Imidazopyrazinones as PDE1 inhibitors

1. A pharmaceutical composition comprising a therapeutically effective amount of a compound according to formula (I), or a tautomer or pharmaceutically acceptable salt thereof, and one or more pharmaceutically acceptable carriers, diluents and excipients:

wherein

n is 0 or 1;

q is 0 or 1;

R1 is selected from the group consisting of benzyl, indanyl, indoline and 5-membered heteroaryls; all of which can be substituted with a substituent selected from the group consisting of halogen and C 1 -C 3 alkyl; or

R1 is selected from the group consisting of saturated monocyclic rings containing 4-6 carbon atoms and 1-2 nitrogen atoms; all of which can be substituted one or more times with one or more substituents selected from the group consisting of methyl, fluorine and sulfonamide; or

R1 is selected from the group consisting of lactams containing 4-6 carbon atoms; all of which can be substituted one or more times with one or more substituents selected from the group consisting of methyl and fluorine; or

R1 is selected from the group consisting of bicyclic ethers such as, 7-oxabicyclo[2.2.1]heptane; all of which can be substituted one or more times with one or more substituents selected from the group consisting of methyl and fluorine; or

R1 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, saturated monocyclic C 3 -C 8 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrathydropyranyl; all of which can be substituted one or more times with one or more substituents selected from the group consisting of methyl, fluorine, hydroxy, cyano or methoxy; or

R1 is a linear or branched C 1 -C 3 alkyl, which is substituted with a substituent selected from phenyl and 5-membered heteroaryl, wherein said 5-membered heteroaryl can be substituted with one or more C 1 -C 3 alkyls; or

R1 is selected from the group consisting of morpholine, tetrahydrofuran-3-amine, hexahydro-2H-furo[3,2-b]pyrrole and homomorpholine; all of which can be subsituted with one or more substituents selected from the group consisting of C 1 -C 3 alkyl;

R2 is selected from the group consisting of hydrogen, linear or branched C 1 -C 8 alkyl, phenyl, saturated monocyclic C 3 -C 8 cycloalkyl, oxetanyl, benzo[d][1,3]dioxolyl, tetrahydrofuranyl and tetrahydropyranyl; or

R2 is phenyl or pyridyl substituted with one or more substituents selected from the group consisting of hydroxyl, amino, cyano, halogen, C 1 -C 3 alkyl, C 1 -C 3 alkoxy, C 3 -C 5 cycloalkoxy, C 3 -C 5 cycloalkyl-methoxy, C 1 -C 3 fluoroalkoxy, and —NC(O)CH 3 ; or

R2 is a 5-membered heteroaryl which can be substituted with one or more C 1 -C 3 alkyl;

R3 is selected from the group consisting of hydrogen, halogen, C 1 -C 5 alkyl, C 3 -C 5 cycloalkyl and phenyl; or

R3 is selected from the group consisting of phenyl substituted one or more times with C 1 -C 3 alkyl; methyl substituted one, two or three times with fluorine; ethyl substituted one, two or three times with fluorine;

R4 is hydrogen;

with the proviso that R2 and R3 cannot be hydrogen at the same time;

with the proviso, that the compound of formula (I) is not one of the three following compounds:

3-methyl-7-(4-(trifluoromethoxy)benzyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-butyl-3-methylimidazo[1,5-a]pyrazin-8(7H)-one; and

7-(4-methoxybenzyl)-3-methylimidazo[1,5-a]pyrazin-8(7H)-one.

2. The pharmaceutical composition according to claim 1 , wherein

R1 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, saturated monocyclic C 3 -C 8 cycloalkyl, oxetanyl, tetrahydrofuranyl, and tetrahydropyranyl;

R2 is selected from the group consisting of, linear or branched C 1 -C 8 alkyl, phenyl, and saturated monocyclic C 3 -C 8 cycloalkyl; or

R2 is selected from the group consisting of phenyl substituted with a substituent selected from the group consisting of halogen, C 1 -C 3 alkyl and methoxy;

R3 is selected from the group consisting of hydrogen, C 1 -C 3 alkyl, and halogen and bcnzyl;

R4 is hydrogen.

3. The pharmaceutical composition according to claim 1 , wherein R1 is C 1 -C 3 alkyl.

4. The pharmaceutical composition according to claim 1 , wherein R1 is selected from tetrahydrofuranyl and tetrahydropyranyl.

5. The pharmaceutical composition according to claim 1 , wherein R1 is C 3 -C 5 cycloalkyl.

6. The pharmaceutical composition according to claim 1 , wherein R2 is C 1 -C 3 alkyl.

7. The pharmaceutical composition according to claim 1 , wherein R2 is phenyl.

8. The pharmaceutical composition according to claim 1 , wherein R2 is phenyl substituted with a substituent selected from the group consisting of fluorine, chlorine, methyl and methoxy.

9. The pharmaceutical composition according to claim 1 , wherein R2 is saturated monocyclic C 5 -C 7 cycloalkyl.

10. The pharmaceutical composition according to claim 1 , wherein R3 is selected from hydrogen, methyl, benzyl and bromine.

11. The pharmaceutical composition according to claim 1 , wherein R3 is selected from hydrogen and methyl; and

wherein R2 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, phenyl, saturated monocyclic C 3 -C 8 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrahydropyranyl; or

R2 is phenyl or pyridyl substituted with one or more substituents selected from the group consisting of hydroxyl, amino, cyano, halogen, C 1 -C 3 alkyl, C 1 -C 3 alkoxy, C 1 -C 3 fluoroalkoxy, and —NC(O)CH 3 ; or

R2 is a 5-membered heteroaryl which can be substituted with C 1 -C 3 alkyl.

12. The pharmaceutical composition according to claim 1 , wherein the compound or pharmaceutically acceptable salt thereof is selected from the group consisting of:

7-(3-Fluorobenzyl)-3-propylimidazo[1,5-a]pyrazin-8(7H)-one;

6-Benzyl-7-(3-fluorobenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-Benzyl-7-(cyclohexylmethyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cyclohexylmethyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-Fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-Cyclopropyl-7-(3-fluorobenzyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cyclopentylmethyl)-3-cyclopropylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cyclohexylmethyl)-3-cyclopropylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-Fluorobenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cyclopentylmethyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cyclohexylmethyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cycloheptylmethyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(Cycloheptylmethyl)-3-cyclopropylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-Chlorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-Bromo-7-(3-fluorobenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-Benzyl-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(2-Fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-Chlorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(2-Chlorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-Methoxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-Methyl-7-(2-methylbenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-Methyl-7-(4-methylbenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-Methoxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-Fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-Methyl-7-(3-methylbenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-(4-methyltetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

4-(7-(3-fluorobenzyl)-6-methyl-8-oxo-7,8-dihydroimidazo[1,5-a]pyrazin-3-yl)tetrahydro-2H-pyran-4-carbonitrile;

7-(3-fluorobenzyl)-3-(4-methoxytetrahydro-2H-pyran-4-yl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-(4-fluorotetrahydro-2H-pyran-4-yl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-2-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-2-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(3-fluorobenzyl)-6-methyl-3-(3-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(3-fluorobenzyl)-6-methyl-3-(3-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-(1-methylcyclopropyl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(2,2-difluorocyclopropyl)-7-(3-fluorobenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((1R,2S)-2-methylcyclopropyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((1R,2R)-2-methylcyclopropyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((1S,2S)-2-methylcyclopropyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((1S,2R)-2-methylcyclopropyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((2S,3R)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((2S,3S)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((2R,3R)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-6-methyl-3-((2R,3S)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((1R,2S)-2-fluorocyclopropyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((1R,2R)-2-fluorocyclopropyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((1S,2S)-2-fluorocyclopropyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((1S,2R)-2-fluorocyclopropyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-cyclopropoxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-(difluoromethoxy)benzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-3-(tetrahydro-2H-pyran-4-yl)-7-(4-(trifluoromethoxy)benzyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-(cyclopropylmethoxy)benzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-benzyl-6-ethyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-ethyl-7-(4-methoxybenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-((6-methyl-8-oxo-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-7(8H)-yl)methyl)benzonitrile;

4-((6-methyl-8-oxo-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-7(8H)-yl)methyl)benzonitrile;

N-(4-((6-methyl-8-oxo-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-7(8H)-yl)methyl)phenyl)acetamide;

7-(4-chloro-3-methoxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(2-ethylbenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(benzo[d][1,3]dioxol-5-ylmethyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-chloro-4-methoxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-aminobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-hydroxybenzyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-ethyl-7-(3-fluorobenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((2S,3R)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((2S,3S)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((2R,3R)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((2R,3S)-2-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-propylimidazo[1,5-a]pyrazin-8(7H)-one;

7-((6-methoxypyridin-3-yl)methyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6,7-dimethyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-ethyl-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-7-propyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-isopropyl-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-isopentyl-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(cyclopentylmethyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

2-((6-methyl-8-oxo-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-7(8H)-yl)methyl)benzonitrile;

7-(cycloheptylmethyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(3-methyltetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((1R,2R,4S)-2-methyl-7-oxabicyclo[2.2.1]heptan-2-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(4-methoxybenzyl)-6-methyl-3-(1-phenylethyl)imidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(4-methoxybenzyl)-6-methyl-3-(1-phenylethyl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(1,4-dimethylpiperidin-4-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one, 3-(6-chloro-2,3-dihydro-1H-inden-1-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(3-methyl-5-oxopyrrolidin-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(1-methoxy-2-methylpropan-2-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

3-isopropyl-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-7-((2-methylthiazol-4-yl)methyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-3-(tetrahydro-2H-pyran-4-yl)-7-(thiophen-3-ylmethyl)imidazo[1,5-a]pyrazin-8(7H)-one, 6-methyl-3-(tetrahydro-2H-pyran-4-yl)-7-(thiazol-4-ylmethyl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-((3,5-dimethylisoxazol-4-yl)methyl)-6-methyl-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-7-((5-methylisoxazol-3-yl)methyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

6-methyl-7-((3-methylisoxazol-5-yl)methyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(2,6-dimethyltetrahydro-2H-pyran-4-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(cyclohexylmethyl)-6-methyl-3-propylimidazo[1,5-a]pyrazin-8(7H)-one;

3-(2-hydroxypropan-2-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

3-(2-fluoropropan-2-yl)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(7-oxoazepan-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(5-methyltetrahydrofuran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(1-(4-methylthiazol-2-yl)ethyl)imidazo[1,5-a]pyrazin-8(7H)-one 3-(7-(4-methoxybenzyl)-6-methyl-8-oxo-7,8-dihydroimidazo[1,5-a]pyrazin-3-yl)-3-methylpyrrolidine-1-sulfonamide;

6-(cyclopentylmethyl)-7-(4-methoxybenzyl)-3-(tetrahydro-2H-pyran-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(morpholino)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-((tetrahydrofuran-3-yl)amino)imidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(4-methoxybenzyl)-6-methyl-3-(3-methylmorpholino)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(4-methoxybenzyl)-6-methyl-3-(3-methylmorpholino)imidazo[1,5-a]pyrazin-8(7H)-one;

7-(4-methoxybenzyl)-6-methyl-3-(1,4-oxazepan-4-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

3-(2,2-dimethylmorpholino)-7-(4-methoxybenzyl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((3aS,6aS)-hexahydro-4H-furo[3,2-b]pyrrol-4-yl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

7-(3-fluorobenzyl)-3-((3aR,6aR)-hexahydro-4H-furo[3,2-b]pyrrol-4-yl)-6-methylimidazo[1,5-a]pyrazin-8(7H)-one;

(R)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

(S)-7-(3-fluorobenzyl)-6-methyl-3-(tetrahydro-2H-pyran-3-yl)imidazo[1,5-a]pyrazin-8(7H)-one;

and pharmaceutically acceptable salts of any of these compounds.