Binding and Stabilization of a Semiquinone Radical by an Artificial Metalloenzyme Containing a Binuclear Copper (II) Cofactor.

A binuclear Cu(II) cofactor was covalently bound to a lauric acid anchor. The resulting conjugate was characterized then combined with beta-lactoglobulin (ßLG) to generate a new biohybrid following the so-called "Trojan horse" strategy. This biohybrid was examined for its effectiveness in the oxidation of a catechol derivative to the corresponding quinone. The resulting biohybrid did not exhibit the sought after catecholase activity, likely due to its ability to bind and stabilize the semiquinone radical intermediate DTB-SQ. This semi-quinone radical was stabilized only in the presence of the protein and was characterized using optical and magnetic spectroscopic techniques, demonstrating stability for over 16 hours. Molecular docking studies revealed that this stabilization could occur owing to interactions of the semi-quinone with hydrophobic amino acid residues of ßLG.

Design and synthesis of 4-amino-2',4'-dihydroxyindanone derivatives as potent inhibitors of tyrosinase and melanin biosynthesis in human melanoma cells.

Melanogenesis inhibition constitutes a privileged therapeutic solution to treat skin hyperpigmentation, a major dermatological concern associated with the overproduction of melanin by human tyrosinase (hsTYR). Despite the existence of many well-known TYR (tyrosinase) inhibitors commercialized in skin formulations, their hsTYR-inhibition efficacy remains poor since most of them were investigated over mushroom tyrosinase (abTYR), a model with low homology relative to hsTYR. Considering the need for new potent hsTYR inhibitors, we designed and synthesized a series of indanones starting from 4-hydroxy compound 1a, one of the two most active derivatives reported to date against the human enzyme, together with marketed thiamidol. We observed that analogues featuring 4-amino and 4-amido-2',4'-dihydroxyindanone motifs showed two-to ten-fold increase in activity over human melanoma MNT-1 cell lysates, and a ten-fold improvement in a 4-days whole-cell experiment, compared to parent analogue 1a. Molecular docking investigation was performed for the most promising 4-amido derivatives and suggested a plausible interaction pattern with the second coordination sphere of hsTYR, notably through hydrogen bonding with Glu203, confirming their impact in the binding mode with hsTYR active site.