PYRIDO[4,3-d]PYRIMIDIN-4(3H)-ONE DERIVATIVES AS CALCIUM RECEPTOR ANTAGONISTS

Abstract

The present invention is directed to novel pyrido[4,3-d]pyrimidin-4(3H)-one derivatives and pharmaceutically acceptable salts thereof of structural formula I wherein the variables R 1 , R 2 , R 3 , R 4 and R 5 are as described herein. Also provided are pharmaceutical compositions comprising the compounds of formula I as well as methods of treatment employing compounds of formula I to treat a disease or disorder characterized by abnormal bone or mineral homeostasis such as hypoparathyroidism, osteoporosis, osteopenia, periodontal disease, Paget's disease, bone fracture, osteoarthritis, rheumatoid arthritis, and humoral hypercalcemia of malignancy.

1 . A compound of formula I 
       
         
           
           
               
               
           
         
         wherein 
         R 1  is -Q or (C 1 -C 6 )alkyl-Q; 
         R 2  is (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, aryl or heteroaryl; wherein said aryl or heteroaryl is substituted with hydroxy and additionally said (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, aryl or heteroaryl within the definition of R 2  is optionally substituted with one to three substituents independently selected from halo, cyano, trifluoromethyl, trifluoromethoxy, (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy or hydroxy; 
         R 3  is hydrogen, (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, (C 1 -C 6 )alkyl-Q, aryl, heteroaryl, OR 6 , or NR 7 R 8 ; wherein said (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, aryl or heteroaryl is optionally substituted with one to three substituents independently selected from halo, cyano, trifluoromethyl, trifluoromethoxy, (C 1 -C 6 )alkyl; (C 1 -C 6 )alkoxy, NR 7 R 8  or hydroxy; 
         R 4  and R 5  are each independently hydrogen, halo, cyano, (C 1 -C 6 )alkyl optionally substituted with one to three fluoro, aryl, heteroaryl, or OR 6 ; 
         R 6  at each occurrence is independently (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, (C 3 -C 7 )cycloalkyl-(C 1 -C 6 )alkyl, aryl, heteroaryl, (C 1 -C 6 )alkylaryl, or (C 1 -C 6 )alkylheteroaryl; each of said (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, (C 3 -C 7 )cycloalkyl-(C 1 -C 6 )alkyl, aryl, heteroaryl, (C 1 -C 6 )alkylaryl, or (C 1 -C 6 )alkylheteroaryl optionally substituted with one to three substituents independently selected from halo, hydroxy or (C 1 -C 3 )alkyl; 
         R 7  and R 8 , at each occurrence, are independently hydrogen, (C 1 -C 6 )alkyl, or (C 3 -C 7 )cycloalkyl; or R 7  and R 8  taken together with the nitrogen to which they are attached form a 3 to 7 membered fully saturated, partially saturated or fully unsaturated ring optionally containing one to two additional heteroatoms independently selected from N(R 9 ) n ; O or S(O) p ; 
         n is 0 or 1; 
         p is 0, 1 or 2; 
         R 9  is hydrogen or (C 1 -C 6 )alkyl; 
         Q, at each occurrence, is independently aryl or heteroaryl; wherein said aryl or heteroaryl is optionally substituted with one to three substituents independently selected from halo, cyano, trifluoromethyl, trifluoromethoxy, (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy or hydroxy; 
         or a pharmaceutically acceptable salt thereof. 
       
     
     
         2 . A compound according to  claim 1 , wherein R 2  is aryl or heteroaryl, wherein said aryl or heteroaryl is substituted with hydroxy and optionally substituted with one to three substituents independently selected from (C 1 -C 6 )alkoxy or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         3 . A compound according to  claim 2 , wherein R 2  is aryl, wherein said aryl is substituted with hydroxy and optionally substituted with one to three substituents independently selected from (C 1 -C 6 )alkoxy or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         4 . A compound according to  claim 1 , wherein R 2  is heteroaryl, wherein said heteroaryl is substituted with hydroxy and optionally substituted with one to three substituents independently selected from (C 1 -C 6 )alkoxy or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         5 . A compound according to  claim 2 , wherein R 2  is 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl; wherein said 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl is optionally substituted with one to two substituents independently selected from (C 1 -C 6 )alkoxy or fluoro; or a pharmaceutically acceptable salt thereof. 
     
     
         6 . A compound according to  claim 5 , wherein R 1  is (C 1 -C 6 )alkyl-Q; and Q is phenyl optionally substituted with one or two fluoro; or a pharmaceutically acceptable salt thereof. 
     
     
         7 . A compound according to  claim 1 , wherein R 1  is phenethyl or 1-methyl-2-(phenyl)ethyl, wherein said phenethyl or 1-methyl-2-(phenyl)ethyl is optionally substituted on phenyl with one or two halo; R 2  is 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl, wherein said 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl is optionally substituted with one or two substituents independently selected from (C 1 -C 3 )alkyl or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         8 . A compound according to  claim 7  wherein R 3  is (C 1 -C 6 )alkyl, (C 1 -C 6 )alkyl-Q, aryl, heteroaryl, OR 6 , or NR 7 R 8 , wherein said (C 1 -C 6 )alkyl, aryl or heteroaryl is optionally substituted with one to three substituents independently selected from halo, cyano, trifluoromethyl, trifluoromethoxy, (C 1 -C 6 )alkyl, (C 1 -C 6 )alkoxy, NR 7 R 8  or hydroxy; and
 R 4  and R 5  are each hydrogen; or a pharmaceutically acceptable salt thereof. 
 
     
     
         9 . A compound according to  claim 8 , wherein R 3  is trifluoromethyl; or a pharmaceutically acceptable salt thereof. 
     
     
         10 . A compound according to  claim 1 , wherein R 3  is trifluoromethyl; or a pharmaceutically acceptable salt thereof. 
     
     
         11 . A compound according to  claim 10 , wherein R 4  and R 5  are each independently hydrogen or methyl; or a pharmaceutically acceptable salt thereof. 
     
     
         12 . A compound according to  claim 11 , wherein R 2  is aryl or heteroaryl, wherein said aryl or heteroaryl is substituted with hydroxy and optionally substituted with one to three substituents independently selected from (C 1 -C 6 )alkoxy or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         13 . A compound according to  claim 12 , wherein R 2  is hydroxy-phenyl or hydroxy-pyridyl; wherein said hydroxy-phenyl or hydroxy-pyridyl is optionally substituted with one to two substituents independently selected from (C 1 -C 6 )alkoxy or fluoro; or a pharmaceutically acceptable salt thereof. 
     
     
         14 . A compound according to  claim 13 , wherein R 1  is (C 1 -C 6 )alkyl-Q; and Q is phenyl optionally substituted with one or two substituents independently selected from fluoro, methyl or methoxy; or a pharmaceutically acceptable salt thereof. 
     
     
         15 . A compound according to  claim 11 , wherein R 1  is phenethyl or 1-methyl-2-(phenyl)ethyl, wherein said phenethyl or 1-methyl-2-(phenyl)ethyl is optionally substituted on phenyl with one or two fluoro; or a pharmaceutically acceptable salt thereof. 
     
     
         16 . A compound according to  claim 11 , wherein R 2  is 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl, wherein said 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl is optionally substituted with one or two substituents independently selected from (C 1 -C 3 )alkyl or halo; or a pharmaceutically acceptable salt thereof. 
     
     
         17 . A compound according to  claim 1  wherein R 1  is phenethyl or 1-methyl-2-(phenyl)ethyl, wherein said phenethyl or 1-methyl-2-(phenyl)ethyl is optionally substituted on phenyl with one or two substituents independently selected from halo or (C 1 -C 3 )alkyl or (C 1 -C 3 )alkoxy;
 R 2  is 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl, wherein said 2-hydroxy-phenyl or 3-hydroxy-pyridin-2-yl is optionally substituted with one or two substituents independently selected from (C 1 -C 3 )alkyl or halo; 
 R 3  is (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, (C 1 -C 6 )alkyl-Q, aryl, heteroaryl, or OR 6 ; wherein said (C 1 -C 6 )alkyl, (C 3 -C 7 )cycloalkyl, aryl or heteroaryl is optionally substituted with one to three substituents independently selected from fluoro, cyano, trifluoromethyl, trifluoromethoxy, (C 1 -C 3 )alkyl; (C 1 -C 3 )alkoxy, NR 7 R 8  or hydroxy; and 
 R 4  and R 5  are each independently hydrogen or methyl; or a pharmaceutically acceptable salt thereof. 
 
     
     
         18 . A compound selected from the group consisting of:
 2-(2-Hydroxy-phenyl)-3-phenethyl-5-trifluoromethyl-3H-pyrido[4,3-d]pyri-midin-4-one;   2-(3-Fluoro-2-hydroxy-phenyl)-3-phenethyl-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(3-Hydroxy-pyridin-2-yl)-3-phenethyl-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (R)-2-(2-Hydroxy-phenyl)-3-(1-methyl-2-phenyl-ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (S)-2-(2-Hydroxy-phenyl)-3-(1-methyl-2-phenyl-ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (R)-2-(3-Hydroxy-pyridin-2-yl)-3-(1-methyl-2-phenyl-ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (R,S)-2-(3-Hydroxy-pyridin-2-yl)-3-(1-methyl-2-(2-fluorophenyl)ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (R)-2-(3-Hydroxy-pyridin-2-yl)-3-(1-methyl-2-(2-fluorophenyl)ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   (S)-2-(3-Hydroxy-pyridin-2-yl)-3-(1-methyl-2-(2-fluorophenyl)ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxyphenyl)-3-(2-fluorophenyl)ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxyphenyl)-3-(3-fluorophenyl)ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(3-Fluoro-2-hydroxy-phenyl)-3-[2-(2-fluoro-phenyl)-ethyl]-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-7-methyl-3-(phenyl-ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(3-Fluoro-2-hydroxy-phenyl)-3-[2-(3-fluoro-phenyl)-ethyl]-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   3-[2-(2-Fluoro-phenyl)-ethyl]-2-(3-hydroxy-pyridin-2-yl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   3-[2-(3,4-Difluoro-phenyl)-ethyl]-2-(3-hydroxy-pyridin-2-yl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   3-[2-(2,4-Difluoro-phenyl)-ethyl]-2-(3-hydroxy-pyridin-2-yl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   3-[2-(3,4-Difluoro-phenyl)-ethyl]-2-(3-hydroxy-pyridin-2-yl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-methylamino-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-isopropylamino-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-3-phenethyl-5-pyrrolidin-1-yl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-(4-methyl-piperazin-1-yl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-3-phenethyl-5-piperazin-1-yl-3H-pyrido[4,3-d]pyrimidin-4-one;   5-Dimethylamino-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-morpholin-4-yl-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   5-Azetidin-1-yl-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d-pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-3-phenethyl-5-phenyl-3H-pyrido[4,3-d]pyrimidin-4-one;   5-Benzyl-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-methyl-3-phenethyl-3H-pyrido[4,3-d]pyrimidi-4-one;   5-(6-Dimethylamino-pyridin-3-yl)-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   5-(6-Dimethylamino-5-methyl-pyridin-3-yl)-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   5-(6-pyrrolidine-5-pyridin-3-yl)-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-methoxy-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-(1-methyl-cyclopropylmethoxy)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-3-phenethyl-5-propoxy-3H-pyrido[4,3-d]pyrimidin-4-one;   5-Cyclobutyloxy-2-(2-hydroxy-phenyl)-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-isobutoxy-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-5-isopropoxy-3-phenethyl-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(2-Hydroxy-phenyl)-3-phenethyl-5-(2,2,2-trifluoro-ethoxy)-3H-pyrido[4,3-d]pyrimidin-4-one;   3-(1-(3,4-difluorophenyl)propan-2-yl)-2-(3-hydroxypyridin-2-yl) 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R)-3-(1-(3,4-difluorophenyl)propan-2-yl)-2-(3-hydroxypyridin-2-yl) 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (S)-3-(1-(3,4-difluorophenyl)propan-2-yl)-2-(3-hydroxypyridin-2-yl) 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(1-(2,4-difluorophenyl)propan-2-yl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(1-(2,4-difluorophenyl)propan-2-yl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2,3-difluorophenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(5-fluoro-2-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-fluoro-6-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-(1-(2-methoxyphenyl)propan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-(1-(2-methoxyphenyl)propan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-(1-(2-methoxyphenyl)propan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(1-(2-fluorophenyl)butan-2-yl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(3-fluoro-2-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-cyclopentylethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-cyclohexylethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R)-3-(1-cyclohexylpropan-2-yl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (S)-3-(1-cyclohexylpropan-2-yl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R,S)-2-(3-hydroxypyridin-2-yl)-3-(2-(tetrahydro-2H-pyran-2-yl)ethyl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R)-2-(3-fluoro-2-hydroxyphenyl)-3-(1-phenylpropan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R)-2-(1H-imidazol-2-yl)-3-(1-phenylpropan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   N-(2-(3-(2-fluorophenethyl)-4-oxo-5-(trifluoromethyl)-3,4-dihydropyrido[4,3-d]pyrimidin-2-yl)pyridin-3-yl)acetamide;   (R)-3-(1-phenylpropan-2-yl)-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-phenethyl-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-methoxyphenethyl)-2-(2-hydroxyphenyl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-fluorophenethyl)-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   (R)-2-cyclopentyl-3-(1-phenylpropan-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-isopropyl-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one   2-cyclopentyl-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-methoxyphenethyl)-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-cyclohexylethyl)-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-(2-cyclohexylethyl)-4-oxo-5-(trifluoromethyl)-3,4-dihydropyrido[4,3-d]pyrimidin-2-yl)benzonitrile;   2-(3-aminopyridin-2-yl)-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   N-(2-(4-oxo-3-phenethyl-5-(trifluoromethyl)-3,4-dihydropyrido[4,3-d]pyrimidin-2-yl)pyridin-3-yl)methanesulfonamide;   3-(1-(2-fluorophenyl)propan-2-yl)-2-(thiazol-4-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-isopentyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-((tetrahydro-2H-pyran-4-yl)methyl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-hydroxypyridin-2-yl)-3-(2-(tetrahydro-2H-pyran-4-yl)ethyl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-fluoro-5-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-fluoro-3-methoxyphenethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-(2-fluorophenethyl)-4-oxo-5-(trifluoromethyl)-3,4-dihydroquinazolin-2-yl)benzonitrile;   N-(2-(3-(2-fluorophenethyl)-4-oxo-5-(trifluoromethyl)-3,4-dihydropyrido[4,3-d]pyrimidin-2-yl)pyridin-3-yl)-2,2,2-trifluoroacetamide;   (R)-2,2,2-trifluoro-N-(2-(4-oxo-3-(1-phenylpropan-2-yl)-5-(trifluoromethyl)-3,4-dihydropyrido[4,3-d]pyrimidin-2-yl)pyridin-3-yl)acetamide;   3-cyclohexyl-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(cyclohexylmethyl)-2-(3-hydroxypyridin-2-yl)-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-Phenethyl-5-trifluoromethyl-2-(3-trifluoromethyl-pyridin-2-yl)-3H-pyrido[4,3-d]pyrimidin-4-one;   2-(5-aminothiazol-4-yl)-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(2-(difluoromethyl)phenyl)-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   2-(3-(difluoromethyl)pyridin-2-yl)-3-phenethyl-5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one;   3-(2-cyclohexylethyl)-5-(trifluoromethyl)-2-(2-(trifluoromethyl)phenyl)pyrido[4,3-d]pyrimidin-4(3H)-one; and   3-(2-cyclohexylethyl)-5-(trifluoromethyl)-2-(3-(trifluoromethyl)pyridin-2-yl)pyrido[4,3-d]pyrimidin-4(3H)-one; or a pharmaceutically acceptable salt thereof.   
     
     
         19 . A compound according to  claim 1  which is (R)-2-(2-Hydroxy-phenyl)-3-(1-methyl-2-phenyl-ethyl)-5-trifluoromethyl-3H-pyrido[4,3-d]pyrimidin-4-one or a pharmaceutically acceptable salt thereof. 
     
     
         20 . A compound according to  claim 1  which is (R)-3-(1-(3,4-difluorophenyl) propan-2-yl)-2-(3-hydroxypyridin-2-yl) 5-(trifluoromethyl)pyrido[4,3-d]pyrimidin-4(3H)-one or a pharmaceutically acceptable salt thereof. 
     
     
         21 . A pharmaceutical composition comprising a compound according to  claim 1  and a pharmaceutically acceptable carrier, adjuvant or diluent. 
     
     
         22 . A method of treating a disease or disorder selected from hypoparathyroidism, osteoporosis, osteopenia, periodontal disease, Paget's disease, bone fracture, osteoarthritis, rheumatoid arthritis and humoral hypercalcemia of malignancy, the method comprising administration to a patient in need of treatment thereof a therapeutically effective amount of a compound according to  claim 1 . 
     
     
         23 . The method according to  claim 22  wherein the disease or disorder is osteoporosis.