From Phenols to Antimicrobial Phenazines: Tyrosinase‐like Catalytic Activity of a Bisguanidine Based Bis(μ‐oxido) Complex

Abstract

The catalytically active center of the enzyme tyrosinase, standing out for its unusual substrate diversity, consists of a side‐on µ‐η²:η²‐peroxido complex (SP). Several ligand systems stabilizing a SP and able to mimic the catalytic activity of the enzyme towards simple phenolic substrates are known. Only a few catalytically active systems based on the isoelectronic isomer structure of SP, a bis(µ‐oxido)dicopper(III) complex (O), were investigated until now. Two years ago, we presented with the TMGbenza a hybrid guanidine based tyrosinase model system stabilizing an O species with an exceptional substrate diversity. Herein we studied the catalytic activity of another O species stabilized by the bisguanidine ligand TMG2tol. The reaction conditions for the catalytic oxygenation were optimized and a broad spectrum of phenolic substrates like naphthol, quinolinols and indolols was tested. Naturally occurring phenazine derivatives like phenazine‐1‐carboxylamide (PCN) and phenazine‐1‐carboxylic acid (PCA) show antifungal as well as antibacterial activity, functioning as biological control agents against crop disease like take‐all. Hence, the synthesized phenazines were evaluated for their potential antimicrobial activities against representative gram‐positive and gram‐negative bacteria.

Copper–oxygen adducts: new trends in characterization and properties towards C–H activation

“…[187][188][189] Alternatively, Herres-Pawlis and co-workers developed hybrid guanidine based ligands that led to the formation of dinuclear catalytic systems (Chart 1). [190][191][192] Their reactivities towards various natural and non-natural phenolic substrates in presence of molecular oxygen, yielded mono-and bicyclic quinones. Besides, chiral tyrosinase biomimetic model complexes for stereoselective oxidation was reviewed in 2018 by Casella and Monzani 193 and a new dinuclear chiral complex was described in 2019 194 by the same group.…”