This invention relates to compounds of the formula: ##STR1## or a pharmaceutically acceptable salt thereof wherein Z is selected from the group consisting of ##STR2## R.sub.1 is alkoxy of one to six carbon atoms; R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are the same or different and are selected from the group consisting of hydrogen, halogen, CF.sub.3, 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, C.sub.2 -C.sub.7 acylamino, aminocarbonyl, aminosulfone optionally substituted by one or two alkyl groups of one to six carbon atoms, C.sub.1 -C.sub.6 alkylsulfone and nitro;n is 0, 1 or 2;m is 0 or 1;X is O or NR.sub.7 ; andR.sub.7 is hydrogen or alkyl of 1 to 6 carbon atoms.