Abstract
A series of aldo-bis-indole derivatives (aldo-BINs) was prepared by aromatic C-alkylation reactions of aldoses and indole in acetic acid solution. Common monosaccharides such as glucose, mannose, galactose, fucose, xylose, rhamnose, ribose, arabinose and N-acetylglucosamine were smoothly derivatized to form the UV absorbing aldo-BINs. The use of a capillary electrophoretic method to separate these novel aldo-BIN derivatives was established. The capillary electrophoresis conditions were set by using borate buffer (100 mM) at high pH (pH 9.0). The limit of determination was assessed to be 25 nM. The enantioseparation of D, L-pairs of aldo-BINs based on chiral ligand-exchange capillary electrophoresis technology was also achieved by using modified hydroxypropyl-β-cyclodextrin as the chiral selector in the presence of borate buffer. This aldose labeling method was applied successfully to the compositional and configurational analysis of saccharides, exemplified by a rapid and efficient method to simultaneously analyze the composition and configuration of saccharides from the medicinal herbs Cordyceps sinensis and Dendrobium huoshanense.
Highlights
Carbohydrates are one of the most important components of organisms and they are essential materials in many biological processes [1]
In continuation of our studies on a rapid transformation of aldose to its imidazole derivative using 2,3-naphthalene diamine and catalytic iodine in acetic acid solution [11], we developed a new protocol for the synthesis of various aldo-BINs by direct reductive condensation of aldoses with two moles of indoles in H2O/HOAc solution
Several neutral and amino-containing monosaccharides were derivatized by such chemical labeling. This reaction can be carried out with/without molecular iodine as a catalyst, even though Ji et al had reported that a catalytic amount of molecular iodine improved synthesis of bis(indolyl)methanes at room temperature [6]
Summary
Carbohydrates are one of the most important components of organisms and they are essential materials in many biological processes [1]. Sato reported a Lewis acid ([Sc(OTf)3], catalyzed synthesis of bis(3’-indolyl)alkanes in aqueous media by the C-glycosylation of indole with unprotected aldoses (Scheme 1) [7,8]. We used a mild and environmental friendly protic acid (HOAc) for the reaction of unprotected and unmodified aldoses with indole to generate aldo-bis(3’-indolyl)alkanes (aldo-BINs) in a rapid and convenient process. These products should be promising in further application to investigate the composition and stereoconfiguration of saccharides in biological systems. The use of borate buffers with chiral selectors has been reported for the enantioseparation of saccharides [17] by derivation with aromatic reagents. The electrophoretic patterns of several aldo-PMPs were enantioseparated [19]
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