Isotachophoretic analysis of the end‐product and intermediates in the synthesis of the C‐terminal pentapeptide of bombinin

Capillary isotachophoresis has been applied as an analytical monitor during the synthesis of the C‐terminal pentapeptide, Gln‐His‐Phe‐Ala‐Asn, of bombinin. The samples were separated as cations since the C‐terminal carboxyl group was modified to an uncharged amide. Potassium and beeta‐alanine were employed as leading and terminating ions and acetate was the common counter‐ion. The analyses demonstrated that the stages of synthesis up to the tripeptide, Phe‐Ala‐Asn, gave quite pure products, whereas a considerable amount of impurity was detectable after the introduction of His into the molecule. From the peptide chemist's point of view, this amino acid presents special problems. However, the impurities found in the isotachopherograms were not detectable by conventional methods such as thin‐lyer chromatography. The rapid and sensitive method of isotachophoresis should prove useful to the peptide chemist for assessment of his products, and for redesign or modification of non‐optimal synthetic strategies.