α-Glucosidase inhibitors from the bark of Mangifera mekongensis

BACKGROUND Mangifera mekongensis (Anacardiaceae) is cultivated for its edible fruit and has been used in traditional Vietnamese medicine for its anti-aging properties and for treating diabetes, vermifuge, and dysentery. As part of a search for biologically active compounds with reduction of the rate of glucose absorption, a screening has been initiated to evaluate natural product extracts for the inhibition of enzyme α-glucosidase. A n-hexane extract of the bark of M. mekongensis showed strong α-glucosidase inhibitory activity with IC50 value of 1.71 µg/mL. Thus, the constituents of this plant were examined. RESULTS Two new steroids named mekongsterol A (1) and mekongsterol B (2), were isolated from the n-hexane extract of the bark of M. mekongensis (Anacardiaceae), together with seven known compounds (3-9). Their chemical structures were elucidated on the basis of spectroscopic data. All compounds possessed significant α-glucosidase inhibitory activity in a concentration-dependent manner, except for 3 and 4. Compounds 1, 2, 5-9 showed more potent inhibitory activity, with IC50 values ranging from 1.2 to 112.0 µM, than that of a positive control acarbose (IC50, 214.5 µM). CONCLUSIONS These results suggested that the traditional use of the bark of M. mekongensis for the treatment of diabetes diseases in Vietnam may be attributable to the α-glucosidase inhibitory activity of its steroid and cycloartane constituents.