Unsaturated amino acids

A compound of formula I ##STR23## in which the carbon double bond is in the trans-configuration in relation to R.sup.3 and R.sup.4 or to A and B, and wherein R.sup.1 represents hydroxy, lower alkoxy or hydroxy-lower alkoxy, R.sup.2 represents hydrogen, alkyl, hydroxy, lower alkoxy or hydroxy-lower alkoxy, R.sup.3 represents hydrogen, lower alkyl, halo-lower alkyl, lower alkoxy-lower alkyl, hydroxy-lower alkyl, phenyl-lower alkyl that is unsubstituted or substituted in the phenyl moiety, lower alkenyl, halogen, or unsubstituted or substituted phenyl, R.sup.4 represents hydrogen, lower alkyl or unsubstituted or substituted phenyl, R.sup.5 represents hydrogen or lower alkyl, R.sup.6 represents carboxy, alkoxycarbonyl, alkoxycarbonyl substituted in a position higher than the .alpha.-position by amino, mono- or di-lower alkylamino, hydroxy or by lower alkanoyloxy, or phenyl-lower alkoxycarbonyl that is unsubstituted or substituted in the phenyl moiety, R.sup.7 represents amino, mono- or di-lower alkylamino or lower alkanoylamino, A represents unsubstituted or lower alkylsubstituted .alpha.,.omega.-alkylene having from 1 to 3 carbon atoms, and B represents a bond, wherein the substituents of phenyl are selected from the group consisting of lower alkyl, hydroxy, lower alkoxy, halogen, amino, halo-lower alkyl, hydroxy-lower alkyl, amino-lower alkyl and nitro, or a pharmaceutically acceptable salt thereof.