Organic compounds

1. A compound of formula I

in free or salt form, wherein

R1 is aryl or heterocyclyl,

R1 being optionally substituted by one or more groups R3 independently selected from: hydroxyl, carbonyl, aminocarbonyl, C 1 -C 7 alkylaminocarbonyl, amino, C 1 -C 7 alkylamino, C 1 -C 7 alkylthio, sulfonylamino, carbonylamino, C 1 -C 7 alkylcarbonylamino, halo, carboxy, C 1 -C 7 alkoxy, benzyloxy, C 1 -C 7 alkyloxycarbonyl, aminosulfonyl, C 1 -C 7 alkyl, cyano, sulfonyl, sulfanyl, sulfoxide, aryl, heterocyclyl, carbonyloxy, amino C 1 -C 7 alkyl, C 1 -C 7 alkylamino-C 1 -C 7 alkyl, aryl-C 1 -C 7 -alkyl and heterocyclyl-C 1 -C 7 -alkyl, C 4 -C 15 -cycloalkenyl and C 2 -C 8 -cycloalkynyl; and when R3 includes two groups, such R3 groups may be joined together to form a ring which is fused to R1;

wherein R3 is optionally substituted by one or more groups selected from hydroxyl, C 1 -C 7 alkyl, aryl, amino, C 1 -C 7 alkylamino, heterocyclyl, cyano, halo, sulfonyl, sulfanyl, sulfoxide, di(C 1 -C 7 ) alkylamino, hydroxyl-C 1 -C 7 alkyl, alkoxy, di-C 1 -C 7 alkylamino-C 1 -C 7 alkyl;

R2 is aryl, heteroaryl, heteroaryl-aryl, heteroaryl-heterocyclyl, aryl-heterocyclyl, biaryl, heterocyclyl-heterocyclyl;

R2 being optionally substituted by one or more groups R4 independently selected from aryl, heteroaryl, heterocycloalkyl, C 1 -C 7 alkyl, C 3 -C 10 -cycloalkyl, aminocarbonyl, C 1 -C 7 alkylaminocarbonyl, halo, C 1 -C 7 alkoxy, C 1 -C 7 alkylthio, hydroxyl, C 1 -C 7 alkylcarbonyl, carboxy, carbonyl, cyano, sulfonamide and from C 4 -C 15 -cycloalkenyl; and when R4 includes two groups, such R4 groups may be joined together to form a ring which is fused to R2;

wherein R4 is optionally substituted by one or more groups selected from hydroxyl, C 1 -C 7 alkyl, aryl, amino, C 1 -C 7 alkylamino, heterocyclyl, cyano, halo, sulfonyl, sulfanyl, sulfoxide;

R5 is H or NH 2 .

2. A compound in free or salt form according to claim 1 wherein

R1 is aryl or heterocyclyl

R1 being optionally substituted by one or more groups R3 independently selected from: hydroxyl, carbonyl, aminocarbonyl, C 1 -C 7 alkylaminocarbonyl, amino, C 1 -C 7 alkylamino, C 1 -C 7 alkylthio, sulfonylamino, carbonylamino, C 1 -C 7 alkylcarbonylamino, halo, carboxy, C 1 -C 7 alkoxy, benzyloxy, C 1 -C 7 alkyloxycarbonyl, aminosulfonyl, C 1 -C 7 alkyl, cyano, sulfonyl, sulfanyl, sulfoxide, aryl, heterocyclyl, carbonyloxy, amino C 1 -C 7 alkyl and C 1 -C 7 alkylamino-C 1 -C 7 alkyl; and when R3 includes two groups, such R3 groups may be joined together to form a ring which is fused to R1;

wherein R3 is optionally substituted by one or more groups selected from hydroxyl, C 1 -C 7 alkyl, aryl, amino, C 1 -C 7 alkylamino, heterocyclyl, cyano, halo, sulfonyl, sulfanyl, sulfoxide, di(C 1 -C 7 ) alkylamino, hydroxyl-C 1 -C 7 alkyl, alkoxy, di-C 1 -C 7 alkylamino-C 1 -C 7 alkyl;

and R2 is defined as in claim 1 .

3. A compound according to claim 1 wherein R1 is optionally substituted phenyl or pyridinyl.

4. A compound according to claim 1 wherein R2 is optionally substituted phenyl or pyridinyl.

5. A compound in free or salt form, selected from the group consisting of

N-methyl-3-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide,

3-[3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-N-methyl-benzamide,

3-{3-[2-(3-fluoro-phenyl)-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-N-methyl-benzamide,

3-[3-(2-furan-2-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-N-methyl-benzamide,

3-{3-[2-(4-fluoro-phenyl)-pyridin-4-yl]-imidazo[1,2-b]pyridazin-7-yl}-N-methyl-benzamide,

3-(2-phenyl-pyridin-4-yl)-7-pyridin-4-yl-imidazo[1,2-b]pyridazine,

3-(2-furan-3-yl-pyridin-4-yl)-7-pyridin-4-yl-imidazo[1,2-b]pyridazine,

N-{3-[3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-phenyl}-methanesulfonamide,

3-{-4-[7-(3-methanesulfonylamino-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-pyridin-2-yl}-benzamide,

7-(3-fluoro-phenyl)-3-(2-thiophen-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

7-(3-fluoro-phenyl)-3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

7-(3-fluoro-phenyl)-3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

3-{4-[7-(3-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-pyridin-2-yl}-benzamide,

7-[6-(4-methyl-piperazin-1-yl)-pyridin-3-yl]-3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

7-(3-benzyloxy-phenyl)-3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

3-(2-furan-3-yl-pyridin-4-yl)-7-(3-methoxy-phenyl)-imidazo[1,2-b]pyridazine,

7-(3-methoxy-phenyl)-3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazine,

4-[7-(3-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-[2,4′]bipyridinyl,

3-[3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid ethyl ester,

3-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid ethyl ester,

dimethyl-{5-[3-(2-thiophen-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-pyridin-2-yl}-amine,

dimethyl-(5-{3-[2-(5-methyl-furan-2-yl)-pyridin-4-yl]-imidazo[1,2-b]pyridazin-7-yl}-pyridin-2-yl)-amine,

{5-[3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-pyridin-2-yl}-amine,

dimethyl-{5-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-pyridin-2-yl}-amine,

4-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid ethyl ester,

N-methyl-3-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide,

4-[7-(3-methylcarbamoyl-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-pyridine-2-carboxylic acid methylamide,

3-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-phenol,

4-[7-(3-hydroxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-2-methoxy-phenol,

3-(2-chloro-pyridin-4-yl)-7-pyridin-4-yl-imidazo[1,2-b]pyridazine,

2-methoxy-4-(7-pyridin-4-yl-imidazo[1,2-b]pyridazin-3-yl)-phenol,

N-{3-[3-(2-chloro-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-phenyl}-methanesulfonamide,

4-[7-(3-methanesulfonylamino-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-benzamide,

3-(3-pyrazol-1-yl-phenyl)-7-pyridin-3-yl-imidazo[1,2-b]pyridazine,

3-(7-pyridine-3-yl-imidazo[1,2-b]pyridazin-3-yl)-benzamide,

2-methoxy-4-(7-pyridin-3-yl-imidazo[1,2-b]pyridazin-3-yl)-phenol,

3-(7-pyridine-3-yl-imidazo[1,2-b]pyridazin-3-yl)-benzoic acid,

1-[3-(7-pyridin-3-yl-imidazo[1,2-b]pyridazin-3-yl)-phenyl]-ethanone,

N-{3-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-phenyl}-acetamide,

3-[7-(3-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]benzamide,

7-(3-fluoro-phenyl)-3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazine,

4-[7-(3-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-2-methoxy-phenol,

7-[6-(4-methyl-piperazin-1-yl)-pyridin-3-yl]-3-[2-(1H-pyrazol-4-yl)-pyridin-4-yl]-imidazo [1,2-b]pyridazine,

7-(6-morpholin-4-yl-pyridin-3-yl)-3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazine,

4-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid ethyl ester,

2-methoxy-4-[7-(3-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-phenol,

3-[3-(4-hydroxy-3-methoxy-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid ethyl ester,

dimethyl-{5-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-pyridin-2-yl}-amine,

N-(2-hydroxy-ethyl)-4-[3-(3-pyrazol-1-yl-phenyl)-imidazo-[1,2-b]-pyridazin-7-yl]-benzamide,

N-(2-hydroxy-ethyl)-4-[3-(2-phenyl-pyridin-4-yl)-imidazo-[1,2-b]-pyridazin-7-yl]-benzamide,

{3-[3-(2-furan-3-yl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-phenyl}-methanol,

-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzoic acid

3-[3-(4-hydroxy-3-methoxy-phenyl)-imidazo-[1,2-b]-pyridazin-7-yl]-benzoic acid,

3-(2-amino-3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-N-methyl-benzamide

N-(3-dimethylamino-propyl)-3-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide,

3-[3-(2-phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-N-(2-piperidin-1-yl-ethyl)-benzamide,

N-methyl-N-(2-methylamino-ethyl)-3-[3-(2-Phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide,

N-(2-hydroxy-ethyl)-3-[3-(2-Phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide,

N-butyl-3-[3-(2-Phenyl-pyridin-4-yl)-imidazo[1,2-b]pyridazin-7-yl]-benzamide and

1-(3-piperidin-1-yl-propyl)-4-[3-(3-pyrazol-1-yl-phenyl)-imidazo[1,2-b]pyridazin-7-yl]-1H-pyridin-2-one.

6. A pharmaceutical composition comprising a compound according to claim 1 , in admixture with a pharmaceutically acceptable excipient, diluent or carrier.

7. A method of treating bone conditions which are associated with increased calcium depletion or resorption or in which stimulation of bone formation and calcium fixation in the bone is desirable comprising administering a compound according to claim 1 in an effective amount to a patient in need thereof.