Separation of the enantiomers of β-receptor blocking agents and other cationic drugs using a CHIRAL-AGP ® column : Binding properties and characterization of immobilized α 1-acid glycoprotein

Abstract

The effect of the immobilization procedure on the conformation of α 1-acid glycoprotein (AGP) was investigated by recording the fluorescence spectra of native and immobilized AGP. A 20-nm red shift was obtained for the immobilized form of AGP compared with the emission maximum of 338 nm obtained for native AGP. This demonstrates that the tryptophan residues are exposed on the protein surface after immobilization, indicating that the immobilized form of AGP has a more unfolded structure than the native AGP. The effect of N,N-dimethyloctylamine on the enantioselectivity for some fentiazine derivatives, observed with immobilized AGP, was equal to that obtained with AGP as a chiral complexing agent in the mobile phase. This demonstrates that even though the immobilization procedure affects the conformation of the protein there still exist large similarities between native and immobilized AGP concerning chiral recognition. The adsorption isotherm of (−)-terodiline was studied by use of the breakthrough technique. The adsorption isotherm indicates that (−)-terodiline is adsorbed to one site with high affinity and at least one more site with lower affinity. It was also observed that the enantiomers of amines, acids and non-protolytic compounds compete with the cationic compound, (−)-terodiline, for binding to the same sites. The β-receptor blocking agents atenolol, metoprolol, pindolol, alprenolol, oxprenolol and propranolol were resolved on a CHIRAL-AGP ® column. The retention and enantioselectivity are highly influenced by the structure of the solute and the nature of the uncharged mobile phase additives. Separation factors of 1.2–1.8 were obtained for the β-blockers under the studied conditions.