Gold(I) Bis(1,2,3-triazol-5-ylidene) Complexes as Promising Selective Anticancer Compounds

The synthesis and antiproliferative activity of Mes- and iPr-substituted gold(I) bis(1,2,3-triazol-5-ylidene) complexes in various cancer cell lines are reported, showing nanomolar IC₅₀ values of 50 nM (lymphoma cells) and 500 nM (leukemia cells), respectively (Mes < iPr). The compounds exclusively induce apoptosis (50 nM to 5 μM) instead of necrosis in common malignant blood cells (leukemia cells) and do not affect non-malignant leucocytes. Remarkably, the complexes not only overcome resistances against the well-established cytostatic etoposide, cytarabine, daunorubicin, and cisplatin but also promote a synergistic effect of up to 182% when used with daunorubicin. The present results demonstrate that gold(I) bis(1,2,3-triazol-5-ylidene) complexes are highly promising and easily modifiable anticancer metallodrugs.

Mimicking reactive high-valent diiron-μ2-oxo intermediates of nonheme enzymes by an iron tetracarbene complex

The first diiron(iii,iv)-μ2-oxo tetracarbene complex is isolated and characterized by SC-XRD, UV/Vis, EPR, Evans' NMR and elemental analysis. CV indicates the presence of a transient high-valent diiron(iv)-μ2-oxo species. Its formation and decay is investigated via UV/Vis kinetics and NMR.

Fluorescent palladium(II) and platinum(II) NHC/1,2,3-triazole complexes: antiproliferative activity and selectivity against cancer cells

Fluorescent Pd(ii) and Pt(ii) complexes bearing 4-methylene-7-methoxycoumarin (MMC) and 2,6-diispropylphenyl (Dipp) substituted NHC/1,2,3-triazole hybrid ligands are described. Depending on the reaction conditions two different ligand coordination modes are observed, i.e., bidentate solely coordinating via NHCs or tetradentate coordinating via NHCs and 1,2,3-triazoles. All Dipp substituted complexes show antiproliferative activity against cervix (HeLa) and breast (MCF-7) human carcinoma cells. The activity significantly depends on the coordination mode, with the tetradentate motif being notably more effective (HeLa: IC50 = 3.9 μM to 4.7 μM; MCF-7: IC50 = 2.07 μM to 2.35 μM). Amongst the MMC series, only the Pd(ii) complex featuring the bidentate coordination mode is active against HeLa (IC50 = 6.1 μM). In contrast to its structurally related Dipp derivative (SI = 0.6), it shows a high selectivity for HeLa (SI > 16) compared to healthy skin cells (HaCaT). According to fluorescence microscopy, this compound is presumably located in late endosomes or lysosomes.

Degradation pathways of a highly active iron(iii) tetra-NHC epoxidation catalyst

Elucidation of different decomposition pathways of a highly active tetradentate iron–NHC epoxidation catalyst reveals direct carbene oxidation to be the decisive cause of catalyst degradation.

Improved Antiproliferative Activity and Fluorescence of a Dinuclear Gold(I) Bisimidazolylidene Complex via Anthracene-Modification

A straightforward modification route to obtain mono- and di-substituted anthroyl ester bridge functionalized dinuclear Au(I) bis-N-heterocyclic carbene complexes is presented. The functionalization can be achieved starting from a hydroxyl-functionalized ligand precursor followed by transmetallation of the corresponding Ag complex or via esterification of the hydroxyl-functionalized gold complex. The compounds are characterized by NMR-spectroscopy, ESI-MS, elemental analysis and SC-XRD. The mono-ester Au complex shows quantum yields around 18%. In contrast, the corresponding syn-di-ester Au complex, exhibits significantly lower quantum yields of around 8%. Due to insufficient water solubility of the di-ester, only the mono-ester complex has been tested regarding its antiproliferative activity against HeLa- (cervix) and MCF-7- (breast) cancer cell lines and a healthy fibroblast cell line (V79). IC50 values of 7.26 μM in the HeLa cell line and 7.92 μM in the MCF-7 cell line along with selectivity indices of 8.8 (HeLa) and 8.0 (MCF-7) are obtained. These selectivity indices are significantly higher than those obtained for the reference drugs cisplatin or auranofin.

Antiproliferative Activity of Functionalized Histidine-derived Au(I) bis-NHC Complexes for Bioconjugation

A series of histidine derived Au(I) bis-NHC complexes bearing different ester, amide and carboxylic acid functionalities as well as wingtip substituents is synthesized and characterized. The stability in aqueous media, in vitro cytotoxicity in a set of cancer cell lines (MCF7, PC3 and A2780/A2780cisR) along with the cellular uptake are evaluated. Stability tests suggest hydrolysis of the ester within 8 h, which might lead to deactivation. Furthermore, the bis-NHC system shows a sufficient stability against cysteine and the thiol containing peptide GSH. The benzyl ester and amide show the highest activity comparable to the benchmark compound cisplatin, with the ester only displaying a slightly lower cytotoxicity than the amide. A cellular uptake study revealed that the benzyl ester and the amide could have different intracellular distribution profiles but both complexes induce perturbations of the cellular physiological processes. The simple modifiability and high stability of the complexes provides a promising system for upcoming post modifications to enable targeted cancer therapy.

Dinuclear Gold(I) Complexes Bearing N,N'-Allyl-Bridged Bisimidazolylidene Ligands

A novel N,N'-allyl-bridged bisimidazolium salt and a novel dinuclear Ag(I) and a Au(I) NHC complex are reported. Both metallacyclic complexes have a twisted structural shape due to the rigid allylic system and form two different isomers relating to the position of the double bonds. The allyl-group shows photoisomerisation, but no reactivity towards bases for the additional coordination of Pd(II).