A compound of formula wherein X 1, X 2 and X 3 are each independently selected from the group consisting of H, F, Cl, Br, I, -OT 1, -N(T 2)(T 3), -NHC(=O)T 4, nitro, cyano, cyclopropyl and -C 1-3 alkyl, with the proviso that at least two substituents selected from X 1, X 2 and X 3 are each independently selected from the group consisting of F, Cl, Br and I; Z 1 and Z 2 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); Z 3 and Z 4 are either taken together to form an oxo group at the carbon atom to which they are attached; or Z 3 and Z 4 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); Z 5 and Z 6 are either taken together to form an oxo group at the carbon atom to which they are attached; or Z 5 and Z 6 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); X 4 is either absent or selected from the group consisting of -NR 4 -, -N(R 4)(CH 2)-, -C(=O)NH- and -C(=O)-; 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 -C(=O)NH-, wherein said -C I-6 alkyl is optionally substituted with one or more substituents independently selected from -OT 1, -ST 1, -N(T 2)(T 3) and a 5- to 6-membered saturated heterocycle, and wherein said 4-to 7-membered saturated or unsaturated aromatic carbocycle or heterocycle is optionally substituted with one or more substituents independently selected from F, Cl, Br, I, -C(=O)H, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1 and -C 1-3 alkyl, wherein said -C 1-3 alkyl is optionally substituted with one or more substituents independently selected from -OT 1 and -N(T 2)(T 3); 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 -N(T 5)(T 6), -OT 7, -ST 7, nitro, 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 -N(T 5)(T 6), -OT 7, -ST 7, nitro, 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 amino, hydroxyl, thiol, nitro and cyano; and T 8 is selected from -C 1-6 alkyl optionally substituted with one or more substituents independently selected from amino, hydroxyl, thiol, nitro and cyano; or a pharmaceutically acceptable salt thereof. X 1, X 2 and X 3 are each independently selected from the group consisting of H, F, Cl, Br, I, -OT 1, -N(T 2)(T 3), -NHC(=O)T 4, nitro, cyano, cyclopropyl and -C 1-3 alkyl, with the proviso that at least two substituents selected from X 1, X 2 and X 3 are each independently selected from the group consisting of F, Cl, Br and I; Z 1 and Z 2 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); Z 3 and Z 4 are either taken together to form an oxo group at the carbon atom to which they are attached; or Z 3 and Z 4 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); Z 5 and Z 6 are either taken together to form an oxo group at the carbon atom to which they are attached; or Z 5 and Z 6 are each independently selected from the group consisting of H, -C 1-6 alkyl, -OT 1 and -N(T 2)(T 3); X 4 is either absent or selected from the group consisting of -NR 4 -, -N(R 4)(CH 2)-, -C(=O)NH- and -C(=O)-; 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 -C(=O)NH-, wherein said -C I-6 alkyl is optionally substituted with one or more substituents independently selected from -OT 1, -ST 1, -N(T 2)(T 3) and a 5- to 6-membered saturated heterocycle, and wherein said 4-to 7-membered saturated or unsaturated aromatic carbocycle or heterocycle is optionally substituted with one or more substituents independently selected from F, Cl, Br, I, -C(=O)H, -OT 1, -N(T 2)(T 3), -C(=O)N(T 2)(T 3), -C(=O)OT 1, -ST 1 and -C 1-3 alkyl, wherein said -C 1-3 alkyl is optionally substituted with one or more substituents independently selected from -OT 1 and -N(T 2)(T 3); 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 -N(T 5)(T 6), -OT 7, -ST 7, nitro, 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 -N(T 5)(T 6), -OT 7, -ST 7, nitro, 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 amino, hydroxyl, thiol, nitro and cyano; and T 8 is selected from -C 1-6 alkyl optionally substituted with one or more substituents independently selected from amino, hydroxyl, thiol, nitro and cyano;