Synthesis, characterization and antitumor properties of two highly cytotoxic ruthenium(III) complexes with bulky triazolopyrimidine ligands

Two ruthenium(III) complexes composed of 5,7-ditertbutyl-1,2,4-triazolo[1,5-a] pyrimidine (dbtp) ligands were prepared and structurally characterized by X-ray crystallography, IR, UV-Vis, EPR spectroscopies and cyclic voltammetry (CV). The crystal structures of trans-[RuCl3(H2O)(dbtp)(2)] 1 and mer-[RuCl3(dbtp)(3)]center dot 0.815OCMe(2) 2 showed slightly distorted octahedral geometries with two 1 or three 2 monodentate dbtp ligands bound in a head-to-head orientation. In both complexes, the heterocyclic dbtp ligands were bound to the ruthenium(III) ion through the N3 nitrogen atom. A cytotoxicity assay of both ruthenium(III) compounds against two human cell lines (A549 - non-small cell lung carcinoma and T47D - breast carcinoma) was performed. The ruthenium(III) complexes showed excellent cytotoxicity with IC50 values in the range of 0.02-2.4 mu M against both cancer cell lines. In addition, the in vitro cytotoxic values of the ruthenium(III) compounds were 35-times for 1 and 172-times for 2 higher against T47D than the clinically used antitumor drug cisplatin.