Disclosed are compounds, compositions and methods for treating viral infections caused by a flaviviridae family virus, such as hepatitis C virus. Such compounds are represented by Formula IB as follows: ##STR00001## and pharmaceutically acceptable prodrugs and salts thereof, where R, R.sup.1, R.sup.13, R.sup.14, W, W.sup.2, W.sup.3, Y and Z are as defined herein.