A compound of formula I or a pharmaceutically acceptable salt thereof, wherein: A is selected from pyrazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyrrolopyridinyl, dihydropyrrolopyridinyl and imidazopyridinyl; B is selected from phenyl and pyridinyl; C is selected from phenyl, indanyl, pyrazolyl, imidazolyl, thienyl, thiazolyl, triazolyl, thiadiazolyl, oxazolyl, isoxazolyl, oxadiazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, indolyl, pyrrolopyridinyl, dihydropyrrolopyridinyl, imidazopyridinyl, pyrazolopyridinyl, quinolinyl, isoquinolinyl, benzothiazolyl, benzofuranyl, dihydrobenzofuranyl, benzodioxolanyl, benzodioxolinyl, dihydroindolyl, naphthyridinyl, pyrimidinopyridinyl, thiazolopyridinyl, tetrahydrothiazolopyridinyl and benzothienyl; R 2 and R 3 together with the carbon atom to which they are attached form a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or a tetrahydropyranyl ring; R 1a and R 1b are each independently selected from -H, C 1-6 alkyl, methoxy, -CH 2 -OH, hydroxy, -C -CH 3 and -NR 5 R 6; R 4a and R 4b are each independently selected from -H, C 1-3 alkyl, C 1-3 alkoxyl, -C 1-3 alkyl-OH, phenyl, -O-phenyl, thiazolyl, oxazolyl, isoxazolyl, furanyl, thienyl, pyrrolyl, thiadiazolyl, tetrazolyl, pyridinyl, pyrimidinyl, pyridazinyl, pyrazinyl, cyclopropyl, cyclopbutyl, cyclopenyl, cyclohexyl, pyrrolidinyl, tetrahydrothienyl, piperidinyl, piperazinyl, morpholinyl, -C 1-3 alkyl-phenyl, -C 1-3 alkyl-pyridinyl, -C 1-3 alkyl-pyrimidinyl, -C 1-3 alkyl-pyridazinyl, -C 1-3 alkyl-pyrazinyl, -C 1-3 alkyl-heterocyclyl, -O-C 1-3 alkyl-phenyl, -O-C 1-3 alkyl-pyridinyl, -O-C 1-3 alkyl, CF 3, -O-CF 3, -COOR 5, -C -C 1-3 alkyl, -S 2 -NR 5 R 6, -S 2 CF 3, -S 2 C 1-3 alkyl, -C NR 7 R 8, hydroxy, halogen, and cyano, wherein each group is optionally independently substituted with 1-3 substituents chosen from C 1-6 alkyl, C 1-6 alkoxyl, hydroxy and halogen; R 5 and R 6 are each independently chosen from H, C 1-5 alkyl, -C 1-3 alkylhydroxy and -C 1-3 alkyl-O-C 1-3 alkyl; or, R 5 and R 6 together with the nitrogen atom to which they are attached form a piperidinyl, morpholinyl or thiomorpholinyl ring; R 7 and R 8 are each independently chosen from H, C 1-6 alkyl, -S 2 C 1-3 alkyl, and -C -NH 2. A is selected from pyrazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyrrolopyridinyl, dihydropyrrolopyridinyl and imidazopyridinyl; B is selected from phenyl and pyridinyl; C is selected from phenyl, indanyl, pyrazolyl, imidazolyl, thienyl, thiazolyl, triazolyl, thiadiazolyl, oxazolyl, isoxazolyl, oxadiazolyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridazinyl, indolyl, pyrrolopyridinyl, dihydropyrrolopyridinyl, imidazopyridinyl, pyrazolopyridinyl, quinolinyl, isoquinolinyl, benzothiazolyl, benzofuranyl, dihydrobenzofuranyl, benzodioxolanyl, benzodioxolinyl, dihydroindolyl, naphthyridinyl, pyrimidinopyridinyl, thiazolopyridinyl, tetrahydrothiazolopyridinyl and benzothienyl; R 2 and R 3 together with the carbon atom to which they are attached form a cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or a tetrahydropyranyl ring; R 1a and R 1b are each independently selected from -H, C 1-6 alkyl, methoxy, -CH 2 -OH, hydroxy, -C -CH 3 and -NR 5 R 6; R 4a and R 4b are each independently selected from -H, C 1-3 alkyl, C 1-3 alkoxyl, -C 1-3 alkyl-OH, phenyl, -O-phenyl, thiazolyl, oxazolyl, isoxazolyl, furanyl, thienyl, pyrrolyl, thiadiazolyl, tetrazolyl, pyridinyl, pyrimidinyl, pyridazinyl, pyrazinyl, cyclopropyl, cyclopbutyl, cyclopenyl, cyclohexyl, pyrrolidinyl, tetrahydrothienyl, piperidinyl, piperazinyl, morpholinyl, -C 1-3 alkyl-phenyl, -C 1-3 alkyl-pyridinyl, -C 1-3 alkyl-pyrimidinyl, -C 1-3 alkyl-pyridazinyl, -C 1-3 alkyl-pyrazinyl, -C 1-3 alkyl-heterocyclyl, -O-C 1-3 alkyl-phenyl, -O-C 1-3 alkyl-pyridinyl, -O-C 1-3 alkyl, CF 3, -O-CF 3, -COOR 5, -C -C 1-3 alkyl, -S 2 -NR 5 R 6, -S 2 CF 3, -S 2 C 1-3 alkyl, -C NR 7 R 8, hydroxy, halogen, and cyano, wherein each group is optionally independently substituted with 1-3 substituents chosen from C 1-6 alkyl, C 1-6 alkoxyl, hydroxy and halogen; R 5 and R 6 are each independently chosen from H, C 1-5 alkyl, -C 1-3 alkylhydroxy and -C 1-3 alkyl-O-C 1-3 alkyl; or, R 5 and R 6 together with the nitrogen atom to which they are attached form a piperidinyl, morpholinyl or thiomorpholinyl ring; R 7 and R 8 are each independently chosen from H, C 1-6 alkyl, -S 2 C 1-3 alkyl, and -C -NH 2.