Of glycosyl ester

Scheme 3.20 Silicon activation of glycosyl ester donors.

The purpose of this Chapter is to summarize the present knowledge concerning the isolation, structure, preparation, and chemical reactions of glycosyl esters of nucleoside pyrophosphates. These aspects have been considered only briefly in the articles cited. Another important topic, which has not been treated previously in a comprehensive manner from a chemical viewpoint, is the mechanism of the enzymic reactions of these compounds, and the specificity of their interaction with the corresponding enzymes. These topics will also be considered here. 

Preparative, paper-chromatography is frequently used for further fractionation of the resulting mixtures. The high lability of glycosyl esters of nucleoside pyrophosphates seriously limits the choice of solvent systems. Systems used most commonly are neutral or slighdy acidic mixtures of ethanol with ammonium acetate,24,25 or weakly acidic solvents based on 2-methylpropionic acid.26 A solvent system containing morpholinium borate has also been found extremely useful.27... 

The unambiguous characterization of glycosyl esters of nucleoside pyrophosphates is difficult, as no suitable crystalline derivatives are known for them, and the hygroscopic nature of their ammonium and metal salts prevents reliable interpretation of the data of elementary analysis. 

The preparative isolation from natural sources of glycosyl esters of nucleoside pyrophosphates is rather laborious, and such isolative procedures are usually applied only until more convenient, synthetic procedures become available. However, the natural source... 

The only general approach to the chemical synthesis of glycosyl esters of nucleoside pyrophosphates thus far found useful involves... 

The high lability of glycosyl esters of nucleoside pyrophosphates strongly limits the possibilities for their chemical modification. However, some conversions may be accomplished on a preparative scale. 

IV. Chemical Reactivity of Glycosyl Esters of Nucleoside Pyrophosphates... 

From hen oviduct, enzymes have been isolated and purified that catalyze sulfation of glycosyl esters of nucleoside 5-pyrophosphates by the action of 3 -0-phosphono-5 -adenylyl hydrogen sulfate.448-449... 

Many enzyme-catalyzed glycosylation reactions are known, and participation in these reactions seems to be the main function in Nature of glycosyl esters of nucleoside pyrophosphates. 

A large number of glycosyl ester nucleotide transferases are known to exist these include those involving cytidylic acid-sialic acid336,337... 

However, the reaction of glycosyl esters with allyltrimethylsilane, when catalyzed by zinc bromide, shows only slight evidence of anchimeric assistance in the four cases investigated.5... 

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