The present invention provides the compounds of Formulas I: and its pharmaceutically acceptable salt and ester. Provided compound, composition and method can treat virus infection, especially hepatitis c virus infection with what.本發明提供了式I的化合物:及其藥學上可接受的鹽和酯。所提供的化合物、組合物和方法可用於治療病毒感染,尤其是丙肝病毒感染。