Rhuschalcones II-VI, five new bichalcones from the root bark of Rhus pyroides

Biflavonoids detected in trace amounts in an earlier investigation of the twigs of Rhus pyroides have now been found in the root bark of this species. These new flavonoids belong to a rare bichalcone class and have been identified as 2',4',4' ',2' ",4' "-pentahydroxy-4-O-5' "-bichalcone (rhuschalcone II, 2), 2',4',4' ',2' "-tetrahydroxy-4' "-methoxy-4-O-5' "-bichalcone (rhuschalcone III, 3), 4,2',4' ',2' "-tetrahydroxy-4' "-methoxy-4'-O-5' "-bichalcone (rhuschalcone IV, 4), 4,2',4',4' ',2' ",4' "-hexahydroxy-3,5' "-dihydrochalcone-chalcone (rhuschalcone V, 5), and 4,2',4',4' ',2' ",4' "-hexahydroxy-3,5' "-bichalcone (rhuschalcone VI, 6), repectively. Also obtained was the known compound rhuschalcone I (1). Their structures were determined by spectroscopic and chemical methods, and for 1-3 by total synthesis. All the bichalcones (1-6) tested exhibited selective cytotoxic activity against the HT29 and HCT-116 colon tumor cell lines.