Determination of stereoselective effects in complexes of salicylaldehyde and a copper ion with alanine di- and tripeptides

Abstract

1. The method of liquid chromatography has been used to study the stereoselective effects in complexes of salicylaldehyde and the copper ion with alanine di- and tripeptides. 2. With a dipeptide copper ion salicylaldehyde reactant ratio equal to 1∶1∶1 the first and second N-terminal amino-acid residues undergo racemization in the dipeptide, the rate of the racemization of the first amino-acid residue in the dipeptide being much greater than the rate for the second. Under these conditions only the first N-terminal residue undergoes racemization in the tripeptide. 3. When there is an insufficient amount of the copper ion, the ratio between the racemization rates of the two residues in the dipeptide remains unchanged. When there is an insufficient amount of the copper ion, the first and second N-terminal amino-acid residues in the tripeptide under racemization, the racemization rate of the first being much greater than the racemization rate of the second. In the tetrapeptide the racemization rates of the first and second N-terminal amino-acid residues are similar when there is an insufficient amount of the copper ion. 4. The position of the equilibrium between the diastereomers of the alanine peptides depends on the relative concentrations of the copper ions and the salicylaldehyde in the mixture.