Ruthenium(II)–Arene Complexes with Glycosylated NHC-Carbene Co-Ligands: Synthesis, Hydrolytic Behavior, and Binding to Biological Molecules

Abstract

Ruthenium(II) complexes with a three-legged piano-stool structure based on an arene ring, an N-heterocyclic carbene (NHC)-carbene ligand with a peracetylated glucose moiety and two chlorides or one bidentate ligand, were prepared and characterized by spectroscopy and crystallography. In one case, the sugar substituent is replaced by an ethyl. The chirality of the sugar results in the formation of two diastereomers that interconvert through rotations around the Ccarbene–Ru and Carene–Ru bonds. In water, the complexes undergo a series of equilibrium hydrolysis steps involving the Ru–Cl bonds. The Ru–arene bond and the sugar acetyls are also partially hydrolyzed, and the selectivity of the process is governed by the nature of the arene and the pH of the solution. The reactivity of the compounds was studied against model nucleophiles and biological macromolecules. In the former case, mass experiments demonstrated a variety of binding modes with a trend reflecting the stability in aqueous environment. In the latter case, protein crystallography was used to characterize the preferential binding sites of one of the complexes. The X-ray structure of the adduct formed upon reaction of one representative complex with hen egg white lysozyme contains a Ru center, which retains the carbene ligand, close to the side chain of Asp119. In the adduct with bovine pancreatic ribonuclease, there are two protein molecules in the asymmetric unit. In one molecule, two Ru centers are located close to the side chains of His105 and of His119, which is the protein active site. In the second molecule, only one Ru center was found in the proximity of the side chain of His105. The Ru complexes also interact with calf-thymus DNA, although without displacing the intercalating probe EB. Finally, the complexes are essentially inactive against the human ovarian carcinoma A2780 cells, the cisplatin-resistant A2780cis cells, and the human embryonic kidney HEK293T cells.