Chem. Pharm. Bull. 54(8) 1150—1154 (2006)

DNA is the primary intracellular target of anticancer drugs due to the interaction between small molecules and DNA, which cause DNA damage in cancer cells, blocking the division of cancer cells and resulting in cell death. Of these studies, the interaction of transition metal complexes containing multidentate aromatic ligands, with DNA has gained much attention. This is due to their possible application as new therapeutic agents and their photochemical properties which make them potential probes of DNA structure and conformation. The design of small complexes that bind and react at specific sequences of DNA becomes important. A more complete understanding of how to target DNA sites with specificity will lead not only to novel chemotherapeutics but also to a greatly expand ability for chemists to probe DNA and to develop highly sensitive diagnostic agents. Transition–metal complexes are being used at the forefront of many of these efforts. Stable, inert complexes containing spectroscopically active metal centers are extremely valuable as probes of biological systems. As both spectroscopic tags and functional models for the active centers of proteins, metal complexes have helped elucidate the mechanisms by which metalloproteins function. In order to develop new antitumor drugs which specifically target DNA, it is necessary to understand the different binding modes a complex is capable of undertaking. Basically, metal complexes interact with the double helix DNA in either a non-covalent or a covalent way. The former way includes three binding modes: intercalation, groove binding and external static electronic effects. Among these interactions, intercalation is one of the most important DNA binding modes as it invariably leads to cellular degradation. It was reported that the intercalating ability increases with the planarity of ligands. Additionally, the coordination geometry and ligand donor atom type also play key roles in determining the binding extent of complexes to DNA. The metal ion type and its valence, which are responsible for the geometry of complexes, also affect the intercalating ability of metal complexes to DNA. Amide-based open-chain crown ethers offer many advantages in extraction and analysis of the rare earth ions because of their ring-like coordination structure and terminal group effects. A series of multi-functional ligands having selective ability to coordinate lanthanides ions have been designed. People reported the novel luminescence properties of these lanthanide complexes. However, up to now, the interactions with DNA of the lanthanide complexes are not reported by any references. This aroused our interest in the synthesis a ligand, 2,2 -[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)) (L) (Chart 1) and its gadolinium(III) nitrate complex with a view to evaluating the binding behaviors of it with CT-DNA.