Pyrazine derivatives and pharmaceutical use thereof

1. A pyrazine compound shown by the following formula (I):

wherein

R 1 is hydrogen, lower alkyl or substituted lower alkyl

X is hydrogen, halogen, hydroxy, mercapto, cyano or acyl, or

lower alkyl, substituted lower alkyl, lower alkenyl, substituted lower alkenyl, lower alkynyl, substituted lower alkynyl, lower alkoxy, substituted lower alkoxy, cyclo(lower)alkoxy, lower alkylthio, aryloxy, arylthio, amino, substituted amino, aryl, substituted aryl, heterocyclic group, substituted heterocyclic group or heterocyclyloxy;

Y is hydrogen, halogen, hydroxy, mercapto, cyano, acyl or

lower alkyl, substituted lower alkyl, lower alkoxy, substituted lower alkoxy, lower alkylthio, amino, substituted amino, aryl, substituted aryl, or heteroaryl; and

Z is aryl, substituted aryl, or heteroaryl;

or a salt thereof

wherein substituted lower alkyl is substituted with a substituent selected from the group consisting of halogen, lower alkenyl, lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, substituted amino, acylamino, aryl, substituted aryl, heterocyclic group and acyl;

wherein substituted lower alkenyl is substituted with a substituent selected from the group consisting of lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, aryl, heterocyclic group and acyl;

wherein substituted lower alkynyl is substituted with a substituent selected from the group consisting of lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, aryl, heterocyclic group and acyl;

wherein substituted lower alkoxy is substituted with a substituent selected from the group consisting of hydroxy, halogen, cyclo(lower)alkyl, lower alkoxy, amino, substituted amino, aryl, substituted aryl, heterocyclic group and acyl;

wherein substituted amino is substituted with a substituent selected from the group consisting of lower alkyl, acyl, sulfonyl, methylene, (dimethylamino)methylene and dimethylsulfanylidene;

wherein substituted aryl is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxyl and halogen; and

wherein substituted heterocyclic group is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxy, oxo, halogen, benzyl, amino, substituted amino and aryl.

2. A pyrazine compound of claim 1 , wherein

R 1 is hydrogen or lower alkyl; and

Y is hydrogen, hydroxy, lower alkoxy, cyano, acyl or amino, substituted amino or a salt thereof

wherein substituted amino is substituted with a substituent selected from the group consisting of lower alkyl, acyl, sulfonyl, methylene, (dimethylamino)methylene and dimethylsulfanylidene.

3. A pyrazine compound of claim 2 , wherein

R 1 is lower alkyl;

Y is hydrogen, amino or dimethylsulfanylideneamino; and

Z is phenyl, substituted phenyl, pyridyl or thienyl or a salt thereof

wherein substituted phenyl is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxy, halogen.

4. A pyrazine compound of claim 3 , wherein

X is hydrogen, halogen, hydroxy, cyano, carboxy, lower alkyl carbonyl, lower alkoxy carbonyl, lower alkyl sulfinyl, lower alkyl sulfonyl;

or a salt thereof.

5. A pyrazine compound of claim 3 , wherein

X is lower alkyl, substituted lower alkyl, lower alkoxy, substituted lower alkoxy, cyclo(lower)alkoxy, lower alkylthio, carbamoyl, thiocarbamoyl, aryloxy, arylthio, amino, substituted amino, aryl, substituted aryl, heterocyclic group, substituted heterocyclic group or heterocyclyloxy;

or a salt thereof

wherein substituted lower alkyl is substituted with a substituent selected from the group consisting of halogen, lower alkenyl, lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, substituted amino, acylamino, aryl, substituted aryl, heterocyclic group and acyl;

wherein substituted lower alkoxy is substituted with a substituent selected from the group consisting of hydroxy, halogen, cyclo(lower)alkyl, lower alkoxy, amino, substituted amino, aryl, substituted aryl, heterocyclic group and acyl;

wherein substituted amino is substituted with a substituent selected from the group consisting of lower alkyl, acyl, sulfonyl, methylene, (dimethylamino)methylene and dimethylsulfanylidene;

wherein substituted aryl is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxyl and halogen; and

wherein substituted heterocyclic group is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxy, oxo, halogen, benzyl, amino, substituted amino and aryl.

6. A pyrazine compound of claim 3 , wherein

Y is hydrogen or amino; and

Z is phenyl, substituted phenyl, or thienyl;

or a salt thereof

wherein substituted phenyl is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxyl and halogen.

7. A pyrazine compound of claim 6 , wherein

X is hydrogen, chloro, bromo, hydroxy, cyano, methylcarbonyl, methylthio, carbamoyl, furyl, thienyl, pyrrolyl, pyrazolyl, triazolyl, phenoxy, fluorophenoxy, pyrrolidinyloxy, benzylpyrrolidinyloxy, thiazolyl, methylthiazolyl or phenylthiazolyl;

or a salt thereof.

8. A pyrazine compound of claim 6 , wherein

X is amino, substituted amino, vinyl, substituted vinyl,

ethynyl, substituted ethynyl, lower alkoxy, substituted lower alkoxy;

or a salt thereof

wherein substituted amino is substituted with a substituent selected from the group consisting of lower alkyl, acyl, sulfonyl, methylene, (dimethylamino)methylene and dimethylsulfanylidene;

wherein substituted vinyl is substituted with a substituent selected from the group consisting of lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, aryl, heterocyclic group and acyl;

wherein substituted ethynyl is substituted with a substituent selected from the group consisting of lower alkoxy, hydroxy, cyclo(lower)alkyl, amino, aryl, heterocyclic group and acyl;

wherein substituted lower alkoxy is substituted with a substituent selected from the group consisting of hydroxy, halogen, cyclo(lower)alkyl, lower alkoxy, amino, substituted amino, aryl, substituted aryl, heterocyclic group and acyl; and

wherein substituted aryl is substituted with a substituent selected from the group consisting of lower alkyl, lower alkoxy, hydroxyl and halogen.

9. A pyrazine compound of claim 1 , wherein

R 1 is methyl, ethyl or isopropyl;

X is hydrogen, chloro, bromo, hydroxy, cyano, methylcarbonyl, carbamoyl, pyrazolyl, triazolyl, methylthiazolyl, pyridylmethylamino, methoxyethylamino, furylmethylamino, cyclohexylethynyl, trifluoromethylmethoxy or butoxy;

Y is amino; and

Z is phenyl or fluorophenyl;

or a salt thereof.

10. A pyrazine compound of claim 1 , wherein

R 1 is lower alkyl;

X is hydrogen, carbamoyl or triazolyl;

Y is amino; and

Z is phenyl;

or a salt thereof.

11. A pyrazine compound of claim 10 , which is selected from the group consisting of

1) 3-amino-6-(1-isopropyl-6-oxo-1,6-dihydro-3-pyridazinyl)-5-phenyl-2-pyrazinecarboxamide,

2) 6-(5-amino-3-phenyl-2-pyrazinyl)-2-isopropyl-3(2H)-pyridazinone,

3) 3-amino-6-(1-ethyl-6-oxo-1,6-dihydro-3-pyridazinyl)-5-phenyl-2-pyrazinecarboxamide,

4) 3-amino-6-(1-methyl-6-oxo-1,6-dihydro-3-pyridazinyl)-5-phenyl-2-pyrazinecarboxamide,

5) 6-(5-amino-3-phenyl-2-pyrazinyl)-2-methyl-3(2H)-pyridazinone,

6) 6-(5-amino-3-phenyl-2-pyrazinyl)-2-ethyl-3(2H)-pyridazinone,

7) 6-[5-amino-3-phenyl-6-(1H-1,2,4-triazol-1-yl)-2-pyrazinyl]-2-isopropyl-3(2H)-pyridazinone,

8) 6-[5-amino-3-phenyl-6-(1H-1,2,4-triazol-1-yl)-2-pyrazinyl]-2-methyl-3(2H)-pyridazinone,

or a salt thereof.

12. A process for preparing the pyrazine compound of the following formula (I):

wherein R 1 , X, Y and Z are each as defined in claim 1 , or a salt thereof;

which comprises

(1) halogenation of a compound of the formula (Id):

wherein R 1 , Y and Z are each as defined above, or a salt thereof with N-halosuccinimide to give a compound of the formula (Ie):

wherein R 1 , Y, Z and Hal are each as defined above, or a salt thereof,

(2) pyrazine ring-formation of a compound of the formula (V):

wherein R 1 and Z are each as defined above, or a salt thereof, which is prepared in two steps from a compound of the formula (XVII):

wherein Z is as defined above, or a salt thereof,

with 2,3-diamino-2-butenedinitrile,

to give a compound of the formula (If):

wherein R 1 and Z are each as defined above, or a salt thereof,

(3) nucleophilic substitution of a compound of the formula (Ig):

wherein R 1 , X and Z are each as defined above, or a salt thereof,

with a compound of the formula (VI):

wherein R 4 is lower alkoxy;

or a salt thereof to give a compound of the formula (Ih):

wherein R 1 , R 4 , X and Z are each as defined above, or a salt thereof,

(4) reacting a compound of the formula (VII):

wherein R 1 is as defined above, or a salt thereof, which is prepared in three steps from a compound of the formula (XXI):

wherein R 1 is as defined above, or a salt thereof,

with an organoboron compound of the formula (VIII):

Z—BW 2   (VIII)

wherein Z is as defined above; and

BW 2 is a constituent of boronic acid,

or a salt thereof,

to give a compound of the formula (Ii):

wherein R 1 and Z are each as defined above, or a salt thereof.

13. A pharmaceutical composition comprising the compound of claim 1 or a pharmaceutically acceptable salt thereof in admixture with a pharmaceutically acceptable carrier.

14. A method for treating a disease selected from the group consisting of depression, dementia, Parkinson's disease, anxiety, pain, hypertension, obesity, gout and bronchial asthma which comprises administering the compound of claim 1 or a pharmaceutically acceptable salt thereof to a human being or an animal.

15. A process for preparing a pharmaceutical composition which comprises admixing the compound of claim 1 or a pharmaceutically acceptable salt thereof with a pharmaceutically acceptable carrier.