Minutaside A, new α-amylase inhibitor flavonol glucoside from Tagetes minuta: Antidiabetic, antioxidant, and molecular modeling studies

Investigation of the EtOAc fraction of Tagetes minuta L. (Asteraceae) aerial parts has afforded a new flavonol glucoside, minutaside A (quercetagetin 6-O-(6-O-hexanoyl)-β-D-glucopyranoside) (1), together with four known flavonoids: axillarin 7-O-β-D-glucopyranoside (2), quercetagetin 3,7-dimethoxy-6-O-β-D-glucopyranoside (3), quercetagetin 7-methoxy-6-O-β-D-glucopyranoside (4), and quercetagetin 6-O-β-D-glucopyranoside (5). Their structures were established by multiple spectroscopic methods in addition to HRESIMS (high-resolution electrospray ionisation mass spectra) and comparison with literature data. The antioxidant and anti-diabetic activities of the isolated flavonoids were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and α-amylase inhibition assays. Compounds 1 and 5 showed significant antioxidant activity (84.1 and 83.0% at a 20 μM dose, respectively). Compounds 1, 4, and 5 exhibited strong α-amylase inhibitory activity compared with acarbose (a reference α-amylase inhibitor). However, 2 and 3 showed moderate activity. Molecular modeling studies of 1–5 that included docking, flexible alignment, and surface mapping were performed to evaluate their recognition profile α-amylase receptor. In docking simulations, 5 displayed a binding mode similar to that of acarbose in the active site of α-amylase enzyme.