A compound effective in the treatment of diabetic angiopathy, i.e. a selective .beta.-receptor blocker has the formula ##STR1## wherein: R.sup.2 is a hydrogen or alkyl having one to five carbon atoms,R.sup.3 is alkyl having one to five carbon atoms, cycloalkyl or phenyl optionally substituted with hydroxyl or phenyl, or R.sup.2 and R.sup.3 together form a five- to eight-membered ring optionally containing also other heteroatoms and/or fused with another ring, preferably phenyl, naphthyl, quinolyl, isoquinolyl, pyridyl, pyrazolyl,R.sup.5 is hydrogen or alkyl having one to four carbon atoms, cycloalkyl or phenyl optionally substituted with halogen, alkoxy having one to four carbon atoms or alkyl having one to four carbons,R.sup.6 is hydrogen, alkyl having one to four carbon atoms or phenyl, m=0, 1 or 2, and n=0, 1 or 2.