Compounds α

1. A compound of formula (I):

wherein R is H or F;

or a pharmaceutically acceptable salt thereof.

2. The compound according to claim 1 which is 4-(3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(3-morpholinophenyl)butanoic acid

or a pharmaceutically acceptable salt thereof.

3. The compound according to claim 2 which is (S)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(3-morpholinophenyl)butanoic acid

or a pharmaceutically acceptable salt thereof.

4. The compound according to claim 1 which is 4-(3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(2-fluoro-5-morpholinophenyl)butanoic acid

or a pharmaceutically acceptable salt thereof.

5. The compound according to claim 4 which is (S)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(2-fluoro-5-morpholinophenyl)butanoic acid

or a pharmaceutically acceptable salt thereof.

6. A method of treating a disorder in a human, wherein the disorder is responsive to antagonism of an α v β 6 receptor and is a fibrotic disease or condition, the method comprising administering to the human in need thereof a therapeutically effective amount of the compound or pharmaceutically acceptable salt according to claim 1 .

7. A method of treating a disorder in a human, wherein the disorder is responsive to antagonism of an α v β 6 receptor and is a fibrotic disease or condition, the method comprising administering to the human in need thereof a therapeutically effective amount of the compound or pharmaceutically acceptable salt according to claim 3 .

8. A method of treating a disorder in a human, wherein the disorder is responsive to antagonism of an α v β 6 receptor and is a fibrotic disease or condition, the method comprising administering to the human in need thereof a therapeutically effective amount of the compound or pharmaceutically acceptable salt according to claim 5 .

9. The method according to claim 6 , wherein the disorder is idiopathic pulmonary fibrosis.

10. The method according to claim 7 , wherein the disorder is idiopathic pulmonary fibrosis.

11. The method according to claim 8 , wherein the disorder is idiopathic pulmonary fibrosis.

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

13. A pharmaceutical composition comprising the compound or pharmaceutically acceptable salt according to claim 3 , and a pharmaceutically acceptable excipient.

14. A pharmaceutical composition comprising the compound or pharmaceutically acceptable salt according to claim 5 , and a pharmaceutically acceptable excipient.

15. The pharmaceutical composition according to claim 12 , wherein the pharmaceutical composition is for oral administration.

16. The pharmaceutical composition according to claim 13 , wherein the pharmaceutical composition is for oral administration.

17. The pharmaceutical composition according to claim 14 , wherein the pharmaceutical composition is for oral administration.