A compound of formula, or a pharmaceutically acceptable salt thereof, wherein: R 1 represents: (i) C 3-6 cycloalkyl optionally substituted with one or more substituents independently selected from -OH, -C 1-3 alkyl and hydroxyC 1-3 alkyl; (ii) aryl or heteroaryl, each of which is optionally substituted with 1 to 3 substituents independently selected from halo, -CN, =O, -OH, -O-C 1-3 alkyl, -C 1-3 alkyl, C 3-6 cycloalkyl, haloC 1-3 alkyl, hydroxyC 1-3 alkyl, C 1-3 alkoxy, haloC 1-3 alkoxy and -S 2 C 1-4 alkyl; or (iii) heterocyclyl, optionally substituted with 1 to 3 substituents independently selected from =O, C 1-3 alkyl and C 3-6 cycloalkyl; R 2 represents: (i) C 1-3 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (ii) C 3-6 cycloalkyl; or (iii) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; R 3 represents: (i) hydrogen; (ii) halo; (iii) C 1-4 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (iv) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; (v) C 3-6 cycloalkyl; or (vi) -OC 1-3 alkyl. R 1 represents: (i) C 3-6 cycloalkyl optionally substituted with one or more substituents independently selected from -OH, -C 1-3 alkyl and hydroxyC 1-3 alkyl; (ii) aryl or heteroaryl, each of which is optionally substituted with 1 to 3 substituents independently selected from halo, -CN, =O, -OH, -O-C 1-3 alkyl, -C 1-3 alkyl, C 3-6 cycloalkyl, haloC 1-3 alkyl, hydroxyC 1-3 alkyl, C 1-3 alkoxy, haloC 1-3 alkoxy and -S 2 C 1-4 alkyl; or (iii) heterocyclyl, optionally substituted with 1 to 3 substituents independently selected from =O, C 1-3 alkyl and C 3-6 cycloalkyl; (i) C 3-6 cycloalkyl optionally substituted with one or more substituents independently selected from -OH, -C 1-3 alkyl and hydroxyC 1-3 alkyl; (ii) aryl or heteroaryl, each of which is optionally substituted with 1 to 3 substituents independently selected from halo, -CN, =O, -OH, -O-C 1-3 alkyl, -C 1-3 alkyl, C 3-6 cycloalkyl, haloC 1-3 alkyl, hydroxyC 1-3 alkyl, C 1-3 alkoxy, haloC 1-3 alkoxy and -S 2 C 1-4 alkyl; or (iii) heterocyclyl, optionally substituted with 1 to 3 substituents independently selected from =O, C 1-3 alkyl and C 3-6 cycloalkyl; R 2 represents: (i) C 1-3 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (ii) C 3-6 cycloalkyl; or (iii) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; (i) C 1-3 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (ii) C 3-6 cycloalkyl; or (iii) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; R 3 represents: (i) hydrogen; (ii) halo; (iii) C 1-4 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (iv) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; (v) C 3-6 cycloalkyl; or (vi) -OC 1-3 alkyl. (i) hydrogen; (ii) halo; (iii) C 1-4 alkyl optionally substituted with one or more substituents independently selected from halo, -OH and -OC 1-3 alkyl; (iv) C 2-4 alkenyl optionally substituted with -OC 1-3 alkyl; (v) C 3-6 cycloalkyl; or (vi) -OC 1-3 alkyl.