Isolation of natural compounds from Phlomis stewartii showing α-glucosidase inhibitory activity

Stewartiiside (1) and stewertiisins A-C (2-4) together with eight known compounds (5-12) were isolated from Phlomis stewartii. The structures were elucidated by using 1D, 2D NMR spectroscopy and mass spectrometry. All the isolates (1-12) showed α-glucosidase inhibitory activity with IC50 values ranging between 14.5 and 355.4 μM.