Anticancer activity of osmium metalla-rectangles

A series of cationic metalla-rectangles of the general formula [(p-cymene)(4)Os-4(OO boolean AND OO)(2)(N boolean AND N)(2)](4+) have been obtained in methanol from the dinuclear arene osmium precursors [(p-cymene)(2)Os-2(OO boolean AND OO)(2)Cl-2] (OO boolean AND OO = 2,5-dioxydo-1,4-benzoquinonato (dhbq), 2,5-dichloro-1,4-benzoquinonato (dcbq)) by reaction with bipyridine linkers (N boolean AND N = 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, [(p-cymene)(4)Os-4(dhbq)(2)(4,4'-bipyridine)(2)](4+), shows an IC50 value of 5.7 mu M (comparable to cisplatin) against A2780 cancer cells and 7.5 mu M against the cisplatin resistant A2780cisR cells.