Fig. 3. Two-dimensional structural representation of the HCV RdRp covalent inhibitor, compound 47. Red: C-3 pyridone ring; blue: indole core and yellow: benzene ring. The compound exhibited covalent binding to RdRp whereby the thiol group of Cys366 attacked the benzene ring at the para position to the nitro group and the fluoro group is released presumably through an aromatic nucleophilic substitution reaction.⁶.