Substituted-1-phthalazinamines as vr-1 antagonists

1. A compound of formula (I):

wherein Ar is phenyl, a six-membered heteroaromatic group containing one, two or three nitrogen atoms or a five-membered heteroaromatic group containing one, two, three or four heteroatoms chosen from oxygen, nitrogen and sulfur, at most one heteroatom being oxygen or sulfur, Ar being optionally substituted with one, two or three groups independently chosen from halogen, hydroxy, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 1-6 alkoxy, C 2-6 alkenyloxy, C 2-6 alkynyloxy, amino, haloC 1-6 alkyl, haloC 2-6 alkenyl, haloC 2-6 alkynyl, hydroxyC 1-6 alkyl, hydroxyC 2-6 alkenyl, hydroxyC 2-6 alkynyl, cyano, nitro, aminoC 1-6 alkyl, aminoC 2-6 alkenyl, aminoC 2-6 alkynyl, C 1-6 alkylsulfonyl, C 1-6 alkylsulfinyl, C 1-6 alkylthio, C 1-6 alkoxycarbonyl, haloC 1-6 alkoxy, haloC 2-6 alkenyloxy, haloC 2-6 alkynyloxy, NR 4 R 5 , CONR 4 R 5 or CO 2 NR 4 R 5 where each R 4 and R 5 is independently hydrogen or C 1-6 alkyl;

R 1 is phenyl, a six-membered heteroaromatic group containing one, two or three nitrogen atoms or a five-membered heteroaromatic group containing one, two, three or four heteroatoms chosen from oxygen, nitrogen and sulfur, at most one heteroatom being oxygen or sulfur, Ar being optionally substituted with one, two or three groups independently chosen from halogen, hydroxy, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 1-6 alkoxy, C 2-6 alkenyloxy, C 2-6 alkynyloxy, amino, haloC 1-6 alkyl, haloC 2-6 alkenyl, haloC 2-6 alkynyl, hydroxyC 1-6 alkyl, hydroxyC 2-6 alkenyl, hydroxyC 2-6 alkynyl, cyano, nitro, aminoC 1-6 alkyl, aminoC 2-6 alkenyl, aminoC 2-6 alkynyl, C 1-6 alkylsulfonyl, C 1-6 alkylsulfinyl, C 1-6 alkylthio, C 1-6 alkoxycarbonyl, haloC 1-6 alkoxy, haloC 2-6 alkenyloxy, haloC 2-6 alkynyloxy, NR 4 R 5 , CONR 4 R 5 or CO 2 NR 4 R 5 where R 4 and R 5 are as defined above;

R 2 is hydrogen, halogen, hydroxy, C 1-6 alkyl, C 2-6 alkenyl, C 2-6 alkynyl, C 1-6 alkoxy, C 2-6 alkenyloxy, C 2-6 alkynyloxy, NR 6 R 7 where R 6 and R 7 are, independently, hydrogen, C 1-6 alkyl or C 1-6 hydroxyalkyl, or R 6 and R 7 , together with the nitrogen atom to which they are attached form a 4, 5 or 6-membered stable heterocycle optionally containing an oxygen ring atom;

R 3 is hydrogen or C 1-6 alkyl;

one X, Y and Z is N and the other two are CR 8 where R 8 is hydrogen, halogen or C 1-6 alkyl;

or a pharmaceutically acceptable salt thereof.

2. A compound according to claim 1 in which Z is N and X and Y are CH.

3. A compound according to claim 1 in which R 1 is para-substituted phenyl or pyridyl.

4. A compound according to claim 1 , in which Ar is pyridyl monosubstituted at the ring position adjacent to the point of attachment of Ar to the rest of the molecule.

5. A compound according to claim 4 in which R 2 is hydrogen, dimethylamino or morpholino.

6. A compound according to claim 1 which is:

N-(4-trifluoromethylphenyl)-2-(3-trifluoromethyl-2-pyridinyl)pyrido[2,3-d]pyridazin-5-amine;

7-(3-methyl-2-pyridinyl)-N-(4-trifluoromethylphenyl)pyrido[3,4-d]pyridazin-4-amine;

3-(3-methylpyridin-2-yl)-N-(4-trifluoromethylphenyl)pyrido[2,3-d]pyridazin-8-amine;

N-(4-trifluoromethylphenyl)-2-(3-chloro-2-pyridinyl)pyrido[2,3-d]pyridazin-5-amine; and

N-(5-trifluoromethyl-2-pyridinyl)-2-(3-trifluoromethyl-2-pyridinyl)pyrido[2,3-d]pyridazin-5-amine; or a pharmaceutically acceptable salt thereof.

7. A pharmaceutical composition comprising a compound according to any one of claims 1 or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable excipient.

8. A method for treating pain, which method comprises administering to a mammalian patient in need thereof a therapeutically effective amount of the compound of claim 1 or a pharmaceutically acceptable salt thereof.