Flavonoids from litchi(Litchi chinensis Sonn.) seeds and their inhibitory activities on α-glucosidase

With the bioactivity-guided method, a new flavanone glycoside, together with nine known flavonoids were isolated from 50% aqueous ethanol of litchi(Litchi chinensis Sonn.) seeds. The chemical structure of the new compound was elucidated via 1D and 2D nuclear magnetic resonance(NMR) techniques and mass spectrometry to be (2S)-pinocembrin-7-O-(6aEuro(3)-O-alpha-L-arabinosyl-beta-D-glucopyranoside)(1), and the nine known compounds were determined to be quercetin(2), phlorhizin(3), pinocembrin-7-O-glucoside(4), kaempferol-7-O-beta-D-glucopyranoside(5), onychin(6), nairutin(7), narcissin(8), pinocembrin-7-O-[(6aEuro(3)-O-beta-D-glucopyranoside)-beta-D-glucopyranoside](9) and pinocembrin-7-O-[(2aEuro(3),6aEuro(3)-di-O-alpha-L-rhamnopyranosyl)-beta-D-glucopyranoside](10). Some of the isolated flavonoids were tested for their inhibitory effects on alpha-glucosidase. And compounds 2 and 3 showed stronger inhibitory activity than positive control.