Highly selective anti-cancer properties of ester functionalized enantiopure dinuclear gold(I)-diphosphine.

Two chiral (-)-diphosphine-digold(I) complexes containing mono- and di-methylester substituted diphosphine ligands have been prepared and structurally characterized. Both complexes are highly potent against breast cancer cell line MDA-MB-231 but showed much lower cytotoxicity against the normal human breast epithelial cells MCF10A. When compared with its mono-substituted analogue, the di-methylester substituted complex caused markedly lower and relatively insignificant damage to the normal breast cells. The analogous mono- and di-ethylester substituted complexes with the same stereochemistry exhibited similar anti-cancer properties but with noticeably higher cytotoxicity against the MCF10A cells. The enantiomeric complex (+)-diphosphine-digold(I) complexes containing the di-methylester substituted diphosphine ligand exhibited clearly different biological properties from its (-)-enantiomer. Furthermore, a structurally similar diphosphine-digold(I) complex but in the absence of an ester substituent, killed both the cancerous and the healthy cells indiscriminately. The current study thus revealed that the introduction of multi-esters, particularly methylesters, is an efficient approach to suppress the side-effects and to improve the efficiency of potential gold-based anti-cancer reagents. When combined with the biological observations, the chirality of gold complexes may serve as a sensitive probe for the future mechanistic studies.