Synthesis, X-ray structure and cytotoxicity evaluation of carbene-based gold(I) complexes of selenones

Gold(I)-carbene complexes containing a selenone ligand (L), [Au(IPr)(L)]PF₆ {where, IPr = 1,3-Bis(2,6-di-isopropylphenyl)imidazol-2-ylidene and L = N-i-propyl-1,3-imidazolidine-2-selenone, i-PrImSe (1), 1,3-diazinane-2-selenone, DiazSe (2), N-methyl-1,3-diazinane-2-selenone, MeDiazSe (3), 5-hydroxy-1,3-diazinane-2-selenone, HO-DiazSe (4) and 1,3-diazepane-2-selenone, DiapSe (5)} were synthesized using [Au(IPr)Cl] (0) and selenones. The complexes (1–5) were characterized by elemental analysis, IR and NMR (¹H, ¹³C & ⁷⁷Se) spectroscopy. The crystal structure of complex 1 was determined by single crystal X-ray diffraction technique and the analysis reveals that the complex exhibits a distorted linear geometry around gold(I) atom. In vitro cytotoxic assays of the complexes were performed on three human cancer cell lines; HCT15 (colon cancer), A549 (lung cancer) and MCF7 (breast adenocarcinoma). Complexes 1 and 3 exhibited greater activities against HCT15 cells compared to the other complexes (2, 4 and 5). All complexes exhibited moderate to high IC₅₀ values (less active) against A549 and MCF7 cell lines with respect to cisplatin. Molecular docking studies showed the potential inhibitory capacity of the gold complexes towards DNA topoisomerase 1 with complex 1 having the highest binding affinity with a score of −38.68. The distance between the gold atom in the complex and the oxygen atom of the carbonyl group of thymine was measured for all complexes. Complex 4 had the shortest bond distance of 3.64 Å while complex 5 had the longest one of 6.89 Å.