New chalcone dimers from Caesalpinia ferrea Mart act as potent inhibitors of DNA topoisomerase II

New chalcone dimers, pauferrol B (2), and pauferrol C (3), were isolated from the stems of Caesalpinia ferrea Mart, and their structures were determined on the basis of 2D NMR spectroscopy. These new chalcone dimers showed potent inhibitory activities against human topoisomerase II and cell proliferation via the induction of apoptosis in human leukemia HL 60 cells. Absolute configurations of 2 and 3 were estimated by the comparison of CD spectra with a dihydrobenzofuran derivative 4, which was enantioselectively synthesized from 2-hydroxyphenyl acetic acid. (C) 2013 Elsevier Ltd. All rights reserved.