The Design, Synthesis, and Antiviral Activity of Monofluoro and Difluoro Analogues of 4′-Azidocytidine against Hepatitis C Virus Replication: The Discovery of 4′-Azido-2′-deoxy-2′-fluorocytidine and 4′-Azido-2′-dideoxy-2′,2′-difluorocytidine | doi.page