A step forward from PTA: Ru-arene complexes of CAP ligand as promising in vitro anticancer agents

For several years, the interest of our research group focused on the synthesis and coordination properties of the neutral water-soluble aminophosphine PTA (1,3,5-triaza-7-phosphadamantane, Figure 1 left) and its derivatives. In our laboratories, some PTA transition metal complexes were successfully employed as catalysts for water-phase hydrogenations and hydroformylations, and their use as anticancer agents in medicinal inorganic chemistry was also demonstrated. Recently, a higher homologue of PTA, namely ligand 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP, Figure 1 right), was reported in the literature. With the aim of exploring its coordination ability and properties, we obtained and characterized three novel ruthenium(II)-arene half-sandwich complexes bearing CAP as monodentate ligand. The new Ru(II)-CAP complexes (RACAP) showed modest activity in homogenous C=C bond catalytic reduction tests. On the other hand, when tested in vitro against selected cancer cell lines, they revealed higher activity than the corresponding well-known PTA analogues (RAPTA), still exhibiting a reasonable degree of cancer cell selectivity.