Flavonoids and sesquiterpenes from Tecurium ramosissimum promote antiproliferation of human cancer cells and enhance antioxidant activity: A structure-activity relationship study

Fractionation of the chloroformic extracts from Teucrium ramosissimum leaves resulted in the isolation of three flavonoids: genkwanin (1), cirsimaritin (2) and 4',7-dimethoxy apigenin (4) and one sesquiterpene: beta-eudesmol (3). The structures were determined using data obtained from H-1 and C-13 NMR spectra, as well as by various correlation experiments (COSY, HMQC and HMBC). The antioxidant activities of the isolated flavonoids from T. ramosissimum leaves were evaluated by measuring their ability to scavenge the radical ABTS(+center dot) and through chemical assays: cupric reducing antioxidant capacity (CUPRAC), reducing power (RP) and ferric reducing antioxidant power (FRAP). Furthermore, the effects of T. ramosissimum isolated molecules, on inhibition of cell proliferation and induction of apoptosis in human leukemia cells, were also examined. Cirsimaritin showed the best activity in the ABTS assay with TEAC value 2.04 mu M, whereas apigenin and 4',7-dimethoxy apigenin exhibited the highest antioxidant activity using the CUPRAC, RP and FRAP assays with TEAC values 10.5, 1.39 and 0.71 mu M respectively. The cytotoxic activity revealed that the beta-eudesmol inhibited significantly the proliferation of K562 cells (IC50 = 20 mu g/ml). (C) 2011 Elsevier B.V. All rights reserved.