Depigmenting action and bioimaging of luminescent BODIPY-based piperazinyl phenol derivatives

Melanin biosynthesis is a complex enzymatic process regulated by tyrosinase (TYR, EC 1.14.18.1) that initiates the process catalyzing the conversion of L-tyrosine to L-DOPA and L-DOPA to dopaquinone. The two transformations occur on the same active site of the enzyme composed of six histidine residues that coordinate two copper ions. TYR has been recognized as one of the most popular therapeutic targets for controlling melanin synthesis. Herein we report the synthesis of BODIPY-based piperazinyl phenol derivatives, that were designed to develop luminescent probes for the detection of TYR activity; additionally, these molecules might contemporarily act as TYR inhibitors through the piperazinyl phenolic fragment. Molecular docking studies pointed out the ability of the new compounds to bind the active site of Agaricus bisporus mushroom tyrosinase (AbTYR). Mitochondrial cytotoxic assay revealed that all the synthesized compounds were not cytotoxic up to 50 μM concentration. Their inhibitory effects were tested against monophenolase and diphenolase activities of AbTYR; as results two of the three new compounds provided to be more active than the starting reagent 4-(piperazin-1-yl)phenol for monophenolase activity. The most active inhibitor (IC₅₀ value of 17.10 μM) was investigated through fluorescence spectroscopy and results corroborate the binding with AbTYR. Moreover, zebrafish embryos were used as a model organism for depigmentation studies and the introduction of fluorescent BODIPY moiety on the pharmacophoric fragment deeply improved its biocompatibility when compared to parent compounds and reflected its biodistribution.