Efficient DNA Cleavage by Acridine Conjugates of Mono- and Dinuclear Cu(II) Complexes

Abstract

There have been reported suitably designed, simple monoand dinuclear metal complexes which are efficient in hydrolyzing phosphate esters including DNA. 1 We have previously reported the dinuclear Cu(II) 2 L1 complex (L1: 1,3-bis(1,4,7-triaza-1-cyclononyl)propane) efficiently hydrolyzed DNA, producing nicked and linearized DNA over the mononuclear CuL2 complex (L2: 1,4,7-triazacyclononane). 2 We were interested in nuclease activity of the Cu complexes having DNA binding groups since it would provide valuable information in developing sequence specific artificial nucleases. Several acridine conjugates of mononuclear Cu, Zn complexes had been reported, where strong binding through an intercalation of acridine moiety to DNA was the main factor for the nuclease activity, yet the cleavage mechanisms were not well established. In this study, we synthesized new acridine conjugates, L3 and L4 (Figure 1). Instead of using repeating alkyl chain as used in most of model studies, 3 polyethylene glycol unit was chosen for the linker since it allowed a significant increase in the length of the linker with relatively small change in the hydrophobicity of the molecule. 4 Determination of the association constants for the binding and the cleavage rate measurements would allow for a detailed dissection of the factors responsible for the rate enhancement in cleaving DNA by the acridine conjugates of the Cu complexes. Experimental SectionMaterials. Amberlyst 21 resin was purchased from Alpha. All other chemicals were from Aldrich and used without further purification. Supercoiled pCMV-Myc DNA was purchased from Clonetech. Labs (Mountain View, CA). Calf tymus-DNA was purchased from Sigma and dialyzed against water.Synthetic procedure. H and 13C NMR spectrum were obtained from VARIAN UNITY-INOVA 300 MHz spectrometer. Mass spectra were recorded on a Thermo Finnigan AQA Lc-Mass. The ligands, L3 and L4 were synthesized by modified literature methods.5 Cu(II) complexes of L1-L4 were prepared according to the known method by mixing ethanolic solution of the ligand and 1.0-2.0 equivalents of Cu(NO 3 ) 2 , respectively.