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

A chemical study on Chenopodium quinoa Willd. bran identified four new triterpene saponins (1-4) and 12 known analogues (5-16). The structures were determined through extensive spectroscopic analysis. Compounds 1 and 2 were identified as rare dodecandralol triterpenoid saponins, marking their first discovery in C. quinoa. Compounds 1-16 were evaluated for α-glucosidase inhibitory activity, with queretaroic acid 28-O-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 C. quinoa bran as a source of quinoa saponins with potential for hypoglycemic drug development.