Tsaokopyranols A–M, 2,6-epoxydiarylheptanoids from Amomum tsao-ko and their α-glucosidase inhibitory activity.

• Thirteen new 2,6-epoxydiarylheptanoids were isolated from A. tsao-ko. • Eight diarylheptanoids showed obvious α -glucosidase inhibitory activity. • Compounds 12 and 13 were noncompetitive inhibitors of α -glucosidase. • The K i values of compounds 12 and 13 on α -glucosidase were 539.6 and 385.2 μM. The dried fruits of Amomum tsao-ko are well-known dietary spices and traditional Chinese medicines. The random screen revealed that 50% ethanol-water extract of A. tsao-ko demonstrated significant α -glucosidase inhibitory activity with an IC 50 value of 38.6 μg/mL. Bioactivity-guided isolation on the active fraction afforded 13 new 2,6-epoxy diarylheptanoids, tsaokopyranols A–M (1 – 13), and four known ones (14–17). Their structures featuring a 2,6-epoxy pyran ring were established by extensively spectroscopic analyses (HRESIMS, IR, UV, 1D and 2D NMR) and ECD calculations. Seven new (4 – 6 , 8 – 11) and one known (16) compounds showed obvious α -glucosidase inhibitory activity with IC 50 values ranging from 59.4 to 116.5 μM, higher than acarbose (IC 50 : 219.0 μM). An enzyme kinetic analysis indicated that compounds 12 and 13 were noncompetitive-type inhibitors of α -glucosidase with K i values of 539.6 and 385.2 μM. This result provided new insights for the usage of A. tsao-ko , and 2,6-epoxydiarylheptanoids as new anti-diabetic candidates. [ABSTRACT FROM AUTHOR]