New triterpenoids from acorns of Quercus liaotungensis and their inhibitory activity against α-glucosidase, α-amylase and protein-tyrosine phosphatase 1B

Acorn has been used as a functional food with numerous nutritional and active ingredients. In this study, 3 new triterpenoids, together with 22 known compounds were isolated from acorns (Quercus liaotungensis) and further confirmed by NMR. In order to disclose the hypoglycaemic ingredients, the extracts and all the discovered compounds were researched for enzyme inhibition using in-vitro assays on α-amylase, α-glucosidase, and protein-tyrosine phosphatase 1B (PTP1B). The results suggested that 75% EtOH, PE, EtOAc, and n-BuOH extracts of acorns all exhibited potent inhibitory activities against PTP1B and α-glucosidase. Most of the compounds showed strong inhibitory effects on PTP1B and α-glucosidase, especially new compounds and compound 12, their IC50 values were about 6-fold to 20-fold lower than positive control, all showed competitive inhibitory pattern. The result suggested that triterpenoids from acorns are potential functional food ingredients that can be used as new anti-diabetic agent.