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

Abstract

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 K_i 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 K_a 1.02 × 10⁶ M^-1. The antioxidant activity was studied by inhibited autoxidation of styrene and cumene (PhCl, 30 °C) affording inhibition constant k_inh = 18.1 ± 6.6 (10⁴M^-1s^-1, 30 °C) and of MeLin in Triton™ X-100 micelles giving k_inh = 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.

Keywords: (S)-Bakuchiol, CAS 10309‐37‐2 (PubChem CID: 5468522); Antioxidant; Bakuchiol; Food browning; Kojic acid, CAS: 501-30-4 (PubChem CID: 3840); Melanin; Mushroom Tyrosinase (EC 1.14.18.1), CAS: 9002-10-2; O-methylbakuchiol, CAS 10309-44-1 (PubChem CID: 14610678); Peroxyl radicals; Skin-whitening.