Stilbenoids and Flavonoids from Cajanus cajan (L.) Millsp. and Their α-Glucosidase Inhibitory Activities

Two new stilbenoids, cajanstilbenoid C (1) and cajanstilbenoid D (2), together with eight other known stilbenoids (3-10) and seventeen known flavonoids (11-27), were isolated from the petroleum ether and ethyl acetate portions of the 95% ethanol extract of leaves ofCajanus cajan(L.) Millsp. The planar structures of the new compounds were elucidated by NMR and high-resolution mass spectrometry, and their absolute configurations were determined by comparison of their experimental and calculated electronic circular dichroism (ECD) values. All the compounds were assayed for their inhibitory activities against yeastα-glucosidase. The results demonstrated that compounds3,8-9,11,13,19-21,and24-26had strong inhibitory activities againstα-glucosidase, with compound11(IC50= 0.87 ± 0.05 μM) exhibiting the strongest activity. The structure–activity relationships were preliminarily summarized. Moreover, enzyme kinetics showed that compound8was a noncompetitive inhibitor, compounds11,24-26were anticompetitive, and compounds9and13were mixed-competitive.Keywords:Cajanus cajan;stilbenoid;flavonoid;α-glucosidase inhibitory activity