A compound of formula wherein R 1 represents a hydrogen or fluorine atom; A represents a group -X-Y-R 3; B represents R; R 2 represents a hydrogen or halogen atom, or a C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl or C 1 -C 6 alkoxy group, each of which may be optionally substituted by at least one substituent selected from hydroxyl, halogen, cyano, nitro, C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, -S m R 4 and -NR 5 R 6; m is 0, 1 or 2; R 4 represents a C 1 -C 6 alkyl group; R 5 and R 6 each independently represent a hydrogen atom or a C 1 -C 6 alkyl group; X represents a group -S n or -CHR 7 and Y represents a group -CHR 7; n is 0, 1 or 2; each R 7 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; R 3 represents a 3- to 10-membered saturated or unsaturated carbocyclic or heterocyclic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 9) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl, - p -(CH 2) q -O-R 10 and a 4- to 6-membered saturated or unsaturated heterocyclic ring (optionally substituted with at least one substituent selected from C 1 -C 4 alkyl and C 1 -C 4 alkoxy); each R 9 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; p is 0 or 1; q is 1, 2, 3 or 4; and R 10 represents a C 1 -C 6 alkyl group; or a pharmaceutically acceptable salt thereof. R 1 represents a hydrogen or fluorine atom; A represents a group -X-Y-R 3; B represents R; R 2 represents a hydrogen or halogen atom, or a C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl or C 1 -C 6 alkoxy group, each of which may be optionally substituted by at least one substituent selected from hydroxyl, halogen, cyano, nitro, C 1 -C 6 alkyl, C 3 -C 6 cycloalkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, -S m R 4 and -NR 5 R 6; m is 0, 1 or 2; R 4 represents a C 1 -C 6 alkyl group; R 5 and R 6 each independently represent a hydrogen atom or a C 1 -C 6 alkyl group; X represents a group -S n or -CHR 7 and Y represents a group -CHR 7; n is 0, 1 or 2; each R 7 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; R 3 represents a 3- to 10-membered saturated or unsaturated carbocyclic or heterocyclic ring system, the ring system itself being optionally substituted by at least one substituent selected from halogen, hydroxyl, cyano, oxo, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 1 -C 6 haloalkyl, C 1 -C 6 hydroxyalkyl, C 1 -C 6 alkoxy, C 1 -C 6 haloalkoxy, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulphinyl, C 1 -C 6 alkylsulphonyl, C 1 -C 6 alkylcarbonyl, C 1 -C 6 alkylcarbonyloxy, C 1 -C 6 alkoxycarbonyl, amino, -CON(R 9) 2, C 1 -C 6 alkylamino, di-(C 1 -C 6 alkyl)amino, C 3 -C 6 cycloalkyl, C 3 -C 6 cycloalkyloxy, C 3 -C 6 cycloalkylmethyl, - p -(CH 2) q -O-R 10 and a 4- to 6-membered saturated or unsaturated heterocyclic ring (optionally substituted with at least one substituent selected from C 1 -C 4 alkyl and C 1 -C 4 alkoxy); each R 9 independently represents a hydrogen atom or a C 1 -C 6 alkyl group; p is 0 or 1; q is 1, 2, 3 or 4; and R 10 represents a C 1 -C 6 alkyl group;