New original derivates of D,L-glutamic acid and D,L-aspartic acid having formula (I), where n is 1 or 2, R1 is a mono- or di-substituted phenyl group substituted with halogens such as chlorine and fluorine or with a methyl group in the 3 and 4 positions and in which R2 consists of a linear or branched alkyl group with 4 to 7 carbon atoms (preferably a pentyl group) and R3 is an alkyl group having 3 to 6 carbon atoms overall and containing an oxygen atom in the form of an ether linkage, such as for example the groups 2-ethoxyethyl, 3-methoxypropyl, 3-ethoxypropyl etc. or in the form of a hydroxyl group such as for example 3-hydroxypropyl etc. The compounds have antagonistic activity towards bio-active polypeptydes and are usable particularly in the treatment of illnesses of the digestive tract, or the central nervous system and anorexia and of all those affections (for example tumours) in which exogenic or endogenic bio-active polypeptydes are involved.