The First Ruthenium-Based Paullones:  Syntheses, X-ray Diffraction Structures, and Spectroscopic and Antiproliferative Properties in Vitro

Two novel paullone derivatives, namely, 6-(α-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L¹) and 9-bromo-6-(α-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L²), have been prepared. The reaction of cis-[RuCl₂(DMSO)₄] (DMSO = dimethyl sulfoxide) with L¹ and L² in a 1:1 molar ratio in dry ethanol at 50 °C afforded the complexes trans-[Ru^IICl₂(DMSO)₂L¹] (1a) and trans-[Ru^IICl₂(DMSO)₂L²] (1b) in 26 and 30% yield, respectively. The reaction carried out from the same starting compounds in a 1:2 molar ratio at 75 °C led to the formation of [Ru^IICl(DMSO)(L¹)₂]Cl (2a) and [Ru^IICl(DMSO)(L²)₂]Cl (2b) in 16 and 23% yield, correspondingly. The products were characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, electrospray ionization mass spectrometry, IR spectroscopy, electronic spectra, cyclic voltammetry, and X-ray crystallography (L¹, L², 1a, and 2b). Complexes 2a and 2b exhibit remarkable antiproliferative activity in three human carcinoma cell lines, A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma). The novel complexes show an intercalative mode of interaction with DNA, which may render them attractive alternatives to metal compounds with a coordinative mode of interaction.