Coumarins and Polar Constituents from Eupatorium triplinerve and Evaluation of Their α-Glucosidase Inhibitory Activity

Abstract

In our study of antidiabetic compounds from the leaves of Eupatorium triplinerve Vahl. (Asteraceae), ten compounds were isolated from the methanol leaf extract. They were determined to be β-sitosterol (1), stigmasterol (2), β-sitosterol 3-O-β-D-glucopyranoside (3), ayapanin (4), ayapin (5), thymoquinol 5-O-β-D-glucopyranoside (6), thyrsifloside (8), (E)-4-methoxymelilotoside (9), and kaempferol 3,7-di-O-β-D-glucopyranoside (10) by using ESI-MS, 1D (1H-, 13C-, DEPT) and 2D NMR (HSQC, HMBC, and NOESY) techniques. This is the first report of water-soluble compounds from E. triplinerve and compounds 6–10 were isolated for the first time from E. triplinerve. NMR profiling and HPLC analysis are fast and reliable methods to screen phytochemicals in plant samples. Due to their high concentrations in the leaf extracts of E. triplinerve, coumarins 4 and 5 could be fast screened by NMR profiling and RP-HPLC-PDA analysis. In the in vitro test for α-glucosidase inhibition of compounds 4–9, compounds 4, 5, and 7 showed the enzymatic inhibition of 40%, 46%, and 81%, respectively, at 256 μg/mL. An IC50 value of 58.65 ± 1.20 μg/mL (302 μM) was calculated for compound 7 which is lower than that of the positive control acarbose (IC50 197.33 ± 2.51 μg/mL; 306 μM).