Highly potent tyrosinase inhibitor, neorauflavane from Campylotropis hirtella and inhibitory mechanism with molecular docking

Tyrosinase inhibition may be a means to alleviate not only skin hyperpigmentation but also neurodegeneration associated with Parkinson's disease. In the course of metabolite analysis from tyrosinase inhibitory methanol extract (80% inhibition at 20 mu g/ml) of Campylotropis hirtella, we isolated fourteen phenolic compounds, among which neorauflavane 3 emerged as a lead structure for tyrosinase inhibition. Neorauflavane 3 inhibited tyrosinase monophenolase activity with an IC50 of 30 nM. Thus this compound is 400-fold more active than kojic acid. It also inhibited diphenolase (IC50 = 500 nM), significantly. Another potent inhibitor 1 (IC50 = 2.9 mu M) was found to be the most abundant metabolite in C. hirtella. In kinetic studies, compounds 3 showed competitive inhibitory behavior against both monophenolase and diphenolase. It manifested simple reversible slow-binding inhibition against monophenolase with the following kinetic parameters: K-i(app) = 1.48 nM, k(3) = 0.0033 nM (1) min (1) and k(4) = 0.0049 min (1). Neorauflavane 3 efficiently reduced melanin content in B16 melanoma cells with 12.95 mu M of IC50. To develop a pharmacophore model, we explored the binding mode of neuroflavane 3 in the active site of tyrosinase. Docking results show that resorcinol motif of B-ring and methoxy group in A-ring play crucial roles in the binding the enzyme. (C) 2015 Elsevier Ltd. All rights reserved.