Azabenzimidazole compounds

1. A compound of formula I:

or a pharmaceutically acceptable salt thereof, wherein:

R 1 is represented by a substituent selected from the group consisting of (C 3 -C 10 )cycloalkyl, a (4- to 10-membered)heterocycloalkyl, (C 6 -C 10 )aryl, and a (5- to 10-membered) heteroaryl; wherein said (C 3 -C 10 )cycloalkyl, (C 6 -C 10 )aryl and (5- to 10-membered)heteroaryl are substituted with (R 2 ) b ; and said (4- to 10-membered)heterocycloalkyl is optionally substituted at one to five carbon atoms with a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano, and optionally substituted at each available nitrogen with (C 1 -C 6 )alkyl;

R 2 is represented by a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio; —C(O)NR 4 R 5 , hydroxy, and cyano;

R 3 , if present, at each occurrence is represented by a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano;

R 4 and R 5 are each represented by a substituent independently selected from the group consisting of hydrogen, (C 1 -C 6 )alkyl, and (C 3 -C 6 )cycloalkyl;

one of R 6 and R 7 is represented by a substituent selected from the group consisting of hydrogen, (C 1 -C 6 )alkyl, —(CH 2 ) m —(C 3 -C 10 )cycloalkyl, —(CH 2 ) m -(4- to 10-membered)-heterocycloalkyl, —(CH 2 ) m —(C 6 -C 10 )aryl, and —(CH 2 ) m -(5- to 10-membered)heteroaryl and the other is represented by a substituent selected from the group consisting of (C 1 -C 6 )alkyl, —(CH 2 ) m —(C 3 -C 10 )cycloalkyl, —(CH 2 ) m -(4- to 10-membered)-heterocycloalkyl, —(CH 2 ) m —(C 6 -C 10 )aryl, and —(CH 2 ) m -(5- to 10-membered)heteroaryl; wherein:

i) said R 6 and R 7 (C 1 -C 6 )alkyl substituent is optionally substituted with one to five substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , and cyano;

ii) said R 6 and R 7 (C 3 -C 10 )cycloalkyl substituent is optionally substituted with one to five substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy and cyano;

iii) said R 6 and R 7 (C 6 -C 10 )aryl substituent is optionally substituted with one to five substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy and cyano;

iv) said R 6 and R 7 (5- to 10-membered)heteroaryl substituent is optionally substituted with one to five substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano; and

v) said R 6 and R 7 (4- to 10-membered)heterocycloalkyl substituent is optionally substituted at one to five carbon atoms with a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano, and optionally substituted at each available nitrogen with (C 1 -C 6 )alkyl; or R 6 and R 7 taken together with the nitrogen to which they are attached form a (4- to 10-membered)heterocycloalkyl, wherein said (4- to 10-membered) heterocycloalkyl is optionally substituted at one to five carbon atoms with a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano;

a is represented by an integer selected from 0, 1, 2 or 3;

b is represented by an integer selected from 0, 1, 2, 3, 4 or 5; and

m is represented by an integer selected from 0, 1, 2 or 3.

2. The compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein a is represented by the integer 0.

3. The compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by a (5 to 10-membered)heteroaryl and b is an integer selected from 0, 1, 2 or 3.

4. The compound according to claim 3 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by pyridinyl; b is an integer selected from 1, 2, or 3; and each R 2 is independently selected from the group consisting of chloro, fluoro, methyl, methoxy, trifluoromethyl, trifluoromethoxy, cyano, and methylthio.

5. The compound according to claim 4 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by the group consisting of 5-chloropyridin-3-yl, 6-methylpyridin-3-yl, 5-methoxypyridin-3-yl, 2-trifluoromethylpyridin-4-yl, and 6-cyanopyridin-3-yl.

6. The compound according to claim 3 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by 1-methyl-1H-indazol-5-yl, quinolin-6-yl, 1,3-benzothiazol-6-yl, and 2-methyl-1,3-benzothiazol-6-yl.

7. The compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by (C 3 -C 10 )cycloalkyl, and b is and integer selected from 0, 1, 2, or 3.

8. The compound according to claim 7 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by cyclopentyl; b is an integer selected from 1, 2 or 3; and each R 2 is independently selected from the group consisting of chloro, fluoro, methyl, methoxy, trifluoromethyl, trifluoromethoxy, cyano, and methylthio.

9. The compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by a (4 to 10-membered)heterocycloalkyl optionally substituted at one to three carbon atoms with a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano, and optionally substituted at each available nitrogen with a (C 1 -C 6 )alkyl.

10. The compound according to claim 9 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by tetrahydropyranyl optionally substituted at one to three carbon atoms with a substituent independently selected from the group consisting of chloro, fluoro, methyl, methoxy, trifluoromethyl, trifluoromethoxy, cyano, and methylthio.

11. The compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein R 1 is represented by (C 6 -C 10 )aryl; b is an integer selected from 0, 1, 2 or 3; and when present each R 2 is independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano.

12. The compound of claim 11 , or a pharmaceutically acceptable salt thereof, wherein said (C 6 -C 10 )aryl is selected from the group consisting of 2,3-dihydro-1H-inden-5-yl and 1,3-dihydro-2-benzofuran-5-yl.

13. A compound of formula Ia:

or a pharmaceutically acceptable salt thereof, wherein:

b is represented by an integer selected from 0, 1, 2, or 3;

each R 2 , if present, is represented by a substituent independently selected from the group consisting of fluoro, chloro, cyano, methyl, trifluoromethyl, methylthio, methoxy, and trifluoromethoxy;

one of R 6 and R 7 is selected from the group consisting of hydrogen, (C 1 -C 6 )alkyl, —(CH 2 ) m —(C 3 -C 10 )cycloalkyl, and —(CH 2 ) m -(5- to 10-membered)heteroaryl and the other is selected from the group consisting of (C 1 -C 6 )alkyl, —(CH 2 ) m —(C 3 -C 10 )cycloalkyl, and —(CH 2 ) m -(5- to 10-membered)heteroaryl; wherein:

i) said R 6 and R 7 (C 1 -C 6 )alkyl substituent is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, and cyano;

ii) said R 6 and R 7 (C 3 -C 10 )cycloalkyl substituent is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, hydroxy, and cyano;

iii) said R 6 and R 7 (5- to 10-membered)heteroaryl substituent is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, hydroxy, and cyano; or R 6 and R 7 taken together with the nitrogen to which they are attached form a (4 to 6-membered)heterocycloalkyl, in which up to three carbon atoms of said heterocycloalkyl are optionally substituted with a substituent independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, —C(O)NR 4 R 5 , hydroxy, and cyano;

wherein R 4 and R 5 are each independently selected from the group consisting of hydrogen and (C 1 -C 6 )alkyl;

and m is represented by an integer selected from 0, 1, or 2.

14. The compound according to claim 13 , or a pharmaceutically acceptable salt thereof, wherein R 6 and R 7 taken together with the nitrogen to which they are attached form a (4- to 6-membered)heterocycloalkyl optionally substituted at one to three carbon atoms with halogen.

15. The compound of claim 14 , or a pharmaceutically acceptable salt thereof, wherein R 6 and R 7 taken together with the nitrogen to which they are attached form azetidinyl, optionally substituted with one to three halogen.

16. The compound according to claim 15 , or a pharmaceutically acceptable salt thereof, wherein said azetidinyl is selected from azetidin-1-yl or 3-fluoroazetidin-1-yl.

17. The compound according to claim 13 , or a pharmaceutically acceptable salt thereof, wherein b is represented by an integer selected from 0, 1, 2, or 3; each R 2 , if present, is represented by a substituent independently selected from the group consisting of fluoro, chloro, cyano, methyl, trifluoromethyl, methylthio, methoxy, and trifluoromethoxy; one of R 6 and R 7 is represented by hydrogen and the other represented by a substituent selected from the group consisting of (C 1 -C 6 )alkyl, —(CH 2 ) m —(C 3 -C 6 )cycloalkyl, and —(CH 2 ) m -(5- to 10-membered)heteroaryl; wherein:

i) said (C 1 -C 6 )alkyl is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, and cyano;

ii) said (C 3 -C 10 )cycloalkyl is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, hydroxy, and cyano; and

iii) said (5- to 10-membered)heteroaryl is optionally substituted with one to three substituents independently selected from the group consisting of halogen, (C 1 -C 6 )alkyl, halo(C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, halo(C 1 -C 6 )alkoxy, (C 1 -C 6 )alkylthio, hydroxy, and cyano; and m is represented by an integer selected from 0, 1 or 2.

18. The compound according to claim 17 , or a pharmaceutically acceptable salt thereof, wherein b is represented by an integer selected from 0, 1, 2, or 3; and each R 2 , if present, is represented by a substituent independently selected from the group consisting of chloro, fluoro, methyl, and cyano; and one of R 6 and R 7 is represented by hydrogen and the other is represented by (C 1 -C 6 )alkyl.

19. The compound according to claim 18 , or a pharmaceutically acceptable salt thereof, wherein one of R 6 and R 7 is represented by hydrogen and the other is represented by the group consisting of ethyl or propyl.

20. The compound according to claim 17 , or a pharmaceutically acceptable salt thereof, wherein b is represented by an integer selected from 0, 1, 2, or 3; and each R 2 , if present, is represented by a substituent independently selected from the group consisting of chloro, fluoro, methyl, and cyano; and one of R 6 and R 7 is represented by hydrogen and the other is represented by —(CH 2 ) m —(C 3 -C 6 )cycloalkyl.

21. The compound according to claim 20 , or a pharmaceutically acceptable salt thereof, wherein one of R 6 and R 7 is represented by hydrogen and the other is represented by cyclopropyl.

22. The compound according to claim 17 , or a pharmaceutically acceptable salt thereof, wherein b is represented by an integer selected from 0, 1, 2, or 3; and each R 2 , if present, is represented by a substituent independently selected from the group consisting of chloro, fluoro, methyl, and cyano; and one of R 6 and R 7 is represented by hydrogen and the other is represented by —(CH 2 ) m -(5- to 10-membered)heteroaryl optionally substituted by a (C 1 -C 6 )alkyl.

23. The compound according to claim 22 , or a pharmaceutically acceptable salt thereof, wherein one of R 6 and R 7 is represented by hydrogen and the other is represented by pyrazolyl optionally substituted by methyl.

24. The compound according to claim 23 , or a pharmaceutically acceptable salt thereof, wherein one of R 6 and R 7 is represented by hydrogen and the other is represented by N-1-methyl-1H-pyrazol-3-yl.

25. A method of treating a patient suffering from a disease or condition mediated by the PDE4B isoform, comprising administering to said patient in need of said treatment a therapeutically effective amount of a compound of formula I according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein said disease or condition is selected from the group consisting of schizophrenia, depression, anxiety, and Alzheimer's disease.

26. A pharmaceutical composition comprising a compound according to claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable excipient.

27. A compound selected from the group consisting of:

N-Cyclopropyl-3-(3-fluoro-4-methylphenyl)-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-Cyclopentyl-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-(4-Chlorophenyl)-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-(4-Chloro-3-fluorophenyl)-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-(4-Chloro-3-fluorophenyl)-N-(1-methyl-1H-pyrazol-3-yl)-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-(4-Chloro-3-fluorophenyl)-N-propyl-3H-imidazo[4,5-b]pyridine-2-carboxamide;

3-(4-Cyano-3-fluorophenyl)-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide;

4-[2-(Azetidin-1-ylcarbonyl)-3H-imidazo[4,5-b]pyridin-3-yl]-2-fluorobenzonitrile;

azetidin-1-yl[3-(4-chloro-3,5-difluorophenyl)-3H-imidazo[4,5-b]pyridin-2-yl]methanone; and

azetidin-1-yl[3-(4-chloro-3-fluorophenyl)-3H-imidazo[4,5-b]pyridin-2-yl]methanone;

or a pharmaceutically acceptable salt thereof.

28. A pharmaceutical composition comprising a compound of claim 27 , or a pharmaceutically acceptable salt thereof, and at least one pharmaceutically acceptable excipient.

29. N-Cyclopropyl-3-(3-fluoro-4-methylphenyl)-3H-imidazo[4,5-b]pyridine-2-carboxamide, or a pharmaceutically acceptable salt thereof.

30. 3-Cyclopentyl-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide, or a pharmaceutically acceptable salt thereof.

31. 3-(4-Chloro-3-fluorophenyl)-N-cyclopropyl-3H-imidazo[4,5-b]pyridine-2-carboxamide, or a pharmaceutically acceptable salt thereof.

32. 3-(4-Chloro-3-fluorophenyl)-N-(1-methyl-1H-pyrazol-3-yl)-3H-imidazo[4,5-b]pyridine-2-carboxamide, or a pharmaceutically acceptable salt thereof.

33. 4-[2-(Azetidin-1-ylcarbonyl)-3H-imidazo[4,5-b]pyridin-3-yl]-2-fluorobenzonitrile, or a pharmaceutically acceptable salt thereof.