The present invention provides compounds of Formula (I): and tautomers, isomers, and esters of said compounds, and pharmaceutically acceptable salts, solvates, and pro-drugs of said compounds, wherein each of R, R1, X, Y, Z, R2, R3, R4, R5, R6, R7, R8, R9, R18, R19 and n is selected independently and as defined herein. Compositions comprising such compounds are also provided. The compounds of the invention are effective as inhibitors of HCV, and are useful, alone and together with other therapeutic agents, in treating or preventing diseases or disorders such as viral infections and virus-related disorders.