Ruthenium(II) polypyridyl complexes with hydrophobic ancillary ligand as Aβ aggregation inhibitors

The synthesis, spectral and electrochemical characterization of the complexes of the type [Ru(N-N)2(txbg)](2+) where N N is 2,2'-bipyridine (bpy) (1), 1,10-phenanthroline (phen) (2), dipyrido [3,2d:2',3f] quinoxaline (dpq) (3), and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (4) which incorporate the tetra-xylene bipyridine glycoluril (txbg) as the ancillary ligand are described in detail. Crystal structures of ligand txbg and complex 2 were solved by single crystal X-ray diffraction. Thioflavin T (ThT) fluorescence and Transmission Electron Microscopy (TEM) results indicated that at micromolar concentration all complexes exhibit significant potential of AR aggregation inhibition, while the ligand txbg displayed weak activity towards AO aggregation. Complex 1 showed relatively low inhibition (70%) while complexes 2-4 inhibited nearly 100% A beta aggregation after 240 h of incubation. The similar potential of complexes 2-4 and absence of any trend in their activity with the planarity of polypyridyl ligands suggests there is no marked effect of planarity of coligands on their inhibitory potential. Further studies on acetylcholinesterase (AChE) inhibition indicated very weak activity of these complexes against AChE. Detailed interactions of A beta with both ligand and complex 2 have been studied by molecular modeling. Complex 2 showed interactions involving all three polypyridyl ligands with hydrophobic region of A beta. Furthermore, the toxicity of these complexes towards human neuroblastoma cells was evaluated by MIT assay and except complex 4, the complexes displayed very low toxicity. (C) 2016 Elsevier Masson SAS. All rights reserved.