Synthesis, Anti-Tyrosinase Activity, and Spectroscopic Inhibition Mechanism of Cinnamic Acid–Eugenol Esters

Tyrosinase plays crucial roles in mediating the production of melanin pigment; thus, its inhibitors could be useful in preventing melanin-related diseases. To find potential tyrosinase inhibitors, a series of cinnamic acid–eugenol esters (c1~c29) was synthesized and their chemical structures were confirmed by (1)H NMR, (13)C NMR, HRMS, and FT-IR, respectively. The biological evaluation results showed that all compounds c1~c29 exhibited definite tyrosinase inhibitory activity; especially, compound c27 was the strongest tyrosinase inhibitor (IC(50): 3.07 ± 0.26 μM), being ~4.6-fold stronger than the positive control, kojic acid (IC(50): 14.15 ± 0.46 μM). Inhibition kinetic studies validated compound c27 as a reversible mixed-type inhibitor against tyrosinase. Three-dimensional fluorescence and circular dichroism (CD) spectra results indicated that compound c27 could change the conformation and secondary structure of tyrosinase. Fluorescence-quenching results showed that compound c27 quenched tyrosinase fluorescence in the static manner with one binding site. Molecular docking results also revealed the binding interactions between compound c27 and tyrosinase. Therefore, cinnamic acid–eugenol esters, especially c27, could be used as lead compounds to find potential tyrosinase inhibitors.