A new flavone glucoside together with known ellagitannins and flavones with anti-diabetic and anti-obesity activities from the flowers of pomegranate (Punica granatum)

A new flavone glucoside tricetin 4′-O-β-glucopyranoside (1) and four known ellagitannins and flavones tricetin (2), luteolin (3), ellagic acid (4), and granatin B (5) were isolated from the flowers of Punica granatum L. (Lythraceae). Their structures were established by 1D and 2D NMR as well as mass spectrometry analyses. Among all tested compounds, tricetin (2) exhibited the strongest α-glucosidase inhibitory activity that was comparable to the anti-diabetic drug acarbose. Comparative structure-function analysis of tri-, tetra-, and pentahydroxy flavones [apigenin, luteolin (3), and tricetin (2), respectively] suggested that a greater number of hydroxyl groups on the flavone molecule enhanced its suppression of α-glucosidase, α-amylase, and lipase activities.