A compound of formula or a pharmaceutically acceptable ester, amide, carbamate, solvate or salt thereof, including a salt of such an ester, amide or carbamate, and a solvate of such an ester, amide, carbamate or salt, wherein R 1 is selected from the group consisting of halogen, cyano, nitro, OR A, N(R B) 2, -C C 1-4 alkyl, -SO 2 C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, haloC 2-6 alkenyl, dihaloC 2-6 alkenyl, trihaloC 2-6 alkenyl, cyanoC 1-6 alkyl, C 1-4 alkoxyC -6 alkyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl, and 5-10 membered heterocyclyl, wherein said phenyl, benzyl or heterocyclyl group can be either unsubstituted or substituted with from 1 to 3 substituents, each substituent being selected from the group consisting of OR A, halogen, cyano, nitro, -C C 1-4 alkyl, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloc 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; R 2 is selected from the group consisting of halogen, cyano, nitro, OR A, N(R B) 2, N 2, -C C 1-4 alkyl optionally substituted with from 1 to 3 halogens, -SO 2 C 1-4 alkyl, -C NH-OH, -C(NH 2)=N-OH, -C(CO 2 H)=N-OH, -C(NH 2)=NH, -C(NH C 1-4 alkyl)=NH, -C(O-C 1-4 alkyl)=NH, -C(NH 2)=N-NH 2, -NH-C(NH 2)=NH, -NH-C NH 2, -N=C(-NH-CH 2 CH 2 -NH-), -S-CN, -S-C(NH 2)=NH, -S-C(NH 2)=N-OH, -CO 2 H, -CH 2 -CO 2 H, -CH CO 2 H, -C CO 2 H, SO 3 H, CH 2 SO 3 H, C 1-6 alkyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl, trihaloC 1-6 alkyl, cyanoC 1-6 alkyl, C 1-4 alkoxyC 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, phenyl, benzyl and 5-10 membered heterocyclyl wherein said phenyl, benzyl or heterocyclyl group can be either unsubstituted or substituted with from 1 to 3 substituents each substituent being selected from the group consisting of OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; provided that if one of R 1 and R 2 represents halogen, the other must represent a group other than halogen; each of R 3, R 4, R 5 and R 6 is independently selected from the group consisting of hydrogen, OR A, halogen, cyano, nitro, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, haloC 1-6 alkyl, dihaloC 1-6 alkyl and trihaloC 1-6 alkyl; each R A is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, C 6-10 aryl and C 6-10 arylC 1-6 alkyl, each optionally substituted by from 1 to 3 halogen atoms; and each R B is independently selected from the group consisting of hydrogen, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-6 alkyl, C 6-10 aryl and C 6-10 arylC 1-6 alkyl, each optionally substituted by from 1 to 3 halogen atoms; with the proviso that the compound of formula is not 4-[3-(4,5-Dihydro-1H-imidazol-2-yl)-2-(3,5-dimethyl-isoxazol-4-yl)-indol-1-yl]-phenol; 1-(4-Hydroxy-phenyl)-2-(4-methyl-imidazol-1-yl)-1H-indole-3-carbonitrile; 1-(4-Hydroxy-phenyl)-2-(1H-pyrazol-3-yl)-1H-indole-3-carbonitrile; 1-(3-Chloro-4-hydroxy-phenyl)-2-(1-methyl-1H-pyrazol-4-yl)-1H-indole-3-carbonitrile; 1-(4-Hydroxy-phenyl)-2-prop-1-ynyl-1H-indole-3-carboxylic acid amide; or 1-(4-Hydroxy-phenyl)-2-thiazol-2-yl-1H-indole-3-carboxylic acid.