Synthesis, characterization, and biological activities of 2-phenylpyridine gold(III) complexes with thiolate ligands

A series of new 2-phenylpyridine Au(III) complexes [Au(ppy)X] with various thiolate ligands has been synthesized and characterized (X =(SCN)(NCS)(1), tlc (thiolactate)(2), tsc (thiosalicylate)(3), dmp (2,3-dimercapto-1-propanol)(4), dms (2,3-dimercaptosuccinic acid)(5), cys (cysteine)(6)). The crystal structure of [Au(ppy)(SCN)(NCS)](1) shows the two soft carbanion and sulfur donors mutually cis to each other in the thermodynamically most stable isomer. It is noteworthy that the two thiocyanate ions bind to gold through nitrogen (trans to C) and sulfur (trans to N) atom, respectively, with the Au-NCS group linear whereas the Au-SCN is bent. Crystal structures of [Au(ppy) (tsc)]·1.5H2O (3) and [Au(ppy)(cys)]·0.5(Cl-+ ClO4-+ H2O)(6) show the expected square-planar coordination around the gold atom and the stronger trans influence groups S and C adopting the cis-orientated configuration. Complexes 1-5 have been tested in vitro against MOLT-4 human leukemia and C2Cl2 mouse tumour cell lines, where they are more cytotoxic than the clinically used cisplatin.