Enantiomeric Separations of Cationic and Neutral Compounds by Capillary Electrochromatography with β-Cyclodextrin-Bonded Charged Polyacrylamide Gels

Abstract

Enantiomeric separation is one of the most important research themes in analytical chemistry, especially in the pharmaceutical field. A large number of drugs, which have one or more asymmetric centers, exist as a couple of enantiomers. Since the pharmacological activity and metabolism of two enantiomers of a certain drug may very often differ, enantioselective analytical methods are required for chiral purity control, pharmacokinetic studies and other work. During the last decade, tremendous efforts have been expended to develop enantiomeric separation methods. Important advances have been achieved with HPLC, gas chromatography and capillary electrophoresis (CE). In particular, CE is attractive because of its advantages of high efficiency, relatively short analysis time and minimal sample volume requirement.Capillary electrochromatography (CEC), which is in essence a hybrid of HPLC and CE and is based on a fascinating new chromatographic concept 1 , has become increasingly popular. CEC is a powerful separation method which affords a higher theoretical plate number and superior efficiency due to its flat flow profile, compared with micro-HPLC which uses the same packing material. The separation mechanism of neutral compounds in CEC is the same as that of HPLC in principle, with separations essentially resulting from differences in the partitioning of solutes between a mobile phase and a stationary phase.Currently, capillaries packed with the typical stationary phase for HPLC are still used in the majority of CEC studies. However, monolithic stationary phases 2-8 , which are ungranular polymeric separation media, are increasingly gaining attention due to their simple preparation method, wide varieties of functionalization and better stability. Very recently, the enantiomeric separation of N-(3,5-dinitrobenzoyl)leucine diallylamide was obtained using monolithic chiral stationary phases for CEC prepared within the confines of untreated fused-silica capillaries by the direct copolymerization of the chiral monomer 2-hydroxyethyl methacrylate (N-L-valine-3,5-dimethylanilide) carbamate with ethylene dimethacrylate, 2-acrylamido-2-methylpropanesulfonic acid and butyl or glycidyl methacrylate in the presence of a porogenic solvent. 9 In our previous paper 10 , the enantiomeric separations of cationic and neutral compounds by CEC using a charged polyacrylamide gel as a monolithic stationary phase, in which polymeric β-cyclodextrins (β-CD) as chiral selectors are immobilized by incorporation, were reported. Unfortunately, no enantiomeric separation was achieved using monomeric β-CD, because it was eluted out of the capillary column by electroosmotic flow (EOF) to the cathodic solution during preelectrophoresis.In this paper, successful enantiomeric separations of cationic and neutral compounds by CEC using charged polyacrylamide gels to which allyl carbamoylated β-CD derivatives (AC-β -CD) covalently bind as monomeric β-CD are reported. ExperimentalApparatus CEC experiments were carried out at room temperature (approximatel...

Polymeric monolithic stationary phases for capillary electrochromatography

“…For example, Koide and Ueno [73,74] prepared a monolithic gel for chiral resolution by polymerizing acrylamide, bisacrylamide, and AMPS in the presence of polymeric carboxymethyl-b-cyclodextrin. This capillary column afforded 26 000 plates for the separation of terbutaline enantiomers, effecting baseline separation even with a separation factor a of only 1.03.…”

Chiral separation by chromatographic and electromigration techniques. A Review

“…Koide and Ueno [530] prepared monolithic CSPs by incorporating b-CD polymers such as poly b-CD and CM-b-CD polymer in a polyacrylamide gel or by in situ polymerization of allyl carbamoylated b-CD (AC-b-CD), acrylamide, N,N 0 -methylenebisacrylamide and N-(2-acrylamidoethyl) triethylammonium iodide, in the presence of N,N,N 0 ,N 0 -tetramethylethylendiamine and ammonium peroxodisulfate in the capillary [531]. Recently, the same group developed a monolithic CSP containing a chiral crown ether, which was applied to the chiral separation of compounds containing primary amino groups [532].…”

Enantioseparation of hydroxy acids on easy-to-prepare continuous beds for capillary electrochromatography

“…Later, continuous beds, often called monolithic polymeric phases, were also prepared for CEC [8][9][10][11]. Chiral monolithic polymeric phases for CEC containing (N-L-valine-3,5-dimethylanilide) carbamate [12], b-cyclodextrin [13][14][15][16], quinidine derivatives [17,18] and crown ethers [19] have been reported. A special technique represents the use of molecularly imprinted polymers as monolithic chiral stationery phases (CSPs) for CEC [20,21].…”