The present invention provides compounds of formula (4), and their pharmaceutically acceptable salts and solvates, which are useful as inhibitors of the Hepatitis C virus (HCV) polymerase enzyme and are also useful for the treatment of HCV infections in HCV-infected mammals. The present invention also provides pharmaceutical compositions comprising compounds of formula (4), their pharmaceutically acceptable salts and solvates. Furthermore, the present invention provides intermediate compounds and methods useful in the preparation of compounds of formula (4).本發明提供具有化學式(4)之化合物,以及它們藥學上可接受的鹽類和溶劑化物,它們可用作為C型肝炎病毒(HCV)聚合酶酵素的抑制劑,且亦可供用於治療HCV-感染的哺乳動物體內的HCV感染。本發明亦提供藥學組成物,其包含有化學式(4)化合物或它們藥學上可接受的鹽類和溶劑化物。再者,本發明提供可用於製備具有化學式(4)的化合物之中間化合物與方法。