Inhibition of tyrosinase activity by polyphenol compounds from Flemingia philippinensis roots.

Abstract: Flemingia philippinensis is used as a foodstuff or medicinal plant in the tropical regions of China. The methanol (95%) extract of the roots of this plant showed potent tyrosinase inhibition (80% inhibition at 30μg/ml). Activity-guided isolation yielded six polyphenols that inhibited both the monophenolase (IC50 =1.01–18.4μM) and diphenolase (IC50 =5.22–84.1μM) actions of tyrosinase. Compounds 1–6 emerged to be three new polyphenols and three known flavanones, flemichin D, lupinifolin and khonklonginol H. The new compounds (1–3) were identified as dihydrochalcones which we named fleminchalcones (A–C), respectively. The most potent inhibitor, dihydrochalcone (3) showed significant inhibitions against both the monophenolase (IC50 =1.28μM) and diphenolase (IC50 =5.22μM) activities of tyrosinase. Flavanone (4) possessing a resorcinol group also inhibited monophenolase (IC50 =1.79μM) and diphenolase (IC50 =7.48μM) significantly. In kinetic studies, all isolated compounds behaved as competitive inhibitors. Fleminchalcone A was found to have simple reversible slow-binding inhibition against monophenolase. [Copyright &y& Elsevier]