Chemical Constituents from Mentha haplocalyx Briq. (Mentha canadensis L.) and Their α-Glucosidase Inhibitory Activities.

Mentha haplocalyx (Mentha canadensis) is widely used as a medicinal plant in traditional Chinese medicine, and the extracts of its aerial parts are found to significantly inhibit the activity of α-glucosidase with an IC50 value of 21.0 μg/mL. Bioactivity-guided isolation of the extracts afforded two new compounds (1 and 2), together with 23 known ones (3-25). Their structures were established by extensive spectroscopic analyses (1D and 2D NMR, MS, IR and UV). Compounds 1-17 and 21-25 were evaluated for their α-glucosidase inhibitory activities. Compound 11 was the most active ones with an IC50 values of 83.4 μM. These results verify the α-glucosidase inhibitory activity of M. haplocalyx (M. canadensis) and specify its active compounds for the first time.