α-glucosidase Inhibitory Activity of Extracts and Compounds from the Leaves of Ruellia tuberosa L.

Background: In recent years, the study of the structure and biological activity of medicinal plants has been particularly important to search for diabetes medicine. Ruellia tuberosa is used to treat various diseases such as diabetes by inhibiting the activity of α-glucosidase. Objective: In this study, an experiment was designed to isolatedisolate and identifiedidentifyα-glucosidase inhibitory extracts and compounds from Ruellia tuberosa L. through bio-assay guided isolation. Methods: Dry powder of Ruellia tuberosa L. was extracted with 70% ethanol, followed by liquidliquid partition with n-hexane, ethyl acetate and butanol, respectively. The extracts were evaluated withα-glucosidase inhibition. The potential extracts were isolated to identifynew compounds. The effects of these compounds on the α-glucosidase inhibitory were evaluated. Results: The a-glucosidase inhibitory activities showed that the n-hexane, ethyl acetate and the butanol extract had the α-glucosidase inhibition with an IC50 of 46.2 ± 0.9, 6.6 ± 2.9 and 8.9 ± 0.9 μg/mL, respectively. From the n-hexane and ethyl acetate extracts, the structures of four compounds were elucidated by NMR spectroscopic method, including lupeol (1), syringaresinol (2), apigenin (3), verbascoside (4). The α-glucosidase inhibitory activities showed that all isolated compounds were more active than the positive control - acarbose with an IC50 of 37.5 ± 0.4; 19.5 ± 0.2; 20.1 ± 0.3; 69.3 ± 0.2 μg/mL, respectively. Conclusion: The ethyl acetate extract showed strong activity about 19 times more than the positive control - acarbose. The compound syringaresinol (2) was the most powerful α-glucosidase inhibitor. Therefore, Ruellia tuberosa L. contains many compounds that can inhibit α-glucosidase activity.