Chemical Composition of Roots Flemingia philippinensis and Their Inhibitory Kinetics on Aromatase

Aromatase is the key enzyme responsible for catalyzing the conversion of C-19 steroids to estrogens. Its inhibitors are widely used in breast cancer therapy. The CH2Cl2 partition of a crude ethanolic extract from the roots of Flemingia philippinensis showed potent inhibitory activity of aromatase. The constituents of the extract were analyzed and identified by liquid chromatography tandem mass spectrometry. Five purified prenylated isoflavones were evaluated for aromatase inhibition and their IC50 values ranged between 2.98 and 58.08 m. In kinetic studies, all tested compounds behaved as reversible competitive inhibitors and their K-i values were calculated by Dixon plots. The most potent inhibitor (6,8-diprenylorobol) had a K-i value of 1.42 m. Furthermore, using UPLC and LC/MS, 6,8-diprenylorobol was proven to be present in the native roots in high quantities.