Derivatization of the Peptidic Xxx-Zzz-His Motif toward a Ligand with Attomolar Cu II Affinity under Maintaining High Selectivity and Fast Redox Silencing.

Cu chelation in biological systems is of interest as a tool to study the metabolism of this essential metal or for applications in the case of diseases with a systemic or local Cu overload, such as Wilson's or Alzheimer's disease. The choice of the chelating agent must meet several criteria. Among others, affinities and kinetics of metal binding and related metal selectivity are important parameters of the chelators to consider. Here, we report on the synthesis and characterization of Cu-binding properties of two ligands, L1 and L2, derivatives of the well-known peptidic Cu II -binding motif Xxx-Zzz-His (also called ATCUN), where Cu II is bound to the N-terminal amine, two amidates, and the imidazole. In either L, the N-terminal amine was replaced with a pyridine, and for L2, one amide was replaced with an amine compared to Xxx-Zzz-His. In particular, L2 showed several interesting features, including a Cu II -binding affinity with a log  K D app = -16.0 similar to that of EDTA and stronger than all reported ATCUN peptides. L2 showed high selectivity for Cu II over Zn II and other essential metal ions, even under the challenging conditions of the presence of human serum albumin. Further, L2 showed fast and efficient Cu II redox silencing qualities and Cu II -L2 was stable in the presence of mM GSH concentrations. Benefitting the fact that L2 can be easily elongated on its peptide part by standard SPPS to add other functions, L2 has attractive properties as a Cu II chelator for application in biological systems.