Triterpene Saponins from the Bran of <i>Chenopodium quinoa</i> Willd. and Their α-Glucosidase Inhibition Activity

A chemical study on <i>Chenopodium quinoa</i> Willd. bran identified four new triterpene saponins (<b>1</b>-<b>4</b>) and 12 known analogues (<b>5</b>-<b>16</b>). The structures were determined through extensive spectroscopic analysis. Compounds <b>1</b> and <b>2</b> were identified as rare dodecandralol triterpenoid saponins, marking their first discovery in <i>C. quinoa</i>. Compounds <b>1</b>-<b>16</b> were evaluated for α-glucosidase inhibitory activity, with queretaroic acid 28-<i>O</i>-β-d-glucopyranosyl ester (QA, IC₅₀ = 42.3 ± 4.1 μM) showing potent inhibitory activity in a mixed-type manner. Surface plasmon resonance (SPR) and Fourier transform infrared (FT-IR) assays confirmed QA's strong binding affinity to α-glucosidase. Molecular docking and dynamics simulations revealed QA interacts with the enzyme primarily via hydrogen bonding and hydrophobic contacts, resulting in conformational changes and inhibition activity of α-glucosidase. Additionally, QA strongly suppressed postprandial hyperglycemia in diabetes mellitus (DM) mice in vivo. These findings establish <i>C. quinoa</i> bran as a source of quinoa saponins with potential for hypoglycemic drug development.