Antioxidant and free radical scavenging activity of phenolics from Bidens humilis

A bio-assay oriented approach led to the isolation of eleven compounds, including three new natural flavonoids, (2S)-isookanin 7-O-α-L-arabinopyranoside (1), (2S)-isookanin 7-O-(2''-acetyl)-α-L-arabinopyranoside (2), and luteolin 7-O-β-D-glucopyranosyl-(1→6)-β-D-galactopyranoside (6), from Bidens humilis aerial parts. Their structures were determined via spectroscopic analyses including 2D NMR. The antioxidant activity of all compounds was also tested by three different assays. The Relative Antioxidant Capacity Index (RACI) is applied herein, from the perspective of statistics, by integrating the antioxidant capacity data determined by these chemical methods.