Antidiabetic Ellagitannins from Pomegranate Flowers: Inhibition of α-Glucosidase and Lipogenic Gene Expression

Two new ellagitannins containing a rare 3-oxo-1,3,3a,8b-tetrahydrofuro[3,4-b]benzofuran moiety, namely punicatannins A (1) and B (2), were isolated from pomegranate (Punica granatum) flowers. Their structures with absolute configuration were determined by detailed analysis of spectroscopic data, electronic circular dichroism (ECD) calculation, and chemical hydrolysis. A plausible biogenetic route involving a key enzymatic 1,4-Michael addition is proposed. Punicatannin A showed potent inhibition of alpha-glucosidase and lipogenic gene expression.