Synthesis and Anti-HCV Activities of 4′-Fluoro-2′-Substituted Uridine Triphosphates and Nucleotide Prodrugs: Discovery of 4′-Fluoro-2′‑C‑methyluridine 5′-Phosphoramidate Prodrug (AL-335) for the Treatment of Hepatitis C Infection

We report the synthesis and biological evaluation of a series of 4′-fluoro-2′-C-substituted uridines. Triphosphates of the uridine analogues exhibited a potent inhibition of hepatitis C virus (HCV) NS5B polymerase with IC50 values as low as 27 nM. In an HCV subgenomic replicon assay, the phosphoramidate prodrugs of these uridine analogues demonstrated a very potent activity with EC50 values as low as 20 nM. A lead compound AL-335 (53) demonstrated high levels of the nucleoside triphosphate in vitro in primary human hepatocytes and Huh-7 cells as well as in dog liver following a single oral dose. Compound 53 was selected for the clinical development where it showed promising results in phase 1 and 2 trials.