A compound of formula or a pharmaceutically acceptable salt thereof; wherein, R1 is hydrogen, C 1 -C 6 alkyl optionally substituted by hydroxy; R2 is hydrogen or halogen; R3 is hydrogen or halogen; R4 is hydrogen, R5 is phenyl optionally substituted by halogen; SF 5; NR6R7; hydroxy; C 1 -C 6 alkoxy; C 1 -C 6 alkenyl; C 1 -C 6 alkyl carbonyl; C 1 -C 6 alkyl optionally substituted by hydroxy, halogen, or C 1 -C 6 alkoxy; or C 3 -C 6 cycloalkyl optionally substituted by halogen, hydroxy, or C 1 -C 6 alkyl optionally substituted by halogen; or R5 is a 4 - 14 membered mono- or bicyclic heterocyclyl or heteroaryl ring system comprising 1, 2 or 3 heteroatoms selected from N, S and O that ring being optionally substituted by halogen; hydroxy; C 1 -C 6 alkoxy optionally substituted by hydroxy or halogen; or C 1 -C 6 alkyl optionally substituted by hydroxy or halogen; or R4 and R5 together with the atoms to which they are bound form a piperidone ring, optionally comprising an annulated phenyl ring, any such ring being optionally substituted by C 1 -C 6 alkyl, C 1 -C 6 alkoxy, or C 3 -C 6 cycloalkyl each of which substitution member may optionally be substituted by halogen or hydroxy; R6 and R7 are independently selected from hydrogen or C 1 -C 6 alkyl; or R6 and R7 together with the nitrogen atom to which they are bound form a 4 - 8 membered saturated azacycloalkane ring, optionally substituted by halogen, hydroxy or C 1 -C 6 alkyl; X is O, S n wherein n is 0, 1 or 2, or absent; wherein q is 2 or 3, and R10 is or X is CH or N; and R10 is hydrogen, hydroxy, -NR6R7, -CO-R11, -S p -R12 wherein p is 1 or 2, R 11 is C 1 -C 6 alkyl optionally substituted by hydroxy, cyano, halogen, carboxy or C 1 -C 6 alkoxy carbonyloxy; or NR6R7; and R12 is C 1 -C 6 alkyl or NR6R7. R1 is hydrogen, C 1 -C 6 alkyl optionally substituted by hydroxy; R2 is hydrogen or halogen; R3 is hydrogen or halogen; R4 is hydrogen, R5 is phenyl optionally substituted by halogen; SF 5; NR6R7; hydroxy; C 1 -C 6 alkoxy; C 1 -C 6 alkenyl; C 1 -C 6 alkyl carbonyl; C 1 -C 6 alkyl optionally substituted by hydroxy, halogen, or C 1 -C 6 alkoxy; or C 3 -C 6 cycloalkyl optionally substituted by halogen, hydroxy, or C 1 -C 6 alkyl optionally substituted by halogen; or R5 is a 4 - 14 membered mono- or bicyclic heterocyclyl or heteroaryl ring system comprising 1, 2 or 3 heteroatoms selected from N, S and O that ring being optionally substituted by halogen; hydroxy; C 1 -C 6 alkoxy optionally substituted by hydroxy or halogen; or C 1 -C 6 alkyl optionally substituted by hydroxy or halogen; or R4 and R5 together with the atoms to which they are bound form a piperidone ring, optionally comprising an annulated phenyl ring, any such ring being optionally substituted by C 1 -C 6 alkyl, C 1 -C 6 alkoxy, or C 3 -C 6 cycloalkyl each of which substitution member may optionally be substituted by halogen or hydroxy; R6 and R7 are independently selected from hydrogen or C 1 -C 6 alkyl; or R6 and R7 together with the nitrogen atom to which they are bound form a 4 - 8 membered saturated azacycloalkane ring, optionally substituted by halogen, hydroxy or C 1 -C 6 alkyl; X is O, S n wherein n is 0, 1 or 2, or absent; wherein q is 2 or 3, and R10 is or X is CH or N; and R10 is hydrogen, hydroxy, -NR6R7, -CO-R11, -S p -R12 wherein p is 1 or 2, R 11 is C 1 -C 6 alkyl optionally substituted by hydroxy, cyano, halogen, carboxy or C 1 -C 6 alkoxy carbonyloxy; or NR6R7; and R12 is C 1 -C 6 alkyl or NR6R7.