Amino acid compounds and methods of use

Abstract

The invention relates to compounds of formula (I): formula (I) or a salt thereof wherein R1, R5, R7, R8, X, m, n, p and q are as described herein. Compounds of formula (I) and pharmaceutical compositions thereof are αvβ6 integrin inhibitors that are useful for treating tissue specific fibrosis such as idiopathic pulmonary fibrosis (IPF) and nonspecific interstitial pneumonia (NSIP).

The invention claimed is: 
     
       1. A compound of formula (I): 
       
         
           
           
               
               
           
         
       
       or a salt thereof, wherein:
 R 1  is C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, 3- to 12-membered heterocyclyl, —OR 2  or —NR 3a R 3b , wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 1  are independently optionally substituted by R 10 ; 
 R 2  is C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, or 3- to 12-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 2  are independently optionally substituted by R 10 ; 
 R 3a  and R 3b  are independently hydrogen, C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, or 3- to 12-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 3a  and R 3b  are independently optionally substituted by R 10 ;
 or R 3a  and R 3b  are taken together with the nitrogen to which they are attached to form a 4- to 8-membered heterocyclyl optionally substituted by R 10 ; 
 
 n is 1 or 2; 
 m is 0 to 6; 
 each R 5 , where present, is independently C 1 -C 6  alkyl, C 3 -C 6  cycloalkyl, halogen, —CN, —OR 5a , —C(O)OR 5a , —NR 5a C(O)R 5b ; —NR 5c R 5d , —C(O)NR 5c R 5d , —SO 2 R 5e , or —SO 2 NR 5c R 5d , wherein the C 1 -C 6  alkyl and C 3 -C 6  cycloalkyl are independently optionally substituted by R 10 ; 
 each R 5a  and R 5b  is independently hydrogen, C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, or 3- to 12-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 5a  and R 5b  are independently optionally substituted by R 10 ; 
 each R 5c  and R 5d  is independently hydrogen, C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, or 3- to 12-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 5c  and R 5d  are independently optionally substituted by R 10 ;
 or R 5c  and R 5d  are taken together with the nitrogen to which they are attached to form a 4- to 8-membered heterocyclyl optionally substituted by R 10 ; 
 
 each R 5e  is independently C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, or 3- to 12-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 3 -C 8  cycloalkyl, C 6 -C 14  aryl, 5- to 10-membered heteroaryl, and 3- to 12-membered heterocyclyl of R 5e  are independently optionally substituted by R 10 ; 
 X is C 1 -C 3  alkylene optionally substituted by R 10 ; 
 p is 0 to 2; 
 q is 0 to 6; 
 each R 7 , where present, is independently C 1 -C 6  alkyl optionally substituted by halogen or —OH, C 3 -C 6  cycloalkyl, halogen, —CN, —NO 2 , —OR 7a , or —NR 7b R 7c ; 
 each R 7a , R 7b  and R 7c  is independently hydrogen or C 1 -C 3  alkyl; 
 each R 8 , where present, is independently C 1 -C 6  alkyl, C 3 -C 6  cycloalkyl; halogen, oxo or —OR 8a , wherein the C 1 -C 6  alkyl and C 3 -C 6  cycloalkyl are independently optionally substituted by R 10 ; 
 R 8a  is hydrogen or C 1 -C 6  alkyl; 
 each R 9  is independently C 1 -C 6  alkyl, C 2 -C 6  alkenyl, C 2 -C 6  alkynyl, halogen, —CN, —OR 11 , —SR 11 , —NR 12 R 13 , —NO 2 , —C═NH(OR 11 ), —C(O)R 11 , —OC(O)R 11 , —C(O)OR 11 , —C(O)NR 12 R 13 , —NR 11 C(O)R 12 , NR 11 C(O)OR 12 , —NR 11 C(O)NR 12 R 13 , —S(O)R 11 , —S(O) 2 R 11 , —NR 11 S(O)R 12 , —NR 11 S(O) 2 R 12 , —S(O)NR 12 R 13 , —S(O) 2 NR 12 R 13 , —P(O)(OR 12 ) (OR 13 ), C 3 -C 8  cycloalkyl, 3- to 12-membered heterocyclyl, 5- to 10-membered heteroaryl, C 6 -C 14  aryl, wherein each R 9  is independently optionally substituted by halogen, oxo, —OR 14 —NR 14 R 15 , —C(O)R 14 , —CN, —S(O)R 14 , —S(O) 2 R 14 , —P(O)(OR 14 )(OR 15 ), C 3 -C 8  cycloalkyl, 3- to 12-membered heterocyclyl, 5- to 10-membered heteroaryl, C 6 -C 14  aryl, or C 1 -C 6  alkyl optionally substituted by oxo, —OH or halogen; 
 each R 10  is independently oxo or R 9 ; 
 R 11  is independently hydrogen, C 1 -C 6  alkyl, C 2 -C 6  alkenyl, C 2 -C 6  alkynyl, C 3 -C 6  cycloalkyl, C 6 -C 14  aryl, 5- to 6-membered heteroaryl or 3- to 6-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 2 -C 6  alkenyl, C 2 -C 6  alkynyl, C 3 -C 6  cycloalkyl, C 6 -C 14  aryl, 5- to 6-membered heteroaryl and 3- to 6-membered heterocyclyl are independently optionally substituted by halogen, oxo, —CN, —OR 16 , —NR 16 R 17 , P(O)(OR 16 )(OR 17 ), or C 1 -C 6  alkyl optionally substituted by halogen, —OH or oxo; 
 R 12  and R 13  are each independently hydrogen, C 1 -C 6  alkyl, C 2 -C 6  alkenyl, C 2 -C 6  alkynyl, C 3 -C 6  cycloalkyl, C 6 -C 14  aryl, 5- to 6-membered heteroaryl or 3- to 6-membered heterocyclyl, wherein the C 1 -C 6  alkyl, C 2 -C 6  alkenyl, C 2 -C 6  alkynyl, C 3 -C 6  cycloalkyl, C 6 -C 14  aryl, 5- to 6-membered heteroaryl and 3- to 6-membered heterocyclyl are independently optionally substituted by halogen, oxo, —CN, —OR 16 , —NR 16 R 17  or C 1 -C 6  alkyl optionally substituted by halogen, —OH or oxo;
 or R 12  and R 13  are taken together with the atom to which they attached to form a 3- to 6-membered heterocyclyl optionally substituted by halogen, oxo, —OR 16 , —NR 16 R 17  or C 1 -C 6  alkyl optionally substituted by halogen, oxo or —OH; 
 
 R 14  and R 15  are each independently hydrogen, C 1 -C 6  alkyl optionally substituted by halogen or oxo, C 2 -C 6  alkenyl optionally substituted by halogen or oxo, or C 2 -C 6  alkynyl optionally substituted by halogen or oxo;
 or R 14  and R 15  are taken together with the atom to which they attached to form a 3- to 6-membered heterocyclyl optionally substituted by halogen, oxo or C 1 -C 6  alkyl optionally substituted by halogen or oxo; and 
 
 R 16  and R 17  are each independently hydrogen, C 1 -C 6  alkyl optionally substituted by halogen or oxo, C 2 -C 6  alkenyl optionally substituted by halogen or oxo, or C 2 -C 6  alkynyl optionally substituted by halogen or oxo;
 or R 16  and R 17  are taken together with the atom to which they attached to form a 3-6 membered heterocyclyl optionally substituted by halogen, oxo or C 1 -C 6  alkyl optionally substituted by oxo or halogen. 
 
 
     
     
       2. The compound of  claim 1 , wherein the compound is of the formula (Ia): 
       
         
           
           
               
               
           
         
         or a salt thereof. 
       
     
     
       3. The compound of  claim 1 , or a salt thereof, wherein n is 1. 
     
     
       4. The compound of  claim 1 , or a salt thereof, wherein n is 2. 
     
     
       5. The compound of  claim 1 , or a salt thereof, wherein X is C 1 -C 3  alkylene. 
     
     
       6. The compound of  claim 1 , or a salt thereof, wherein X is C 1 -C 2  alkylene optionally substituted by R 10 . 
     
     
       7. The compound of  claim 1 , or a salt thereof, wherein X is ethylene. 
     
     
       8. The compound of  claim 1 , wherein the compound is of the formula (IVa): 
       
         
           
           
               
               
           
         
         or a salt thereof. 
       
     
     
       9. The compound of  claim 1 , or a salt thereof, wherein R 1  is a C 1 -C 6  alkyl optionally substituted by R 10 . 
     
     
       10. The compound of  claim 9 , wherein R 1  is t-butyl. 
     
     
       11. The compound of  claim 1 , or a salt thereof, wherein R 1  is —OR 2  or —NR 3a R 3b . 
     
     
       12. The compound of  claim 11 , or a salt thereof, wherein R 1  is —OR 2 . 
     
     
       13. The compound of  claim 12 , or a salt thereof, wherein R 2  is C 1 -C 6  alkyl. 
     
     
       14. The compound of  claim 13 , wherein R 2  is t-butyl. 
     
     
       15. The compound of  claim 1 , or a salt thereof, wherein R 1  is C 3 -C 8  cycloalkyl optionally substituted by R 10 . 
     
     
       16. The compound of  claim 1 , or a salt thereof, wherein R 1  is C 6 -C 14  aryl optionally substituted by R 10 . 
     
     
       17. The compound of  claim 1 , or a salt thereof, wherein R 1  is phenyl optionally substituted by R 10 . 
     
     
       18. The compound of  claim 1 , or a salt thereof, wherein R 1  is 5- to 10-membered heteroaryl optionally substituted by R 10 . 
     
     
       19. The compound of  claim 18 , or a salt thereof, wherein R 1  is pyridyl optionally substituted by R 10 . 
     
     
       20. The compound of  claim 18 , or a salt thereof, wherein R 1  is indazolyl optionally substituted by R 10 . 
     
     
       21. The compound of  claim 1 , or a salt thereof, wherein R 1  is 3- to 12-membered heterocyclyl optionally substituted by R 10 . 
     
     
       22. The compound of  claim 21 , or a salt thereof, wherein R 1  is piperidinyl optionally substituted by R 10 . 
     
     
       23. The compound of  claim 21 , or a salt thereof, wherein R 1  is tetrahydropyranyl optionally substituted by R 10 . 
     
     
       24. The compound of  claim 1 , or a salt thereof, wherein R 1  is C 3 -C 8  cycloalkyl optionally substituted by R 10 . 
     
     
       25. The compound of  claim 24 , or a salt thereof, wherein R 1  is cyclohexyl optionally substituted by R 10 . 
     
     
       26. The compound of  claim 1 , or a salt thereof, wherein R 1  is selected from the group consisting of: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
       27. The compound of  claim 1 , wherein the compound is selected from the group consisting of:
 2-pivalamido-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-pivalamido-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-pivalamido-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-pivalamido-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-pivalamido-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-((tert-butoxycarbonyl)amino)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((tert-butoxycarbonyl)amino)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((tert-butoxycarbonyl)amino)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-((tert-butoxycarbonyl)amino)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-((tert-butoxycarbonyl)amino)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-benzamido-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-benzamido-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-benzamido-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-benzamido-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-benzamido-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(2,6-dimethylbenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dimethylbenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dimethylbenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dimethylbenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dimethylbenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(2-chloro-3-fluorobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-chloro-3-fluorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-chloro-3-fluorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2-chloro-3-fluorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2-chloro-3-fluorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(2,6-dichloro-4-cyanobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichloro-4-cyanobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichloro-4-cyanobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dichloro-4-cyanobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dichloro-4-cyanobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(2-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(2-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(2-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(2-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(2-(trifluoromethyl)benzamido)butanoic acid, 
 4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(trifluoromethyl)benzamido)butanoic acid, 
 4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(4-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(4-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(4-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(4-(trifluoromethyl)benzamido)butanoic acid, 
 (R)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(4-(trifluoromethyl)benzamido)butanoic acid, 
 2-(2,6-dichlorobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-11dyl)butanoic acid, 
 (R)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin -1-yl)butanoic acid, 
 (R)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-(4-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-(4-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (R)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-(4-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(2-morpholinobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(2-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(3-morpholinobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(4-morpholinobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4-morpholinobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4-morpholinobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(picolinamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(picolinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(picolinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(picolinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(picolinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(isonicotinamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(isonicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(isonicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(isonicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(isonicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(nicotinamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(nicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(nicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(nicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(nicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(3,5-dichloroisonicotinamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3,5-dichloroisonicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3,5-dichloroisonicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3,5-dichloroisonicotinamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3,5-dichloroisonicotinamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(4,4-difluorocyclohexane-1-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(4-methyltetrahydro-2H-pyran-4-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4-methyltetrahydro-2H-pyran-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4-methyltetrahydro-2H-pyran-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4-methyltetrahydro-2H-pyran-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(4-methyltetrahydro-2H-pyran-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-cyclopropylpiperidine-4-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-cyclopropylpiperidine-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-cyclopropylpiperidine-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-cyclopropylpiperidine-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-cyclopropylpiperidine-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-methyl-1H-indazole-6-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((s)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (r)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2 -yl)ethyl)pyrrolidin-1-yl)butanoic, 
 (r)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((s)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-6-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2 -yl)ethyl(pyrrolidin-1-yl)butanoic acid, 
 2-(1-methyl-1H-indazole-5-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1H-indazole-7-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1H-indazole-7-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1H-indazole-7-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-methyl-1H-indazole-4-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-4-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-methyl-1H-indazole-7-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-indazole-7-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-methyl-1H-indazole-7-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-(difluoromethyl)-1H-indazole-6-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-(difluoromethyl)-1H-indazole-6-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-(difluoromethyl)-1H-indazole-6-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-(difluoromethyl)-1H-indazole-6-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-(difluoromethyl)-1H-indazole-6-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(1-(difluoromethyl)-1H-indazole-5-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-(difluoromethyl)-1H-indazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-(difluoromethyl)-1H-indazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-(difluoromethyl)-1H-indazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(1-(difluoromethyl)-1H-indazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 2-(benzo[d]oxazole-5-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(benzo[d]oxazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(benzo[d]oxazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(benzo[d]oxazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(benzo[d]oxazole-5-carboxamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-formamido-4-hydroxybenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-(4-(5,6,7,8-tetrahydro-1,8-naphthyridine-2-carboxamido)piperidin-1-yl)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-(4-(((5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)methyl)amino)piperidin-1-yl)butanoic acid, 
 (S)-2-(1H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylpyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-(pyridin-3-yl)propanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(tetrahydro-2H-pyran-4-carboxamido)butanoic acid, 
 (2S)-2-benzamido-4-(3,3-difluoro-4-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (2S)-2-((tert-butoxycarbonyl)amino)-4-(3,3-difluoro-5-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (2S)-2-benzamido-4-(3,3-difluoro-5-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (2S)-4-(3,3-difluoro-5-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)butanoic acid, 
 (S)-2-((S)-1-phenylpyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-phenylpropanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,2-dimethyl-3-phenylpropanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((R)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-cyanobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-pyrazole-5-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(pyrazine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(thiophene-2-carboxamido)butanoic acid, 
 (S)-2-benzamido-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (2S)-2-benzamido-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(thiophen-2-yl)benzamido)butanoic acid, 
 (S)-2-([1,1′-biphenyl]-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(1-methyl-1H-pyrazol-5-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(1-methyl-1H-pyrazol-4-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(oxazol-2-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-isopropyl-1H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-isobutyl-1H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-chloro-3-fluorobenzamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(thiazol-4-yl)benzamido)butanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(thiazol-5-yl)benzamido)butanoic acid, 
 (S)-2-(2,3-difluorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(tert-butyl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-1H-pyrazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(pyrimidine-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-isopropyl-2H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-isobutyl-2H-indazole-4-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-pentanoylpiperidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(cyclobutanecarbonyl)piperidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-(2-chlorophenyl)acetamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-fluoro-5-(trifluoromethyl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(2-hydroxy-2-methylpropyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((R)-1-pentanoylpiperidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((R)-1-pivaloylpiperidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((R)-1-(methoxycarbonyl)piperidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylazetidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-3-phenyl-1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-([1,1′-biphenyl]-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(thiazol-5-yl)benzamido)butanoic acid, 
 (R)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-2-(3-(thiazol-4-yl)benzamido)butanoic acid, 
 (R)-2-(3-(1-methyl-1H-pyrazol-5-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-(1-methyl-1H-pyrazol-4-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (R)-2-(3-(oxazol-2-yl)benzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-4-benzylmorpholine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyrimidin-2-ylmethyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(cyclopropylmethyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(cyclobutylmethyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylpiperidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-ethylbutanamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(2-ethylbutanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(3-morpholinobenzamido)butanoic acid, 
 (S)-2-(3,5-difluorobenzamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(3-(1,3-dimethyl-1H-pyrazol-4-yl)-1-methyl-1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyridin-3-ylmethyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(3-(2-methoxyethoxy)benzamido)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(1-methyl-3-(1-methyl-1H-pyrazol-4-yl)-1H-indazole-7-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-chloro-3-fluorobenzamido)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(3,5-difluorobenzamido)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(3-fluoro-5-(trifluoromethyl)benzamido)butanoic acid, 
 (S)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(1-methyl-1H-indazole-6-carboxamido)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((R)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(2-ethylbutanamido)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-2-(4,4-difluorocyclohexane-1-carboxamido)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)butanoic acid, 
 (S)-4-((S)-3-fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperidin-1-yl)-2-(1-methyl-1H-indazole-6-carboxamido)butanoic acid, 
 (S)-2-((tert-butoxycarbonyl)amino)-4-((R)-3-((5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)methoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-benzamido-4-((R)-3-((5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)methoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(3-(3,5-dimethyl-1H-pyrazol-1-yl)benzamido)-4-((R)-3-((5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)methoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-4-((S)-4-acetyl-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)piperazin-1-yl)-2-benzamidobutanoic acid, 
 (S)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)-2-(tetrahydro-2H-pyran-4-carboxamido)butanoic acid, 
 (S)-2-(2-methyl-2-phenylpropanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2,2-dimethyl-3-phenylpropanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-phenylpropanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylpyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-(pyridin-3-yl)propanamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylpyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)-2-(tetrahydro-2H-pyran-4-carboxamido)butanoic acid, 
 (S)-2-((R)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-phenylpyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-(pyridin-3-yl)propanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-phenylpyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2,2-dimethyl-3-phenylpropanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-((R)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-phenylpyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (2S)-2-(1-(2-hydroxy-2-methylpropyl)pyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)azetidin-1-yl)butanoic acid, 
 (2S)-2-(1-benzylpyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-phenylpropanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2,2-dimethyl-3-phenylpropanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-(pyridin-2-yl)pyrrolidine-3-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(3-fluoro-5-(trifluoromethyl)benzamido)-4-((1R,2R,4S)-2-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)-7-azabicyclo[2.2.1]heptan-7-yl)butanoic acid, 
 (S)-2-(3-fluoro-5-(trifluoromethyl)benzamido)-4-((1R,2R,4S)-2-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)-7-azabicyclo[2.2.1]heptan-7-yl)butanoic acid, 
 (S)-2-((S)-1-(2-hydroxy-2-methylpropyl)pyrrolidine-2-carboxamido)-4-((R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethoxy)pyrrolidin-1-yl)butanoic acid, 
 (S)-2-((S)-1-benzylpyrrolidine-2-carboxamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2-methyl-2-(pyridin-3-yl)propanamido)-4-(3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)azetidin-1-yl)butanoic acid, 
 (S)-2-(2-ethylbutanamido)-4-((1R,2R,4S)-2-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)-7-azabicyclo[2.2.1]heptan-7-yl)butanoic acid, 
 (S)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid, or and  
 (R)-2-(2,6-dichlorobenzamido)-4-((S)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid; 
 
       or a salt thereof. 
     
     
       28. A pharmaceutical composition comprising a compound of  claim 1 , or a salt thereof, and a pharmaceutically acceptable carrier or excipient. 
     
     
       29. A method of treating a fibrotic disease in an individual in need thereof comprising administering a compound of  claim 1  or a pharmaceutically acceptable salt thereof. 
     
     
       30. The method of  claim 29 , wherein the fibrotic disease is pulmonary fibrosis, liver fibrosis, skin fibrosis, cardiac fibrosis, kidney fibrosis, gastrointestinal fibrosis, primary sclerosing cholangitis, or biliary fibrosis. 
     
     
       31. A kit comprising a compound of  claim 1 , or a pharmaceutically acceptable salt thereof. 
     
     
       32. The kit of  claim 31 , further comprising instructions for the treatment of a fibrotic disease. 
     
     
       33. A method of inhibiting αvβ6 integrin in an individual comprising administering a compound of  claim 1  or a pharmaceutically acceptable salt thereof. 
     
     
       34. A method of inhibiting TGFβ activation in a cell comprising administering to the cell a compound of  claim 1  or a pharmaceutically acceptable salt thereof.