Cyclic Polyketides with α-Glucosidase Inhibitory Activity from Endiandra kingiana Gamble and Molecular Docking Study

A phytochemical investigation of the methanolic extract of Endiandra kingiana (bark) led to the isolation of four major compounds which are kingianic acid A (1), tsangibeilin B (2), kingianin A (3) and kingianin F (4). The structures were determined by 1D- and 2D-NMR analysis in combination with HRMS experiments. The compounds were screened for their in vitro α-glucosidase inhibition activity. Among them, compounds 3-4 showed potent α-glucosidase inhibition activity with IC50 value at 11.9 ± 2.0 µM and 19.7 ± 1.5 µM, respectively. The molecular docking study found that both compounds were bound into the active site of the N-terminal of MGAM, and thus agreed with the in vitro α-glucosidase enzyme inhibition activity results.