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.