4-Amino-1-((2R,3S,4S,5R)-5-azido-4-hydroxy-5-hydroxymethyl-3-methyl-tetrahydro-furan-2-yl)-1H-pyrimidin-2-one (22) and prodrugs thereof are hepatitis C (HCV) polymerase inhibitors. Also disclosed are compositions and methods for inhibiting HCV and treating HCV-mediated diseases, processes for making the compounds and synthetic intermediates employed in the process.