Organizing co mmittee

E. coli
 PURINE NUCLEOSIDE PHOSPHORYLASE
:
 IS THE SYNTHESIS OF 
MODIFIED NUCLEOSIDES ALWAYS REGIOSELECTIVE
? 
Irina D. Konstantinova, Ilya V. Fateev, Vera D. Knorre, Roman S. Esipov, 
Anatoly I. Miroshnikov 
Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy 
of Sciences, Miklukho-Maklaya St. 16/10, 117997, Moscow B-437, Russian 
Federation. 
E. coli
purine nucleoside phosphorylases (PNP) are often used in the enzymatic 
synthesis of modified nucleosides. It is known that the transglycosylation reaction is 
characterized by high stereo- and regio-selectivity and is environmentally friendly. PNP 
has a wide substrate specificity: it effectively glycosylates various purines, 
benzimidazoles, and 1,2,4-triazoles. Carbohydrate residues of the natural D-
configuration are represented by ribose, 2-deoxyribose, arabinose, 2-deoxy-2-fluoro-
arabinose, etc. The conversion of a base into a nucleoside depends on complexity of 
substituents and the type of carbohydrate fragment and can reach 95%. 
Thermodynamically unfavorable N7 isomers of natural adenosine and 
guanosine appear in the transglycosylation reaction. The process of their transition 
to natural N9 isomers was described more than 20 years ago. We found that the 
synthesis of N9-modified nucleosides proceeds regioselectively with purines 
having amino groups in the C2 or C6 positions of purine or if there is a bulky 
substituent in the C6 position of purine. In the case of substituted benzimidazole, a 
mixture of N1- and N3-regioisomers is always formed in transglycosylation 
reaction. In synthesis of 1,2,4-triazole nucleosides the glycosylation 
regioisomerism by N1 atom is preserved in 99% of cases. We observed only one 
case of formation of both N2 and N4 regioisomers in the reaction. The largest 
number of errors was found in synthesis of nucleosides in the case of glycosylation 
of fleximer heterocyclic bases in which the purine and pyrrole/pyrazole rings are 
separated by a single C-C bond. Namely in enzymatic synthesis of fleximer 
nucleosides we detected nucleosides with two carbohydrate residues. 

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Plenary presentation
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