Improved reaction conditions for the synthesis of new NKP-1339 derivatives and preliminary investigations on their anticancer potential.

The very promising results of Na-trans-[RuCl4(1H-indazole)2] (NKP-1339) in clinical studies have fuelled renewed interest in the research and development of ruthenium(III) coordination compounds for cancer therapy. By applying an improved synthetic approach to this class of coordination compounds, six new examples of the general formula (cation)-trans-[RuCl4(azole)2], where (cation) = tetrabutylammonium (Bu4N)(+) (1, 2), sodium (3, 4), azolium (5, 6), and azole = 1-methyl-indazole (1, 3, 5), 1-ethyl-indazole (2, 4, 6), have been prepared. All compounds have been characterized by elemental analysis, electrospray ionization (ESI) mass spectrometry, UV-vis-, and NMR-spectroscopy and, if possible, X-ray diffraction analysis. Furthermore, the influence of the alkyl substituent at the position N1 of the indazole backbone on the stability in aqueous media as well as on the biological activity in three human cancer cell lines (CH1, A549, and SW480) and on the cellular accumulation in SW480 cells is discussed.