Retro-dihydrochalcones from the resin of Daemonorops draco and their inhibitory activities against renal fibrosis.

Daedracoflavan A-E (1-5), five new flavonoids were isolated from the resin of Daemonorops draco. Their structures including absolute configurations were established by using spectroscopic and computational methods. All the compounds are new chalcones with the same retro-dihydrochalcone skeleton. Compound 1 features the presence of a cyclohexadienone unit originating from a benzene ring, and the ketone group of C-9 reduced to a hydroxyl group. The bioactivity of all isolated compounds was evaluated in kidney fibrosis and found that compound 2 could dose-dependently inhibit the expression of fibronectin, collagen I, and α-SMA in TGF-β1-induced rat kidney proximal tubular cells (NRK-52E). Interestingly, the replacement of a proton by a hydroxyl group at C-4' seems to play a crucial role in anti-renal fibrosis activity.