Design and synthesis of 5-(substituted benzylidene)thiazolidine-2,4-dione derivatives as novel tyrosinase inhibitors.

In continuing our search for novel tyrosinase inhibitors, a series of 5-(substituted benzylidene)thiazolidine-2,4-diones were rationally designed and synthesized, and their inhibitory effects on mushroom tyrosinase activity were evaluated. Twelve target compounds 2a-2l were designed and synthesized based on the structural characteristics of N-phenylthiourea, a tyrosinase inhibitor, and tyrosine and L-DOPA, the natural substrates of tyrosinase. Among them, (Z)-5-(4-hydroxybenzylidene)thiazolidine-2,4-dione (2a) and (Z)-5-(3-hydroxy-4-methoxybenzylidene)thiazolidine-2,4-dione (2f) exhibited much higher tyrosinase inhibitory activities, with IC(50) values of 13.36 and 9.87 μM, respectively, than kojic acid (IC(50) = 24.72 μM). Kinetic analysis of tyrosinase inhibition revealed that 2a and 2f are competitive inhibitors of mushroom tyrosinase. In addition, through prediction of the potato catechol oxidase tertiary structure and simulation of docking with compounds 2a and 2f using DOCK6, we found that these inhibitors likely bind to the active site of the enzyme. Docking simulation results suggested that 2a and 2f have high binding affinities with potato catechol oxidase. In addition, compounds 2a and 2f effectively inhibited tyrosinase activity and reduced melanin levels in B16 cells treated with α-melanocyte-stimulating hormone (α-MSH). These data strongly suggest that compounds 2a and 2f suppress the production of melanin via the inhibition of tyrosinase activity.