Compounds of the formula ##STR00001## where the variables are as defined in the specification inhibit the NS3 protease of flavivirus such as hepatitis C virus (HCV). The compounds comprise a novel linkage between a heterocyclic P2 unit and those portions of the inhibitor more distal to the nominal cleavage site of the native substrate, which linkage reverses the orientation of peptidic bonds on the distal side relative to those proximal to the cleavage site.