Group separation of peptides by ligand-exchange chromatography with a Sephadex containing N-(2-pyridylmethyl)glycine

The synthesis of 2-hydroxy-3[N-(2-pyridylmethyl)glycine]propyl Sephadex ether--a new chelating resin--is described. This resin has been employed in the form of its Cu2+ complex to separate peptides, as a group, from alpha-amino acids and NaCl. Ninety-seven ligands of different structures were separated chromatographically at room temperature. It was shown that two structural parameters of the ligands control the separation process, namely, the presence of ligand donor groups and the possibility for them to form chelate rings of suitable size. Separation of peptides from alpha-, gamma-, delta-amino acids, N-acetyl derivatives of amino acids (except N-Ac-Trp), and NaCl is possible if the peptides fulfill the following structural requirements: the peptide molecule must have a free terminal amino group; a carbonyl group (of the peptide linkage) must be situated in the alpha- or beta-position of the free amino group; and the peptide may not contain an imidazole residue (except Gly-Gly-His). A relationship was found between the log k' and the corresponding pKHHL, log KCuCuL, and log KCuBipyCuBipyL values. Interpretation of the different K' values was possible based on the different basicities of the terminal amino groups and on the structures of the different side chains of the peptides.