Aldopentoses oxidation

Sugar X is known to be a D-aldohexose. On oxidation with HNO3, X gives an optically inactive aldaric acid When X is degraded to an aldopentose, oxidation of the aldopentose gives an optically active aldaric acid Determine the structure of X. 

Compound A is a D aldopentose that can be oxidized to an optically inactive aldaric acid B. On Kiliani-Fischei chain extension, A is converted into C and D C can be oxidized to an optically active aldaric acid E, but D is oxidized to an optically inactive aldaric acid F. What are the structures of A-F ... 

In the aldopentose series, 2,3,4-tri-O-acetyl-a-D-xylopyranose afforded the corresponding unsaturated 1,5-lactone by oxidation - elimination. Likewise, hepta-O-acetylcellobiose gave, upon oxidation (184), the product of -elimination at the reducing end. 2,3,4,6-Tetra-O-benzoyl-D-gluco- and D-mannopyranoses were not oxidized by the same reagents. 

Carbohydrates such as 6-deoxyhexoses [210] and aldopentose [211] have been oxidized electrochemically by using manganese mediators. Manganese mediators are also useful for the oxidation of a-amino acids [212]. Sorbic acid precursors... 

The synthetic procedure currently used consists in the direct oxidation of an isolated hydroxyl group in the sugar moiety of suitably protected nucleosides. In the meantime, the synthesis of some keto derivatives of aldopentose nucleosides by selective-elimination processes has been reported.4 8... 

An aldopentose (A) of the D-configuration on oxidation with concentrated nitric acid gives a 2,3,4-trihydroxypentanedioic acid (a trihydroxyglutaric acid) (B) which is optically inactive. (A) on addition of HCN, hydrolysis, lactonization, and reduction gives two stereoiso-meric aldohexoses (C) and (D). (D) on oxidation affords a 2,3,4,5-tetrahydroxy-hexanedioic acid (a saccharic acid) (E) which is optically inactive. Give structures of compounds (A)-(E). 

Isbell and co-workers (51) have tried to minimize the oxygen reaction and to maximize the peroxide reaction. When a large excess of peroxide and a low temperature were maintained, they found that the monosaccharides are converted almost quantitatively to formic and two-carbon acids. Table II presents results for the peroxide oxidation of 14 sugars. The total acid produced from aldo-hexoses under favorable conditions is about six moles, consisting almost entirely of formic acid. Aldopentoses react more rapidly than aldo-hexoses and yield about five moles of formic acid per mole of pentose. Fructose and sorbose yield approximately five moles of total acid of which four moles are formic acid. Glycolic acid was identified qualitatively but not determined quantitatively. L-Rham-nose and L-fucose yield about five moles of acid, including four moles of formic acid. Acetic acid was identified only qualitatively. 

By means of the cyanohydrin reaction, higher sugars of the heptose. octosc, and nonosc types have been prepared. A monosaccharide such as an aldohexosc may be converted into the next lower monosaccharide, such as an aldopeniosc. by oxidation to the acid, which corresponds to the aldohexose. then treating the calcium salt solution of this acid with a solution or ferrous acetate plus hydrogen peroxide. Carbon dioxide is evolved and aldopentose formed. 

Of these, 11 is achiral (meso), whereas 10 is chiral. Therefore, by simply determining which oxidation product is optically active, and hence chiral, we can assign the configurations of 8 and 9. Direct comparison of these synthetic aldopentoses with the naturally occurring compounds then could be used as proof of the structure of natural aldopentoses. By this reasoning 8 turns out to be D-arabinose and 9 is D-ribose. 

T. A. Iyengar, P. Swamy, and D. S. Mahadevappa, Oxidation of some aldopentoses by chloramine-B in alkaline medium a kinetic and mechanistic study, Carbohydr. Res., 204 (1990) 197-204. 

Oxidation of Methylglycosid e s.8 4 The following directions for the oxidation of a-methyl-D-glucopyranoside apply generally to the methyl-pyranosides of the aldohexoses and aldopentoses. 

Identify all of the D-aldopentoses from Figure 25.1 that, on oxidation with nitric acid, give diacids that do not rotate plane-polarized light. 

Sample Problem 27.4 a o-aldopentose a is oxidized to an opticaiiy inactive aidaric acid with HNO3. A is formed by the... 

A D-aldohexose A is formed from an aldopentose B by the Kiliani-Fischer synthesis. Reduction of A with NaBH4 forms an optically inactive alditol. Oxidation of B forms an optically active aldaric acid. What are the structures of A and B ... 

Which D-aldopentose is oxidized to an optically active aldaric acid and undergoes the Wohl degradation to yield a D-aldotetrose that is oxidized to an optically active aldaric acid ... 

The two remaining aldopentoses, ( + )-xylose and ( —)-Iyxose, must have the configurations XI and XII. Oxidation by nitric acid converts (4-)-xylose into an... 

Arabinose is oxidized by warm MKO to an optically aldaric acid. Of the four aldopentoses (A, B, C, and D in Figure 25.9) A and C give optically inactive meso aldaric acids when oxidized, whereas B and D give optically active products. Thus, arabinose must be cither B or D, and mannose and glucose must be either 3 and 4 or 7 and 8 (Figure 25.10). 

Oxidation of aldopentoses to aldark adds. Only structures B and D lead to optically active products. 

Thus in the Ruff degradation, for example of o-glucose to o-arabinose, the aldose is oxidized electrolytically to the aldonic acid and this on treatment with hydrogen peroxide and ferric acetate affords the 2-ketoaldonic acid (aldosulose), which yields D-arabinose by loss of carbon dioxide. The yield of aldopentose from the aldonic acid... 

Oxidation of aldoses by chlorites also results in the formation of the corresponding aldonic acids. The aldopentoses react faster than aldo-hexoses, and monosaccharides are oxidized more rapidly than are the disaccharides. The ketoses remain unaffected unless drastic conditions are employed. The principal reaction has been shown to be as follows. 

L-Nucleosides represent a class of nucleoside analogs with an excellent profile for antiviral activity combined with minimal host toxicity [105]. Synthesis of new L-nucleosides can use L-ribose and 2-deoxy-L-ribose as starting materials. Synthetic preparations of L-ribose from natural epimeric L-aldopentoses such as L-arabinose or L-xylose has recently been reviewed [106]. The simpler approach used an oxidation-reduction at C-2 from L-arabinose as depicted in Scheme 18 [107, 108]. 

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