This invention relates to compounds of formula (I) or a pharmaceutically acceptable salt thereof, wherein Z is selected from the group consisting of (a) and (b), R1 is alkoxy of one to six carbon atoms; R2, R3, R4 and R5 are the same or different and are selected from the group consisting of hydrogen, halogen, CF3, hydroxy, alkoxy of one to six carbon atoms, acyl of two to seven carbon atoms, amino, amino substituted by one or two alkyl groups of one to six carbon atoms, C2-C7 acylamino, aminocarbonyl, aminosulfone optionally substituted by one or two alkyl groups of one to six carbon atoms, C1-C6 alkylsulfone and nitro; m is 1 or 2; X is 0 or NR7; and R7 is hydrogen or alkyl of 1 to 6 carbon atoms.