A compound of formula: or a pharmaceutically acceptable salt or solvate thereof, wherein: A 1 is N and A 2 is CH; G is N or CX 4; R 1 is -NR 11 R 14; R 11 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclyl, aryl, and heteroaryl, each group except hydrogen optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, oxo, acyl, cyano, nitro, and amino group; R 14 is selected from the group consisting of hydrogen, alkyl and cycloalkyl; R 2a and R 2b are independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclyl, aryl, and heteroaryl; or alternatively R 2a and R 2b together with the carbon atom to which they are attached form a cyclic moiety selected from the group consisting of cycloalkyl, cycloalkenyl, and heterocyclyl, each optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, oxo, acyl, cyano, nitro, and amino group; R 3 is selected from the group consisting of hydrogen, halogen, hydroxyl, alkyl, alkoxy, and NR 31 R 32; R 31 and R 32 are independently hydrogen or alkyl; X 1 through X 4 are independently selected from the group consisting of hydrogen, halogen, cyano, nitro, hydroxyl, alkyl, alkoxy, and amino; U is selected from the group consisting of -NHS 2 - and -S 2 NH-; and W is selected from the group consisting of alkyl and aryl, each optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, cyano, nitro, and amino. A 1 is N and A 2 is CH; G is N or CX 4; R 1 is -NR 11 R 14; R 11 is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclyl, aryl, and heteroaryl, each group except hydrogen optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, oxo, acyl, cyano, nitro, and amino group; R 14 is selected from the group consisting of hydrogen, alkyl and cycloalkyl; R 2a and R 2b are independently selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclyl, aryl, and heteroaryl; or alternatively R 2a and R 2b together with the carbon atom to which they are attached form a cyclic moiety selected from the group consisting of cycloalkyl, cycloalkenyl, and heterocyclyl, each optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, oxo, acyl, cyano, nitro, and amino group; R 3 is selected from the group consisting of hydrogen, halogen, hydroxyl, alkyl, alkoxy, and NR 31 R 32; R 31 and R 32 are independently hydrogen or alkyl; X 1 through X 4 are independently selected from the group consisting of hydrogen, halogen, cyano, nitro, hydroxyl, alkyl, alkoxy, and amino; U is selected from the group consisting of -NHS 2 - and -S 2 NH-; and W is selected from the group consisting of alkyl and aryl, each optionally substituted by 1 to 5 substituents independently selected from the group consisting of halogen, alkyl, alkoxy, haloalkyl, haloalkoxy, hydroxy, cyano, nitro, and amino.