Cu(II) Complexes with Heterocyclic Substituted Thiosemicarbazones:  The Case of 5-Formyluracil. Synthesis, Characterization, X-ray Structures, DNA Interaction Studies, and Biological Activity

Two new 5-formyluracil thiosemicarbazone (H₃ut) derivatives, Me-H₃ut (1) and Me₂-H₃ut (2), were synthesized by reacting thiosemicarbazides, mono- and dimethylated on the aminic nitrogen, with 5-formyluracil and were subsequently characterized. These ligands, treated with copper chloride and nitrate, afforded three complexes:  [Cu(Me-H₃ut)Cl₂]·H₂O (3), [Cu(Me₂-H₃ut)Cl₂]·H₂O (4), and [Cu(Me-H₃ut)(NO₃)(OH₂)₂]NO₃ (5). The crystal structures of these complexes have been determined by single-crystal X-ray diffraction. In 3 and 4, a similar pentacoordination is present; the copper atom is surrounded by the ligand SNO donor atoms and by two chloride ions. The structure of 5 consists of [Cu(Me-H₃ut)(NO₃)(OH₂)₂]⁺ cations and nitrate anions. The copper coordination (4 + 2) involves the SNO ligand atoms and a water oxygen in the basal plane; the apical positions are occupied by a second water oxygen and by an oxygen of a monodentate nitrate group. Two biochemical techniques, namely DNA titration in the UV−vis region and thermal denaturation, have been employed to probe the details of DNA binding of these compounds. Analysis of the results suggests that our compounds are able to interact with DNA by electrostatic and groove binding but not by intercalation. The compounds have been also tested in vitro on human leukemic cell line U937, but they are not able to inhibit significantly cell proliferation.