Nucleosides glycosyl nucleoside pyrophosphates

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. 

II. Isolation, Characterization, and Elucidation of Structure of Natural Glycosyl Esters of Nucleoside Pyrophosphates... 

Dilute perchloric acid or trichloroacetic acid, or ethanol, is usually employed for extraction of the glycosyl esters of nucleoside pyrophosphates from biological materials.19 The high lability of these compounds in acidic media (see Section IV, p. 356) leads to unavoidable losses during extraction with acids. Extraction with ethanol can lead to difficulties, as ethanol may not completely inactivate pyrophosphatases present in the tissue the action of these enzymes may result in partial degradation of the nucleoside pyrophosphate derivatives. Such a situation has been encountered particularly with plant tissues.20... 

The isolation of an individual glycosyl ester of a nucleoside pyrophosphate is a rather difficult task. Ion-exchange column-chromatography and preparative, paper-chromatography have been the main methods used for solving problems in separation. 

The ion-exchange separation usually affords individual fractions of structurally related glycosyl esters of nucleoside pyrophosphates, containing the same nucleotide residue, but differing in the structure of the glycosyl groups. Separation of the esters of N-acetylhexos-amines, uronic acids, and neutral monosaccharides from one another is also usually achieved. 

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. 

Comparative identification of a glycosyl ester of a nucleoside pyrophosphate with an authentic sample is usually based on the identity of their ultraviolet spectra and by comparison of chromatographic mobilities of the samples and their degradation products. In addition to paper-chromatographic techniques, it may be of value to use paper... 

F. Eisenberg and A. H. Bolden, Anal. Biochem., 29, 284 (1969). The procedure used results in a degradation of the glycosyl esters of nucleoside pyrophosphates, but the pattern obtained seems to be characteristic. 

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... 

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