Capillary Zone Electrophoresis Method for the Separation of Glucosidase Inhibitors in Extracts of Salacia reticulata, a Plant Used in Ayurvedic Treatments of Type-2 Diabetes

Abstract

A simple and reproducible capillary-zone electrophoresis (CZE) method was developed for the separation and quantitation of sulfonium-ion-containing compounds isolated from plants of the Salacia genus which are traditionally used in Ayurvedic medicine for the treatment of type-2 diabetes. The method sufficiently resolved four different compounds with confirmed glucosidase inhibitory activity, namely, salacinol, ponkoranol, kotalanol and de-O-sulfonated kotalanol. Separation could be achieved in less than 9 min, and calibration curves showed good linearity. Detection limits were determined to be in the low mug/mL range. This method was used to demonstrate that de-O-sulfonated kotalanol isolated from natural sources has identical ionic mobility to a synthetic standard. Furthermore, new extraction conditions were developed by which the zwitterionic compounds (salacinol, ponkoranol, and kotalanol) could be separated from de-O-sulfonated kotalanol in a single solid-phase extraction (SPE) procedure. The extraction gave reproducibly high recoveries and was used to process four commercial Salacia extracts for CZE analysis to reduce the complexity of resulting electropherograms and to facilitate the detection of the four inhibitors in question. De-O-sulfonated kotalanol was detected in two of four Salacia samples while ponkoranol was present in all four. A comparison of all samples tested demonstrated that they had remarkably similar patterns of peaks, suggesting that this CZE method may be useful in the chemical fingerprinting of Salacia-containing products.