Inhibitory Effect of Curcumin‐Inspired Derivatives on Tyrosinase Activity and Melanogenesis

: Tyrosinase is a well‐known copper‐containing metalloenzyme typically involved in the
synthesis of melanin. Recently, curcumin and several synthetic derivatives have been recognized as
tyrosinase inhibitors with interesting anti‐melanogenic therapeutic activity. In this study, three
curcumin‐inspired compounds 1, 6 and 7 were prepared in yields ranging from 60 to 88 % and
spectrophotometric, electrochemical, in vitro and in silico analyses were carried out. The viability
of PC12 cells, a rat pheochromocytoma derived‐cell line, with compounds 1, 6 and 7, showed values
around 80% at 5 μM concentration. In cell proliferation assays, compounds 1, 6 and 7 did not show
significant toxicity on fibroblasts nor melanoma cells up to 10 μM with viability values over 90%.
The inhibition of tyrosinase activity was evaluated both by a UV‐Vis spectroscopic method at two
different concentrations, 0.2 and 2.0 μM, and by amperometric assay with IC50 for compounds 1, 6
and 7 ranging from 11 to 24 nM. Melanin content assays on human melanoma cells were performed
to test the capability of compounds to inhibit melanin biosynthesis. All compounds exerted a
decrease in melanin content, with compound 7 being the most effective by showing a melanogenesis
inhibition up to four times greater than arbutin at 100 μM. Moreover, the antioxidant activity of the
selected inhibitors was evaluated against H2O2 in amperometric experiments, whereby compound
7 was about three times more effective compared to compounds 1 and 6. The tyrosinase X‐ray
structure of Bacterium megaterium crystal was used to carry out molecular docking studies in the
presence of compounds 1, 6 and 7 in comparison with that of kojic acid and arbutin, two
conventional tyrosinase inhibitors. Molecular docking of compounds 6 and 7 confirmed the high
affinity of these compounds to tyrosinase protein