Radiolabeled compounds

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

wherein

R 1 is

(1) a 3- to 8-membered monocyclic non-aromatic heterocyclic group substituted by 1 to 3 radiolabeled halogen atoms, or

(2) an amino group mono- or di-substituted by substituent(s) selected from the group consisting of:

(a) a C 1-6 alkyl group substituted by 1 to 3 radiolabeled halogen atoms, and

(b) a radiolabeled C 1-6 alkyl group,

and optionally further substituted by a substituent selected from the group consisting of:

(c) a C 1-6 alkyl group substituted by 1 to 3 halogen atoms,

(d) a C 1-6 alkyl group optionally substituted by C 6-14 aryl group(s) optionally substituted by 1 to 3 halogen atoms,

(e) a C 3-8 cycloalkyl group, and

(f) a 3- to 8-membered monocyclic non-aromatic heterocyclic group;

R 2 is

(1) a C 6-14 aryl group optionally substituted by 1 to 3 halogen atoms, or

(2) a 5- or 6-membered monocyclic aromatic heterocyclic group optionally substituted by 1 to 3 substituents selected from the group consisting of:

(a) a halogen atom,

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

(c) a C 3-8 cycloalkyl group;

X 1 is CH or N; and

Ring A is

or a salt thereof.

2. The compound or salt of claim 1 , wherein R 1 is

(1) a 3- to 8-membered monocyclic non-aromatic heterocyclic group substituted by one radiolabeled halogen atom, or

(2) an amino group substituted by one substituent selected from the group consisting of:

(a) a C 1-6 alkyl group substituted by one radiolabeled halogen atom, and

(b) a radiolabeled C 1-6 alkyl group,

and further substituted by one substituent selected from the group consisting of:

(c) a C 1-6 alkyl group optionally substituted by C 6-14 aryl group(s) optionally substituted by 1 to 3 halogen atoms,

(d) a C 3-8 cycloalkyl group, and

(e) a 3- to 8-membered monocyclic non-aromatic heterocyclic group.

3. The compound or salt of claim 1 , wherein R 1 is a 3- to 8-membered monocyclic non-aromatic heterocyclic group substituted by one radiolabeled halogen atom.

4. The compound or salt of claim 1 , wherein

R 1 is

(1) an azetizinyl group or a pyrrolidinyl group, each substituted by 1 to 3 radiolabeled halogen atoms, or

(2) an amino group mono- or di-substituted by substituent(s) selected from the group consisting of:

(a) a C 1-6 alkyl group substituted by 1 to 3 radiolabeled halogen atoms, and

(b) a radiolabeled C 1-6 alkyl group,

and optionally further substituted by a substituent selected from the group consisting of:

(c) a C 1-6 alkyl group substituted by 1 to 3 halogen atoms,

(d) a C 1-6 alkyl group optionally substituted by phenyl group(s) optionally substituted by 1 to 3 halogen atoms,

(e) a C 3-8 cycloalkyl group,

(f) a tetrahydropyranyl group, and

(g) a tetrahydrofuryl group;

R 2 is

(1) a phenyl group optionally substituted by 1 to 3 halogen atoms, or

(2) a pyrazolyl group or a thiazolyl group, each optionally substituted by 1 to 3 substituents selected from the group consisting of:

(a) a halogen atom,

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

(c) a C 3-8 cycloalkyl group;

X 1 is CH or N; and

Ring A is

5. The compound or salt of claim 1 , wherein

R 1 is

(1) an azetizinyl group or a pyrrolidinyl group, each substituted by one radiolabeled halogen atom, or

(2) an amino group substituted by one substituent selected from the group consisting of:

(a) a C 1-6 alkyl group substituted by one radiolabeled halogen atom, and

(b) a radiolabeled C 1-6 alkyl group,

and further substituted by one substituent selected from the group consisting of:

(c) a C 1-6 alkyl group optionally substituted by phenyl group(s) optionally substituted by 1 to 3 halogen atoms,

(d) a C 3-8 cycloalkyl group,

(e) a tetrahydropyranyl group, and

(f) a tetrahydrofuryl group;

R 2 is

(1) a phenyl group optionally substituted by 1 to 3 halogen atoms, or

(2) a pyrazolyl group or a thiazolyl group, each optionally substituted by 1 to 3 substituents selected from the group consisting of:

(a) a halogen atom,

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

(c) a C 3-8 cycloalkyl group;

X 1 is CH or N; and

Ring A is

6. The compound or salt of claim 1 , wherein

R 1 is an azetizinyl group or a pyrrolidinyl group, each substituted by one radiolabeled halogen atom;

R 2 is

(1) a phenyl group optionally substituted by 1 to 3 halogen atoms, or

(2) a pyrazolyl group or a thiazolyl group, each optionally substituted by 1 to 3 substituents selected from the group consisting of:

(a) a halogen atom,

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

(c) a C 3-8 cycloalkyl group;

X 1 is CH or N; and

Ring A is

7. The compound or salt of claim 5 , wherein R 1 is

(1) an azetizinyl group or a pyrrolidinyl group, each substituted by one 18 F, or

(2) an amino group substituted by one substituent selected from the group consisting of:

(a) a C 1-6 alkyl group substituted by one 18 F, and

(b) a C 1-6 alkyl group radiolabeled by one 11 C,

and further substituted by one substituent selected from the group consisting of:

(c) a C 1-6 alkyl group optionally substituted by phenyl group(s) optionally substituted by 1 to 3 halogen atoms,

(d) a C 3-8 cycloalkyl group,

(e) a tetrahydropyranyl group, and

(f) a tetrahydrofuryl group.

8. The compound or salt of claim 6 , wherein R 1 is an azetizinyl group or a pyrrolidinyl group, each substituted by one 18 F.

9. The compound or salt of claim 1 , wherein

R 1 is an azetizinyl group or a pyrrolidinyl group, each substituted by one 18 F;

R 2 is

(1) a phenyl group optionally substituted by 1 to 3 halogen atoms, or

(2) a pyrazolyl group or a thiazolyl group, each optionally substituted by 1 to 3 substituents selected from the group consisting of:

(a) a halogen atom,

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

(c) a C 3-8 cycloalkyl group;

X 1 is CH or N; and

Ring A is

10. (3-[ 18 F]Fluoroazetidin-1-yl)(1-(4-(4-fluorophenyl)pyrimidin-5-yl)piperidin-4-yl)methanone or a salt thereof.

11. (1-(4-(4-Chloro-1H-pyrazol-1-yl)pyridin-3-yl)piperidin-4-yl)(3-[ 18 F]fluoroazetidin-1-yl)methanone or a salt thereof.

12. (1-(4-(4-Bromo-1H-pyrazol-1-yl)pyridin-3-yl)piperidin-4-yl)(3-[ 18 F]fluoroazetidin-1-yl)methanone or a salt thereof.

13. A method for quantitative imaging of cholesterol 24-hydroxylase in a mammal, which comprises administering to the mammal in need of such imaging an effective amount of the compound or salt of claim 1 , and obtaining an image useful for quantifying cholesterol 24-hydroxylase in the mammal using positron emission tomography.

14. A method for quantitative imaging of cholesterol 24-hydroxylase in the brain in a mammal, which comprises administering to the mammal in need of such imaging an effective amount of the compound or salt of claim 1 , and obtaining an image useful for quantifying cholesterol 24-hydroxylase in the brain in the mammal using positron emission tomography.

15. A method for diagnostic imaging of epilepsy or neurodegenerative disease associated with cholesterol 24-hydroxylase dysfunction in the brain in a mammal, which comprises administering to the mammal in need of such diagnostic imaging an effective amount of the compound or salt of claim 1 , and obtaining an image useful for quantifying cholesterol 24-hydroxylase in the brain in the mammal using positron emission tomography.

16. The method of claim 15 , wherein the neurodegenerative disease is Alzheimer's disease, mild cognitive disorder, Huntington's disease, Parkinson's disease or multiple sclerosis.

17. A method for the quantification of cholesterol 24-hydroxylase occupancy by a test compound or a salt thereof in mammalian tissue, which comprises contacting such mammalian tissue with an effective amount of the compound or salt of claim 1 , contacting such mammalian tissue with the test compound or a salt thereof and quantifying the cholesterol 24-hydroxylase using positron emission tomography.

18. A composition comprising the compound or salt of claim 1 .

19. A method of imaging a tissue, cells or a host, which comprises contacting the compound or salt of claim 1 , with or administering to a tissue, cells or a host, and imaging the tissue, cells or host with a PET imaging system.

20. The compound or salt of claim 1 , which is for use of quantitative imaging of cholesterol 24-hydroxylase.