Securidacaxanthone D: a new xanthone with free radical scavenging activity from the roots of <i>Securidaca longepedunculata</i> (Polygalaceae)

A previously unpublished xanthone named securidacaxanthone D (<b>1</b>) and five known analogues: 1,7-dihydroxyxanthone (<b>2</b>), 7-hydroxy-1,2-dimethoxy-xanthone (<b>3</b>), 1,5-dihydroxy-6,7-dimethoxyxanthone (<b>4</b>), 1,7-dihydroxy-3-methoxyxanthone (<b>5</b>), 1,7-dihydroxy-4-methxyxanthone (<b>6</b>) were isolated from the ethyl acetate soluble fraction obtained from the liquid-liquid partition of the crude hydro-ethanolic extract of the roots of <i>Securidaca longipedunculata</i>. Their structures were determined by analysis of 1D -(¹H and ¹³C), 2D-(COSY, HSQC and HMBC) NMR data in conjunction with mass spectrometry (TOF-ESI-MS) and by comparison with reported data. Free radical scavenging activity were evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) as a free radical. Crude extract, ethyl acetate and <i>n</i>-butanol fractions as well as isolated compounds showed different degrees of free radical scavenging activity. Among the extract and fractions tested, the hydro-ethanolic extract was the most active with an IC₅₀ value of 32 μg/mL. Among the compounds, compound <b>2</b> was the most active with an IC₅₀ value of 282 μg/mL.