A compound of formula: or a pharmaceutically acceptable salt thereof, wherein: R 1 is selected from the group consisting of F, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C R 5, C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 1 -C 4 alkyl or C 1 -C 4 alkoxy is optionally substituted by one or more R 6, and each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; R 2 is H, F or C 1 -C 4 alkyl; L is a bond or a C 1 -C 4 alkylene; R 3 is selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 alkoxy, OH, CN, C R 8, COOR 9, NR 10 R 11, OR 12, C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 1 -C 4 alkyl or C 1 -C 4 alkoxy is optionally substituted by one or more R 6, and each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; R 4 is H, halo or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 6; R 5 is C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; each R 6 is independently OH, F, CN or C 1 -C 4 alkoxy; each R 7 is independently C 1 -C 4 alkyl, OH, F, CN, C 1 -C 4 alkoxy, =O, or C R 13; R 8 is C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 9 is H or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 10 and R 11 are independently H or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 12 is selected from the group consisting of C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; each R 13 is independently C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 15; each R 14 and R 15 is independently OH, F, CN or C 1 -C 4 alkoxy; and X and Z are independently C 1 -C 4 alkyl, C 1 -C 4 fluoroalkyl, C 1 -C 4 alkoxy or C 1 -C 4 fluoroalkoxy. R 1 is selected from the group consisting of F, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C R 5, C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 1 -C 4 alkyl or C 1 -C 4 alkoxy is optionally substituted by one or more R 6, and each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; R 2 is H, F or C 1 -C 4 alkyl; L is a bond or a C 1 -C 4 alkylene; R 3 is selected from the group consisting of C 1 -C 4 alkyl, C 1 -C 4 alkoxy, OH, CN, C R 8, COOR 9, NR 10 R 11, OR 12, C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 1 -C 4 alkyl or C 1 -C 4 alkoxy is optionally substituted by one or more R 6, and each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; R 4 is H, halo or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 6; R 5 is C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; each R 6 is independently OH, F, CN or C 1 -C 4 alkoxy; each R 7 is independently C 1 -C 4 alkyl, OH, F, CN, C 1 -C 4 alkoxy, =O, or C R 13; R 8 is C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 9 is H or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 10 and R 11 are independently H or C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 14; R 12 is selected from the group consisting of C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl and 5-12 membered heteroaryl, where each said C 3 -C 8 cycloalkyl, 3-12 membered heterocyclyl or 5-12 membered heteroaryl is optionally substituted by one or more R 7; each R 13 is independently C 1 -C 4 alkyl, where each said C 1 -C 4 alkyl is optionally substituted by one or more R 15; each R 14 and R 15 is independently OH, F, CN or C 1 -C 4 alkoxy; and X and Z are independently C 1 -C 4 alkyl, C 1 -C 4 fluoroalkyl, C 1 -C 4 alkoxy or C 1 -C 4 fluoroalkoxy.