Non-chelating 2-(arylthio)acetophenone derivatives as broad-spectrum tyrosinase inhibitors: Synthesis, in silico profiling, in vitro, and in vivo antimelanogenic efficacy

A series of 2-(arylthio)acetophenone (2-ATAP) derivatives ( 1 − 12 ) were designed and synthesized as novel tyrosinase inhibitors (TYRIs). Among them, five derivatives exhibited superior mushroom tyrosinase (mTYR) inhibitory activities compared to kojic acid, with derivative 5 demonstrating a potent nanomolar IC 50 value. Docking simulations and Cu 2+ chelation experiments revealed that the two aryl groups, connected via a 2-mercaptoacetyl moiety, effectively interact with amino acid residues within the mTYR active site to suppress enzymatic activity without requiring direct Cu 2+ chelation. Enzyme kinetic studies revealed that derivatives 1 , 5 , and 10 act as competitive inhibitors, whereas derivatives 6 and 9 function as mixed-type inhibitors. Furthermore, four derivatives, including derivative 5 , exhibited anti-melanogenic effects in B16F10 cells that were comparable to those of N -phenylthiourea (PTU), one of the most potent known TYRIs. This cellular anti-melanogenic efficacy was directly attributed to the suppression of intracellular TYR activity. In a phenotypic assay, three derivatives potently reduced pigmentation in zebrafish larvae (ZFL); notably, derivative 5 demonstrated a depigmenting efficacy that surpassed PTU, yielding nearly transparent larvae at 100 μM. Additionally, derivatives 5 and 7 showed strong anti-browning properties in potato juice. Overall, derivative 5 exhibited broad-spectrum anti-melanogenic and anti-TYR activities across various models (mTYR, B16F10 cells, potato, and ZFL), whereas derivative 7 displayed a highly species-specific effect, exclusively inhibiting browning in potato juice.