Investigation of the reactivity between a ruthenium hexacationic prism and biological ligands

The relative affinity of the cationic triangular metallaprism, [(?6-p-cymene)6Ru6(?3-tpt)2(?-dhbq)3]6+ ([1]6+; tpt = 2,4,6-tri-4-pyridyl-1,3,5-triazine, H2dhbq = 2,5-dihydroxy-1,4-benzoquinone), for various amino acids, ascorbic acid, and glutathione (GSH) has been detd. at 37° in aq. solns. at pD 7, using NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The metallaprism [1]6+, which is constituted of six (1,4-MeC6H4iPr)Ru corners bridged by three 1,4-benzoquinonato (dhbq) ligands and connected by two 2,4,6-tri-4-pyridinyl-1,3,5-triazine (tpt) triangular panels, disassembled in the presence of Arg, His, and Lys, while it remains intact with Met. Coordination to the imidazole nitrogen atom in His or to the basic NH/NH2 groups in Arg and Lys displaces the dhbq and tpt ligands from the (p-cymene)Ru units, and subsequent coordination to the amino and carboxylato groups forms stable N,N,O chelates. The binding to amino acids proceeds rapidly, as detd. by NMR spectroscopy. Interestingly, solns. of [1]6+ are able to catalyze oxidn. of the thiol group of Cys and GSH to give the corresponding disulfides and of ascorbic acid to give the corresponding dehydroascorbic acid. Competition expts. with Arg, Cys, His, and Lys show the simultaneous formation of one single adduct, the (p-cymene)Ru-His complex, and oxidn. of Cys to cystine. Furthermore, the (p-cymene)Ru-His complex formed upon the addn. of His to [1][CF3SO3]6 is able to oxidize Cys to cystine much more efficiently than [1]6+. These results provide evidence against interaction with proteins as process in the release of encapsulated guest mols. Oxidn. of Cys and GSH to give the corresponding disulfides may explain the in vitro anticancer activity of [1]6+. [on SciFinder(R)]