Combined Use of High-Resolution α‑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
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Abstract
Type 2 diabetes is a metabolic disorder
affecting millions of people
worldwide, and new drug leads or functional foods containing selective
α-glucosidase inhibitors are needed. Crude extract of 24 plants
were assessed for α-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
IC<sub>50</sub> values below 20 μg/mL. Subsequently, high-resolution
α-glucosidase profiling was used in combination with high-performance
liquid chromatography–high-resolution mass spectrometry–solid-phase
extraction–nuclear magnetic resonance spectroscopy for identification
of metabolites responsible for the α-glucosidase inhibitory
activity. Quercetin (<b>1</b>) and its dimer (<b>2</b>), trimer (<b>3</b>), and tetramer (<b>4</b>) were identified
as main α-glucosidase inhibitors in A. ascalonicum peel, whereas (<i>E</i>)-piceatannol 3′-<i>O</i>-β-d-glucopyranoside (<b>5</b>), (<i>E</i>)-rhapontigenin 3′-<i>O</i>-β-d-glucopyranoside (<b>6</b>), (<i>E</i>)-piceatannol
(<b>8</b>), and emodin (<b>12</b>) were identified as
main α-glucosidase inhibitors in R. palmatum root