R¹ represents hydrogen, —C_1-6alkyl, —C_3-6alkenyl, —C_2-3alkylNR^bR^c, —C_2-3alkylNHCOR^b, phenyl being optionally substituted by halogen, or R¹ represents a group X—W, wherein X represents —C_1-3alkylene- and W represents —CN, —CO₂H, —CONR^bR^c, —COC_1-6alkyl, —CO₂C_1-6alkyl, or phenyl, the phenyl being optionally substituted by one or more substitutents selected from: —C_1-3alkyl, —C_1-3alkoxy, —C_1-3alkylOH, halogen, —CN, —CF₃, —NH₂, —CO₂H and —OH;

R² and R³ independently represent hydrogen, —C_1-3alkyl or —CF₃ with the proviso that one of R² and R³ is —C_1-3alkyl or —CF₃ and the other is hydrogen;

R^b and R^c independently represent hydrogen or —C_1-3alkyl;

A represents:

Z represents one or two optional substituents independently selected from halogen and OH,

B represents one or more optional substituents on ring carbon atoms selected from:

(i) one or more substituents selected from —CF₃, —F, —CO₂H, —C_1-6alkyl, —C_1-6alkylOH, —(C_1-3alkyl)NR^bR^c, —(C_0-3alkyl)CONR^bR^c and —(C_0-3alkyl)CO₂C_1-3alkyl, —CONHC_2-3alkylOH, —CH₂NHC_2-3alkylOH, —CH₂OC_1-3alkyl and —CH₂SO₂C_1-3alkyl;

(ii) a group —Y—R^e,

Y represents —C_1-3alkylene-, —CO—, —C_1-3alkylNH—, —C_1-3alkylNHCO—, —C_1-3alkylNHSO₂—, —CH₂NHSO₂CH₂— or a direct link,

R^e represents phenyl, a 5- or 6-membered cycloalkyl or a 5- or 6-membered heterocycle consisting of at least one heteroatom selected from O or S, each of which is optionally substituted by one or more substituents selected from: —C_1-3alkyl, —C_1-3alkoxy, —C_1-3alkylOH, halogen, —CN, —CF₃, —NH₂, —CO₂H and —OH; or

(iii) a second ring R^f which is fused to the heterocyclic ring, wherein R^f represents phenyl, a 5- or 6-membered cycloalkyl group or a 5- or 6-membered aromatic heterocyclic group consisting of at least one heteroatom selected from O, N or S, and the fused bicyclic group is optionally substituted by one or more substituents selected from: —C_1-3alkyl, —C_1-3alkoxy, —C_1-3alkylOH, halogen, —CN, —CF₃, —NH₂, —CO₂H and —OH;

or a pharmaceutically acceptable salt thereof.