One group of preferred compounds of this invention are those of the formula (III): ##STR5## or a pharmaceutically acceptable salt, ester or amide thereof, wherein R13 is a hydrogen, fluorine or chlorine atom or a trifluoromethyl group, Z is as defined in relation to formula (II), R11 is a hydrogen atom or a methyl group; R12 is a hydrogen atom or a methyl group; and m is 1, 2 or 3.