Use of 2′-Spirocyclic Ethers in HCV Nucleoside Design

Conformationally restricted 2'-spironucleosides and their prodrugs were synthesized as potential anti-HCV agents. Although the replicon activity of the new agents containing pyrimidine bases was modest, the triphosphate of a 2'-oxetane cytidine analogue demonstrated potent intrinsic biochemical activity against the NS5B polymerase, with IC50 = 8.48 mu M. Activity against NS5B bearing the S282T mutation was reduced. Phosphoramidate prodrugs of a 2'-oxetane 2-amino-6-O-methylpurine nucleoside demonstrated potent anti-HCV activity in vitro, and the corresponding triphosphate retained similar potent activity against both wild-type and S282T HCV NS5B polymerase.