Pyridazin-3(2

1. A compound of formula (I)

wherein

R 1 represents:

a hydrogen atom;

an alkyl, alkenyl or alkynyl group, which is optionally substituted by one or more substituents chosen from halogen atoms and hydroxy, alkoxy, aryloxy, alkylthio, arylthio, oxo, amino, mono-alkylamino, di-alkylamino, acylamino, hydroxycarbonyl, alkoxycarbonyl, carbamoyl, mono-alkylcarbamoyl, and di-alkylcarbamoyl groups;

R 2 represents a monocyclic or polycyclic heteroaryl group, which is optionally substituted by one or more substituents chosen from:

halogen atoms;

alkyl and alkylene groups, which are optionally substituted by one or more substituents chosen from halogen atoms and phenyl, hydroxy, alkoxy, aryloxy, alkylthio, arylthio, oxo, amino, mono-alkylamino, di-alkylamino, acylamino, hydroxycarbonyl, alkoxycarbonyl, carbamoyl, mono-alkylcarbamoyl, and di-alkylcarbamoyl groups; and

phenyl, hydroxy, hydroxycarbonyl, hydroxyalkyl, alkoxycarbonyl, alkoxy, cycloalkoxy, nitro, cyano, aryloxy, alkylthio, arylthio, alkylsulfinyl, alkylsulfonyl, alkylsulfamoyl, acyl, amino, mono-alkylamino, di-alkylamino, acylamino, hydroxycarbonyl, alkoxycarbonyl, carbamoyl, mono-alkylcarbamoyl, di-alkylcarbamoyl, ureido, N′-alkylureido, N′, N′-dialkylureido, alkylsulfamido, aminosuphonyl, mono-alkylaminosulfonyl, di-alkylaminosulfonyl, cyano, difluoromethoxy, and trifluoromethoxy groups;

R 3 represents a hydrogen atom or an alkylcarbonyl group wherein the alkyl group is optionally substituted by one or more substituents chosen from halogen atoms and phenyl, hydroxy, hydroxyalkyl, alkoxy, aryloxy, alkylthio, arylthio, oxo, amino, mono-alkylamino, di-alkylamino, acylamino, hydroxycarbonyl, alkoxycarbonyl, carbamoyl, mono-alkylcarbamoyl, and di-alkylcarbamoyl groups; and

R 4 represents a group of formula:

G-L1-(CRR′) n —

wherein

n is an integer from 0 to 3;

R and R′ are each independently chosen from hydrogen atoms or lower alkyl groups;

L1 is a linker chosen from a direct bond, or —O—, —CO—, —NR″—, —O(CO)NR″—, —O(CO)O—, —O—(CO)—, —(CO)O—, —NR″—(CO)— or —O(R″O)(PO)O— groups wherein R″ is chosen from hydrogen atoms or lower alkyl groups;

G is chosen from hydrogen atoms or alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclyl, aryl, arylalkyl or heteroaryl groups, said groups being optionally substituted with one or more substituents chosen from:

halogen atoms;

alkyl and alkenyl groups, which are optionally substituted by one or more substituents chosen from halogen atoms; and

hydroxy, alkoxy, cycloalkyloxy, alkylthio, alkylsulfinyl, alkylsulfonyl, alkylsulfamoyl, amino, mono- or di-alkylamino, acylamino, nitro, acyl, hydroxycarbonyl, alkoxycarbonyl, carbamoyl, mono-alkylcarbamoyl, di-alkylcarbamoyl, ureido, N′-alkylureido, N′,N′-dialkylureido, alkylsulfamido, aminosuphonyl, mono-alkylaminosulfonyl, di-alkylaminosulfonyl, cyano, difluoromethoxy and trifluoromethoxy groups;

or pharmaceutically acceptable salts or N-oxides thereof.

2. The compound according to claim 1 , wherein R 1 is a hydrogen atom or lower alkyl group, which is optionally substituted by one or more substituents chosen from halogen atoms and hydroxy, alkoxy, alkylthio, hydroxycarbonyl, and alkoxycarbonyl groups.

3. The compound according to claim 1 , wherein R 2 is a monocyclic or polycyclic heteroaryl group which is optionally substituted by one or more substituents chosen from halogen atoms and alkyl, hydroxy, hydroxyalkyl, hydroxycarbonyl, alkoxy, alkylenedioxy, alkoxycarbonyl, aryloxy, acyl, acyloxy, alkylthio, arylthio, amino, nitro, cyano, mono-alkylamino, di-alkylamino, acylamino, carbamoyl, mono-alkylcarbamoyl, di-alkylcarbamoyl, difluoromethyl, trifluoromethyl, difluoromethoxy, and trifluoromethoxy groups.

4. The compound according to claim 3 , wherein R 2 is a monocyclic or polycyclic N-containing heteroaryl group.

5. The compound according to claim 4 , wherein the monocyclic or polycyclic N-containing heteroaryl group is optionally substituted by one or more substituents chosen from halogen atoms and lower alkyl groups.

6. The compound according to claim 1 , wherein R 4 represents a group of formula:

G-L1-(CRR′) n —

wherein

n is an integer from 1 to 3;

R and R′ are independently chosen from hydrogen atoms and lower alkyl groups;

L1 is a linker chosen from a direct bond, or —O—, —O(CO)—, —(CO)O— or —O(CO)O— groups; and

G is chosen from alkyl, cycloalkyl, heterocyclyl, aryl, or heteroaryl groups, said groups being optionally substituted with one or more substituents chosen from:

halogen atoms;

alkyl and alkenyl groups, which are optionally substituted by one or more substituents chosen from halogen atoms; and

hydroxy, alkoxy, cyano, and cycloalkyloxy groups.

7. The compound according to claim 6 , wherein R 4 represents a group of formula:

G-L1-(CRR′) n —

wherein

n is an integer from 1 to 3;

R and R′ are independently chosen from hydrogen atoms and lower alkyl groups;

L1 is a linker chosen from a direct bond or —O—, —O(CO)— or —O(CO)O— groups; and

G is chosen from alkyl, cycloalkyl, heterocyclyl, aryl, or heteroaryl groups, said groups being optionally substituted with one or more substituents chosen from:

halogen atoms;

alkyl and alkenyl groups, which are optionally substituted by one or more substituents chosen from halogen atoms; and

hydroxy, alkoxy, and cycloalkyloxy groups.

8. The compound according to claim 7 , wherein R 4 represents a group of formula:

G-L1-(CRR′) n —

wherein

n is an integer from 1 to 2;

R and R′ are independently chosen from hydrogen atoms and methyl groups;

L1 is a linker chosen from a direct bond or —O—, —(CO)O—, or —O(CO)O— groups; and

G is chosen from alkyl, cycloalkyl, aryl, or heteroaryl groups, said groups being optionally substituted with one or more substituents chosen from halogen atoms, and alkoxy, cyano, alkyl, and —CF 3 groups.

9. The compound according to claim 1 , wherein R 3 represents a hydrogen atom or an acyl group.

10. The compound according to claim 1 chosen from:

ethyl 4-acetyl-1-ethyl-6-oxo-5-(quinolin-5-ylamino)-1,6-dihydropyridazine-3-carboxylate;

ethyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

ethyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

ethyl 4-acetyl-1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

isopropyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

benzyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

isopropyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-methylbutyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

2-methoxyethyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

cyclopropylmethyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino) -1,6-dihydropyridazine-3-carboxylate;

methyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

2-phenylethyl 4-acetyl-1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

benzyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

cyclohexyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

tert-butyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

cyclobutyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

cyclohexyl 4-acetyl-1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-methyl-2-phenylethyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-phenylethyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

tert-butyl 4-acetyl-1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6- dihydropyridazine-3-carboxylate;

1-phenylethyl 4-acetyl-1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

sec-butyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-(dimethylamino)-2-oxoethyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-methoxy-1-methyl-2-oxoethyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

benzyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

ethyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

ethyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

isopropyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

pyridin-2-ylmethyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

isopropyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

ethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

isopropyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-thienylmethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-thienylmethyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-methoxybenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1 ,6-dihydropyridazine-3-carboxylate;

3-methoxybenzyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-chlorobenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-phenylethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-phenylethyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-pyridin-4-ylethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate; 1-pyridin-4-ylethyl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-pyridin-4-ylethyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino) -1,6-dihydropyridazine-3-carboxylate;

2,3-dihydro-1H-inden-1-yl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2,3-dihydro-1H-inden-1-yl 1-ethyl-5-[(4-methylpyridin-3-yl)amino]-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1,3,3-Trimethylbutyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate; 3-Chlorobenzyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Methoxybenzyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

Benzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate; Octyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1,5-Dimethylhex-4-en-1-yl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

Allyl 4-acetyl-1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

Benzyloxycarbonylmethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-Oxo-2-phenylethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

Dimethylcarbamoylmethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-Phenoxyethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-Dimethylaminoethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

4-Bromobenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

4-Bromobenzyl 1-ethyl-5-(4-methyl-pyridin-3-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

4-Bromobenzyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

2-Chlorobenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2-Chlorobenzyl 1-ethyl-5-(4-methyl-pyridin-3-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Methylbenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Trifluoromethylbenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Trifluoromethylbenzyl 1-ethyl-5-(4-methyl-pyridin-3-ylamino) -6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Trifluoromethylbenzyl 1-ethyl-6-oxo-5-(pyridin-3-ylamino)-1,6-dihydropyridazine-3-carboxylate;

2-(Benzylmethylamino)-ethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

4-Methoxybenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Cyanobenzyl 1-ethyl-5-(4-methyl-pyridin-3-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

3-Cyanobenzyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

Cyclohexyloxycarbonyloxymethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

1-Cyclohexyloxycarbonyloxyethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

2,2-Dimethylbutyryloxymethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate; or (S)-2-Amino-4-methylpentanoyloxymethyl 1-ethyl-5-(isoquinolin-4-ylamino)-6-oxo-1,6-dihydropyridazine-3-carboxylate;

or a pharmaceutically acceptable salt thereof.

11. The pharmaceutical composition comprising a compound according to claim 1 in admixture with a pharmaceutically acceptable diluent or carrier.

12. The combination product comprising:

(i) a compound according to claim 1 ; and

(ii) another compound chosen from (a) steroids, (b) immunosuppressive agents, (c) T-cell receptor blockers, (d) antiinflammatory drugs, (e) β2-adrenergic agonists, and (f) antagonists of M3 muscarinic receptors;

for simultaneous, separate, or sequential administration to a human or animal.