Compounds represented by formula (I) : or pharmaceutically acceptable salts and solvates thereof, wherein R1, X, Y, Y1, and Z are as defined herein, are useful for treating flavivipdae viral infections Said viral infection is Hepatitis C virus (HCV), bovme viral diarrhea virus (BVDV), hog cholera virus, dengue fever virus, Japanese encephalitis virus or yellow fever virus.