Synthesis, DNA-binding And Antiproliferative Activity Of N-(Nitrogen Heterocyclic) Norcantharidin Acylamide Acid And Their Rare Earth Complex

Cantharidin (cantliaridin, CA) is the dried body of the Chinese Mylabris phalerata Pall, and M. cichorII Linn. Cantharidin which isused as a traditional medicine in China can be traced back more than 2000 years. In recent studies, it has been found that cantharidin possesses anticancer properties, increases the number of leucocytes, and has irritant effects on the urinary organs. But the renal toxicity of this drug has prevented it from useing in mainstream oncology. Therefore, design and synthesis of a number of cantharidin derivatives of selective inhibition to tumor cells, but small toxicity and less effect on the immune response is of great significance. Norcantharidin (NCTD), the demethylated analogue of cantharidin, also possesses anticancer activity and stimulates the bone marrow, but its nephrotoxicity weakens significantly. Many derivatives of cantharidin and norcantharidin have been synthesized and some of them have good anti-tumor activity in vitro. The research about the rare earth ions and their complexes as artificial enzymes has attracted more and more attention because they can break the phosphodiesters bonds of nucleic acids through hydrolysis with high efficiency. So we have designed and synthesized of series of rare earth complexes of N-(Nitrogen heterocyclic) norcantharidin acylamide acid and the complexes of norcantharidin acid with 1, 10-phenanthroline (phen). We also have studied the interaction between Calf ThymusDNA (ct-DNA) and the antiproliferative activity of the compounds.We synthesized three novel N-pyrimidine norcantharidin acylamide acid (HL¹), N-pyridine norcantharidin acylamide acid (HL²) and N-phenyl norcantharidin acylamide acid (HL³). Their structures were characterized by elemental analysis, IR, UV and ¹HNMR. The interaction between the compounds and DNA was studied by means of fluorescence spectra, viscometric titration and agarose gel electrophoresis. The results showed that the compounds could bind calf thymus DNA via partial intercalation. The binding ability followed the trend from high to low: HL¹, HL² and HL³. This result demonstrates that the increased nitrogen atoms of heterocycle could form more hydrogen bonds with base pairs of DNA, which facilitates intercalation of compounds to DNA. The test of antiproliferation activity showed that the compounds had moderate to strong antiproliferative ability against the tested cell lines except of HL3 against the SMMC7721 cell line. The results indicated that the heterocycle attached to the norcantharidin was favorable to antiproliferative activity. This result was consistent with the DNA binding experiment.Then we synthesized the rare earth complexes [RE(L¹)(NO₃)(H₂O)₂]NO₃·2H₂O (RE=Y, Nd, Sm, Eu, Gd, Dy, Er); [RE(L²)(NO₃)(H₂O)₂]NO₃·2H₂O(RE=La, Nd, Gd, Dy, Er, Yb) and [RE(L³)(NO₃)(H₂O)₂]NO₃·2H₂O(RE=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb). Their chemical compositions were confirmed by elemental analysis, IR spectra, conductivity measurement and thermal analysis. The interaction between the three series complexes and DNA was studied by means of fluorescence spectra, viscometric titration and agarose gel electrophoresis. The results showed that some complexes can bind to DNA strongly. Series of complexes can bind to DNA probably by inserting their HL molecule to the base pairs of DNA. The results are probably attributed to the extension of theÏ€system of the intercalated ligand due to the coordination of RE(â…¢), which also leads to a greater planar area than that of the free ligand, which leads to the coordinated ligand penetrating more deeply into, and stacking more strongly with the base pairs of the DNA. The antiproliferative activities of the compounds toward human hepatoma cells SMMC7721 and human lung cancer cells A549 in vitro were also evaluated with MTT cell viability assay and some complexes have strong activity.Three rare earth complexes of norcantharidin acid with 1, 10-phenanthroline (phen) were synthesized and characterized via elemental analysis, molar conductance, IR and TG-DTG. The results confirmed their chemical composition was [RE₂(NCTD)₂ (phen)₂](NO₃)₂·6H₂O(RE=Sm, Er, Yb). The interaction of the complexes with DNA was studied by means of UV-visible spectra, fluorescence spectra, viscometric titration and agarose gel electrophoresis. The results indicate that the complexes bind DNA via nonclassical intercalation. The complexes have been found to cleave pBR322 plasmid DNA at physiological pH and temperature.