Combined Use of High-Resolution a-Glucosidase Inhibition Profiling and High-Performance Liquid Chromatography High-Resolution. Mass Spectrometry Solid-Phase Extraction Nuclear Magnetic Resonance Spectroscopy for Investigation of Antidiabetic Principles in Crude Plant Extracts

Type 2 diabetes is a metabolic disorder affecting millions of people worldwide, and new drug leads or functional foods containing selective a-glucosidase inhibitors are needed. Crude extract of 24 plants were assessed for a-glucosidase inhibitory activity. Methanol extracts of Cinnamomum zeylanicum bark, Rheum rhabarbarum peel, and Rheum palmatum root and ethyl acetate extracts of C. zeylanicum bark, Allium ascalonicum peel, and R. palmatum root showed IC50 values below 20 mu g/mL. Subsequently, high-resolution a-glucosidase profiling was used in combination with high-performance liquid chromatographyhigh-resolution mass spectrometrysolid-phase extractionnuclear magnetic resonance spectroscopy for identification of metabolites responsible for the a-glucosidase inhibitory activity. Quercetin (1) and its dimer (2), trimer (3), and tetramer (4) were identified as main a-glucosidase inhibitors in A. ascalonicum peel, whereas (E)-piceatannol 3'-O-beta-D-glucopyranoside (5), (E)-rhapontigenin 3'-O-beta-D-glucopyranoside (6), (E)-piceatannol (8), and emodin (12) were identified as main alpha-glucosidase inhibitors in R. palmatum root.