Pyrazolopyrazine compound and pharmaceutical use thereof

1. A pyrazolopyrazine compound of the following formula (I):

wherein

R 1 is hydrogen, lower alkyl, ar(lower)alkyl or cyclo(lower)alkyl which may be interrupted by an oxygen atom;

R 2 is hydrogen or halogen,

or a salt thereof.

2. A process for the preparation of the pyrazolopyrazine compound of claim 1 or a salt thereof, which comprises,

(1) hydrolyzing a compound of the formula (II):

wherein

R 2 is hydrogen or halogen;

R 3 is lower alkyl;

or a salt thereof,

to give a compound of the formula (Ia):

wherein R 2 is as defined above or a salt thereof,

(2) reacting a compound of the formula (Ia) or a salt thereof, with a compound of the formula (III):

R 1a —X  (III)

wherein R 1a is hydrogen, lower alkyl, ar(lower)alkyl or cyclo(lower)alkyl which may be interrupted by an oxygen atom;

X is a leaving group,

or a salt thereof

to give a compound of the formula (Ib):

wherein R 1a and R 2 are as defined above or a salt thereof.

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

4. A method for treating a disease selected from the group consisting of depression, dementia, Parkinson's disease and anxiety, which comprises administering the compound of claim 1 or a pharmaceutically acceptable salt thereof to a human being or an animal in need thereof.

5. 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.

6. An in vitro method for evaluation of adenosine antagonism which comprises contacting the compound of claim 1 or a pharmaceutically acceptable salt thereof with a human A 1 or A 2a receptor.