Antioxidant and α-glucosidase inhibitory activities of constituents from Euonymus alatus twigs

Euonymus alatus (Thunb.) Sieb. (Celastraceae) well-known as winged euonymus, is a deciduous and popular ornamental tree. The cork cambium on E. alatus twigs is called 'gui-jun woo' and is known to have anticancer activity. The chemical constituents of E. alatus twigs were investigated and their antioxidant and α-glucosidase inhibitory activities thoroughly studied. The chopped plant material was extracted with 80% aqueous MeOH under reflux. Phytochemical investigation of CHCl₃-soluble and n-BuOH-soluble fractions from the crude MeOH extract resulted in the isolation and identification of 12 constituents (1-12) using the repeated column chromatography, followed by semi-preparative HPLC purification. The structures were identified as lupeol (1), betulin (2), betulinic acid (3), hederagenin (4), quercetin (5), kaempferol (6), naringenin (7), hyperoside (8), rutin (9), (+)-catechin (10), ferulic acid (11), and vanillic acid (12) by spectroscopic methods including ¹H NMR and ¹³C NMR, and MS analysis. The isolated compounds (1-12) were examined for antioxidant and α-glucosidase inhibitory activities. The isolated compounds 5, 8, 9 and 10 showed antioxidant activities with IC₅₀ values in the range of 39.6-59.4μM. In addition, the compounds 3, 4, 6 and 7 showed α-glucosidase inhibition activities with IC₅₀ values in the range of 83.6-107.8μM. These findings strongly suggest that E. alatus twigs can be a potential source of natural antioxidants and/or anti-diabetic agents in pharmaceutical and health functional foods. The isolated compounds are the likely contributors to the antioxidant and anti-diabetic effects.