Synthesis, Characterization, and Antileishmanial Activity of Neutral Gold(I) Complexes with N-heterocyclic Carbene Ligands Bearing Sulfur-Containing Side Arms

Antileishmanial activity and insights into the mechanisms of action of symmetric Au(I) benzyl and aryl-N-heterocyclic carbenes

Leishmania amazonensis and L. braziliensis are the main etiological agents of the American Tegumentary Leishmaniasis (ATL). Taking into account the limited effectiveness and high toxicity of the current drug arsenal to treat ATL, novel options are urgently needed. Inspired by the fact that gold-based compounds are promising candidates for antileishmanial drugs, we studied the biological action of a systematic series of six (1)-(6) symmetric Au(I) benzyl and aryl-N-heterocyclic carbenes. All compounds were active at low micromolar concentrations with 50% effective concentrations ranging from 1.57 to 8.30 μM against Leishmania promastigotes. The mesityl derivative (3) proved to be the best candidate from this series, with a selectivity index ~13 against both species. The results suggest an effect of the steric and electronic parameters of the N-substituent in the activity. Intracellular infections were drastically reduced after 24h of (2)-(5) incubation in terms of infection rate and amastigote burden. Further investigations showed that our compounds induced significant parasites' morphological alterations and membrane permeability. Also, (3) and (6) were able to reduce the residual activity of three Leishmania recombinant cysteine proteases, known as possible targets for Au(I) complexes. Our promising results open the possibility of exploring gold complexes as leishmanicidal molecules to be further screened in in vivo models of infection.

DNA interaction, anticancer, cytotoxicity and genotoxicity studies with potential pyrazine-bipyrazole dinuclear µ-oxo bridged Au(III) complexes

Pyrazine-bipyrazole-based µ-oxo bridged dinuclear Au(III) complexes were synthesized and characterized by various spectrometric (¹H-NMR, ¹³C (APT) NMR, FT-IR, Mass spectrometry) and analytical techniques (elemental analysis and conductance measurement). The evaluation of DNA binding activity by UV-Vis absorption spectra and viscosity measurement demonstrated that all the compounds intercalate in between the stacks of DNA base pair and the binding constant values were observed in the range of 5.4 × 10⁴-2.17 × 10⁵ M^-1. The molecular docking study also supports the intercalation mode of binding. The anti-proliferation activity of complexes on A549 (Lung adenocarcinoma) cells by MTT assay demonstrated IC₅₀ values in the range of 47.46 -298.12 μg/mL. The genotoxicity of compounds was checked by smearing observed in the DNA of S. pombe cell under the influence of complexes. The in vivo cytotoxicity of compounds against brine shrimp demonstrated the LC₅₀ values in the range of 4.59-27.22 μg/mL. The promising results of the Au(III) complexes received significant attention and make them suitable for the new metallodrugs after the detailed mechanistic biological study.

A hybrid bipy–NHC ligand for the construction of group 11 mixed-metal bimetallic complexes

An asymmetric bipy/NHC ligand L has been used to construct Au/Au, Au/Ag and Au/Cu bimetallic complexes through prior coordination of the NHC to Au(i) and subsequent introduction of the second group 11 metal ion at the bipy donor of the hybrid ligand. The complex [Au(κ^C-L)₂]BF_4,1, has been used as the precursor for the formation of [AuAg(κ-C^Au,κ²-N,N′^Ag-1)₂](BF₄)₂, 2a, [AuCu(κ-C^Au,κ²-N,N′^Cu-1)₂](BF₄)₂, 2b and [AuAu′(κ-C^Au/Au′,κ¹-N^Au/Au′-1)₂](BF₄)₂, 3.

A ditopic bipy–NHC ligand has been used to construct hetero-bimetallic complexes of the monovalent group 11 metals.