Cytotoxic prenylated flavones from the stem and root bark of Daphne giraldii

Three new prenylated flavones (1-3), along with three known analogues (4-6), were isolated from the stem and root bark of Daphne giraldii. Their structures were determined by comprehensive NMR and HRESIMS spectroscopic data analyses. The absolute configurations of compounds 2 and 3 were assigned by optical rotation comparison, CD and [Rh-2(OCOCF3)(4)]-induced CD spectral methods. The in vitro cytotoxicity experiments carried out involving five cancer cell lines (U251, A549, HepG2, MCF-7 and Bcap37) showed that 2 markedly inhibited the proliferation of all tested cells with IC50 values ranging from 4.26 to 20.82 mu M. The preliminary structure-activity relationships of these flavones are discussed. In addition, compound 2 was found to effectively induce apoptosis in HepG2 cells according to a flow cytometry analysis. (C) 2016 Elsevier Ltd. All rights reserved.