6-deoxy-sugar formation

Many pyrazine and quinoxaline syntheses yield mono- or di-N-oxides (76H(4)769). The condensation of a-aminooximes with 1,2-diketones results in the direct formation of pyrazine mono-N-oxides. The a-aminooximes themselves are not easily prepared but 2-amino-2-deoxy sugars readily form the oximes, which have been condensed with glyoxal to yield the pyrazine 4-oxides (Scheme 18) (72JOC2635, 80JOC1693). 

To obtain reliable, accurate, and reproducible methods for quantitative estimation of deoxy sugars, certain conditions must be fulfilled. Thus, it is necessary that the chromogen be formed quantitatively from the sugar. The chromogen must then react quantitatively with the compound used for color formation, and lastly, the dye, once formed, should be stable and have a well defined molar extinction coefficient. In methods in which all of these conditions are not or cannot be fulfilled, recourse must be had to simultaneous determinations with suitable standard substances, a requirement not always easy to fulfil. 

Despite several attractive features in this method of direct halogen introduction and the obvious applications in the synthesis of deoxy sugars, its uses have not been further exploited by other groups of workers. Some new related methods have become available which reportedly eliminate the difficulties previously encountered such as rearrangement, unreactivity due to steric hindrance, and phosphonate ester formation. The reaction is based on the observation (28) that triethylphosphine reacts with ethanol and carbon tetrachloride to give ethyl chloride, chloroform, and triethylphosphite. In a new adaptation (76, 77) of this... 

Several deoxy sugars have trivial names established by long usage, e.g. fucose (Fuc), quinovose (Qui) and rhamnose (Rha). They are illustrated here in the pyranose form. These names are retained for the unmodified sugars, but systematic names are usually preferred for the formation of names of derivatives, especially where deoxygenation is at a chiral centre of the parent sugar. (See also the alphabetical listing of trivial names in the Appendix.)... 

Methyl 3,4,5,6-tetra-0-acetyl-2-deoxy-2-diazo-D-arabino-hexonate (84) has been irradiated in methanol and in 2-propanol.177 In methanol, the only photoproduct is the enol acetate 85 however, irradiation in 2-propanol results in formation of minor proportions (6%) of 85 and the alkene 86 (7%), but the major product is the deoxy sugar 87 (61%). The difference in reactivity of 84 in these two solvents is probably a reflection of the difference in the ability of methanol and 2-propanol to function as hydrogen donors when reacting with a carbene (see Scheme 31). In methanol, a 1,2-hydrogen atom shift to the divalent... 

If an appropriately situated, unsubstituted hydroxyl group is available, anhydro-ring formation usually takes precedence over substitution or elimination. Thus, with alkali, the bromo-, chloro-, and iodo-deoxy sugars react analogously to sulfonic ester derivatives148 to afford epoxides in good yield.22,169 It has been established170 that l,2 5,6-dianhydro-D-mannitol is formed in aqueous solutions of... 

General Comments. The formation of deoxy sugars by hydrogenation over Raney nickel often leads to the abnormal isomer (namely, that formed by diequatorial opening of the oxirane ring) as the major product, in contrast to the product afforded by lithium aluminum hydride this suggests that a different mechanism is involved in the nickel-catalyzed reaction. 

Piperidines are obtained from 5-amino-5-deoxy sugars by cycliza-tion with C-l their preparation therefore follows the general methods of preparation of such amino sugars. The 5-O-p-tolylsulfonyl- or 5-0-(methylsulfonyl)-pentoses constitute excellent starting-materials, as these sulfonyloxy groups can be replaced by azide, and the azides can be reduced to the 5-amino derivatives, which are capable of cyclization.240-251 The formation of piperidine 178 from 5-O-p-tolyI-sulfonyl-L-arabinose diethyl dithioacetal240 (176) and 177, and of 181 from benzyl 2,3-0-isopropylidene-5-0-(methylsulfonyl)-a-D-lyxofuranoside250 (179) and 180, are examples of this reaction sequence. 

The formation of an a-D-glycoside (52) may be satisfactorily accounted for in terms of the "anomeric effect,MU) particularly applicable with 2-deoxy sugars, in which the absence of substitution at C-2 eliminates factory... 

Biological Mechanisms Involved in the Formation of Deoxy Sugars Enzymatic Hydrogen Mediation... 

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