Oxidation of Ketose Sugars

By careful regulation of conditions, the ketose sugars D-fructose and L-sorbose can be transformed by the agency of nitric acid into the corresponding 2-keto-D-gluconic acid (XXII) and 2-keto-L-gulonic acid (XXVI), respectively. 

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Direct Oxidation of Ketose Sugars. The primary alcoholic group at Cl adjacent to the keto group at C2 of a ketose sugar such as D-fructose (XXI) or l-sorbose, is more sensitive to oxidation than the other primary alcoholic group at C6 or secondary alcoholic groups at C3, C4, and C5. 

Oxidation of Isopropylidene Derivatives of Ketose Sugars. Whenever isopropylidene derivatives can be obtained in which all groups except the primary alcoholic grouping at Cl are blocked this method is undoubtedly the best. It may be illustrated by reference to the preparation of 2-keto-D-gluconic acid from D-fructose.14... 

The Mn(II)-catalysed oxidation of glucose by peroxodisulfate ions occurs via a radical-chain mechanism.26 Kinetics of oxidation of thiodiglycollic acid by (trans-cyclohexane-l,2-diaminc-/V, N, N, /V -tetraacetatolmanganateilJI) have been investigated.27 Oxidations of ketoses and aldoses by manganese(IV) in sulfuric acid media have a first-order dependence on sugar and fractional-order dependence on oxidant.28 A mechanism has been proposed for the oxidation of L-malic acid by Mn(III) pyrophosphate in aqueous acid, involving complex formation and radicals.29... 

Kline and Acree studied the hypoiodite oxidation extensively. The alkali and iodine were both added in small portions throughout the reaction. In this manner the concentration of sugar relative to the sodium hypoiodite was kept at a level favorable to the sugar oxidation (reaction 14). At the end of the reaction, the formation of iodate increased rapidly (reaction 15), taking precedence over the oxidation of ketoses and non-reducing sugars. 

Of considerable importance for the preparation of the ketose sugars is the oxidation of the sugar alcohols by bacteria. It was first observed that the occurrence of L-sorbose in the juice of the mountain ash Sorhus aucu-paria) is due to the bacterial oxidation of the precursor, sorbitol. The bacteria responsible were isolated and their oxidizing action on a series of poly-hydric alcohols was extensively studied by Bertrand 238). The active organism was shown to be identical with Acetobacter xylinum previously... 

Amadori compounds, N-substituted 1-amino-l-deoxy-2-ketoses e.g. (1) in Scheme 1, formed by reaction of free sugars with the primary amino-groups in free amino acids, peptides or proteins can be determined by g.c. analysis of the A-(carboxymethyl)-amino acid derivatives e.g. (2) released by a protocol involving periodate oxidation of the sugar residue. ... 

The simplest carbohydrates, sometimes referred to as monosaccharides, or sugars, are either polyhydroxyaldehydes (aldoses) or polyhydroxyketones (ketoses). They can be derived from polyalcohols (polyols) by oxidation of one carbinol group to a carbonyl group. For example, the simple three-carbon triol, glycerol, can be converted either to the aldotriose, glyceraldehyde, or to the ketotriose, dihydroxyacetone, by loss of two hydrogens (fig. 12.1). 

The oxidation of sugars and polyols by halogens180 has been extensively studied. Polyols may be oxidized to aldoses and ketoses albeit in... 

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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