1H-Pyrazolo[4,3-b]pyridines as PDE1 Inhibitors

A compound according to formula (I):

• or a pharmaceutically acceptable salt thereof;
• wherein:
• L is selected from the group consisting of NH, CH2, S and O;
• R1 is selected from the group consisting of hydrogen, linear or branched C1-C5 alkyl, C1-C5 fluoroalkyl and saturated monocyclic C3-C5 cycloalkyl;
• R2 is selected from the group consisting of linear or branched C1-C8 alkyl, saturated monocyclic C3-C8 cycloalkyl, oxetanyl, tetrahydrofuranyl, and tetrahydropyranyl;
• all of which can be optionally substituted one or more times with one or more substituents selected from the group consisting of methyl, fluorine, hydroxy, cyano and methoxy;
• R3 is methyl substituted with phenyl, pyridonyl, pyridinyl, pyrimidinyl or pyrazinyl all of which can be optionally substituted one or more times with one or more substituents selected from the group consisting of halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• or
• R3 is methyl substituted with a 5-membered heteroaryl which is optionally substituted with one or more substituents selected from halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• or
• R3 is ethyl substituted with phenyl, pyridonyl, pyridinyl, pyrimidinyl or pyrazinyl all of which can be optionally substituted one or more times with one or more substituents selected from the group consisting of halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• or
• R3 is ethyl substituted with a 5-membered heteroaryl which is optionally substituted with one or more substituents selected from halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• or
• L is CH2 and R3 is NH which is substituted with phenyl, pyridonyl, pyridinyl, pyrimidinyl or pyrazinyl all of which can be optionally substituted one or more times with one or more substituents selected from the group consisting of halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• or
• L is CH2 and R3 is NH which is substituted with a 5-membered heteroaryl which is optionally substituted with one or more substituents selected from halogen, cyano, C1-C3 alkyl, C1-C3 fluoroalkyl, C1-C3 fluoroalkoxy and C1-C3 alkoxy;
• and
• R4 is phenyl, pyridinyl or pyridonyl all of which can be optionally substituted one or more times with one or more substituents selected from the group consisting of halogen, cyano, C1-C4 alkyl, C1-C4 fluoroalkyl, C1-C4 deutereoalkyl, C1-C3 fluoroalkoxy, cyclopropyloxy, C1-C3 alkoxy, C1-C3 deutereoalkoxy and —N—R5R6 wherein R5 and R6 are each independently selected from H, C1-C3 alkyl and C1-C3 deutereoalkyl;
• or
• R4 is a 5-membered heteroaryl which is optionally substituted with one or more substituents selected from halogen, cyano, C1-C4 alkyl, C1-C4 fluoroalkyl, C1-C4 deutereoalkyl, C1-C3 fluoroalkoxy, cyclopropyloxy, C1-C3 alkoxy, C1-C3 deutereoalkoxy and —N—R5R6 wherein R5 and R6 are each independently selected from H, C1-C3 alkyl and C1-C3 deutereoalkyl;
• or
• R4 is a 4, 5 or 6 membered saturated heterocycle all of which can be optionally substituted with one or more substituents selected from oxo, C1-C4 alkyl and C1-C4 fluoroalkyl.