Development of coumarin-3-thiosemicarbazones and coumarin-3-oximes as potent inhibitors of mushroom tyrosinase/tyrosine hydroxylase.

Tyrosinase is a copper-dependent oxidase that catalyzes the rate-limiting steps of melanogenesis, directly linking its overexpression to hyperpigmentation disorders and melanoma progression. Previously our researcher team found that a coumarin-thiosemicarbazone analog exhibited potent anti-tyrosinase activity (IC50 = 42.16 ± 5.16 μM). Herein, as part of our efforts in this field of study, we report the synthesis and biological evaluation of a new series of coumarin derivatives functionalized with thiosemicarbazone and/or oxime moieties as potent tyrosinase inhibitors. The most active compound, B5, exhibited an IC₅₀ value of 21.91 ± 0.26 μM, showing 3.3- and 17.6-fold higher inhibitory potency than kojic and ascorbic acids, respectively. Kinetic studies revealed a mixed inhibition pattern, suggesting multiple enzyme-inhibitor interactions. In silico 100-ns molecular dynamics simulations against Agaricus bisporus tyrosinase (PDB ID: 2Y9X) confirmed the structural stability of the B5-tyrosinase complex, with a mean RMSD of 1.85 Å for the enzyme and 0.3 Å for the ligand. The thiosemicarbazone moiety played a pivotal role in complex stabilization through hydrogen bonding and coordination with catalytic Cu2+ ions, while hydrophobic and π-stacking contacts contributed to binding persistence. Altogether, these findings highlight compound B5 as a promising lead compound for developing next-generation tyrosinase inhibitors with potential dermatological and photoprotective applications.