Synthesis, Characterization, and Preliminary In Vitro Anticancer Activity of Zinc Complexes Containing Amino Acid-Derived Imidazolium-Based Dicarboxylate Ligands

Coordination polymers containing zinc and imidazolium-based dicarboxylate ligands, [L^R]^-, were synthesized by reacting zinc acetate with HL^R compounds, <b>1</b>. The resulting complexes were characterized and structurally identified using single-crystal X-ray diffraction, revealing polymeric structures for the complexes [Zn(L^R)₂]_n (R = Gly, <b>2a</b>; βAla, <b>2b</b>) and [Zn(L^Leu)₂(H₂O)₂]_n (<b>2c</b>). In these structures, the [L^R]^- ligands adopt a bridging monodentate μ-κ¹-O¹,κ¹-O³ coordination mode, resulting in distorted tetrahedral (<b>2a</b>, <b>2b</b>) or octahedral (<b>2c</b>) geometries around the zinc center. When the synthesis was carried out in the presence of amino acids, mixed ligand complexes [Zn(L^R)(aa)(H₂O)]_n (R = aa = Val, <b>2d</b>, and R = aa = Ile, <b>2e</b>) were formed. Complexes <b>2d</b>-<b>2e</b> were also structurally characterized using single-crystal X-ray crystallography, revealing that the ligand [L^R]^- maintained the same coordination mode, while the zinc center adopted a five-coordinated geometry. The cytotoxic activity of complexes <b>2a</b>-<b>2e</b> was evaluated against three cancer cell lines and one non-cancerous cell line. Remarkably, these complexes exhibited higher toxicity against cancer cells than against the non-cancerous cell line, and they showed greater selectivity than carboplatin, a commonly used chemotherapy drug. Although, in general, these complexes did not surpass the selectivity of gemcitabine, complex <b>2c</b> stood out for exhibiting a selectivity index value similar to that of gemcitabine against melanoma cells. Among the series, compounds <b>2a</b>-<b>2c</b> demonstrated the highest activity, with <b>2a</b> being the only complex with some selective activity against lung cancer. Complex <b>2b</b> was the most active, though with low selectivity, while complex <b>2c</b> exhibited the highest selectivity for melanoma and bladder cancer (selectivity index of 3.0).