Transition metal complexes with the quinolone antibacterial agent pipemidic acid: Synthesis, characterization and biological activity

Nine new mononuclear metal complexes of the quinolone antibacterial agent pipemidic acid (= HPPA) with VO2+, Mn2+, Fe3+, Co2+, Ni2+, Zn2+, MoO22+, Cd2+ and UO22+ have been prepared and characterized with physicochemical and spectroscopic techniques. In all the complexes, pipemidic acid acts as a bidentate deprotonated ligand bound to the metal through the pyridone oxygen atom and one carboxylate oxygen atom. All the complexes are six-coordinate and the geometry round the metal atom can be described as a slightly distorted octahedron. For VO(PPA)(2)(H2O), the axial position, trans to the vanadyl oxygen, is occupied by one pyridone oxygen atom. Molecular mechanics calculations in the gas state have been performed in order to propose a model for the structure of the Fe3+, VO2+ and MoO22+ complexes. The antimicrobial activity of the complexes has been tested on three different microorganisms. The investigation with diverse spectroscopic techniques of the interaction of the complexes with calf-thymus DNA has shown that the complexes can be bound to DNA resulting in a B -> A DNA transition. (c) 2006 Elsevier Ltd. All rights reserved.