Anomeric derivatives, glycosides

Reduction of aldonolactones and their derivatives with isotopically modified reducing agents leads to sugars labeled at the anomeric center. Glycosides substituted with deuterium or labeled with tritium are widely employed for kinetic isotope-effect measurements, mechanistic studies, isotope-tracing experiments, and so on. 

Additional application of oxidants such as hydrogen peroxide to the selenoethers thus formed gives rise to the corresponding alkenes. Thus, the consecutive treatment of the ribose derivative 3 with phenylselenenyl chloride and hydrogen peroxide resulted in a mixture of the a- and /5-anomeric C-glycosides showdomycin (4) and epishowdomycin (epi-4)55. 

In order to minimize such possible side-reactions as anomerization of glycosides and acetolysis of acetal structures, alternative techniques of acetylation have been studied. Whereas basic catalysis leads to severe complications in certain nitro sugar derivatives (see Section IV,2a and c pp. 124, 129), boron trifluoride etherate has proved to be an excellent agent for satisfactory acetylation of glycosides, O-benzyl-idenated glycosides, and disaccharides that contain a deoxynitro function.148,149... 

The potential of the ambient pressure ion mobility time-of-flight mass spectrometry (AP IMS TOP MS) has been tested for the separation of different anomeric methyl glycosides derived from D-mannose, D-galactose, and D-glucose with the same anomeric configuration on Cl. To study the separation effect, Ag+, Ca Cu +, Hg2+ p j2+ acetates, and Co + and Pb + acetylacetonates were added to hexoses and their glycosides under different drift gas regimens (He, N2, Ar, and CO2). It could be... 

Glycosides are a large and very important class of carbohydrate derivatives character ized by the replacement of the anomeric hydroxyl group by some other substituent Gly cosides are termed O glycosides N glycosides S glycosides and so on according to the atom attached to the anomeric carbon... 

Disacchandes are carbohydrates that yield two monosaccharide molecules on hydroly SIS Structurally disaccharides are glycosides m which the alkoxy group attached to the anomeric carbon is derived from a second sugar molecule... 

The most important derivatives of pyrimidines and purines are nucleosides Nucleosides are N glycosides m which a pyrimidine or purine nitrogen is bonded to the anomeric carbon of a carbohydrate The nucleosides listed m Table 28 2 are the mam building blocks of nucleic acids In RNA the carbohydrate component is d ribofuranose m DNA It IS 2 deoxy d ribofuranose... 

Glycoside (Section 25.13) A carbohydrate derivative in which the hydroxyl group at the anomeric position has been replaced by some other group. An O-glycoside is an ether of a carbohydrate in which the anomeric position bears an alkoxy group. 

Note. Acyl substituents on anomeric OH are designated (as above) by 0-acyl prefixes. However, anomeric 0-alkyl derivatives are named as glycosides (see 2-Carb-33). 

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