Ruthenium(ii) p-cymene complexes of pyridine-2-carboxaldehyde and 2-amino benzothiazole-based ligands: cytoselective and in vitro live cell imaging agents

Five Ru(ii)-arene complexes with the general formula [(eta(6)-p-cymene)RuCl(k(1)L1-L5)(pyridine-2-carboxaldehyde)]Cl were synthesized at ambient temperature, which exhibited 8-11-fold higher cytoselectivity in two cancer cell lines (HeLa and MCF-7) compared to normal kidney cells (HEK-293). Furthermore, these complexes showed higher potency and selectivity compared to cisplatin. Among the synthesized scaffolds, the [(eta(6)-p-cymene)RuCl(k(1)L3)(pyridine-2-carboxaldehyde)]Cl complex (RuL3) contains an -F group, which enhanced its lipophilicity, triggering its selective cellular accumulation in HeLa and MCF-7 cells, and thus it exhibited the highest cytoselectivity. The strong DNA intercalative nature of the RuL3 complex enabled its potency against the cancer cells. All the complexes displayed MLCT (metal-ligand charge transfer) emission maxima in the wavelength range of lambda(ems) 526-535 nm, and among them, the RuL3 complex exhibited the highest quantum yield (0.32), making it an efficient in vitro live cell imaging agent.