Chemical and biological studies of the dichloro(2-phenylpyridine) gold(III) complex and its derivatives

Four new derivatives of the type [Au(ppy)X-2] (ppy = 2-phenylpyridine) together with [Au(ppy)Cl-2] (1) have been synthesized and characterized [X = ac = CH3COO- (2), bz = C6H5COO- (3); mal = CH2(COO-)(2) (4), cbdca = C4H6(COO-)(2) (5)]. The crystal structures of 2 and 3 are similar in which two carboxylate groups are bound to gold through oxygen, but the two Au-O distances are inequivalent. The crystal structure of 5 shows that gold is bound to sigma-C,N-phenylpyridine (ppy) and O,O-cbdca, forming a five-membered and a six-membered chelate ring, respectively. In all four structures the Au(m) center exhibits a square planar coordination geometry and the trans influence of the sigma-bonded phenyl group is apparent. The a-bonded phenyl group contributes to stabilizing these complexes in reducing, biological media. The reaction between 5 and chloride has been investigated by H-1 NMR spectroscopy and reveals slow replacement of cbdca by chlorides through an intermediate [Au(ppy)(O-cbdca)Cl]. All five complexes have been tested for cytotoxic properties in vitro against MOLT-4 (human leukemia) and C2C12 (mouse tumour) cell lines. The results show that these complexes have similar cytotoxicity profile to cisplatin against MOLT-4 but are inactive on C2C12, except for complex 5.