Compounds of the formula: ##STR1## or a pharmaceutically acceptable salt thereof, wherein M is 0, 1 or 2 and n is 0 or 1; R.sup.1 is hydrogen or lower alkyl; R.sup.2 is C.sub.1 -C.sub.6 -alkyl substituted with a heterocyclic group or C.sub.7 -C.sub.16 -arylalkyl, wherein the aryl group is unsubstituted or substituted with from one to three non-hydrogen members independently selected from the group consisting of halogen, C.sub.1 -C.sub.6 -alkyl, halo-C.sub.1 -C.sub.6 -alkyl, C.sub.1 -C.sub.6 -alkoxy, hydroxy, amino and C.sub.1 -C.sub.6 -alkylamino; R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are independently selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 -alkoxy, C.sub.1 -C.sub.6 -alkyl, halogen, and halo-C.sub.1 -C.sub.6 -alkyl, or any two of R.sup.3, R.sup.4, R.sup.5 and R.sup.6 taken together form a methylenedioxy group; and R.sup.7 is hydrogen or C.sub.1 -C.sub.6 -alkyl. These compounds are useful as inhibitors of the neuronal uptake of biogenic amines and for the treatment of affective disorders, such as, for example, depression.