| Summary: | Xanthine oxidase is a frontier enzyme to produce oxidants, which leads to inflammation in the blood. Prenylated isoflavones from <i>Flemingia philippinensis</i> were found to display potent inhibition against xanthine oxidase (XO). All isolates (<b>1</b>–<b>9</b>) inhibited XO enzyme with IC<sub>50</sub> ranging 7.8~36.4 μM. The most active isoflavones (<b>2</b>–<b>5</b>, IC<sub>50</sub> = 7.8~14.8 μM) have the structural feature of a catechol motif in B-ring. Inhibitory behaviors were disclosed as a mixed type I mode of inhibition with <i>K</i><sub>I</sub> < <i>K</i><sub>IS</sub>. Binding affinities to XO enzyme were evaluated. Fluorescence quenching effects agreed with inhibitory potencies (IC<sub>50</sub>s). The compounds (<b>2</b>–<b>5</b>) also showed potent anti-LDL oxidation effects in the thiobarbituric acid-reactive substances (TBARS) assay, the lag time of conjugated diene formation, relative electrophoretic mobility (REM), and fragmentation of apoB-100 on copper-mediated LDL oxidation. The compound <b>4</b> protected LDL oxidation with 0.7 μM in TBARS assay, which was 40-fold more active than genistein (IC<sub>50</sub> = 30.4 μM).
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