R2 is a hydrogen atom; or R1 together with R2 form the group ???NH???C(O)???CH???CH??? wherein the nitrogen atom is bound to the carbon atom in the phenyl ring holding R1 and the carbon atom is bound to the carbon atom in the phenyl ring holding R2 R3 is selected from hydrogen and halogen atoms or groups selected from ???SO???R5, ???SO2???R5, ???NH???CO???NH2, ???CONH2, hydantoino, C1-4alkyl, C1-4