Synthesis and Biological Evaluation of the Thionated Antibacterial Agent Nalidixic Acid and Its Organoruthenium(II) Complex

The thionated derivative of the antibacterial agent nalidixic acid and its organoruthenium complex were prepared, and their crystal structures were determined. The aqueous stability of the complex was studied and, unlike the case for the nalidixicato complex, increased stability of the ruthenium complex in aqueous solution was observed with only a minor degree of thionalidixicato ligand dissociated within 1 week. While the derivatization caused the antibacterial activity of the ligand against E. coli to decrease, the cytotoxicity of the complex against three cancer cell lines was significantly increased and the inhibitory potency against two enzymes of the cathepsin family was increased by 10-fold.