Antioxidant and Antidiabetic Activities of Flavonoid Derivatives from the Outer Skins of Allium cepa L.

• DOI: 10.1021/acs.jafc.0c02122
• Publication Date: 2020-06-30T20:45:36Z
• Authors: Ngoc Khanh Vu; Chung Sub Kim; Manh Tuan Ha; Quynh-Mai Thi Ngo; Se Eun Park; Haeun Kwon; Dongho Lee; Jae Sue Choi; Jeong Ah Kim; Byung Sun Min
• Keywords: Flavonoids; Protein Tyrosine Phosphatase, Non-Receptor Type 1; 0303 health sciences; Molecular Structure; Plant Extracts; alpha-Glucosidases; Antioxidants; 3. Good health; Molecular Docking Simulation; 03 medical and health sciences; Onions; Hypoglycemic Agents; Enzyme Inhibitors

The onion, known as the bulb onion or common onion, is not only a key ingredient in many tasty and healthy vegetarian meals but also many traditional medicines. Nine new flavonoids [cepaflavas A, B (5, 6), cepadials A-D (7-9 and 14), and cepabiflas A-C (10-12)] and six known compounds (1-4, 13, 15) were obtained from the outer skins of Allium cepa L. Among them, compounds 5, 6, and 9 might be artificial products formed during extraction and isolation. New compounds were structurally elucidated using various spectroscopy/spectrometry techniques, including NMR and HRMS, and computational methods. Their absolute configurations were determined using time-dependent density functional theory calculations, combined with ECD spectroscopy, optical rotation calculation, and statistical procedures (CP3 and DP4 analysis). The free radical scavenging assays revealed that the new compounds 10-12 possessed considerable antioxidant activities with IC50 values of 4.25-8.88 and 7.12-8.14 μM against DPPH and ABTS•+, respectively. Compounds 13-15 showed substantial inhibitory activities against both α-glucosidase and protein tyrosine phosphatase 1B (PTP1B), with IC50 values of 0.89-6.80 and 1.13-6.82 μM, respectively. On the basis of molecular docking studies, 13 and 15 were predicted to have high binding capacity and strong affinity toward the active site of PTP1B.