A compound of Formula (I) is provided that has been shown to be useful for treating a disease caused by a viral infection: wherein R1, R2, R3, R4, R5, R6, R7, R8, X1, X2, X3 and X4, are as defined herein.本發明提供式(I)化合物,其展示適用於治療由病毒感染引起之疾病:其中R1、R2、R3、R4、R5、R6、R7、R8、X1、X2、X3及X4如本文中所定義。