New Ruthenium(II)-Arene Complexes of the Water-Soluble Ligand CAP as Promising in vitro Anticancer Agents

For many years, our research groups focused on the synthesis and coordination properties of the neutral water-soluble aminophosphine PTA (1,3,5-triaza-7-phosphadamantane) and its derivatives. Several PTA transition metal complexes were successfully used as catalysts in homogeneous aqueous phase reactions and some Ru(II) arene organometallic derivatives, namely RAPTA-type compounds (Fig. a), were identified as promising anticancer agents. Recently, a higher homologue of PTA, i.e.1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) was reported in the literature. We synthesized and characterized three novel Ru(II)-arene half-sandwich complexes in which CAP binds the metal in k1-P fashion. These new complexes (RACAP-type, Fig. b) showed modest activity in homogenous C=C and C=N bond catalytic reductions under transfer hydrogenation conditions. On the other hand, when tested in vitro against selected cancer cell lines, they revealed higher activity than the corresponding well-known RAPTA compounds, still exhibiting a reasonable degree of cancer cell selectivity.