A compound of Formula I: or a pharmaceutically acceptable salt or solvate thereof, wherein: R 3 is mono- or dihalo-phenyl; R 4 is alkyl, haloalkyl, optionally substituted cycloalkyl, optionally substituted cycloalkylalkyl, optionally substituted benzyl, or optionally substituted benzofused cycloalkyl; R 5 is -SO 2 -, wherein the second end substituent is alkyl, haloalkyl, optionally substituted arylalkyl, or optionally substituted heteroarylalkyl; or -N(R 9) 2, wherein one R 9 is H and the other is optionally substituted arylalkyl or optionally substituted heteroarylalkyl; or R 4 and the second end substituent on R 5 together are -alkenyl-; wherein the optional substituents are independently chosen from alkyl, alkenyl, alkynyl, aryl, heteroaryl, aralkyl, alkylaryl, heteroaralkyl, hetereoarylalkenyl, heteroarylalkynyl, alkylheteroaryl, hydroxy, hydroxyalkyl, alkoxy, trihaloalkoxy, aryloxy, aralkoxy, alkoxyalkoxy, acyl, aroyl, halo, monohaloalky, dihaloalkyl, trihaloalkyl, nitro, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, alkylsulfonyl, arylsulfonyl, heteroarylsulfonyl, alkylthio, arylthio, heteroarylthio, aralkylthio, heteroaralkylthio, cycloalkyl, heterocyclyl, -C(=N-CN)-NH 2,-C(=NH)-NH 2,-C(=NH)-NH(alkyl),-NY 1 Y 2,-alkyl-NY 1 Y 2,-C N 1 Y 2 and -SO 2 NY 1 Y 2, wherein Y 1 and Y 2 can be the same or different and are independently selected from hydrogen, alkyl, aryl, cycloalkyl, and aralkyl; wherein alkyl contains 1 to 20 carbon atoms in the chain; alkenyl contains 2 to 15 carbon atoms in the chain; alkynyl contains 2 to 15 carbon atoms in the chain; heteroaryl is an aromatic monocyclic or multicyclic ring system containing 5 to 14 ring atoms, in which one or more of the ring atoms is nitrogen, oxygen or sulphur; aryl means an aromatic monocyclic or multicyclic ring system containing from 6 to 14 carbon atoms; cycloalkyl means a non-aromatic mono- or multicyclic ring system containing 3 to 10 carbon atoms; aryl means H-C -, alkyl-C - or cycloalkyl-C -; and heterocyclyl means a non-aromatic saturated monocyclic or multicyclic ring system containing 3 to 10 ring atoms in which one or more of the atoms in the ring system is nitrogen, oxygen or sulphur. R 3 is mono- or dihalo-phenyl; R 4 is alkyl, haloalkyl, optionally substituted cycloalkyl, optionally substituted cycloalkylalkyl, optionally substituted benzyl, or optionally substituted benzofused cycloalkyl; R 5 is -SO 2 -, wherein the second end substituent is alkyl, haloalkyl, optionally substituted arylalkyl, or optionally substituted heteroarylalkyl; or -N(R 9) 2, wherein one R 9 is H and the other is optionally substituted arylalkyl or optionally substituted heteroarylalkyl; or R 4 and the second end substituent on R 5 together are -alkenyl-; wherein the optional substituents are independently chosen from alkyl, alkenyl, alkynyl, aryl, heteroaryl, aralkyl, alkylaryl, heteroaralkyl, hetereoarylalkenyl, heteroarylalkynyl, alkylheteroaryl, hydroxy, hydroxyalkyl, alkoxy, trihaloalkoxy, aryloxy, aralkoxy, alkoxyalkoxy, acyl, aroyl, halo, monohaloalky, dihaloalkyl, trihaloalkyl, nitro, cyano, carboxy, alkoxycarbonyl, aryloxycarbonyl, aralkoxycarbonyl, alkylsulfonyl, arylsulfonyl, heteroarylsulfonyl, alkylthio, arylthio, heteroarylthio, aralkylthio, heteroaralkylthio, cycloalkyl, heterocyclyl, -C(=N-CN)-NH 2,-C(=NH)-NH 2,-C(=NH)-NH(alkyl),-NY 1 Y 2,-alkyl-NY 1 Y 2,-C N 1 Y 2 and -SO 2 NY 1 Y 2, wherein Y 1 and Y 2 can be the same or different and are independently selected from hydrogen, alkyl, aryl, cycloalkyl, and aralkyl; wherein alkyl contains 1 to 20 carbon atoms in the chain; alkenyl contains 2 to 15 carbon atoms in the chain; alkynyl contains 2 to 15 carbon atoms in the chain; heteroaryl is an aromatic monocyclic or multicyclic ring system containing 5 to 14 ring atoms, in which one or more of the ring atoms is nitrogen, oxygen or sulphur; aryl means an aromatic monocyclic or multicyclic ring system containing from 6 to 14 carbon atoms; cycloalkyl means a non-aromatic mono- or multicyclic ring system containing 3 to 10 carbon atoms; aryl means H-C -, alkyl-C - or cycloalkyl-C -; and heterocyclyl means a non-aromatic saturated monocyclic or multicyclic ring system containing 3 to 10 ring atoms in which one or more of the atoms in the ring system is nitrogen, oxygen or sulphur.