A compound of formula: wherein X 1 is selected from the group consisting of nitro, cyano, trifluoromethyl and -C(=O)OT 4; Z and X 2 are each independently selected from the group consisting of F, Cl, Br and I; X 3 is isopropyl or ethyl; X 4 is either absent or selected from -NR 4 - and -N(R 4)(CH 2)-; R 4 is selected from H and -C 1-6 alkyl; Y 1 is selected from the group consisting of H, -C 1-6 alkyl and a 4- to 7-membered saturated or unsaturated aromatic carbocycle or heterocycle, with the proviso that the point of attachment on said heterocycle is carbon if X 4 is -NR 4 - or -N(R 4)(CH 2)-, wherein said -C 1-6 alkyl is optionally substituted with one or more substituents independently selected from F, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1, -S(=O) 2 T 1, -S(=O) 2 N(T 2)(T 3) and a 5- to 6-membered saturated heterocycle, and wherein said 4- to 7-membered carbocycle or heterocycle is optionally substituted with one or more substituents independently selected from F, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1, -S(=O) 2 T 1, -S(=O) 2 N(T 2)(T 3), oxo and -C 1-3 alkyl, wherein said -C 1-3 alkyl is optionally substituted with one or more substituents independently selected from -OT 7, -N(T 2)(T 3) and a 6-membered saturated heterocycle; T 1, T 2 and T 3 are each independently selected from H and -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, -N(T 5)(T 6), -OT 7, -ST 7, cyano, -C(=O)OT 7, -C(=O)N(T 5)(T 6), -OC(=O)N(T 5)(T 6), -S(=O) 2 T 7, -S(=O) 2 OT 8 and -S(=O) 2 N(T 5)(T 6); T 4 is -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, -N(T 5)(T 6), -OT 7, -ST 7, cyano, -C(=O)OT 7, -C(=O)N(T 5)(T 6), -OC(=O)N(T 5)(T 6), -S(=O) 2 T 8, -S(=O) 2 OT 7 and -S(=O) 2 N(T 5)(T 6); T 5, T 6 and T 7 are each independently selected from H and -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, amino, hydroxyl, thiol and cyano; and T 8 is selected from -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, amino, hydroxyl, thiol and cyano; or a pharmaceutically acceptable salt thereof. X 1 is selected from the group consisting of nitro, cyano, trifluoromethyl and -C(=O)OT 4; Z and X 2 are each independently selected from the group consisting of F, Cl, Br and I; X 3 is isopropyl or ethyl; X 4 is either absent or selected from -NR 4 - and -N(R 4)(CH 2)-; R 4 is selected from H and -C 1-6 alkyl; Y 1 is selected from the group consisting of H, -C 1-6 alkyl and a 4- to 7-membered saturated or unsaturated aromatic carbocycle or heterocycle, with the proviso that the point of attachment on said heterocycle is carbon if X 4 is -NR 4 - or -N(R 4)(CH 2)-, wherein said -C 1-6 alkyl is optionally substituted with one or more substituents independently selected from F, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1, -S(=O) 2 T 1, -S(=O) 2 N(T 2)(T 3) and a 5- to 6-membered saturated heterocycle, and wherein said 4- to 7-membered carbocycle or heterocycle is optionally substituted with one or more substituents independently selected from F, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1, -S(=O) 2 T 1, -S(=O) 2 N(T 2)(T 3), oxo and -C 1-3 alkyl, wherein said -C 1-3 alkyl is optionally substituted with one or more substituents independently selected from -OT 7, -N(T 2)(T 3) and a 6-membered saturated heterocycle; T 1, T 2 and T 3 are each independently selected from H and -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, -N(T 5)(T 6), -OT 7, -ST 7, cyano, -C(=O)OT 7, -C(=O)N(T 5)(T 6), -OC(=O)N(T 5)(T 6), -S(=O) 2 T 7, -S(=O) 2 OT 8 and -S(=O) 2 N(T 5)(T 6); T 4 is -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, -N(T 5)(T 6), -OT 7, -ST 7, cyano, -C(=O)OT 7, -C(=O)N(T 5)(T 6), -OC(=O)N(T 5)(T 6), -S(=O) 2 T 8, -S(=O) 2 OT 7 and -S(=O) 2 N(T 5)(T 6); T 5, T 6 and T 7 are each independently selected from H and -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, amino, hydroxyl, thiol and cyano; and T 8 is selected from -C 1-6 alkyl optionally substituted with one or more substituents independently selected from F, amino, hydroxyl, thiol and cyano; or a pharmaceutically acceptable salt thereof.