The invention relates to compounds of the formula I ##STR1## in which n denotes 0 or 1, R denotes hydrogen, alkyl, alkenyl or aralkyl, R.sup.1 denotes hydrogen or alkyl, which can optionally be substituted by amino, acylamino or benzoylamino, alkenyl, cycloalkyl, cycloalkenyl, cycloalkylalkyl, aryl or partially hydrogenated aryl, each of which can be substituted by alkyl, alkoxy or halogen, aralkyl or aroylalkyl, both of which can be substituted in the aryl radical as defined previously, a monocyclic or bicyclic S- or O- and/or N-heterocyclic radical or a side chain of an aminoacid, R.sup.2 denotes hydrogen, alkyl, alkenyl or aralkyl, Y denotes hydrogen or hydroxyl, Z denotes hydrogen, or Y and Z together denote oxygen, X denotes alkyl, alkenyl, cycloalkyl, aryl, which can be monosubstituted, disubstituted or trisubstituted by alkyl, alkoxy, hydroxyl, halogen, nitro, amino, acylamino, alkylamino, dialkylamino and/or methylenedioxy, or 3-indolyl, and to a process for their preparation, agents containing them and and their use, and to 2-azabicyclo[3.1.0]hexane derivatives as intermediates, and a process for their preparation.