No 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

To investigate the influence of stereogenic centers of sugar-based surfactants for enantiomeric 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 beta-D-glucose and beta-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 beta-D-mannose and 2-deoxy-beta-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.

Fully acetylated dodecyl thioglycosides found to be used as glycosyl donors by activation with 1-benzenesulfinyl piperidine (BSP) and triflic anhydride (Tf 2 O) at -78 °C, and the glycosyl acceptor was added to the reaction mixture at the same temperature to furnish various disaccharides and Lewis a (Le a ) trisaccharide in good yields.

General Procedures: All chemicals were purchased as reagent grade and used without further purification whereas N-iodosuccinimide (NIS) was recrystallized by 1,4-dioxane and diethyl ether (1:1, v/v) before use. Dichloromethane (CH 2 Cl 2 ) and 1,2-dichloroethane were distilled over calcium hydride (CaH 2 ). Molecular sieves (MS) used for glycosylation were 4Å, which were activated at 200 ˚C under reduced pressure prior to use. Reactions were monitored by thin-layer chromatography (TLC) on a pre-coated plate of silica gel 60F 254 (layer thickness, 0.25 mm; E. Merck, Germany). Spots were detected under UV (254 nm) and/or by spraying with p-methoxybenzaldehyde-H 2 SO 4 -MeOH (1:2:17, v/v/v) and heated for a few minutes. Silica gel 60 with 0.043-0.2 mm (E. Merck, Germany) was used for open column chromatography.Size exclusion column chromatography was performed on Sephadex G-15 (Pharmacia Biotech AB, Uppsala, Sweden) and deionized water as the eluent.1 H and 13 C NMR spectra were recorded with a Bruker ASX 300 (300 and 75.1 MHz, respectively) and JEOL ECA 600 (600 and 125 MHz). Chemical shifts (in ppm) were referenced to tetramethylsilane (δ = 0 ppm) in deuterated chloroform (CDCl 3 ). Coupling constant are given in Hertz. 13 C NMR spectra were obtained by using the same NMR spectrometers and were calibrated with CDCl 3 (δ = 77.00 ppm). Splitting patterns are indicated as s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; brd, broad doublet for 1 H NMR data. ESI-HR mass spectra were measured on a JEOL JMS-T100LCP and FAB-HR mass was carried out using a JEOL JMS-HX100.