Glycosuloses

The 3-deoxyhexos-2-uloses, which had long been hypothesized as intermediates in many important degradation reactions of carbohydrates, have been isolated and studied,412 in particular, 3-deoxy-D- erythro-hexos-2-ulose 3-deoxyglucosone (206), which is found in higher concentrations in diabetic animals.413 In mammals, a significant proportion of 206 is reduced to form 3-deoxy-D-eryt/ ro-hexos-2-ulose (3-deoxy-D-fructose, 207), which was detected in blood and urine. This conversion is likely to be biologically useful, since 207 would be less reactive, and therefore less damaging than 206. 

3-Deoxy-L-g/ycero-pentos-2-ulose is formed by oxidative degradation of 

A more-direct method of preparation is oxidation of aldoses, and optimal yields are afforded by the action of cupric acetate in methanol or ethanol.417 This method is suitable for large-scale preparation of intermediates however, a pure product is obtained only by chromatographic separation from the unreacted sugar byproducts. The synthesis of D-eryt/wo-pentos-2-ulose and its D-threo isomer by oxidation of D-arabinose and D-xylose, respectively, with cupric acetate followed by anion-exchange chromatography has been reported.418 The only product obtained by oxidation of D-glucose with sodium 2-anthraquinonesulfonate in alkaline 

The glycosid-3-ulose derivative 208 was obtained from the corresponding D-ido alcohol by use of acetic anhydride-dimethyl sulfoxide for 4 h at room temperature. However, when the time was extended to 4 days, the doubly branched product 209 was obtained, by sigmatropic rearrangement of the intermediate 210.423 

An improved synthesis of l, 6-anhydro-2,3-di-0-benzyl-/Ti xy7o-hexo-pyranos-4-ulose involves 1,6-anhydride formation from methyl 2,3-di-O-benzyl-a-D-glucopyranoside and subsequent Swern oxidation.424 

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B. Flaherty, S. Nahar, W. G. Overend, and N. R. Williams, Branched-chain sugars. XIV. Reactions of glycosulose derivatives with diazomethane. Ring expansion of glycosulose derivatives, J. Chem. Soc., Perkin Trans. I (1973) 632-638. 

Glycosiduronic acids, of animals, 9, 185-246 poly-, of plants, 1, 329-344 Glycosphingolipids, 24, 381-433 Glycosones, 3-deoxy-. See Glycosuloses, 3-deoxy-. 

Glycosuloses, 3-deoxy-, and the degradation of carbohydrates, 19, 181-218 Glycosylamines, 10, 95-168 Glycosyl azides, 16, 85-103 C-Glycosyl compounds, naturally occurring, 18, 227-258 20, 357-369 Glycosyl esters,... 

A similar condensation has been reported that involves the reaction of the glycosulose monohydrazone 206 with 4,5-diamino-2-phenyl-1,2,3-triazole311 to give 207. 

Reduction of substituted glycosuloses has been valuable in synthetic schemes identihcation of the two epimers obtained by reduction of a ketone has been used to locate the position of the ketone group. Steric factors influence various reducing reagents differently. A good example of stereoselectivity is found in the reduction of l,2 5,6-di-0-isopropylidene-a-i)-r/7)o-hexofuranos-3-ulose (218), which is reduced by... 

Dimethyl phosphite has been added to glycosulose derivatives (for example, 218) as a means of preparing C-phosphono sugars.474 Methyl 2,3,6-tri-0-benzoyl-a-D-n 6o-hexopyranosid-4-ulose reacts with 1,2-ethanedithiol to form the corresponding 4,4-ethylene dithioacetal.475... 

Other methods of preparation and reactions of glycosuloses are described in Ref. 336. 

Reactions in which Carbonyl Groups in Glycosuloses are Converted... 

Type 3. Reactions in which new asymmetric centers are created immediately adjacent to existing asymmetric centers in molecules that contain one asymmetric center (or more). These are the reactions to which the Cram rules5 are usually considered to apply. The stereoselectivity of this type of reaction is usually higher than that normally found in reactions of Types 1 and 2. The synthetic utility of reactions of this type has suffered from the disadvantage that the new asymmetric center in non-carbohydrate compounds cannot usually be detached easily from the original asymmetric framework. However, the ready availability of glycosuloses has provided many examples of Cram-type reactions in carbohydrate chemistry, and the fact that the new asymmetric centers may be detached from the original carbohydrate framework has been exploited. 

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