Synthesis and Avidin Binding of Ruthenium Complexes Functionalized with a Light-Cleavable Free Biotin Moiety

Biotinylated photoactive Pt(iv) anticancer complexes

Novel biotinylated diazido-Pt(iv) complexes exhibit high visible light photocytotoxicity while being stable in the dark. Photocytotoxicity and cellular accumulation of all-trans-[Pt(py)₂(N₃)₂(biotin)(OH)] (2a) were enhanced significantly when bound to avidin; irradiation induced dramatic cellular morphological changes in human ovarian cancer cells treated with 2a.

An anthracene-pendant ruthenium(ii) complex conjugated to a biotin anchor, an essential handle for photo-induced anti-cancer activity

Efficient avidin binding and selective cancer cell response upon light irradiation of an enhanced ROS photogenerator biotinylated ruthenium complex.

Partially Solvated Dinuclear Ruthenium Compounds Bridged by Quinoxaline-Functionalized Ligands as Ru(II) Photocage Architectures for Low-Energy Light Absorption

Ruthenium compounds with coordinated photolabile molecules that can be selectively released by irradiation with a visible light source are finding increasing applications in photoactivated chemotherapy (PCT) as photocages. Earlier photocages based on mononuclear Ru(II) compounds lack absorption in the therapeutic window (λ > 600 nm). In previous work, we synthesized the first partially solvated tppz bridged (tppz= 2,3,5,6-tetrakis(pyridin-2-yl)pyrazine) dinuclear Ru(II) complex capable of photoinduced ligand exchange at both metal centers. To further explore the effect of the bridging ligand on Ru(II) photocage design, we used quinoxaline-functionalized bridging ligand platforms to prepare [{Ru^II(NCCH₃)₄}₂(μ-BL)](PF₆)₄[BL = dpq, 2,3-di(pyridin-2-yl)quinoxaline (1); BL = dpb, 2,3-di(pyridin-2-yl)benzo[g]quinoxaline (2)]. The compounds are capable of absorbing green light with tails extending beyond 650 nm which can be exploited for applications as PCT agents. Experimental results were additionally verified by DFT calculations. The use of two Ru(II) centers equipped with quinoxaline-based bridging ligands is a promising design strategy for the synthesis of a new family of dinuclear Ru(II) photocage prototypes with the ability to absorb low-energy visible light.

Diastereoselective Synthesis and Two-Step Photocleavage of Ruthenium Polypyridyl Complexes Bearing a Bis(thioether) Ligand

Thioethers are good ligands for photoactivatable ruthenium(II) polypyridyl complexes, as they form thermally stable complexes that are prone to ligand photosubstitution. Here, we introduce a novel symmetric chelating bis(thioether) ligand scaffold, based on 1,3-bis(methylthio)-2-propanol (4) and report the synthesis and stereochemical characterization of the series of novel ruthenium(II) polypyridyl complexes [Ru(bpy)₂(L)](PF₆)₂ ([1]–[3](PF₆)₂), where L is ligand 4, its methyl ether, 1,3-bis(methylthio)-2-methoxypropane (5), or its carboxymethyl ether, 1,3-bis(methylthio)-2-(carboxymethoxy)propane (6). Coordination of ligands 4–6 to the bis(bipyridine)ruthenium center gives rise to 16 possible isomers, consisting of 8 possible Λ diastereoisomers and their Δ enantiomers. We found that the synthesis of [1]–[3](PF₆)₂ is diastereoselective, yielding a racemic mixture of the Λ-(S)-eq-(S)-ax-OH_eq-[Ru]²⁺ and Δ-(R)-ax-(R)-eq-OH_eq-[Ru]²⁺ isomers. Upon irradiation with blue light in water, [1]–[3](PF₆)₂ selectively substitute their bis(thioether) ligands for water molecules in a two-step photoreaction, ultimately producing [Ru(bpy)₂(H₂O)₂]²⁺ as the photoproduct. The relatively stable photochemical intermediate was identified as cis-[Ru(bpy)₂(κ¹-L)(H₂O)]²⁺ by mass spectrometry. Global fitting of the time evolution of the UV–vis absorption spectra of [1]–[3](PF₆)₂ was employed to derive the photosubstitution quantum yields (Φ₄₄₃) for each of the two photochemical reaction steps separately, revealing very high quantum yields of 0.16–0.25 for the first step and lower values (0.0055–0.0093) for the second step of the photoreaction. The selective and efficient photochemical reaction makes the photocleavable bis(thioether) ligand scaffold reported here a promising candidate for use in e.g. ruthenium-based photo-activated chemotherapy.

Thioethers are excellent photocleavable ligands for ruthenium(II) polypyridyl complexes but may lead to the formation of several stereoisomers when they are present in bidentate ligands. Here, a chelating bis(thioether) ligand was found to coordinate to Ru(II) diastereoselectively, in spite of the four chiral centers of the resulting complex. Photosubstitution of this bis(thioether) ligand in water occurs via a selective, two-step process that involves a relatively stable mono(aqua) intermediate.