Anti-tyrosinase and antioxidant activity of meroterpene bakuchiol from Psoralea corylifolia (L.)

Bakuchiol is gaining major interest for treatments against skin photoaging. The kinetics of mushroom tyrosinase inhibition by bakuchiol, by real-time oxygen sensing and UV-vis monitoring (475 nm), showed competitive inhibition with average Ki constant (µM, 30 °C, pH 6.8) of 6.71 ± 1.23 and 1.15 ± 0.34 for monophenolase and diphenolase reactions respectively, with respective IC50 37.22 ± 5.18 and 6.91 ± 0.96 ∼ at 1 mM substrate, compared to kojic acid IC50 34.02 ± 5.51 and 16.86 ± 3.28 μM. Fluorescence quenching showed a single binding mode with formation constant Ka 1.02 × 106 M-1. The antioxidant activity was studied by inhibited autoxidation of styrene and cumene (PhCl, 30 °C) affording inhibition constant kinh = 18.1 ± 6.6 (104M-1s-1, 30 °C) and of MeLin in Triton™ X-100 micelles giving kinh = 0.16 ± 0.03 (104M-1s-1, 37 °C). Stoichiometric factor was 1.9 ± 0.1. ReqEPR spectroscopy afforded the BDE(OH) as 81.7 ± 0.1 kcal/mol. Bakuchiol is a potent tyrosinase inhibitor with good antioxidant activity having major potential as natural food preservative against oxidation and food-browning.