Anticancer activity of osmium metalla-rectangles

A series of cationic metalla-rectangles of the general formula [(<i>p</i>-cymene)₄Os₄(<i>O</i>O∩O<i>O</i>)₂(<i>N</i>∩<i>N</i>)₂]⁴⁺ have been obtained in methanol from the dinuclear arene osmium precursors [(<i>p</i>-cymene)₂Os₂ (<i>O</i>O∩O<i>O</i>)₂Cl₂] (<i>O</i>O∩O<i>O</i> = 2,5-dioxydo-1,4-benzoquinonato (dhbq), 2,5-dichloro-1,4-benzoquinonato (dcbq)) by reaction with bipyridine linkers (<i>N</i>∩<i>N</i> = 4,4′-bipyridine, 1,2-bis(4-pyridyl)ethylene) in the presence of AgCF₃SO₃. All complexes were isolated as triflate salts and characterised by NMR, IR and UV-visible spectroscopy. The cytotoxicities of the dinuclear and tetranuclear osmium complexes were established using ovarian A2780 cancer cell lines. The most active metalla-rectangle, [(<i>p</i>-cymene)₄Os₄(dhbq)₂(4,4′-bipyridine)₂]⁴⁺, shows an IC₅₀ value of 5.7 μM (comparable to cisplatin) against A2780 cancer cells and 7.5 μM against the cisplatin resistant A2780cisR cells.