Pharmacologically active compounds of the general formula I ##STR1## wherein R.sup.1 is an alkyl group with 1-6 carbon atoms or a cycloalkylalkyl group with 4-7 carbon atoms, R.sup.2 is lower alkyl, and R.sup.3 is lower alkyl, or R.sup.2 and R.sup.3 together form an alkylene chain with 3-6 carbon atoms, and R.sup.4 represents a phenyl radical monosubstituted in the ortho or para position by nitro, cyano or lower alkanoyl or disubstituted in the ortho and para positions by nitro, and their physiologically compatible acid addition salts are described.