Coumarin-N-acylhydrazone ligands and their Ru(II) complexes: Structure, characterization and antimicrobial activity

Metal-based drugs play an important part in the history of medicinal chemistry. Ruthenium complexes as well as coumarins and hydrazone derivatives have been studied and demonstrated significant biological activities[1,2], including antimicrobial, which has motivated this work. The synthetic methodology of the ligands and complexes is show in the scheme below. The compounds were characterized by IR, UV-Vis, 1H NMR and cyclic voltammetry and the data obtained are in accordance with similar compounds described in the literature[1,2,3]. The compounds HL2, HL4, C2 and C3 presented suitable crystals for X-ray diffraction analyses. The RuII ion is in a distorted octahedral environment, equatorially coordinated by an ON chelate of the hydrazone ligand and two sulfur atoms of the DMSO ligands at cis positions. A pair of chlorine atoms at the axial positions completes the coordination sphere. The molecular structures are show in figure 1. The compounds were studied against 11 certified strains. The ligands and the metal precursor were not active against the bacteria tested at 200 mM. On the other hand, the complexes exhibited inhibition against gram-positive species with a MIC around 100 μM for C3 and C4.