The present invention is further concerned with compounds of the formula: ##STR132## and the pharmaceutically acceptable salts thereof, wherein A is: ##STR133## except when R2 equals H, Y equals O, Z equals N, and there is a 5?? H, R6 and R3 may not be independently selected from H, C1-8 alkyl, C3-6 cycloalkyl, phenyl or when R6 and R3 are taken together with the adjacent N to form a 5-6 membered