Deuterated benzimidazole compound and medical use thereof

1. A compound of formula (I):

or a pharmaceutically acceptable salt thereof, wherein

R 1a , R 1b , R 1c and R 1d are independently hydrogen, halogen, cyano, C 1-4 alkyl, C 1-4 alkoxy, C 1-4 alkylamino (wherein the alkyl and the alkyl moiety in the alkoxy and the alkylamino may be independently substituted with 1 to 5 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), C 3-7 cycloalkyl, C 3-7 cycloalkoxy, C 3-7 cycloalkylamino (wherein the cycloalkyl and the cycloalkyl moiety in the cycloalkoxy and the cycloalkylamino may be independently substituted with 1 to 5 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl, or 5- to 12-membered heteroaryloxy (wherein the aryl and the aryl moiety in the aryloxy, and the heteroaryl and the heteroaryl moiety in the heteroaryloxy may be independently substituted with 1 to 5 substituents selected independently from the group consisting of halogen, cyano, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 1-4 alkylthio optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, and C 1-4 alkylsulfonyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A), provided that at least one of R 1a , R 1b , R 1c and R 1d is the above C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl or 5- to 12-membered heteroaryloxy,

R 2 and R 3 are independently hydrogen, C 1-6 alkyl (which may be independently substituted with 1 to 5 substituents selected independently from the group consisting of cyano, halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), or C 3-10 cycloalkyl,

R 4 is hydrogen, C 1-6 alkyl (which may be substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), or C 3-7 cycloalkyl (which may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B),

m is 0, 1, or 2,

L is CR 7 R 8 provided that when m is 2, each CR 7 R 8 is independently the same or different,

R 7 and R 8 are independently hydrogen, hydroxy group, C 1-4 alkyl, C 1-4 alkoxy (wherein the alkyl and the alkyl moiety in the alkoxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), C 3-7 cycloalkyl, or C 3-7 cycloalkoxy (wherein the cycloalkyl and the cycloalkyl moiety in the cycloalkoxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B), or

in R 2 , R 3 and —OR 4 , R 2 and R 3 may be combined together with the carbon atom to which they are attached to form the following group of formula (II) with —OR 4

in formula (II),

e and f are independently 1, 2 or 3,

R 4 is as defined above,

V is single bond or oxygen atom,

R 5a , R 5b , R 5c , and R 5d are independently hydrogen, halogen, hydroxy group, C 1-4 alkyl, or C 1-4 alkoxy, wherein the alkyl and the alkyl moiety in the alkoxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B,

Substituent-group A is independently halogen, hydroxy group, C 1-4 alkoxy, C 3-7 cycloalkyl, or C 3-7 cycloalkoxy,

Substituent-group B is independently halogen, hydroxy group, C 1-4 alkyl, C 1-4 alkoxy, C 3-7 cycloalkyl, or C 3-7 cycloalkoxy, and further any 1 to 6 hydrogen atoms in the compound of formula (I) may be replaced with deuterium atoms.

2. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 1a , R 1b , R 1c and R 1d are independently, hydrogen, halogen, cyano, C 1-4 alkyl, C 1-4 alkoxy (wherein the alkyl and the alkyl moiety in the alkoxy may be independently substituted with 1 to 3 the same or different halogen atoms), C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl, or 5- to 12-membered heteroaryloxy (wherein the aryl and the aryl moiety in the aryloxy, and the heteroaryl and the heteroaryl moiety in the heteroaryloxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, cyano, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, and C 1-4 alkylsulfonyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A).

3. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 1a , R 1b , R 1c , and R 1d are independently, hydrogen, C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl, or 5- to 12-membered heteroaryloxy, wherein the aryl and the aryl moiety in the aryloxy, and the heteroaryl and the heteroaryl moiety in the heteroaryloxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, and C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A.

4. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein R 1a and R 1d are hydrogen.

5. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 1b or R 1c is C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl, or 5- to 12-membered heteroaryloxy (wherein the aryl and the aryl moiety in the aryloxy, and the heteroaryl and the heteroaryl moiety in the heteroaryloxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, and C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A).

6. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein R 1a , R 1c , and R 1d are hydrogen.

7. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 1b is C 6-10 aryl, C 6-10 aryloxy, 5- to 12-membered heteroaryl, or 5- to 12-membered heteroaryloxy (wherein the aryl and the aryl moiety in the aryloxy, and the heteroaryl and the heteroaryl moiety in the heteroaryloxy may be independently substituted with 1 to 3 substituents selected independently from the group consisting of halogen, C 1-4 alkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, and C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A).

8. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 2 and R 3 are independently hydrogen or C 1-6 alkyl which may be independently substituted with 1 to 5 substituents selected independently from the group consisting of cyano, halogen, hydroxy group, and C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, provided that both of R 2 and R 3 are not hydrogen, or

R 2 and R 3 may be combined together with the carbon atom to which they are attached to form the following group of formula (II a ) with —OR 4

in formula (IIa),

e and f are independently 1 or 2,

R 4 and V are as defined in claim 1 , and

R 5a , R 5b , R 5c , and R 5d are independently hydrogen or halogen.

9. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 2 and R 3 are independently C 1-6 alkyl optionally-substituted with 1 to 5 the same or different halogen atoms, or

R 2 and R 3 may be combined together with the carbon atom to which they are attached to form the following group of formula (IIb) with —OR 4

in formula (II b ),

e and f are 1,

R 4 is hydrogen,

V is oxygen atom,

R 5a , R 5b , R 5c , and R 5d are independently hydrogen or halogen.

10. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 2 and R 3 are independently hydrogen or C 1-6 alkyl optionally-substituted with 1 to 5 the same or different halogen atoms, and R 2 and R 3 are not combined together with the carbon atom to which they are attached to form a ring.

11. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 2 and R 3 may be combined together with the carbon atom to which they are attached to form the following group of formula (IIb) with —OR 4

in formula (IIb),

e and f are 1,

R 4 is hydrogen,

V is oxygen atom,

R 5a , R 5b , R 5c , and R 5d are independently hydrogen or halogen.

12. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 4 is hydrogen, C 1-4 alkyl optionally-substituted with 1 to 3 the same or different halogen atoms, or C 3-7 cycloalkyl which may be substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, and C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A.

13. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein R 4 is hydrogen.

14. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein

R 7 and R 8 are independently hydrogen or C 1-4 alkyl which may be substituted with 1 to 3 substituents selected independently from the group consisting of halogen, hydroxy group, C 1-4 alkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group A, C 3-7 cycloalkyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, C 3-7 cycloalkoxy optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and 3- to 7-membered non-aromatic heterocyclyl optionally-substituted with 1 to 3 substituents selected independently from Substituent-group B, and

m is 0 or 1.

15. The compound of claim 1 or a pharmaceutically acceptable salt thereof, wherein R 7 and R 8 are hydrogen, and m is 0 or 1.

16. The compound of claim 1 or a pharmaceutically acceptable salt thereof, which is selected from the following compounds:

6-(4-fluorophenoxy)-1H-benzimidazol-1-yl]-2-methyl(1,1- 2 H 2 )propan-2-ol,

2-methyl-1-(6-{[5-(trifluoromethyl)pyridin-2-yl]oxy}-1H-benzimidazol-1-yl)(1,1- 2 H 2 )propan-2-ol,

4-[6-(4-chlorophenoxy)-1H-benzimidazol-1-yl]-2-methyl(4,4- 2 H 2 )butan-2-ol,

3-[{6-[4-(trifluoromethoxy)phenoxy]-1H-benzimidazol-1-yl}( 2 H 2 )methyl]oxetan-3-ol, and

3-[{6-[2-methoxy-4-(trifluoromethyl)phenyl]-1H-benzimidazol-1-yl}(2H 2 )methyl]oxetan-3-ol.

17. A pharmaceutical composition comprising the compound of claim 1 or a pharmaceutically acceptable salt thereof.

18. A pharmaceutical combination comprising the compound of claim 1 or a pharmaceutically acceptable salt thereof, and at least one drug selected from the group consisting of an antiepileptic agent, an antidepressive agent, a narcotic analgesic, an anti-inflammatory agent, a reductase inhibitor, and a prostaglandin derivative drug.

19. A method for treating neuropathic pain, nociceptive pain, inflammatory pain, small-fiber neuropathy, erythromelalgia, paroxysmal extreme pain disorder, dysuria, or multiple sclerosis, which comprises administering a therapeutically effective amount of the compound of claim 1 or a pharmaceutically acceptable salt thereof to a mammal in need thereof.