Dipeptidyl Peptidase-IV inhibiting compounds, method of preparing the same, and pharmaceutical compositions containing the same as an active agent

1. A compound of the following formula (1) or pharmaceutically acceptable salt thereof:

wherein

A is a substituent of the following formula (5):

wherein R 3 is hydrogen, or substituted or unsubstituted C 1 -C 4 alkyl, cycloalkyl, aryl or heteroaryl; and R′ 3 is hydrogen, or CF 3 ;

B is selected from the group consisting of substituents of the following formulas (8) to (11):

wherein R 7 , R 8 , R 9 and R 10 are each independently hydrogen, halogen, or substituted or unsubstituted C 1 -C 4 alkyl;

wherein R 11 , R 12 and R 13 are each independently hydrogen, halogen, or substituted or unsubstituted C 1 -C 4 alkyl; and Y is oxygen, sulfur or SO 2;

wherein R 14 and R 15 are each independently hydrogen, halogen, or substituted or unsubstituted C 1 -C 4 alkyl; and Z is —CH— or oxygen, where Z is oxygen, R 14 is nothing; and

wherein R 17 is substituted or unsubstituted C 1 -C 4 alkyl, wherein the substituted C 1 -C 4 alkyl is substituted with halogen.

2. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the halogen is fluoride.

3. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein R 3 is selected from the group consisting of:

hydrogen;

substituted or unsubstituted C 1 -C 4 alkyl;

formula —CH 2 -R 18 , wherein R 18 is C 1 -C 4 alkoxyalkyl, or C 3 -C 7 cycloalkyl unsubstituted or substituted with halogen or hydroxy, or phenyl unsubstituted or substituted with halogen or hydroxy, or heteroaryl;

substituted or unsubstituted C 3 -C 7 cycloalkyl;

formula

wherein R 19 and R 20 are each independently hydrogen, halogen, or substituted or unsubstituted C 1 -C 4 alkyl; and

5-membered or 6-membered heteroaryl unsubstituted or substituted with halogen or hydroxy,

wherein the substituted C 3 -C 7 cycloalkyl and C 1 -C 4 alkyl are the cycloalkyl and alkyl substituted with halogen or hydroxy.

4. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the heteroaryl is a 2-furan, 3-furan, 2-thiophene, 3-thiophene, 2-pyridine, 3-pyridine, 4-pyridine, 2-pyrrole or 3-pyrrole, unsubstituted or substituted with a halogen or hydroxy.

5. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound is a stereoisomer as represented in the following formula (1a):

wherein A and B are the same as in formula (1).

6. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound is selected from the group consisting of:

1-[2S-amino-4-oxo-4-(4-trifluoromethyl-5,8-dihydro-6H-pyrido[3,4-d]pyrimidin-7-yl)-butyl]-5R-methyl-1-piperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-phenyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-oxo-4-[2-phenyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-6-methylmorpholin-3-one;.

1-{(2S)-2-amino-4-oxo-4-[2-phenyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2-cyclopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2-cyclopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-cyclopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

1-{(2S)-2-amino-4-[2-(4-fluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-(4-fluorophenyl)-4-(trifluoromethyl)-5,8- dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-2-one;

1-{(2S)-2-amino-4-[2-(3-fluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4- d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-(3-fluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

(5R)-1-{(2S)-2-amino-4-[2-(4-fluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(3,4-difluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-(3,4-difluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

(5R)-1-{(2S)-2-amino-4-[2-(3,4-difluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-cyclopentyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-cyclopentyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

1-{(2S)-2-amino-4-[2-cyclopentyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(2-methoxyethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(2-methoxyethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(cyclopropylmethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(cyclopropylmethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-pyridin-4-yl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-pyridin-4-yl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(4-fluorobenzyl)-4-(trifluoromethyl)-5,8- dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(4-fluorobenzyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-(3-thienyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-(3-thienyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-(2-thienyl)-4-(trifluoromethyl)-5,8- dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-(2-thienyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(2-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(2-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-(1H-pyrrol-2-yl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-(1H-pyrrol-2-yl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-pyridin-3-yl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-pyridin-3-yl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2-ethyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-ethyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

1-{(2S)-2-amino-4-[2-isopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2-isopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-isopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

(5S)-1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin- 7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin- 7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin- 7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one;

1-{(2S)-2-amino-4-oxo-4-[4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin- 7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-oxo-4-[4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-6-methylmorpholin-3-one;

4-{(2S)-2-amino-4-[2.4-bis(trifluoromethyl)-5,8- dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylthiomorpholin-3-one;

(5R)-1-{(2S)-2-amino-4-[2-ethyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

(6S)-4-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-6-methylmorpholin-3-one;

1-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-oxo-4-[2-propyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-oxo-4-[2-propyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-(fluoromethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one;

1-{(2S)-2-amino-4-[2-(fluoromethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methyl-1,5-dihydro-2H-pyrrol-2-one;

1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methyl-1,5-dihydro-2H-pyrrol-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methyloxopyrolidin-2-one;

1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methylpyrolidin-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-(trifluoromethyl)piperidin-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-(trifluoromethyl)pyrolidin-2-one;

1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-(trifluoromethyl)pyrolidin-2-one;

1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methyloxopiperidin-2-one;

1-{(2S)-2-amino-4-[2-(3-furyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-4-methylpiperidin-2-one;

(5R)-1-{(2S)-2-amino-4-[2-cyclobutyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one; and

1-{(2S)-2-amino-4-[2-cyclobutyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one .

7. A pharmaceutical composition for inhibiting Dipeptidyl Peptidase-IV(DPP-IV) comprising the compound according to claim 1 or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier.

8. The pharmaceutical composition according to claim 7 , wherein the composition is used for treating diabetes mellitus or obesity.

9. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (5R)-1-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

10. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (5R)-1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

11. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of 1-{(2S)-2-amino-4-[2,4-bis(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

12. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of 1-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

13. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (6S)-4-{(2S)-2-amino-4-[2-methyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

14. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (6S)-4-{(2S)-2-amino-4-[2-(4-fluorophenyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

15. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of 1-{(2S)-2-amino-4-[2-t-butyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

16. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (6S)-4-{(2S)-2-amino-4-[2-t-butyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

17. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (6S)-4-{(2S)-2-amino-4-[2-cyclopropyl-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-6-methylmorpholin-3-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

18. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (5R)-1-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5-methylpiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

19. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (6S)-4-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-6-methylmorpholin-3-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

20. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of 1-{(2S)-2-amino-4-oxo-4-[2-(pentafluoroethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]butyl}-5,5-difluoropiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

21. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of (5R)-1-{(2S)-2-amino-4-[2-(fluoromethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5-methylpiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.

22. The compound according to claim 1 , or pharmaceutically acceptable salt thereof, wherein the compound or pharmaceutically acceptable salt is selected from the group consisting of 1-{(2S)-2-amino-4-[2-(fluoromethyl)-4-(trifluoromethyl)-5,8-dihydropyrido[3,4-d]pyrimidin-7(6H)-yl]-4-oxobutyl}-5,5-difluoropiperidin-2-one, and salts thereof with maleic acid, phosphoric acid, tartaric acid, hydrochloric acid, methanesulfonic acid or citric acid.