Selective oxidation of sugars

Oxidation of lactose and maltose with Au/Ti02 catalysts has been reported to give close to 100% selectivity to lactobionic acid and malto-bionic acid, respectively63 which have potential uses in the pharmaceutical and detergent industries, as well as in food. Studies of the catalytic conversion of glucose by hydrogenation and oxidation to produce sorbitol and gluconic acid respectively have also been reported.64 Sorbitol is also manufactured on a 60 000 tonnes per annum scale. 

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Various substituted N-hiomo- and A/-chloroureas have also been prepared (97). These compounds are useful for synthesis of oxazoUdinones, and also hydrazine, hydrazo, and azo compounds. A/-Bromourea [51918-81 -1] is useful for selective oxidation of sugar derivatives (98). 

The use of Au-Pd catalysts, as recently developed at Cardiff University by Hutchings group, for hydrogen peroxide synthesis and selective oxidation reactions, is now being used by David Chadwick at Imperial College, London for selective oxidation of sugars and terpenes [136]. 

When used at room temperature in the presence of an active platinum catalyst in an inert solvent, e.g., acetone or ethyl acetate, oxygen will oxidize nonhindered, saturated hydroxyl groups and exposed allylic alcohols. This reagent has found extensive use in sugar chemistry and is particularly suited for the selective oxidation of either 3a- or 3j -alcohols of steroids. Other hydroxyl groups on the steroid skeleton are much less sensitive to oxidation. As a result, this reaction has been used extensively in research on polyhydroxy cardiac-active principles, e.g., the cardenolides and bufadienolides, where the 3-hydroxyl group is easily oxidized without extensive oxidation or dehydration of other hydroxyl groups. The ordinarily difficult selective oxidation of the... 

Uronic acids are found in nature, but they are formed enzymically by selective oxidation of the primary alcohol function of a sugar. Oxidation takes place not on the free sugar, but on UDPsugar... 

In contrast, if a single aqueous liquid phase is used, and if the aldehyde product has a tendency to be hydrated, the reaction proceeds smoothly to the carboxylic acid salt (413,414). It is believed that the RC(OH)2 hydration product of the aldehyde is the actual reagent. This reaction is highly useful for the selective oxidation of primary alcohol groups in sugars such as methyl-a-D-glucopyranoside to the uronic salt ... 

Most of these liquid phase catalytic oxidations have been used for the selective oxidation of carbohydrates. In the oxidation of a sugar such as glucose, four basic types of selective oxidation are possible. ... 

As depicted in Scheme 21.1 for the oxidation of glucose, three general types of acids can be produced by the oxidation of a sugar aldonic acids in which only the aldehyde of the parent aldose has been oxidized to the acid aldaric acids that are dicarboxylic acids with one carboxy group coming from the oxidation of the aldehyde and the other from the primary alcohol at the other end of the carbon chain or uronic acids derived from the selective oxidation of the primary alcohol without the oxidation of the aldehyde. 

Substituted thiazoles, which on deprotection afford aldehydes, have been utilized in the synthesis of derivatives of dicarbonyl sugars such as the methyl glycoside 3. Various procedures for the selective oxidation of both protected and unprotected glycals at the aUylic position are discussed in Chapter 13. The pyrone 4 and the diketone dihydrate 5 have been... 

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