Dodecyl thioglycopyranoside sulfates: Novel sugar‐based surfactants for enantiomeric separations by micellar electrokinetic capillary chromatography

Abstract

Four novel chiral anionic surfactants having carbohydrate hydrophilic heads, sodium n-dodecyl 1-thio-beta-D-glucopyranoside 6-hydrogen sulfate (6-betaGlcD), sodium n-dodecyl 1-thio-beta-L-glucopyranoside 6-hydrogen sulfate (6-betaGlcL), sodium n-dodecyl 1-thio-beta-L-fucopyranoside 3-hydrogen sulfate (3-betaFucL), and sodium n-dodecyl 1-thio-alpha-L-rhamnopyranoside 3-hydrogen sulfate (3-alphaRhaL), were synthesized by selective sulfation of the corresponding thioglycosides. Their CMC determined by fluorescence using pyrene as a probe in water was 1.3-2.7 mM. These surfactants found to be useful as chiral selectors for enantiomeric separation by MEKC. The enantiomeric separation was optimized with respect to pH, buffer concentration, and surfactant concentration. Under the optimized conditions (50 mM phosphate buffer at pH 6.5, 30 mM surfactant, 20 kV), the enantiomeric separations of five dansylated amino acids (Dns-AAs) were achieved within approximately 20 min with the migration order of Val<Met<Leu<Phe<Trp. With 6-betaGlcD, all D-forms of Dns-AAs were found to migrate faster than the corresponding L-forms, whereas the migration order of the enantiomers was completely reversed with the surfactant 6-betaGlcL having inversed absolute configuration of 6-betaGlcD. Among four surfactants examined, beta-anomers were much superior chiral selectors than alpha-anomers, and the maximum resolution was obtained with the 6-deoxy sugar, 3-betaFucL. These results indicated that the structures of the surfactant head groups including their anomeric configurations have significant effects on the enantiomeric separation and the migration behavior in MEKC.