HETEROCYCLIC COMPOUND AND USE THEREOF

1 . A compound represented by the formula (I):

wherein

R 1 is an optionally substituted C 1-6 alkyl group, an optionally substituted mono- or di-C 1-6 alkylamino group, an optionally substituted C 3-6 cycloalkyl group, or an optionally substituted 3- to 14-membered non-aromatic heterocyclic group;

R 2 is a hydrogen atom, a fluorine atom, an optionally substituted C 1-6 alkyl group, or an optionally substituted C 3-6 cycloalkyl group;

R 3 is an acyl group, an optionally substituted C 1-6 alkyl group, an optionally substituted C 3-6 cycloalkyl group, an optionally substituted C 6-14 aryl group, an optionally substituted 3- to 14-membered non-aromatic heterocyclic group, or an optionally substituted 5- to 14-membered aromatic heterocyclic group; and

Ring A is an optionally further substituted C 6-14 aromatic hydrocarbon ring, or an optionally further substituted 5- to 14-membered aromatic heterocycle,

or a salt thereof.

2 . The compound or salt according to claim 1 , wherein

R 1 is

(1) a C 1-6 alkyl group,

(2) a mono- or di-C 1-6 alkylamino group, or

(3) a C 3-6 cycloalkyl group;

R 2 is

(1) a hydrogen atom,

(2) a fluorine atom, or

(3) a C 1-6 alkyl group;

R 3 is

(1) a C 1-6 alkyl-carbonyl group optionally substituted by 1 to 3 substituents selected from

(a) a halogen atom,

(b) a hydroxy group, and

(c) a cyano group,

(2) a C 1-6 alkoxy-carbonyl group,

(3) a C 3-10 cycloalkyl-carbonyl group (the C 3-10 cycloalkyl moiety of the C 3-10 cycloalkyl-carbonyl group is optionally bridged) optionally substituted by 1 to 3 substituents selected from

(a) a halogen atom,

(b) a hydroxy group,

(c) a cyano group, and

(d) a C 1-6 alkyl group,

(4) a 3- to 14-membered non-aromatic heterocyclylcarbonyl group optionally substituted by 1 to 3 substituents selected from

(a) a halogen atom,

(b) a hydroxy group, and

(c) a C 1-6 alkyl group,

(5) a mono- or di-C 1-6 alkyl-carbamoyl group,

(6) a N—C 1-6 alkyl-N—C 1-6 alkoxy-carbamoyl group, or

(7) a N—C 1-6 alkyl-N′,N′-di-C 1-6 alkylhydrazine-carbonyl group; and

Ring A is

(1) a benzene ring

further substituted by one substituent selected from

(a) a C 6-14 aryl group optionally substituted by 1 to 3 substituents selected from

(i) a halogen atom,

(ii) an optionally halogenated C 1-6 alkyl group, and

(iii) an optionally halogenated C 1-6 alkoxy group, and

(b) a 5- to 14-membered aromatic heterocyclic group optionally substituted by 1 to 3 substituents selected from

(i) a C 1-6 alkyl group optionally substituted by 1 to 3 substituents selected from a halogen atom and a hydroxy group,

(ii) a C 1-6 alkoxy group,

(iii) a halogen atom, and

(iv) a C 1-6 alkoxy-carbonyl group, and

optionally further substituted by 1 to 3 halogen atoms, or

(2) a 5- or 6-membered aromatic heterocycle further substituted by one C 6-14 aryl group optionally substituted by 1 to 3 halogen atoms.

3 . The compound or salt according to claim 1 , wherein

R 1 is

(1) a C 1-6 alkyl group,

(2) a mono- or di-C 1-6 alkylamino group, or

(3) a C 3-6 cycloalkyl group;

R 2 is

(1) a hydrogen atom, or

(2) a fluorine atom;

R 3 is (1) a C 1-6 alkyl-carbonyl group optionally substituted by 1 to 3 hydroxy groups,

(2) a C 3-10 cycloalkyl-carbonyl group (the C 3-10 cycloalkyl moiety of the C 3-10 cycloalkyl-carbonyl group is optionally bridged) optionally substituted by 1 to 3 substituents selected from

(a) a halogen atom, and

(b) a hydroxy group,

(3) a 3- to 8-membered monocyclic non-aromatic heterocyclylcarbonyl group, or

(4) a mono- or di-C 1-6 alkyl-carbamoyl group; and

Ring A is a benzene ring

further substituted by one C 6- i 4 aryl group optionally substituted by 1 to 3 substituents selected from

(i) a halogen atom, and

(ii) an optionally halogenated C 1-6 alkyl group, and

optionally further substituted by 1 to 3 halogen atoms.

4 . The compound or salt according to claim 1 , wherein

R 1 is

(1) a C 1-6 alkyl group, or

(2) a mono- or di-C 1-6 alkylamino group;

R 2 is

(1) a hydrogen atom, or

(2) a fluorine atom;

R 3 is

(1) a C 1-6 alkyl-carbonyl group optionally substituted by 1 to 3 hydroxy groups,

(2) a 3- to 8-membered monocyclic non-aromatic heterocyclylcarbonyl group, or

(3) a mono- or di-C 1-6 alkyl-carbamoyl group; and

Ring A is a benzene ring

further substituted by one C 6-14 aryl group optionally substituted by 1 to 3 substituents selected from

(i) a halogen atom, and

(ii) a C 1-6 alkyl group, and

optionally further substituted by 1 to 3 halogen atoms.

5 .- 7 . (canceled)

8 . A medicament comprising the compound or salt according to claim 1 .

9 . The medicament according to claim 8 , which is an orexin type 2 receptor agonist.

10 .- 11 . (canceled)

12 . A method of activating an orexin type 2 receptor in a mammal, which comprises administering an effective amount of the compound or salt according to claim 1 to the mammal.

13 . A method for the prophylaxis or treatment of narcolepsy in a mammal, which comprises administering an effective amount of the compound or salt according to claim 1 to the mammal.

14 . (canceled)