Abstract 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 ribo-and 2′- deoxyribonucleosides were synthesized. The predominant (OMe and OEt) or exclusive (O ...