Cytotoxic Flavones from the Stem Bark of Bougainvillea spectabilis Willd
received 12 February 2017
revised 15 July 2017
accepted 01 August 2017
11 August 2017 (eFirst)
Five new flavones possessing a fully substituted A-ring with C-6 and C-8 methyl groups, bougainvinones I – M (1–5), along with three known congeners, 2′-hydroxydemethoxymatteucinol (6), 5,7,3′,4′-tetrahydroxy-3-methoxy-6,8-dimethylflavone (7) and 5,7,4′-trihydroxy-3-methoxy-6,8-dimethylflavone (8), were isolated from the EtOAc extract of the stem bark of Bougainvillea spectabilis. Their structures were established by means of spectroscopic data (ultraviolet, infrared, high-resolution electrospray ionization mass spectrometry, and one-dimensional and two-dimensional nuclear magnetic resonance) and single-crystal X-ray crystallographic analysis. The in vitro cytotoxicity of all isolated compounds against five cancer cell lines (KB, HeLa S-3, MCF-7, HT-29, and HepG2) was evaluated. Compound 5 showed promising cytotoxic activity against the KB and HeLa S-3 cell lines, with IC50 values of 7.44 and 6.68 µM. The other compounds exhibited moderate cytotoxicity against the KB cell line.