Nucleoside pyrophosphates

This sub-section is devoted to nucleotide derivatives that may participate in biosynthesis of certain polymers containing carbohydrate. They are generally included among the sugar nucleotides, although their structures differ somewhat from those of the glycosyl esters of nucleoside 5 -pyrophosphates so far discussed. 

Among D-mannopyranosyl derivatives, cyclization should be possible for /3 anomers and prohibited for the a anomers, as the latter have both substituents in axial orientation in the normal (Cl) conformation, as shown in 84. Accordingly, stability toward alkali is a characteristic of the a-D-mannopyranosyl esters of nucleoside 5 -pyrophosphates.13,22 103... 

Glycosyl esters of nucleoside 5 -pyrophosphates that have a hydrogen atom230 or an acetamido group9 instead of a hydroxyl group at C-2" are stable in alkali. 

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... 

Phosphorolysis of the glycosyl esters of sugar nucleotides leads to the corresponding nucleoside 5 -pyrophosphate and glycosyl phosphate. A wheat-germ enzyme specific for adenosine 5 -(a-D-glucopy-ranosyl pyrophosphate),462 and a yeast enzyme specific for guanosine 5 -(a-D-mannopyranosyl pyrophosphate),463,464 are known. 

It is to be noted that nucleoside 5-pyrophosphates containing glucose104 [for example, uridine 5-(D-glucosyl dihydrogen pyrophosphate)] and other hexoses have been isolated as part of a series of coenzymes. Since the hexose is linked to the nucleotide by way of the pyrophosphate group, these coenzymes are more properly to be considered as derivatives of nucleotides and thus fall outside the scope of this Chapter. 

Nucleoside S -phosphoramidates have proved to be useful intermediates in the synthesis of nucleoside 5 -pyrophosphates and nucleotide coenzymes. Nucleoside phosphoramidates may also be prepared by treatment of a nucleoside 5 -phosphate with ammonia in the presence of N, IV -dioyclohexylcarbodiimide [R. W. Chambers and J. G. Moffatt, J. Am. Chem. Soc., 80, 3752 (1958)]. 

III. Enzymic Synthesis of Glycosyl Esters of Nucleoside 5 -Pyrophosphates.. 358... 

This observation led to the suspicion that epimerization at C-2 occurred with difficulty because of the proximity to C-1, and was impossible without the splitting of the glycosidic bond. However, Matsuhashi and Strominger have since found an example of 2-epimerization in which the glycosyl group remains attached to the nucleoside 5 -pyrophosphate ... 

The reaction catalyzed by polynucleotide phosphorylase is the reversible formation of polymer from nucleoside 5 -pyrophosphates. Mg++ is required. The diphosphates of adenosine, inosine, guanosine, uridine, and cytidine all react, but the reaction with GDP is poor compared with the other nucleotides. The polymer contains 3 -5 linkages, and when... 

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