Synthesis and characterization of triruthenium carbonyl incorporating 4-pyridones as potential antitumor agents

Four new organometallic triruthenium carbonyl incorporating 4-pyridones: [Ru₃(CO)₈(2L-2H)] (1, L = N-benzyl-3-hydroxy-2-methyl-4-pyridone; 2, L = 3-hydroxy-2-methyl-N-phenyl-4-pyridone; 3, L = 3-hydroxy-N,2-dimethyl-4-pyridone; 4, L = 2-methyl-4-pyridone) were synthesized and characterized. Proton NMR spectrum of 1 shows doublets for the two-nonequivalent benzylic hydrogens due to restricted rotation around C-N bond upon bonding to Ru(2)—Ru(3) as opposed to a singlet in the unbound N-benzyl-3-hydroxy-2-methyl-4-pyridone. Compounds 1 and 3 were characterized by X-ray diffraction analyses. Compounds 1 and 3 consists of two ruthenium-ruthenium bonds Ru(1)-Ru(2), Ru(1)-Ru(3) and a non-bonded separation of two ruthenium atoms defined by Ru(2) … Ru(3), which is bridged by two 3 electron donar oxygen atoms through two-pyridinonato ligands above and below triruthenium plane, and 8 terminal CO groups. Atoms Ru(2) and Ru(3) ligated by two CO ligands each and Ru(1) with four. Antitumor activity of the compounds 1–4 has been evaluated against five types of human cancer cell lines. Compounds 1 and 2 show excellent antitumor activity due to lipophilic nature of N-substituted arene pyridinonato ligands than compounds 3 and 4. Structure-activity studies show that there is a correlation between the N-substituted arene pyridinonato ligands and an increase in activity following the order 1 > 2>3 > 4. The anticancer activity of compounds 1 and 2 is between 1–2 orders of magnitude more active than cisplatin. This is possibly due to substitution of CO ligands at Ru(1) by transferrin delivery vehicle transporting to cancer cells and lipophilic N-substituted arenes diffuse through lipophic membrane leading to apoptosis and other carbonyl groups under physiological conditions likely function as carbonyl releasing molecules (CORMs).