Anti-hyperglycaemic effect of labdane diterpenes isolated from the rhizome of Amomum maximum Roxb., an edible plant in Southwest China

Amomum maximum Roxb. rhizome is a fork medicine mainly used in South and Southeast Asia. In present study, the hypoglycaemic effects of the ethanolic extract of A. maximum rhizome were demonstrated both on α-glucosidase assay in vitro and streptozotocin (STZ)-induced postprandial hyperglycaemia in mice. Furthermore, six labdane diterpenes, amoxanthin A (1), ottensinin (2), coronarin D (3), coronarin D methyl ether (4), isocoronarin D (5), and zerumin (6), were isolated from its ethyl acetate sub-fraction with the guidance of α-glucosidase inhibitory activity. Among these compounds, 2 and 6 exhibited significant inhibitory effect on α-glucosidase, as well as on STZ-induced high postprandial blood glucose levels in mice. Additionally, molecular docking analysis revealed that 2 and 6 could firmly bind to the active sites of α-glucosidase. These results suggest that compounds 2 and 6 are the main anti-hyperglycaemic agents present in A. maximum, which may demonstrate potential beneficial effects in diabetes management.