Design, Preparation, and Characterization of Zn and Cu Metallopeptides Based On Tetradentate Aminopyridine Ligands Showing Enhanced DNA Cleavage Activity

Abstract

The conjugation of redox-active complexes that can function as chemical nucleases to cationic tetrapeptides is pursued in this work in order to explore the expected synergistic effect between these two elements in DNA oxidative cleavage. Coordination complexes of biologically relevant first row metal ions, such as Zn(II) or Cu(II), containing the tetradentate ligands 1,4-dimethyl-7-(2-pyridylmethyl)-1,4,7-triazacyclononane ((Me2)PyTACN) and (2S,2S')-1,1'-bis(pyrid-2-ylmethyl)-2,2'-bipyrrolidine ((S,S')-BPBP) have been linked to a cationic LKKL tetrapeptide sequence. Solid-phase synthesis of the peptide-tetradentate ligand conjugates has been developed, and the preparation and characterization of the corresponding metallotetrapeptides is described. The DNA cleavage activity of Cu and Zn metallopeptides has been evaluated and compared to their metal binding conjugates as well as to the parent complexes and ligands. Very interestingly, the oxidative Cu metallopeptides 1Cu and 2Cu show an enhanced activity compared to the parent complexes, [Cu(PyTACN)](2+) and [Cu(BPBP)](2+), respectively. Under optimized conditions, 1Cu displays an apparent pseudo first-order rate constant (kobs) of ∼0.16 min(-1) with a supercoiled DNA half-life time (t1/2) of ∼4.3 min. On the other hand, kobs for 2Cu has been found to be ∼0.11 min(-1) with t1/2 ≈ 6.4 min. Hence, these results point out that the DNA cleavage activities promoted by the metallopeptides 1Cu and 2Cu render ∼4-fold and ∼23 rate accelerations in comparison with their parent Cu complexes. Additional binding assays and mechanistic studies demonstrate that the enhanced cleavage activities are explained by the presence of the cationic LKKL tetrapeptide sequence, which induces an improved binding affinity to the DNA, thus bringing the metal ion, which is responsible for cleavage, in close proximity.

Efficient Artificial Nucleases for Mediating DNA Cleavage Based on Tuning the Steric Effect in the Pyridyl Derivatives of Tripod Tetraamine‐Cobalt(II) Complexes

“…Many mononuclear Cu II , Co II , Zn II and Fe II complexes which were derived from a wide range of ligands of varied skeletal structures and geometrical environments have been extensively used as catalysts for DNA cleavage . Model systems incorporating multi‐nuclear 3d metal(II) complexes and sometimes hetero‐dinuclear metal ions were also employed , .…”

“…The rate enhancement observed in these reactions and in the hydrolysis of simple phosphodiester compounds, which were used to mimic the P–O bond situation in DNA, were attributed to the formation of double Lewis structures and the synergistic effect between the two metal ions , . Inspection of literature data for the DNA cleavage under physiological conditions revealed that some mononuclear Cu II and Co II complexes could enhance the rate of DNA cleavage by a factor of 10–100 million when compared to the non‐catalyzed reaction , , , …”

Octa‐1,7‐diene‐4,5‐diamine Derivatives: Useful Intermediates for the Stereoselective Synthesis of Nitrogen Heterocycles and Ligands for Asymmetric Catalysis

“…Epoxidation of alkenes was also possible with the same catalyst mixture. Finally, copper and zinc complexes of 57 showed DNA‐cleavage activity …”

Peptide-mediated vectorization of metal complexes: conjugation strategies and biomedical applications

“…Recently, it has been reported the synthesis of Zn(II) and Cu(II) metallopeptides based on PyTACN and (S,S')-BPBP tetradentate aminopyridine ligands in the context of ROS generation in cancer therapies (Figure 1d). 37 The preparation of these metallopeptides relied on the solid-phase synthesis of the corresponding metal binding peptide, subsequent cleavage from the solid support and metallation with a Zn(II) or Cu(II) salt. These two metal binding peptides were obtained following two different approaches.…”