Benzimidazole 2′-Isonucleosides: Design, Synthesis, and Antiviral Activity of 2-Substituted-5,6-Dichlorobenzimidazole 2′-Isonucleosides

2,5,6-Trihalogenated benzimidazole-β-D-ribofuranosyl nucleosides and 2-substituted amino-5,6-dichlorobenzimidazole-β-L-ribofuranosyl nucleosides are potent and selective inhibitors of human cytomegalovirus (HCMV). The D-ribofuranosyl analogs are metabolized rapidly in vivo rendering them unsuitable as drug candidates. The primary source of instability is thought to be the anomeric bond. The synthesis of a series of chemically stable benzimidazole-2′-isonucleosides is presented. The synthetic schemes employed are based on nucleophilic displacements of a 2′-tosylate from carbohydrate intermediates with 2-bromo-5,6-dichlorobenzidazole. 2-Bromo and 2-isopropyl amino analogs with 3′- and 5′-oxo and deoxy substitutions were prepared. The benzimidazole-2′-isonucleosides presented here demonstrated reduced activity against HCMV when compared to other D-ribofuranosyl benzimidazole analogs. In addition, they were not found to be inhibitors of HIV.