Single-step approach for fabrication of vancomycin-bonded silica monolith as chiral stationary phase.

A vancomycin-bonded silica monolithic column for capillary electrochromatography (CEC) was prepared by a single-step in situ sol-gel approach. This sol-gel process incorporates a synthetic sol-gel precursor which contains a macrocyclic antibiotic, vancomycin, to form a porous silica network inside a fused-silica capillary. To avoid degradation of vancomycin during the column fabrication, a mild step was adopted into the sol-gel process. The performance of the vancomycin chiral stationary phase was investigated by CEC in both the reversed-phase mode and the normal-phase mode. The vancomycin chiral stationary phase was optimized with respect to vancomycin loading in the reversed-phase mode for chiral separation of thalidomide enantiomers. The best efficiency and resolution values of 94600plates/m and 5.79, respectively, were achieved. The optimized column was further applied to chiral separation of alprenolol enantiomers. A plate height of less than 7µm for the first eluted enantiomer of alprenolol was obtained in an aqueous mobile phase at a flow rate of 0.74mm/s. Using enantiomers of seven ß-blockers and some other basic enantiomers as test analytes, separation efficiencies of up to 148100plates/m in the reversed-phase mode and up to 138100plates/m in the normal-phase mode were achieved.

Electrocyclization of cis-dienals in organic synthesis: a new and versatile synthetic method for the preparation of aryl- and heteroaryl-fused coumarins.

Benzo-, furo-, thieno-, and pyrido[f]coumarins were prepared by generating the 2H-pyran-2-one moieties from the oxidation of the corresponding 2H-pyran rings, which were formed in situ from the electrocyclization of cis-dienals.

Single-step approach to beta-cyclodextrin-bonded silica as monolithic stationary phases for CEC.

A novel single-step sol-gel approach for the preparation of beta-CD-bonded silica monolithic electrochromatographic columns is established. The porous silica networks were fabricated inside fused-silica capillaries using sol-gel processing of tetramethoxysilane and an organfunctional silicon alkoxide that contains beta-CD. Scanning electron micrographs and nitrogen adsorption-desorption data showed that these functional monolithic columns have double pores structures with micrometer-size co-continuous through-pores and silica skeletons with open mesopores. The beta-CD monolithic columns have successfully been applied to the separation of several neutral and negatively charged isomers by CEC. The column performance was evaluated by using positional isomers of naphthalenedisulfonic acid as model compounds. A plate height of less than 10 mum for the first eluted isomer of naphthalenedisulfonic acid was obtained at an optimal flow rate (0.47 mm/s) of the mobile phase. Moreover, the columns have been proved to be stable for more than 100 runs during 3 months period and show reasonable column reproducibility.

Analyses of carbohydrate binding property of lectin-chaperone calreticulin.

Calreticulin (CRT) is a soluble molecular chaperone of the endoplasmic reticulum. It is a lectin that promotes the folding of proteins carrying N-linked glycans. Recent investigations have revealed that glucosylated high-mannose-type glycans are employed as key elements in this process. Here, we performed quantitative analyses of the interaction of CRT with various disaccharides, including fluorine-substituted analogues using a quartz-crystal microbalance (QCM). These experiments revealed the weak affinity of 2- and 3-fluoroglucose derivatives. On the other hand, 6-fluoroglucose derivatives exhibited a significant affinity, indicating that the role of 6-position of OH is less significant for binding to CRT. We also characterized binding epitope of the Glcalpha1-3Man(alpha)Me to CRT by saturation transfer difference (STD) NMR spectroscopy. It is proposed that 2-, 3-, and 4-positions of Glc and 3-, 4-, and 6-positions of Man are in close contact with CRT binding pocket, while 6-position of Glc and 2-position of Man are not. These finding are in excellent agreement with our QCM experiment.

8-(1,4,7,10-Tetraoxa-13-azacyclopentadec-13-ylmethyl)quinolin-7-ol: synthesis and application as a highly sensitive metal cation probe.

A new metal ion probe 8-(1,4,7,10-tetraoxa-13-azacyclopentadec-13-ylmethyl)quinolin-7-ol (1a) was synthesized via a modified Mannich reaction, in which the mechanism of recognition incorporates excited-state proton transfer reactions. The remarkable differentiation in spectral properties upon metal complexation makes 1a a highly sensitive fluorescence probe.