Sugars, oxidation, selectivity

The starting materials are prepared by oxidation of selectively blocked epoxy sugars with Ru02-NaI04 (3, 243). 

A practical synthesis of nojirimycin from D-glucose has been described, giving an overall yield of 50% from 1,2-0-isopropylidene-D-glucofuranose oxidation of this compound with tributyltin oxide/ bromine selectively gave the 5-keto sugar, which was then converted to the 5-amino-sugar and hence to nojirimycin. The isolation of... 

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). 

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... 

Nucleoside N -oxides have proved useful in preventing intramolecular cyclizations during manipulation of the sugar moiety. A key step is the reductive removal of the oxide when needed. In the presence of Raney nickel, the oxide can be reduced selectively even when such easily reduced substituents as iodo are present. Azides, however, are reduced concomitantly with the oxide 105). 

Multiple electrodes have been used to obtain selectivity in electrochemical detection. An early example involved the separation of catecholamines from human plasma using a Vydac (The Separation Group Hesperia, CA) SCX cation exchange column eluted with phosphate-EDTA.61 A sensor array using metal oxide-modified surfaces was used with flow injection to analyze multicomponent mixtures of amino acids and sugars.62 An example of the selectivity provided by a multi-electrode system is shown in Figure 2.63... 

Oxidation with Mn02 of N-glycosylhydroxylamines (48), obtained in the reaction of sugars (47), with A -methyl- and N -benzylhydroxylamines, leads selectively to the corresponding C -unsubstituted and C-phenyl-iV-glycosyl nitrones (49) (Scheme 2.18) (118, 119). 

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