A compound of formula: wherein X is S, -N=C(R 1)-, or -C(R 1)=C(R 1)-; each R 1 is independently H, F, Cl, C 1 -C 6 -alkyl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; wherein at least one R 1 is F, Cl, C 1 -C 6 -alkyl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; or both R 1, together with the carbon atoms to which they are bound, form a fused phenyl; R is H, alkyl optionally substituted with -((C 1 -C 6 -alkyl)OC OC 1 -C 6 -alkyl), or benzyl, wherein the benzyl can be unsubstituted or substituted with methoxyl; and Ring A is a bicyclic fully aromatic or partially reduced heteroaryl ring system comprising 3, 4, or 5 N atoms, substituted with 0, 1, 2, 3,or 4 substituents each independently selected from the set consisting of NH 2, cyano, NHC(=O)O-tBu,OH, carboxamido, C 1 -C 6 -alkyl, - S 2 (C 1 -C 6 -alkyl), -S (C 1 -C 6 -alkyl), alkylnitrile, alkoxyl, and haloalkyl; provided that a partially reduced heteroaryl ring system can also be substituted with an oxo group; or a pharmaceutically acceptable salt thereof, or formula: wherein each R 1 is independently H, F, Cl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; wherein at least one R 1 is F, Cl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; or both R 1, together with the carbon atoms to which they are bound, form a fused phenyl; and Ring A is a bicyclic fully aromatic or partially reduced heteroaryl ring system comprising 3, 4, or 5 N atoms, substituted with 0, 1, 2, 3,or 4 substituents each independently selected from the set consisting of NH 2, cyano, NHC(=O)O-tBu,OH, carboxamido, C 1 -C 6 -alkyl, - S 2 (C 1 -C 6 -alkyl), -S (C 1 -C 6 -alkyl), alkylnitrile, alkoxyl, and haloalkyl; provided that a partially reduced heteroaryl ring system can also be substituted with an oxo group; or a pharmaceutically acceptable salt thereof. X is S, -N=C(R 1)-, or -C(R 1)=C(R 1)-; each R 1 is independently H, F, Cl, C 1 -C 6 -alkyl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; wherein at least one R 1 is F, Cl, C 1 -C 6 -alkyl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; or both R 1, together with the carbon atoms to which they are bound, form a fused phenyl; R is H, alkyl optionally substituted with -((C 1 -C 6 -alkyl)OC OC 1 -C 6 -alkyl), or benzyl, wherein the benzyl can be unsubstituted or substituted with methoxyl; and Ring A is a bicyclic fully aromatic or partially reduced heteroaryl ring system comprising 3, 4, or 5 N atoms, substituted with 0, 1, 2, 3,or 4 substituents each independently selected from the set consisting of NH 2, cyano, NHC(=O)O-tBu,OH, carboxamido, C 1 -C 6 -alkyl, - S 2 (C 1 -C 6 -alkyl), -S (C 1 -C 6 -alkyl), alkylnitrile, alkoxyl, and haloalkyl; provided that a partially reduced heteroaryl ring system can also be substituted with an oxo group; each R 1 is independently H, F, Cl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; wherein at least one R 1 is F, Cl, ethenyl or ethynyl either of which can be substituted, cyano, alkoxyl, haloalkyl, or C 3 -C 6 -cycloalkyl; or both R 1, together with the carbon atoms to which they are bound, form a fused phenyl; and Ring A is a bicyclic fully aromatic or partially reduced heteroaryl ring system comprising 3, 4, or 5 N atoms, substituted with 0, 1, 2, 3,or 4 substituents each independently selected from the set consisting of NH 2, cyano, NHC(=O)O-tBu,OH, carboxamido, C 1 -C 6 -alkyl, - S 2 (C 1 -C 6 -alkyl), -S (C 1 -C 6 -alkyl), alkylnitrile, alkoxyl, and haloalkyl; provided that a partially reduced heteroaryl ring system can also be substituted with an oxo group;