Compounds having the formula I wherein A, R1, R2, R3, R4a, R4b, R4c, R5, R6, R7a, R7b, Ar1, Rc, Rd, Re, Rf, X, n and p are as defined herein are Hepatitis C virus NS5b polymerase inhibitors. Also disclosed are compositions and methods for treating an HCV infection and inhibiting HCV replication.