Triterpene acids isolated from Lagerstroemia speciosa leaves as α‐glucosidase inhibitors

The potential antidiabetic activity of ethyl acetate extract of the leaves of Lagerstroemia speciosa (LSL) was investigated by α‐amylase and α‐glucosidase inhibition assay. Six pentacyclic triterpenes (oleanolic acid, arjunolic acid, asiatic acid, maslinic acid, corosolic acid and 23‐hydroxyursolic acid) were isolated from LSL. Their structures were determined by spectroscopic analysis and their α‐glycosidase and α‐amylase inhibitory activities were investigated. They exhibited no or weak inhibitory activity against α‐amylase and middle α‐glucosidase inhibitory activities. Corosolic acid, which shows best bioactivity against α‐glucosidase (IC₅₀ = 3.53 µg/mL), contributes most to the α‐glucosidase inhibitory activity of EtOAc extract. The kinetics of inhibition of corosolic acid was also discussed. Results from this study might provide the scientific evidence for LSL for the treatment of diabetes in traditional medicine. Copyright © 2008 John Wiley & Sons, Ltd.