1,2,3-Triazole‑gold(I)-triethylphosphine derivatives of nutrients as new antimicrobials against antibiotic resistant Gram-positive pathogens

The ongoing rise of bacterial resistance against antibiotics is an incentive to develop radically new antibacterial molecules. Innovative organo-gold(I) antibacterial compounds were synthesized by click chemistry with triethylphosphine‑gold(I) azides and alkyne-functionalized metabolites like amino acids, nicotinic acid and biotin. The resulting organo‑gold(I) compounds exhibited remarkable activities against a panel of Gram-positive pathogens (Staphyloccocus sp., Enterococcus sp. and Clostridium difficile) but failed to inhibit the growth of Gram-negative bacilli (e.g., Escherichia coli) under the conditions used (8 μg. mL-1 maximum).

Quinizarin Gold(I) N-Heterocyclic Carbene Complexes with Synergistic Activity Against Anthracycline-Resistant Leukaemia Cells: Synthesis and Biological Activity Studies

New, asymmetric quinizarin-Au(I)-NHC complexes were designed, isolated, and fully characterised including by single crystal X-ray crystallography. Cytotoxicity studies showed effective growth inhibition in HeLa cervical cancer cells with IC50 values ranging from 2.4 μM to 5.3 μM. The successful cellular uptake was evidenced by X-ray fluorescence imaging on cryo-preserved whole HeLa cells and the sub-cellular localisation was monitored by live-cell fluorescence microscopy. Notably, complex 2 b showed circumvention of acquired anthracycline resistance in K562 leukaemia cells as well as synergistic activity with doxorubicin against both wild-type and anthracycline-resistant Nalm-6 leukaemia cells. Interestingly, sub-cellular localisation towards mitochondria proved to be more important than the compounds' overall cytotoxicity for potent antiproliferative activity and to achieve effective resistance circumvention.

Exploiting click-chemistry: backbone post-functionalisation of homoleptic gold(I) 1,2,3-triazole-5-ylidene complexes

The synthesis of a homoleptic azide-functionalised Au(I) bis-1,2,3-triazole-5-ylidene complex is reported, starting from a backbone-modified 1,2,3-triazolium salt ligand precursor. The incorporated azide handle allows for a straightforward modification of the complex according to click-chemistry protocols without impacting the steric shielding around the metal center, demonstrating the superiority of the presented triazole ligand framework over imidazole based systems. Employing the SPAAC and the CuAAC reactions, post-modification of the complex is facilitated with two model substrates, while retaining very high antiproliferative activity (nanomolar range IC50 values) in A2780 and MCF-7 human cancer cells.

Isostructural Series of Ni(II), Pd(II), Pt(II), and Au(III) Azido Complexes with a N^C^N Pincer Ligand to Elucidate Trends in the iClick Reaction Kinetics and Structural Parameters of the Triazolato Products

An isoelectronic and isostructural series of cyclometalated azido complexes [M(N3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) based on the N^C^N pincer ligand 1,3-di(2-pyridyl)phenide (dpb) was characterized by X-ray diffraction analysis and investigated for reactivity in the iClick reaction with a wide range of internal and terminal alkynes by using 1H and 19F NMR spectroscopy. Reaction rate constants were found to increase with greater charge density in the order Ni(II) > Pd(II) > Pt(II) > Au(III). Terminal alkynes R-C≡C-R' with strongly electron-withdrawing groups R and R' exhibited faster kinetics than those with electron-donating substituents in the order CF3 > ketone > ester > H > phenyl ≫ amide, while R = CH3 resulted in complete loss of reactivity. Four symmetrical triazolato complexes [M(triazolatoCOOCH3,COOCH3)(dpb)] with M = Ni(II), Pd(II), Pt(II), and Au(III) as well as four nonsymmetrically substituted triazolato complexes [Pt(triazolatoR,R')(dpb)] originating from terminal and internal alkynes were shown by X-ray crystal structure analysis to exclusively feature N2-coordination of the five-membered ring ligand. However, the Pt(II) triazolato complexes exist as a mixture of N1- and N2-coordinated species in solution. Torsion angles between the mean planes of the N^C^N pincer and the triazolato ligand increase from a nearly coplanar to a perpendicular arrangement when going from Au(III)/Pt(II)/Pd(II) to Ni(II), while different substituents R and R' on the alkyne have no influence on the torsion angle and were rationalized by DFT calculations. Finally, a carbohydrate derivative obtained by glucuronic acid conjugation to methyl propiolate demonstrates the facile biofunctionalization of metal complexes via the iClick reaction.

Electrospray Mass Spectrometry to Study Combinatorial iClick Reactions and Multiplexed Kinetics of [Ru(N3)(N∧N)(terpy)]PF6 with Alkynes of Different Steric and Electronic Demand

In a combinatorial approach, a family of ruthenium(II) azido complexes [Ru(N₃)(N∧N)(terpy)]PF₆ with terpy = 2,2':6',2″-terpyridine and N∧N as a bidentate chelator derived from 2,2'-biypridine and its 4,4'-disubstituted derivatives, 2,2'-bipyrimidine, and 1,10-phenanthroline were reacted with different internal and terminal alkynes to give access to a total of 7 × 7 = 49 triazolato complexes in a room-temperature catalyst-free iClick reaction. The reactants were mixed in a repurposed high-performance liquid chromatography (HPLC) autosampler, and the reaction progress was monitored by direct injection into an electrospray mass spectrometer. The ratio of the peak intensities of [Ru(N₃)(N∧N)(terpy)]⁺ and [Ru(triazolato)(N∧N)(terpy)]⁺ was converted to a colored heat map for facile visual inspection of the conversion ratio. By automated multiple injections of the reaction mixture in fixed time intervals and plotting peak intensities over reaction time, pseudo-first-order rate constants were easily determined. Finally, nonoverlapping isotope patterns of the azido starting materials and triazolato products enabled multiplexed parallel determination of rate constants for four different ruthenium(II) azido complexes from a single sample vial, thereby reducing experiment time by 75%.

Encapsulation of Gold-Based Anticancer Agents in Protease-Degradable Peptide Nanofilaments Enhances Their Potency

We investigated the use of amphiphilic, protease-cleavable peptides as encapsulation moieties for hydrophobic metallodrugs, in order to enhance their bioavailability and consequent activity. Two hydrophobic, gold-containing anticancer agents varying in aromatic ligand distribution (Au(I)-N-heterocyclic carbene compounds 1 and 2) were investigated. These were encapsulated into amphiphilic decapeptides that form soluble filamentous structures with hydrophobic cores, varying supramolecular packing arrangements and surface charge. Peptide sequence strongly dictates the supramolecular packing within the aromatic core, which in turn dictates drug loading. Anionic peptide filaments can effectively load 1, and to a lesser extent 2, while their cationic counterparts could not, collectively demonstrating that loading efficiency is dictated by both aromatic and electrostatic (mis)matching between drug and peptide. Peptide nanofilaments were nontoxic to cancerous and noncancerous cells. By contrast, those loaded with 1 and 2 displayed enhanced cytotoxicity in comparison to 1 and 2 alone, when exposed to Caki-1 and MDA-MB-231 cancerous cell lines, while no cytotoxicity was observed in noncancerous lung fibroblasts, IMR-90. We propose that the enhanced in vitro activity results from the enhanced proteolytic activity in the vicinity of the cancer cells, thereby breaking the filaments into drug-bound peptide fragments that are taken up by these cells, resulting in enhanced cytotoxicity toward cancer cells.

Highlights of New Strategies to Increase the Efficacy of Transition Metal Complexes for Cancer Treatments

Although important progress has been made, cancer still remains a complex disease to treat. Serious side effects, the insurgence of resistance and poor selectivity are some of the problems associated with the classical metal-based anti-cancer therapies currently in clinical use. New treatment approaches are still needed to increase cancer patient survival without cancer recurrence. Herein, we reviewed two promising-at least in our opinion-new strategies to increase the efficacy of transition metal-based complexes. First, we considered the possibility of assembling two biologically active fragments containing different metal centres into the same molecule, thus obtaining a heterobimetallic complex. A critical comparison with the monometallic counterparts was done. The reviewed literature has been divided into two groups: the case of platinum; the case of gold. Secondly, the conjugation of metal-based complexes to a targeting moiety was discussed. Particularly, we highlighted some interesting examples of compounds targeting cancer cell organelles according to a third-order targeting approach, and complexes targeting the whole cancer cell, according to a second-order targeting strategy.

The straightforward synthesis of N-coordinated ruthenium 4-aryl-1,2,3-triazolato complexes by [3 + 2] cycloaddition reactions of a ruthenium azido complex with terminal phenylacetylenes and non-covalent aromatic interactions in structures

The straightforward preparation of N-coordinated ruthenium triazolato complexes by [3 + 2] cycloaddition reactions of a ruthenium azido complex [Ru]-N3 (1, [Ru] = (η5-C5H5)(dppe)Ru, dppe = Ph2PCH2CH2PPh2) with a series of terminal phenylacetylenes is reported. The reaction products, N(2)-bound ruthenium 4-aryl-1,2,3-triazolato complexes such as [Ru]N3C2H(4-C6H4CN) (2), [Ru]N3C2H(4-C6H4CHO) (3), [Ru]N3C2H(4-C6H4F) (4), [Ru]N3C2H(Ph) (5) and [Ru]N3C2H(4-C6H4CH3) (6) were produced from 4-ethynylbenzonitrile, 4-ethynylbenzaldehyde, 1-ethynyl-4-fluorobenzene, phenylacetylene and 4-ethynyltoluene, respectively, at 80 °C or above under an atmosphere of air. To the best of our knowledge, this is the first example of the preparation of N-coordinated ruthenium aryl-substituted 1,2,3-triazolato complexes by the [3 + 2] cycloaddition of a metal-coordinated azido ligand and a terminal aryl acetylene, less electron-deficient terminal aryl alkynes. All of the compounds have been fully characterized and the structures of complexes 2, 3, 5 and 6 were confirmed by single-crystal X-ray diffraction analysis. Each compound participates in non-covalent aromatic interactions in the solid-state structure which can be favorable in the binding of DNA/biomolecular targets and has shown great potential in the development of biologically active anticancer drugs.

Just Add the Gold: Aggregation-Induced-Emission Properties of Alkynylphosphinegold(I) Complexes Functionalized with Phenylene-Terpyridine Subunits

A series of organometallic complexes containing an alkynylphosphinegold(I) fragment and a phenylene-terpyridine moiety connected together by flexible linker have been prepared using the specially designed terpyridine ligands. The compounds were studied crystallographically to reveal that all of them contain a linearly coordinated Au(I) atom and a free terpyridine moiety. The different orientations of the molecules relative to each other in the solid state determine the multiple noncovalent interactions such as antiparallel ππ stacking, CH-π, and CH-Au, but no aurophilic interactions are realized. The organometallic Au(I) complexes obtained show fluorescence in the solution and dual singlet-triplet emission in the solid state. This means that their photophysical behavior is determined by both intermolecular lattice-defined interactions and Au(I) atom introduction. Density functional theory computational analysis supported the assignment of emission to intraligand electronic transitions only inside the phenylene-terpyridine part with no Au(I) involved. In addition, a study of the nature of the excited states for the "dimer" with an antiparallel orientation of the terpyridine fragment showed that this orientation leads to the generation of abstracted singlet and triplet states, lowering their energy in comparison with the monomer complex. Thus, the complexes obtained can be qualified as examples of Au(I)-containing organometallic aggregation-induced-emission luminogens.

Rollover Cyclometalation vs Nitrogen Coordination in Tetrapyridyl Anticancer Gold(III) Complexes: Effect on Protein Interaction and Toxicity

In this work, a pair of gold(III) complexes derived from the analogous tetrapyridyl ligands H₂biqbpy1 and H₂biqbpy2 was prepared: the rollover, bis-cyclometalated [Au(biqbpy1)Cl ([1]Cl) and its isomer [Au(biqbpy2)Cl ([2]Cl). In [1]⁺, two pyridyl rings coordinate to the metal via a Au-C bond (C^∧N^∧N^∧C coordination) and the two noncoordinated amine bridges of the ligand remain protonated, while in [2]⁺ all four pyridyl rings of the ligand coordinate to the metal via a Au-N bond (N^∧N^∧N^∧N coordination), but both amine bridges are deprotonated. As a result, both complexes are monocationic, which allowed comparison of the sole effect of cyclometalation on the chemistry, protein interaction, and anticancer properties of the gold(III) compounds. Due to their identical monocationic charge and similar molecular shape, both complexes [1]Cl and [2]Cl displaced reference radioligand [³H]dofetilide equally well from cell membranes expressing the K_v11.1 (hERG) potassium channel, and more so than the tetrapyridyl ligands H₂biqbpy1 and H₂biqbpy2. By contrast, cyclometalation rendered [1]Cl coordinatively stable in the presence of biological thiols, while [2]Cl was reduced by a millimolar concentration of glutathione into metastable Au(I) species releasing the free ligand H₂biqbpy2 and TrxR-inhibiting Au⁺ ions. The redox stability of [1]Cl dramatically decreased its thioredoxin reductase (TrxR) inhibition properties, compared to [2]Cl. On the other hand, unlike [2]Cl, [1]Cl aggregated into nanoparticles in FCS-containing medium, which resulted in much more efficient gold cellular uptake. [1]Cl had much more selective anticancer properties than [2]Cl and cisplatin, as it was almost 10 times more cytotoxic to human cancer cells (A549, A431, A375, and MCF7) than to noncancerous cells (MRC5). Mechanistic studies highlight the strikingly different mode of action of the two compounds: while for [1]Cl high gold cellular uptake, nuclear DNA damage, and interaction with hERG may contribute to cell killing, for [2]Cl extracellular reduction released TrxR-inhibiting Au⁺ ions that were taken up in minute amounts in the cytosol, and a toxic tetrapyridyl ligand also capable of binding to hERG. These results demonstrate that bis-cyclometalation is an appealing method to improve the redox stability of Au(III) compounds and to develop gold-based cytotoxic compounds that do not rely on TrxR inhibition to kill cancer cells.

Luminescent Bimetallic IrIII /AuI Peptide Bioconjugates as Potential Theranostic Agents

Diverse iridium peptide bioconjugates and the corresponding iridium/gold bimetallic complexes have been synthesized starting from a cyclometallated carboxylic acid substituted IrIII complex [Ir(ppy)2 (Phen-5-COO)] by solid phase peptide synthesis (SPPS). The selected peptide sequences were an enkephalin derivative Tyr-Gly-Gly-Phe-Leu together with the propargyl-substituted species Tyr-Gly-Pgl-Phe-Leu to allow gold coordination (Pgl: propyrgyl-glycine, HC≡C-Gly), and a specific short peptide, Ala-Cys-Ala-Phen, containing a cysteine residue. Introduction of the gold center has been achieved via a click reaction with the alkynyl group leading to an organometallic Au-C(triazole) species, or by direct coordination to the sulfur atom of the cysteine. The photophysical properties of these species revealed predominantly an emission originating from the Ir complex, using mixed metal-to-ligand and ligand-to-ligand charge transfer excited states of triplet multiplicity. The formation of the peptide bioconjugates caused a systematic redshift of the emission profiles. Lysosomal accumulation was observed for all the complexes, in contrast to the expected mitochondrial accumulation triggered by the gold complexes. Only the cysteine-containing Ir/Au bioconjugate displayed cytotoxic activity. The absence of activity may be related to the lack of endosomal/lysosomal escape for the cationic peptide conjugates. Interestingly, the different coordination sphere of the gold atom may play a crucial role, as the Au-S(cysteine) bond may be more readily cleaved in a biological environment than the Au-C(triazole) bond, and thus the Au fragment could be released from or trapped in the lysosomes, respectively. This work represents a starting point in the development of bimetallic peptide bioconjugates as theranostics and in the knowledge of factors that contribute to anti-proliferative activity.

Potent Inhibition of Thioredoxin Reductase by the Rh Derivatives of Anticancer M(arene/Cp*)(NHC)Cl2 Complexes

Metal complexes provide a versatile platform to develop novel anticancer pharmacophores, and they form stable compounds with N-heterocyclic carbene (NHC) ligands, some of which have been shown to inhibit the cancer-related selenoenzyme thioredoxin reductase (TrxR). To expand a library of isostructural NHC complexes, we report here the preparation of Rh^III- and Ir^III(Cp*)(NHC)Cl₂ (Cp* = η⁵-pentamethylcyclopentadienyl) compounds and comparison of their properties to the Ru^II- and Os^II(cym) analogues (cym = η⁶-p-cymene). Like the Ru^II- and Os^II(cym) complexes, the Rh^III- and Ir^III(Cp*) derivatives exhibit cytotoxic activity with half maximal inhibitory concentration (IC₅₀) values in the low micromolar range against a set of four human cancer cell lines. In studies on the uptake and localization of the compounds in cancer cells by X-ray fluorescence microscopy, the Ru and Os derivatives were shown to accumulate in the cytoplasmic region of treated cells. In an attempt to tie the localization of the compounds to the inhibition of the tentative target TrxR, it was surprisingly found that only the Rh complexes showed significant inhibitory activity at IC₅₀ values of ∼1 μM, independent of the substituents on the NHC ligand. This indicates that, although TrxR may be a potential target for anticancer metal complexes, it is unlikely the main target or the sole target for the Ru, Os, and Ir compounds described here, and other targets should be considered. In contrast, Rh(Cp*)(NHC)Cl₂ complexes may be a scaffold for the development of TrxR inhibitors.

An Application Exploiting Aurophilic Bonding and iClick to Produce White Light Emitting Materials

The paper focuses on exploiting aurophilic bonding to produce white light emitting materials. Inorganic Click (iClick) is employed to link two or four Au(I) metal ions through a triazolate bridge. Depending on the choice of phosphine ligand (PEt3 or PPh3), dinuclear Au2-FO or tetranuclear Au4-FO complexes can be controllably synthesized (FO = 2-(9,9-dioctylfluoreneyl-)). The iClick products Au2-FO and Au4-FO are characterized by combustion analysis and multinuclear NMR, TOCSY 1D, 1H-13C gHMBC, and 1H-13C gHSQC. In addition, the photophysical properties of Au2-FO and Au4-FO were examined in THF solution. Transient absorption spectroscopy was employed to elucidate the excited state features of the gold compounds. Solution processed OLEDs were fabricated and characterized, which gave white light electroluminescence with CIE coordinates (0.34, 0.36), as seen referenced to CIE standard illuminant D65 (0.31, 0.32). TDDFT computational analysis of Au2-FO and Au4-FO reveals the origin of light emission. In the case of Au4-FO, direct excitation leads to increased aurophilic bonding in the excited state, and as a result the emission profile is broadened to cover a larger region of the visible spectrum, thus giving white light emission. Designing molecules that can access or increase aurophilic bonding in the excited state provides another tool for fine-tuning the emission profiles of gold complexes.

Water soluble palladium(ii) and platinum(ii) acyclic diaminocarbene complexes: solution behavior, DNA binding, and antiproliferative activity

Water soluble Pd(ii) and Pt(ii)–ADC species synthesized via the metal-mediated coupling of isocyanides and 1,2-diaminobenzene have demonstrated antitumor potential.

Mitochondria-Targeting Anticancer Metal Complexes

Background:

Since the serendipitous discovery of the antitumor activity of cisplatin there has been a continuous surge in studies aimed at the development of new cytotoxic metal complexes. While the majority of these complexes have been designed to interact with nuclear DNA, other targets for anticancer metallodrugs attract increasing interest. In cancer cells the mitochondrial metabolism is deregulated. Impaired apoptosis, insensitivity to antigrowth signals and unlimited proliferation have been linked to mitochondrial dysfunction. It is therefore not surprising that mitochondria have emerged as a major target for cancer therapy. Mitochondria-targeting agents are able to bypass resistance mechanisms and to (re-) activate cell-death programs.

Methods:

Web-based literature searching tools such as SciFinder were used to search for reports on cytotoxic metal complexes that are taken up by the mitochondria and interact with mitochondrial DNA or mitochondrial proteins, disrupt the mitochondrial membrane potential, facilitate mitochondrial membrane permeabilization or activate mitochondria-dependent celldeath signaling by unbalancing the cellular redox state. Included in the search were publications investigating strategies to selectively accumulate metallodrugs in the mitochondria.

Results:

This review includes 241 references on antimitochondrial metal complexes, the use of mitochondria-targeting carrier ligands and the formation of lipophilic cationic complexes.

Conclusion:

Recent developments in the design, cytotoxic potency, and mechanistic understanding of antimitochondrial metal complexes, in particular of cyclometalated Au, Ru, Ir and Pt complexes, Ru polypyridine complexes and Au-N-heterocyclic carbene and phosphine complexes are summarized and discussed.

Trastuzumab gold-conjugates: synthetic approach and in vitro evaluation of anticancer activities in breast cancer cell lines

We describe the preparation of gold(i)-compounds that are amenable to efficient bioconjugation with monoclonal antibodies via activated ester or maleimide linkers. New Trastuzumab-gold conjugates were synthesized and fully characterized. These bioconjugates are significantly more cytotoxic (sub-micromolar range) to HER2-positive breast cancer cells than the gold complexes and Trastuzumab.

A novel Pt(iv) mono azido mono triazolato complex evolves azidyl radicals following irradiation with visible light

A novel Pt^IV azido triazolato complex exists as an equilibrium between two species in d₃-MeCN and evolves azide radicals (but not hydroxide radicals) when irradiated with visible light.

The platinum(iv) azido complex trans,trans,trans-[Pt^IV(N₃)₂(OH)₂(py)₂] (1) undergoes cycloaddition with 1,4-diphenyl-2-butyne-1,4-dione (2) under mild, catalyst-free conditions, affording a number of mono and bis click products. The major mono click product (3) exists in MeCN as an equilibrium mixture between two species; 3a and 3b rapidly interconvert through nucleophilic attack of the axial Pt–OH group at the adjacent Ph–CO group. The kinetic and thermodynamic parameters for this interconversion have been measured by selective saturation-transfer NMR spectroscopic experiments and are consistent with cyclisation at the Pt centre. Complex 3b was also characterised by X-ray crystallography. Visible light irradiation (440–480 nm) of 3 in d₃-MeCN produces azidyl radicals (N₃˙), as demonstrated by EPR spin-trapping with DMPO; no generation of hydroxyl radicals was observed. ¹H–¹⁹⁵Pt HMBC NMR confirmed that the photoproducts were Pt^IV rather than Pt^II species, and HPLC was consistent with these being [3–N₃]⁺ species; no facile photoejection of the triazolato ligand was observed, consistent with MS/MS fragmentation of 3. When 3 was irradiated in the presence of 5′-GMP, no 5′-GMP photoproducts were observed, suggesting that complex 3 is likely to exhibit significantly simplified biological activity (release of azidyl radicals but not DNA binding) compared with complex 1.

On the interaction of N-heterocyclic carbene Ir+I complexes with His and Cys containing peptides

In the interaction of an [Ir(+i)(COD)(NHC)Cl] complex with model peptides a chelating motif with a particularly interesting bimetallic peptide-bridged Ir(+iii)–NHC motif was identified with loss of the COD and Cl ligands and oxidation of the metal.

A clickable NHC-Au(i)-complex for the preparation of stimulus-responsive metallopeptide amphiphiles

We report the synthesis of an alkyne functionalised NHC-Au(i)-complex which is conjugated with amphiphilic oligopeptides using a copper(i) catalysed cycloaddition. The resulting Au(i)-metalloamphiphiles are shown to self-assemble into charge-regulated stimulus-responsive supramolecular polymers in water via a weakly cooperative polymerisation mechanism.

Platinum(iv) azido complexes undergo copper-free click reactions with alkynes

We report our investigations into the first examples of copper-free 1,3-dipolar cycloaddition (click) reactions of electrophiles with a PtIV azido complex. The Pt-IV azido complex trans, trans, trans-[PtIV(py)2(N3)2(OH)2] (1) was reactive towards dimethyl acetylenedicarboxylate (DMAD) (2), diethyl acetylenedicarboxylate DEACD (3), N-[(1R,8S,9s)-bicyclo[6.1.0]non-4-yn-9-ylmethyloxycarbonyl]-1,8-diamino-3,6-dioxaoctane (BCN) (11) and dibenzocyclooctyne-amine (DBCO) (12) resulting in formation of the corresponding mono (a) and bis-substituted (b) complexes. Complexes of 2 undergo further reactions between the Pt centre and the carbonyl group to form 2a' and 2b'. This is not seen for the products of the corresponding PtII azido complex trans-[Pt(py)2(N3)2] with acetylene 2. Novel complexes 2a', 2b', 11a and 11b have been characterised by multinuclear NMR, IR and UV-vis spectroscopy and ESI-MS. These reactions represent new synthetic routes to novel Pt(iv) complexes.

Synthesis of hydroxyl-functionalized N-heterocyclic carbene gold(i) complexes and peptide conjugates

The synthesis and characterization of a series of new cationic gold(i) complexes with hydroxyl-functionalized N-heterocyclic carbene (NHC) ligands is described. They are valuable building blocks for further derivatization: as a first example, coupling with amino acids and a dipeptide, respectively, successfully results in amino acid and peptide conjugates that are hard to obtain by other synthetic routes.

Dinuclear Au(i) N-heterocyclic carbene complexes derived from unsymmetrical azolium cyclophane salts: potential probes for live cell imaging applications

We have synthesized a new series of azolium cyclophanes and used them as precursors of inherently luminescent dinuclear Au(i)-N-heterocyclic carbene (NHC) complexes. The azolium cyclophanes contained two azolium groups (either imidazolium or benzimidazolium), an o-xylyl group, and an alkyl linker chain (either C2, C3 or C4). All of the azolium cyclophanes were characterised by X-ray diffraction studies and VT NMR studies, and all were fluxional in solution on the NMR timescale. The C3- and C4-linked azolium cyclophanes served as precursors of Au2L2(2+) complexes (L is a cyclophane bis(NHC) ligand). Due to the unsymmetrical nature of the azolium cyclophanes, the Au2L2(2+) complexes each existed as cis and trans isomers. X-ray diffraction studies showed that the Au2L2(2+) complexes had short intramolecular AuAu distances, in the range 2.9-3.3 Å, suggestive of an aurophilic attraction, presumably as a consequence of the geometrical constraints imposed by the cyclophane bis(NHC) ligands. The complexes having the shortest AuAu distances (i.e., those based on C3-linked cyclophanes) exhibited intense luminescence in solution. The uptake of one of the dinuclear Au-NHC complexes by tumorigenic cells, and its subsequent distribution and toxicity in the cells, was monitored by luminescence microscopy over 6 h and proliferation measurements, respectively.

Metal NHC Complexes with Naphthalimide Ligands as DNA-Interacting Antiproliferative Agents

Naphthalimide-based N-heterocyclic carbene (NHC) complexes of the type [(1,5-cyclooctadiene)(NHC)RhCl)] (4 a-c), [(p-cymene)(NHC)RuCl₂ )] (5 a-c), and [(NHC)CuBr] (6 a-c) were synthesized and investigated as antiproliferative agents that target DNA. The cytotoxic effects were largely driven by the naphthalimide structure, which is a DNA-intercalating moiety. Regarding the metal center, the highest activities were observed with the rhodium complexes, and cytotoxic activity was significantly lower for the ruthenium derivatives. The stable coordination of the NHC ligands of selected complexes 4 b and 5 b in solution was confirmed, and their DNA binding properties were studied by UV/Vis spectroscopy, mass spectrometry, and circular dichroism. Stable intercalative binding into the DNA for all selected naphthalimide-based complexes is indicated by high DNA binding constants. Particularly efficient binding was observed in the case of the rhodium complex 4 b. More detailed biological studies on 4 b showed promising activities against multidrug-resistant Nalm-6 cells and confirmed an important role for mitochondrial pathways in 4 b-induced apoptosis.

Chrysin functionalized NHC–Au(i) complexes: synthesis, characterization and effects on the nematode Caenorhabditis elegans

The synthesis and biological effects on the nematodeCaenorhabditis elegansof chrysin functionalized Au(i)–NHC complexes are reported.

(C^Npz^C)AuIII complexes of acyclic carbene ligands: synthesis and anticancer properties

Synthesis of amino ester conjugated (C^N^pz^C)Au acyclic carbene complexes with low micromolar cytotoxicity on human cancer cells.

Novel mitochondria targeted copper(ii) complexes of ferrocenyl terpyridine and anticancer active 8-hydroxyquinolines showing remarkable cytotoxicity, DNA and protein binding affinity

Mixed-ligand ferrocenyl copper(ii) complexes target the mitochondria of cancer cells showing remarkable cytotoxicity against HeLa and MCF-7 cancer cells while being much less toxic to MCF-10A normal cells.

Photophysical and photochemical studies of tricarbonyl rhenium(i) N-heterocyclic carbene complexes containing azide and triazolate ligands

Rhenium NHC complexes bound to azide anions readily react with alkynes to form the corresponding triazolate complexes, a new class of photochemically active species.