Antioxidative Compounds from <i>Garcinia buchananii</i> Stem Bark

Abstract

An aqueous ethanolic extract of the stem bark of <i>Garcinia buchananii</i> showed strong antioxidative activity using H₂O₂ scavenging, oxygen radical absorbance capacity (ORAC), and Trolox equivalent antioxidant capacity (TEAC) assays. Activity-guided fractionation afforded three new compounds, isomanniflavanone (<b>1</b>), an ent-eriodictyol-(3α→6)-dihydroquercetin-linked biflavanone, 1,5-dimethoxyajacareubin (<b>2</b>), and the depsidone garcinisidone-G (<b>3</b>), and six known compounds, (2″<i>R</i>,3″<i>R</i>)-preussianon, euxanthone, 2-isoprenyl-1,3,5,6-tetrahydroxyxanthone, jacareubin, isogarcinol, and garcinol. All compounds were described for the first time in <i>Garcinia buchananii.</i> The absolute configurations were determined by a combination of NMR, ECD spectroscopy, and polarimetry. These natural products showed high in vitro antioxidative power, especially isomanniflavanone, with an EC₅₀ value of 8.5 μM (H₂O₂ scavenging), 3.50/4.95 mmol TE/mmol (H/L-TEAC), and 7.54/14.56 mmol TE/mmol (H/L-ORAC)