Short Communication Enantiomeric separation by MEKC using dodecyl thioglycoside surfactants: Importance of an equatorially oriented hydroxy group at C-2 position in separation of dansylated amino acids To investigate the influence of stereogenic centers of sugar-based surfactants for enan- tiomeric separation, four n-dodecyl thioglycoside sulfates (CMC 1.5–3.6 mM) were chosen as micelle-forming surfactants and five dansylated hydrophobic amino acids were used as test analytes. The analytes were mutually separated by these micelles exhibiting almost similar migration times independent of the used surfactant. Baseline separations of all enantiomers were achieved using both b-D-glucose and b-D-galactose derivates that have an equatorially oriented hydroxy group at C-2 position. In contrast, the ability of enantioseparation was markedly decreased in the case of b-D-mannose and 2-deoxy-b-D- glucose derivatives. These results suggested that the structure of C-2 position of the sugar unit, namely presence of an equatorially oriented hydroxy group, is highly important for the enantiomeric separation of the chosen hydrophobic dansylated amino acids. Keywords: Alkyl thioglycosides / Chiral surfactants / Enantiomeric separation / Micellar electrokinetic chromatography DOI 10.1002/elps.200800685 The enantiomeric separation of racemic compounds has been of great importance in research fields such as pharmaceutical, agrochemical, foods and environmental chemistry. Each enantiomer has different biological activity and usually exhibits different physiological effects through different recognition pathways in biological processes. Numerous versatile methods for the enantiomeric separa- tion and analysis have been developed using HPLC and GC together with CE [1]. Among the various modes of CE, EKC and MEKC are the more prevalent ones and a remarkable number of chiral selectors have been developed for EKC and MEKC analyses [2, 3]. Application of a variety of natural and synthetic chiral surfactants has been investigated to achieve high resolution (Rs) in enantiomeric separation by MEKC [4–6]. The ability of enantiomeric separation is highly depended on detailed structure of the micelle-forming surfactants used. For example, it was reported that the use of amino acid-based surfactants with slightly different head groups resulted in a dramatic change in enantiomeric separation [7–10]. Since carbohydrates are readily available with various structural analogues and with both D and L enantiomers, amphiphilic alkyl glycosides have recently received attention as semi-synthetic chiral selectors in MEKC [11, 12]. Recently, several papers reported fundamental investigations on the relationship between the structure of sugar-based surfactants and their enantiomeric separation ability of dansylated amino acids (Dns-AAs) using O- [13, 14] and S-glycoside-based anionic surfactants [15]. They demonstrated that the b-anomers generally showed better selectivity than the corresponding a-anomers, and that the modifications at the 6-hydroxy group such as deoxygenation resulted in a slight improvement in selectivity. These results prompted us to perform further investigation of the relationship. This communication describes our recent finding that presence of an equatorially oriented hydroxy group is highly important to attain good enantiomeric Rs of Dns-AAs. Similarly to our previous report [15–18], we prepared sulfated n-dodecyl thioglycosides depicted in Fig. 1, through O-acetylation of free monosaccharides followed by boron trifluoride diethyl ether complex promoted thioglycosylation with 1-dodecanthiol, removal of O-acetyl groups, and selec- tive O-sulfation. Electrophoretic experiments were carried out using a HP 3D CE system equipped with a UV-visible detector (Hewlett Packard, Waldbronn, Germany) at 251C Chiharu Tano 1 Sang-Hyun Son 1 Jun-ichi Furukawa 2 Tetsuya Furuike 3 Nobuo Sakairi 1 1 Graduate School of Environmental Science, Hokkaido University, Hokkaido, Japan 2 Graduate School of Advanced Life Science, Hokkaido University, Hokkaido, Japan 3 Faculty of Chemistry, Materials and Bioengineering, and High Technology Research Center, Kansai University, Osaka, Japan Received October 20, 2008 Revised March 15, 2009 Accepted March 17, 2009 Abbreviations: Dns-AA, dansylated amino acid; 6-Gal, sodium n-dodecyl 1-thio-b-D-galactopyranoside 6-sulfate; 6-Glc, sodium n-dodecyl 1-thio-b-D-glucopyranoside 6-sulfate; 6-dGlc, sodium n-dodecyl 2-deoxy-1-thio-b-D- glucopyranoside 6-sulfate; 3-Man, sodium n-dodecyl 1-thio- b-D-mannopyranoside 3-sulfate; 6-Man, sodium n-dodecyl 1-thio-b-D-mannopyranoside 6-sulfate; Rs, resolution Correspondence: Professor Nobuo Sakairi, Graduate School of Environmental Science, Hokkaido University, Kita 10-Nishi 5, Kita-ku, Sapporo 060-0810, Japan E-mail: nsaka@ees.hokudai.ac.jp Fax:181-11-706-2257 & 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.electrophoresis-journal.com Electrophoresis 2009, 30, 2743–2746 2743