7-(heteroaryl-amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol acetic acid derivatives and their use as prostaglandin D2 receptor modulators

1. A compound of formula (I):

wherein

R 1 and R 2 represent independently of each other hydrogen, (C 1 -C 4 )alkyl, (C 1 -C 4 )alkoxy, halogen, trifluoromethoxy or trifluoromethyl;

R 3 represents hydrogen, (C 1 -C 4 )alkyl, (C 1 -C 2 )alkoxy-(C 2 -C 3 )alkyl, (C 1 -C 4 )fluoroalkyl or (C 3 -C 6 )cycloalkyl-(C 1 -C 2 )alkyl; and

R 4 represents a heteroaryl group which is unsubstituted or mono-, di- or tri-substituted, wherein the substituents are independently selected from halogen, (C 1 -C 4 )alkyl, (C 3 -C 6 )cycloalkyl, (C 1 -C 4 )alkoxy, (C 1 -C 4 )fluoroalkyl or phenyl;

or a salt thereof.

2. The compound according to claim 1 , wherein

R 1 represents hydrogen, (C 1 -C 4 )alkyl, (C 1 -C 4 )alkoxy, halogen or trifluoromethoxy;

R 2 represents hydrogen, halogen or trifluoromethyl;

R 3 represents hydrogen or (C 1 -C 4 )alkyl; and

R 4 represents a heteroaryl group which is unsubstituted or mono- or di-substituted, wherein the substituents are independently selected from halogen or (C 1 -C 4 )fluoroalkyl;

or a salt thereof.

3. The compound according to claim 1 , wherein

R 1 represents hydrogen;

R 2 represents hydrogen, fluoro, chloro or trifluoromethyl;

R 3 represents methyl; and

R 4 represents a heteroaryl group which is mono-substituted with fluoro or chloro, wherein the heteroaryl group is pyrimidin-2-yl, benzoxazol-2-yl or benzothiazol-2-yl;

or a salt thereof.

4. The compound according to claim 2 , wherein R 1 represents hydrogen; or a salt thereof.

5. The compound according to claim 4 , wherein R 2 represents hydrogen, halogen or trifluoromethyl;

or a salt thereof.

6. The compound according to claim 4 , wherein R 2 represents fluoro or chloro;

or a salt thereof.

7. The compound according to claim 4 , wherein R 3 represents hydrogen or methyl;

or a salt thereof.

8. The compound according to claim 4 , wherein R 4 represents a heteroaryl group which is mono-substituted with halogen or (C 1 -C 4 )fluoroalkyl;

or a salt thereof.

9. The compound according to claim 8 , wherein the heteroaryl group is pyrimidyl, benzoxazolyl or benzothiazolyl;

or a salt thereof.

10. The compound according to claim 1 , wherein the compound is:

2-(7-((5-chloropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-(methyl(5-(trifluoromethyl)pyrimidin-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((6-fluorobenzo[d]thiazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]thiazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(2-fluoro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid,

2-(2-fluoro-7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluoropyrimidin-2-yl)(methyl)amino)-2-methoxy-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-2-methoxy-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluoropyrimidin-2-yl)(methyl)amino)-2-methyl-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-2-methyl-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(2-chloro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(2-chloro-7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-chloropyrimidin-2-yl)(methyl)amino)-3-fluoro-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-(methyl(5-(trifluoromethyl)pyrimidin-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((5-fluorobenzo[d]thiazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((6-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-chloro-7-((5-chloropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-chloropyrimidin-2-yl)(methyl)amino)-3-(trifluoromethyl)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-chloropyrimidin-2-yl)(methyl)amino)-2-(trifluoromethoxy)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluoropyrimidin-2-yl)(methyl)amino)-3-(trifluoromethyl)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluoropyrimidin-2-yl)(methyl)amino)-2-(trifluoromethoxy)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((6-fluorobenzo[d]thiazol-2-yl)(methyl)amino)-3-(trifluoromethyl)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((6-fluorobenzo[d]thiazol-2-yl)(methyl)amino)-2-(trifluoromethoxy)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-3-(trifluoromethyl)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-2-(trifluoromethoxy)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-chloro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-chloro-7-((5-fluorobenzo[d]oxazol-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

(S)-2-(3-chloro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

(R)-2-(3-chloro-7-((5-fluoropyrimidin-2-yl)(methyl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((5-fluoropyrimidin-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-fluoro-7-((5-fluorobenzo[d]oxazol-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

2-(3-chloro-7-((5-fluoropyrimidin-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid; or

2-(3-chloro-7-((5-chloropyrimidin-2-yl)amino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl)acetic acid;

or a salt thereof.

11. A pharmaceutical composition comprising the compound according to claim 1 , or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

12. A medicament comprising the compound according to claim 1 , or a pharmaceutically acceptable salt thereof.

13. A method for treating a disease comprising administering an effective amount to a patient in need thereof the compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein the disease is asthma, allergic asthma, eosinophilic asthma, severe asthma, rhinitis, allergic rhinitis, angioedema, insect venom allergy, drug allergies, allergic sinusitis, allergic nephritis, allergic conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, anaphylactic shock, urticaria, eczema, or chronic obstructive pulmonary disease (COPD).

14. A method for treating a disease comprising administering an effective amount to a patient in need thereof the compound according to claim 1 , or a pharmaceutically acceptable salt thereof, wherein the disease is small vessel vasculitides, eosinophilic cellulitis (Wells syndrome).

15. A method for the treatment of a disease, comprising administering to a patient in need thereof the compound according to claim 10 , or a pharmaceutically acceptable salt thereof, wherein the administered amount is effective to treat the disease, wherein the disease is asthma, allergic asthma, eosinophilic asthma, severe asthma, rhinitis, allergic rhinitis, angioedema, insect venom allergy, drug allergies, allergic sinusitis, allergic nephritis, allergic conjunctivitis, atopic dermatitis, bronchial asthma, food allergy, anaphylactic shock, urticaria, eczema or chronic obstructive pulmonary disease (COPD).

16. A method for the treatment of a disease, comprising administering to a patient in need thereof the compound according to claim 10 , or a pharmaceutically acceptable salt thereof, wherein the administered amount is effective to treat the disease, wherein the disease is small vessel vasculitides, eosinophilic esophagitis or eosinophilic cellulitis (Wells syndrome).

17. The method according to claim 14 , wherein the small vessel vasculitides is Churg-Strauss syndrome.

18. The method according to claim 16 , wherein the small vessel vasculitides is Churg-Strauss syndrome.