Abstract: A compound of the formula ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different, and each is selected from the group consisting of hydrogen and phenyl groups of the formula ##STR2## wherein R.sub.4 and R.sub.5 are the same or different and each is selected from the group consisting of hydrogen, halogen, alkyl having 1, 2, or 3 carbon atoms, alkoxy having 1, 2, or 3 carbon atoms, alkoxycarbonyl having 2-7 carbon atoms; and alkylcarbonyl groups having 2-7 carbon atoms; or R.sub.4 and R.sub.5 together from a straight saturated alkylene chain having 3 or 4 carbon atoms and being bound to adjacent positions, i.e. 2,3- or 3,4- in the phenyl ring; provided that one of R.sub.1 and R.sub.2 is a phenyl group of the formula II when R.sub.3 is H; and physiologically acceptable salts and optical isomers thereof; methods for preparation of the compounds, pharmaceutical compositions containing them, and their medicinal use.