Bioassay-guided isolation and identification of antidiabetic compounds from Garcinia cowa leaf extract

Garcinia cowa Roxb. ex Choisy (Clusiaceae) is a Thai local edible plant, which has been used for the treatment of diabetes. The aim of this study is to discover and identify bioactive compounds related to antidiabetic properties from the leaf extract of G. cowa. α-Glucosidase inhibitory bioassay-guided isolation of the ethyl acetate extract of the leaves of G.cowa resulted in the isolation and identification of 11 compounds. Of these, a decahydro-1H-xanthene derivative, garciniacowone K (1), was identified as a novel compound. Their structures were characterized by spectroscopic data and by comparison of their NMR spectroscopic data with those previously reported. All compounds were evaluated for their α-glucosidase inhibitory and glucose consumption activities. Compound 2 showed the highest efficacy in inhibiting α-glucosidase enzyme and promoting glucose consumption activity by 3T3-L1 cells, with IC(50) values of 0.5 μM and 13.1 μM, respectively, without causing toxicity to cells.