Unlocking Cu(I)-Mediated Catalytic Pathways for Efficient ROS Generation by Incorporating an Oxazole-Based Histidine Surrogate into Cu(II)-ATCUN Complexes

Abstract

The catalytic redox activity of Cu(II) bound to the amino-terminalcopper and nickel (ATCUN) binding motif (Xxx-Zzz-His, XZH) is stimulatingthe development of catalytic metallodrugs based on reactive oxygenspecies (ROS)-mediated biomolecule oxidation. However, low Cu(I) availabilityresulting from the strong Cu(II) binding affinity of the ATCUN motifis regarded as a limitation to efficient ROS generation. To addressthis, we replaced the imidazole moiety (pK (a) 7.0) of Gly-Gly-His-NH2 (GGHa, acanonical ATCUN peptide) with thiazole (pK (a) 2.7) and oxazole (pK (a) 0.8), yieldingGGThia and GGOxa, respectively. A newly synthesized amino acid, Fmoc-3-(4-oxazolyl)-l-alanine, served as a histidine surrogate featuring an azolering with the lowest pK (a) among known analogues.Despite similar square-planar Cu(II)-N-4 geometriesbeing observed for the three Cu(II)-ATCUN complexes by electronparamagnetic resonance spectroscopy and X-ray crystallography, theazole modification enabled the Cu(II)-ATCUN complexes to exhibitsignificant rate enhancement for ROS-mediated DNA cleavage. Furtheranalyses based on Cu(I)/Cu(II) binding affinities, electrochemicalmeasurements, density functional theory calculations, and X-ray absorptionspectroscopy indicated that the azole modification enhanced the accessibilityof the Cu(I) oxidation state during ROS generation. Our oxazole/thiazole-containingATCUN motifs provide a new design strategy for peptide ligands withmodulated N donor ability, with potential applications in the developmentof ROS-mediated metallodrugs. Substitutingthiazole and oxazole for the imidazole moietyin the amino-terminal copper and nickel binding motif (Xxx-Zzz-His)unlocks Cu(I)-mediated reactive oxygen species (ROS) generation andpromotes catalytic DNA cleavage reaction rates. Our study presentsa de novo design principle for peptide ligands in the developmentof catalytic metallodrugs.