Compounds represented by the formula: ##STR00001## and pharmaceutically acceptable salts thereof and prodrugs thereof; wherein R.sub.1 is H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 R.sub.2 is H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7, CH.dbd.CH.sub.2, CH.sub.2--OH, CH.sub.2F, CF.sub.3 R'.sub.2 is H, OH, NH.sub.2, NH-alkyl, F, N.sub.3, OCH.sub.3, O--C(O)CH(NH.sub.2)alkyl R.sub.3 is H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 R'.sub.3 is H, OH, NH.sub.2, NH-alkyl, F, N.sub.3, OCH.sub.3, O--C(O)CH(NH.sub.2)alkyl R.sub.4 is H, CH.sub.3, C.sub.2H.sub.5, C.sub.3H.sub.7 At least one of R.sub.2, R.sub.3, or R.sub.4has to be other than H, when X.dbd.NH in B ##STR00002## R.sub.6 is H, CH.sub.3, C.sub.2H.sub.5, ##STR00003## R.sub.7 is selected from H, alkyl, alkenyl, aryl, acyloxyalkyl, and pivaloyloxyalkyl, aminoacids, CH.sub.2CH.sub.2SC(O)alkyl; and B is represented by the following structure: ##STR00004## X is independently NR.sup.6, O, S, R.sup.8 and R.sup.9 independently is H, NH.sub.2, OH, SH, F, Cl, Br, I, aryl, heterocycle, alkyl, alkene, alkyne, S-alkyl, S-aryl, S(O)-alkyl, SO.sub.2-alkyl, SO.sub.2NH.sub.2, SO.sub.2NH-alkyl, SO.sub.2NH-aryl, NH-alkyl, NH-aryl, N(alkyl).sub.2, N(aryl).sub.2, O-alkyl, O-aryl, O-heterocycle, NH-(CH.sub.2).sub.n-aryl, NH--C(O)-alkyl, NH--C(O)-aryl are useful for inhibiting viral RNA polymerases and treating patients suffering from diseases caused by various RNA viruses.