Flavonoids from the branches and leaves of Erythrina variegata L. and their PTP1B and α-glucosidase inhibitory activities

Phytochemical investigation of the methanolic extract of the Vietnamese Erythrina variegata branches and leaves resulted in the separation and identification of five flavanones, including 7,4'-dihydroxy-3'-methoxyflavanone (1), abyssinone VII (2), sigmoidin B (3), aromadendrin (4), and sigmoidin D (5). Their chemical structures were confirmed by the nuclear magnetic resonance (NMR) spectral analysis. These isolated compounds showed activities against protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase enzymes, exhibiting varying levels of inhibition. Especially, metabolite 2 strongly inhibited PTP1B and α-glucosidase enzymes with IC50 values of 8.34 ± 0.67 and 12.14 ± 0.39 µM, respectively. In general, hydroxylation at carbons C-5/C-3' and prenylation at C-3ʹ/C-5ʹ mainly caused active enhancements of these metabolites against both enzyme activities.