Welcoming Neighbour or Inhospitable Host? Selective Second Metal Binding in 5- and 6-Phospha-Substituted Bpy Ligands

The controlled formation of mixed-metal bimetallics was realised through use of a fac-[Re(CO)3(N,N'-bpy-P)Cl] complex bearing an exogenous 2,4,6-trioxa-1,3,5,7-tetramethyl-8-phosphaadamantane donor at the 5-position of the bpy. The introduction of gold, silver, and rhodium with appropriate secondary ligands was readily achieved from established starting materials. Restricted rotation about the C(bpy)-P bond was observed in several of the bimetallic complexes and correlated with the relative steric bulk of the second metal moiety. Related chemistry with the 6-substituted derivative proved more limited in scope with only the bimetallic Re/Au complex being isolated.

Gold(I) Complexes with P-Donor Ligands and Their Biological Evaluation

Gold(I) complexes with phosphine ligands—[Au(TrippyPhos)Cl] (1) (TrippyPhos = 1-[2-[bis(tert-butyl)phosphino]phenyl]-3,5-diphenyl-1H-pyrazole), [Au(BippyPhos)Cl]0.5CH2Cl2 (2) (BippyPhos = 5-(di-tert-butylphosphino)-1′, 3′, 5′-triphenyl-1′H-[1,4′]bipyrazole), and [Au(meCgPPh)Cl] (3) (meCgPPh = 1,3,5,7-tetramethyl-6-phenyl-2,4,8-trioxa-6-phosphaadamantane—were investigated as types of bioactive gold metallodrugs. Complexes (1)–(3) were characterized using IR, 1H, 13C, 31P NMR spectroscopy, elemental analysis and mass spectrometry (FAB-MS). Complexes of (1) and (2) exhibited substantial in vitro cytotoxicity (IC50 = 0.5–7.0 μM) against both the cisplatin-sensitive and -resistant variants of the A2780 human ovarian carcinoma cell line, as well as against the A549 human lung carcinoma, K562 chronic myelogenous leukemia, and HeLa (human cervix carcinoma) cells. However, among the compounds studied, complex (2) showed the most promising biological properties: the highest stability in biologically relevant media, selectivity towards cancer cells over the non-cancer cells (HUVEC, human umbilical vein endothelial cells), and the highest inhibitory effect on cytosolic NADPH-dependent reductases in A2780 and A2780cis cells among the gold complexes under analysis.