Chemoenzymatic Synthesis and Antiherpes Activity of 5-Substituted 4,6-Difluorobenzimidazoles Ribo- and 2′-Deoxyribonucleosides

A series of 5,6-disubstituted benzimidazole nucleosides, obtained earlier, did not show any significant antiviral activity at relatively low cytotoxicity in vitro. In the course of our research we have succeeded in introducing an additional fluorine atom into the benzimidazole ring system. A new series of 4,6-difluorobenzimidazoles, bearing various groups (fluoro-, methoxy-, ethoxy-, morpholino-, and pyrrolidino-) in the 5-position of the benzene ring, have been synthesized. All these compounds proved to be substrates for recombinant E. coli purine nucleoside phosphorylase (PNP) in the transglycosylation reaction. Effective methods for the synthesis of ribo-and 2'-deoxyribonucleosides with high yields (60-90%) have been described, and the formation of regioisomeric N3-nucleosides of benzimidazoles have been detected. The biological activity of the nucleosides obtained against herpes simplex virus type 1 (HSV-1) has been elucidated. All compounds show a low cytotoxicity in the cell culture Vero E6. 4,5,6-Trifluoro-1-(beta-D-ribofuranosyl)benzimidazole and 5-methoxy-4,6-difluoro-1-(beta-D-2'-deoxyribofuranosyl) benzimidazole proved to inhibit completely the progression of the virus cytopathic effect (CPE) at a multiplicity of infection (MOI) of 0.01 PFU/cell.