Photochemical Reactivity of Ru^II(η⁶-p-cymene) Flavonolato Compounds

Abstract

Photoactivation is a promising approach for modulating the biological activity of RuII compounds. In this work, RuII flavonolato compounds, [Ru(η6-p-cymene)(L)(3-Hfl)]OTf (8; 3-Hfl = monoanion of 3-hydroxyflavone; L = solvent) and [Ru(η6-p-cymene)Cl(3-Hfl-X)] (3a–3c; 3-Hfl-X = p-H, -Cl, or -F on the flavonolato phenyl substituent), have been evaluated for photoinduced reactivity within the flavonolato unit upon irradiation with UV (300 nm) or visible (419 nm) light under aerobic conditions. For each compound, irradiation in CH3CN was found to result in the loss of the p-cymene ligand and the formation of products resulting from oxidative ring opening of the flavonolato ligand in a dioxygenase-type reaction. This reaction also results in the release of carbon monoxide. The RuII products generated in these reactions are [RuII(solvent)(carboxylato)]+ and [Ru(CO)(solvent)(carboxylato)]+ (carboxylato = O-benzoylsalicylato or benzoato) species, as determined by ESI-MS. The amount of free CO generated depends on the wavelength of irradiation, with 300 nm light giving a higher amount of free CO. Evaluation of the photoinduced reactivity of 8 in DMSO/H2O (10:90) at 300 nm showed similar reactivity to that found in organic solvent, although the reaction occurs more slowly. The products of the photoreactions of 8 and 3a at 419 nm are nontoxic toward human T-lymphocyte (Jurkat) and non-small-cell lung carcinoma (A549) cells. This lack of toxicity versus the starting compounds is likely due to differences in interactions of the [RuII(solvent)(carboxylato)]+ and [RuII(CO)(solvent)(carboxylato)]+ species with biomolecules (e.g., serum proteins), thus resulting in reduced bioavailabilty. 1H NMR studies provide evidence that the photoreaction products coordinate to biologically relevant donors such as histidine and 5′-GMP in d 6-DMSO/D2O (10:90) and exhibit reactivity with these small molecules that is distinctly different from that exhibited by the starting compounds. Overall, the photoreactivity of 8 and 3a–3c may represent an approach toward altering the biological chemistry of these compounds.

Flavonoid‐Based Organometallics with Different Metal Centers – Investigations of the Effects on Reactivity and Cytotoxicity

“…Upon irradiation with UV/Vis light the C‐ring of the flavonoid ligand is cleaved with CO expulsion. However, the resulting complexes did not show improved cytotoxicity 32…”

3-Hydroxyflavones and 3-Hydroxy-4-oxoquinolines as Carbon Monoxide-Releasing Molecules

“…We have also explored the visible light-induced CO release reactivity of the [Ru(η 6 - p -cymene)(CH 3 CN)(3-Hfl)]OTf complex (Scheme 17) [105], as such complexes are promising for anticancer applications [106,107,108]. The combined results from product identification (ESI-MS), CO quantification, and 18 O-isotope labeling studies upon illumination with UV (300 nm) and visible (419 nm) light in CH 3 CN show that oxygenation of the flavonolato ligand occurs in a dioxygenase-type manner with release of CO.…”

“…Reactivity of Ru II 3-hydroxyflavonolato complex with O 2 upon illuination with visible light (λ ill = 419 nm) [105]. …”

Editorial of Special Issue Ruthenium Complex: The Expanding Chemistry of the Ruthenium Complexes

“…Photoactivation of ruthenium complexes for triggering and/or modulating their antitumor activity [110,111,112,113] is presently of great interest. The process enables transformation of unreactive Ru(II) complexes into light-driven cytotoxic species [114] that can subsequently interact with proteins and DNA at the cellular level.…”