László Gagyi 1 Árpád Gyéresi 1 Ferenc Kilár 2 1 Institute of Pharmaceutical Chemistry, University of Medicine and Pharmacy, Târgu-Mures ¸ , Romania 2 Faculty of Medicine, Institute of Bioanalysis, University of Pécs, Pécs, Hungary Received October 18, 2005 Revised November 27, 2005 Accepted November 27, 2005 Research Article Role of chemical structure in stereoselective recognition of beta-blockers and H 1 -antihistamines by human serum transferrin in capillary zone electrophoresis Studies on chiral resolution of beta-blocker and H 1 -antihistamine drugs by CZE using human serum transferrin are described. The drugs with different structures passed a pseudostationary protein zone in a coated capillary applying the partial filling method for the chiral separation. In this study we screened 15 compounds; most of them showed longer migration time, indicating an interaction with transferrin. Stereo- selective interaction was observed only for five beta-blockers (celiprolol, talinolol, mepindolol, bopindolol, and oxprenolol) and for one H 1 -antihistamine (bromphenir- amine). The most important finding was that very small differences in the chemical structure of the drug resulted in significant changes in the stereoselective recognition. Resolution of mepindolol enantiomers was observed showing the essential role of one methyl group compared to pindolol, which is not resolved by transferrin. Bopindolol, also a derivative of pindolol having bigger difference in the structure, showed more experienced separation. The very slight difference between alprenolol and oxprenolol was also revealed with these methods, since only oxprenolol enantiomers, having an extra oxygen in the structure, are resolved. Determining the migration order of the eutomers and distomers (chlorpheniramine, brompheniramine) we can deduct con- clusions about the role of serum proteins in the delivery of drugs within the body. Keywords: Beta-blockers / Capillary electrophoresis / Chiral separation / H 1 -anti- histamines / Transferrin DOI 10.1002/elps.200500787 1 Introduction In the last 20 years, a very important tendency is the use of pure active enantiomer (eutomer) of optically active substances. Considering the stereoselective character of the pharmacological action, the separation techniques are of particular importance for production, therapeutic practice, or pharmacokinetic studies to resolve the anti- podes and/or check the enantiomeric purity. This ques- tion had special attention in the regulations of the recent edition of European Pharmacopoeia [1]. In treating the diseases of the cardiovascular system, most of the 50 b-blocking agents, used widespread, are aryloxy-propanolamine derivatives containing a chiral center. Typically, the S(2)-enantiomers are more active than the R(1)-enantiomers. For this reason some of them (for example, timolol) are used as single enantiomer. H 1 - antihistamines, like chlorphenyramine, brompheniramine, and cetirizine are used, both as racemates and as single enantiomers, but clemastine is used only as single enantiomer – clemastine (R). Stereoselective HPLC methods [1], using chiral stationary phases with cellulose or amylose derivatives and proteins like HSA and a 1 -acid glycoprotein as chiral selectors are generally applied for the separation of beta-blocker and H 1 -antihistamine enantiomers [2–7]. The use of capillary electrophoretic methods for chiral separation has been mentioned in the British Pharmacopoeia 2004 [8]. Chiral selectors, especially CD derivatives dissolved in the BGE, are mentioned for the enantioseparation of pharmaceu- tical substances. Besides CDs and a large variety of other Correspondence: Professor Árpád Gyéresi, Institute of Pharmaceu- tical Chemistry, University of Medicine and Pharmacy, Târgu-Mures ¸, Romania E-mail: agyeresi@umftgm.ro Fax: 140-265-210407 Professor Ferenc Kilár, Institute of Bioanalysis, University of Pécs, H- 7643 Pécs, Hungary E-mail: ferenc.kilar@aok.pte.hu 1510 Electrophoresis 2006, 27, 1510–1516  2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com