperatures and the overall activation parameters have been calculated.52 Aldonic acids were the oxidation products, and a mechanism was suggested in which formation of the enediol anion of the sugar is the rate-limiting step. As aldoses may undergo epimerization in alkaline solutions, the oxidation of monosaccharides with bromamide-T was also performed in hydrochloric acid solution.53 Kinetic parameters revealed a low reactivity of ketoses relative to aldoses, and indicated that the cyclic forms of the latter are involved in the oxidations. 

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