Monosubstituted Acetophenone Thiosemicarbazones as Potent Inhibitors of Tyrosinase: Synthesis, Inhibitory Studies, and Molecular Docking

A set of 12 monosubstituted acetophenone thiosemicarbazone derivatives (TSCs) were synthesized and their inhibitory properties toward tyrosinase activity were tested. Moreover, their ability to inhibit melanogenesis in the B16F10 murine melanoma cell line was studied. In order to investigate the nature of interactions between the enzyme and the inhibitors, molecular docking to the active site was performed. TSCs 5, 6, 8, and 9 revealed a half maximal inhibitory concentration (IC(50)) below 1 µM. Compound 6 turned out to be the most potent tyrosinase inhibitor. All investigated compounds showed reversible inhibition of competitive or mixed type. The para-substituted TSCs had higher affinity for the enzyme as compared to their ortho- and meta-analogues. All investigated compounds inhibited melanin production in B16F10 cells at the micromolar level. Molecular docking showed that the sulfur atom of the thiourea moiety penetrates the active site and interacts with copper ions. The above outcomes might be helpful in the design of new tyrosinase inhibitors in the food and cosmetic industries.