Strategies for conjugating iridium(III) anticancer complexes to targeting peptides via copper-free click chemistry

We report the synthesis and characterization of novel pentamethylcyclopentadienyl (Cp*) iridium(III) complexes [(Cp*)Ir(4-methyl-4'-carboxy-2,2'-bipyridine)Cl]PF6 (Ir-I), the product (Ir-II) from amide coupling of Ir-I to dibenzocyclooctyne-amine, and its conjugate (Ir-CP) with the cyclic nona-peptide c(CRWYDENAC). The familiar three-legged 'piano-stool' configuration for complex Ir-I was confirmed by its single crystal X-ray structure. Significantly, copper-free click strategy has been developed for site-specific conjugation of the parent complex Ir-I to the tumour targeting nona-cyclic peptide. The approach consisted of two steps: (i) the carboxylic acid group of the bipyridine ligand in complex Ir-I was first attached to an amine functionalized dibenzocyclooctyne group via amide formation to generate complex Ir-II; and (ii) the alkyne bond of dibenzocyclooctyne in complex Ir-II underwent a subsequent strain-promoted copper-free cycloaddition with the azide group of the modified peptide. Interestingly, while complex Ir-I was inactive towards A2780 human ovarian cancer cells, complex Ir-II exhibited moderate cytotoxic activity. Targeted complexes such as Ir-CP offer scope for enhanced activity and selectivity of this class of anticancer complexes.

A combined experimental and theoretical study of bimetallic bis- and tris-homocubane analogues

Various bimetallic bis- and tris-homocubane analogues of group 9 transition metals have been isolated and structurally characterized employing Li[BH₂E₃] (E = S or Se).

Design, Synthesis, DNA/HSA Binding, and Cytotoxic Activity of Half-Sandwich Ru(II)-Arene Complexes Containing Triarylamine-Thiosemicarbazone Hybrids

Organoruthenium complexes are potent alternatives for platinum-based complexes because of their superior anticancer activity. In this investigation, a series of new Ru(II)-arene complexes with triarylamine-thiosemicarbazone hybrid ligands with higher anticancer activity than cisplatin are reported. The molecular structure of the ligands and complexes was confirmed spectroscopically and supported by single-crystal X-ray crystallography. These complexes adopted a three-leg piano stool geometry. All the Ru(II)-arene complexes were systematically investigated for their in vitro cytotoxicity against human cervical (HeLa S3), lung (A549) cancer, and human normal lung (IMR-90) cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Interestingly, a pyrrolidine-attached Ru(II)-benzene complex exhibited superior activity against cancer cells with low IC₅₀ values, and colony formation study showed complete inhibition at 5 and 10 μM concentration. Furthermore, morphological changes assessed by acridine orange and propidium iodide staining revealed that the cell death occurred by apoptosis. In addition, the interaction between synthesized Ru(II)-arene complexes and DNA/protein was explored by absorption and emission spectroscopy methods. These synthesized new organoruthenium complexes can be used for developing new metal-based anticancer drugs.

Catalytic reactivity of an iridium complex with a proton responsive N-donor ligand in CO2 hydrogenation to formate

A bibenzimidazole ligated half-sandwich Ir complex [Cp*Ir(BiBzImH₂)Cl]Cl shows superior activity than that of its bipyridine counterpart. Owing to the structural instability, the initial excellent activity of [Cp*Ir(BiBzImH₂)Cl]Cl was reduced when catalytic cycle proceeds.

Synthesis and molecular structure of arene ruthenium(ii) benzhydrazone complexes: impact of substitution at the chelating ligand and arene moiety on antiproliferative activity

A series of ruthenium(ii) arene complexes have been synthesized and evaluated for their in vitro anticancer activities. The complexes exhibit promising anticancer activities in human cancer cells.

Ruthenium(ii) arene complexes containing benzhydrazone ligands: synthesis, structure and antiproliferative activity

Six new Ru(ii) arene anthracene benzhydrazone complexes have been synthesized and show excellent cytotoxicity against human cancer cell lines. The results of apoptosis assays demonstrated that complexes4and6are able to induce apoptosis in human cancer cells.