Abstract: Compounds of the formula I ##STR1## wherein R denotes an aliphatic, cycloaliphatic, cycloaliphatic-aliphatic or araliphatic radical having 2 or more carbon atoms, and wherein one of the groups R.sup.1, R.sup.2 and R.sup.3 represents hydrogen or an aliphatic, cycloaliphatic, araliphatic or aromatic radical, another one of R.sup.1, R.sup.2 and R.sup.3 is hydrogen or, in the case of R.sup.1 and R.sup.2, is hydroxy, and the remaining one of R.sup.1, R.sup.2 and R.sup.3 is hydrogen, and their salts have GABA.sub.B -antagonistic properties and can be used as GABA.sub.B -antagonists. They are obtained when in a compound of formula II ##STR2## in which R, R.sup.1, R.sup.2 and R.sup.3 have their previous significances, Z represents --NH.sub.2 and R.sup.4 denotes a hydroxy-protective group R.sup.5 or, when R.sup.1 and R.sup.3 denote hydrogen and R.sup.2 denotes hydrogen or alkyl, denotes an alkali metal or ammonium ion R.sup.6, or Z represents a protected or latent amino group Z.sup.0 and R.sup.