Chemo-enzymatic syntheses and biological evaluation of 5,6-disubstituted benzimidazole ribo- and 2'-deoxyribo-nucleosides

A number of new 5,6-disubstituted benzimidazoles have been prepared and their substrate properties for recombinant E. coli purine nucleoside phosphorylase (PNP; the product of the deoD gene) in the transglycosylation reaction were investigated. The heterocyclic bases showed good substrate activity for PNP and the riboand 2′-deoxyribonucleosides were synthesized. The predominant (OMe and OEt) or exclusive (Oi-Pr, morpholino, and N-methylpiperazino) formation of the 5-substituted 6-fluoro-1-(β-Dribofuranosyl)benzimidazoles was observed. The formation of the regioisomeric 6methoxy-, 6-ethoxy-, or 6-isopropoxy-substituted 1-(2-deoxy-β-D-ribofuranosyl)-5-fluorobenzimidazoles was observed in the trans-2-deoxyribosylation reaction of the corresponding bases. The predominant or exclusive formation of the regioisomeric N1-nucleosides with bulky 5-substituents of 6-fluorobenzimidazole points to a large hydrophobic pocket in the E. coli PNP active site that can accommodate these groups. The biological activity of the synthesized nucleosides was studied and revealed no inhibitory activity against a broad variety of DNA and RNA viruses. The compounds also lacked significant cytotoxicity.