Abstract: Peptide ester and amide derivatives of the general formula I: ##STR1## in which X is H or an acyl, A and B are structurally defined amino acid residues, n is an integer of from 1 to 3, R.sup.1 is H or a lower alkyl and either R.sup.2 or C is a defined optionally modified amino acid residue and the other is a lower alkoxyl, an amino group or a direct chemical bond, are converted under physiologic conditions, by enzymic hydrolysis in pathologically altered tissues and subsequent spontaneous cyclization, into pharmacodynamically active spirocyclic peptide derivatives of the general formula III: ##STR2## in which R.sup.3 and R.sup.4 are H atoms, optionally substituted alkyl groups or jointly an aliphatic chain forming preferably a 2,5- piperazinedione ring, and hence can act as pro-farmaca (drug precursors) of prolonged biological effect.