Gold(I) Complexes of N-Heterocyclic Carbenes and Pyridines

Amplification of luminescence of stable radicals by coordination to NHC-gold(I) complex

The luminescence of stable radicals can be enhanced by coordination to metal complexes. The 4% fluorescence quantum yield of (3,5-difluoro-4-pyridyl)bis(2,4,6-trichlorophenyl)methyl radical (F₂PyBTM) in dichloromethane was enhanced up to 36% by coordination to Au^I with N-heterocyclic carbene ligand, which is a record for metal-radical complexes.

Gold Metallodrugs to Target Coronavirus Proteins: Inhibitory Effects on the Spike-ACE2 Interaction and on PLpro Protease Activity by Auranofin and Gold Organometallics*

Gold complexes have a long tradition in medicine and for many examples antirheumatic, anticancer or anti-infective effects have been confirmed. Herein, we evaluated the lead compound Auranofin and five selected gold organometallics as inhibitors of two relevant drug targets of severe acute respiratory syndrome coronaviruses (SARS-CoV). The gold metallodrugs were effective inhibitors of the interaction of the SARS-CoV-2 spike protein with the angiotensin converting enzyme 2 (ACE2) host receptor and might thus interfere with the viral entry process. The gold metallodrugs were also efficient inhibitors of the papain-like protease (PLpro) of SARS-CoV-1 and SARS-CoV-2, which is a key enzyme in the viral replication. Regarding PLpro from SARS-CoV-2, the here reported inhibitors are among the very first experimentally confirmed examples with activity against this target enzyme. Importantly, the activity of the complexes against both PLpro enzymes correlated with the ability of the inhibitors to remove zinc ions from the labile zinc center of the enzyme. Taken together, the results of this pilot study suggest further evaluation of gold complexes as SARS-CoV antiviral drugs.

Gold(I) Complexes Containing Phosphanyl- and Arsanylborane Ligands

The structural and photophysical properties of a series of new Au^I compounds have been studied. The reactions of AuCl(tht) with the phosphanyl- and arsanylboranes RR^' EBH₂ NMe₃ (E=P, As; R=H, Ph; R'=H, Ph, tBu) afford the complexes [AuCl(RR^' EBH₂ NMe₃ )]. In the solid state, [AuCl(H₂ PBH₂ NMe₃ )]₂ (2 a) is a dimer showing unsupported intermolecular aurophilic interactions with short Au⋅⋅⋅Au distances. In contrast, [AuCl(H₂ AsBH₂ NMe₃ )]_n (2 b) aggregates to form 1D chains. Organic substituents on the pnictogen atoms lead to discrete molecules in [AuCl(RR^' PBH₂ NMe₃ )] (2 c: R=H, R'=tBu; 2 d: R=R'=Ph). To increase the aurophilicity, the ionic homoleptic complexes [Au(RR^' EBH₂ NMe₃ )₂ ][AlCl₄ ] (3 a-d) have been synthesized, for which 3 a,b form chains in the solid state and exhibit luminescence. The emissions show a drastic redshift with temperature decrease, correlating with decreasing Au⋅⋅⋅Au distances. DFT calculations provide insight into the bonding situation of the products.

N-heterocyclic carbene metal complexes: photoluminescence and applications

This review covers the advances made in the synthesis and applications of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands.

Development of a new class of aromatase inhibitors: design, synthesis and inhibitory activity of 3-phenylchroman-4-one (isoflavanone) derivatives

Aromatase (CYP19) catalyzes the aromatization reaction of androgen substrates to estrogens, the last and rate-limiting step in estrogen biosynthesis. Inhibition of aromatase is a new and promising approach to treat hormone-dependent breast cancer. We present here the design and development of isoflavanone derivatives as potential aromatase inhibitors. Structural modifications were performed on the A and B rings of isoflavanones via microwave-assisted, gold-catalyzed annulation reactions of hydroxyaldehydes and alkynes. The in vitro aromatase inhibition of these compounds was determined by fluorescence-based assays utilizing recombinant human aromatase (baculovirus/insect cell-expressed). The compounds 3-(4-phenoxyphenyl)chroman-4-one (1h), 6-methoxy-3-phenylchroman-4-one (2a) and 3-(pyridin-3-yl)chroman-4-one (3b) exhibited potent inhibitory effects against aromatase with IC(50) values of 2.4 μM, 0.26 μM and 5.8 μM, respectively. Docking simulations were employed to investigate crucial enzyme/inhibitor interactions such as hydrophobic interactions, hydrogen bonding and heme iron coordination. This report provides useful information on aromatase inhibition and serves as a starting point for the development of new flavonoid aromatase inhibitors.

[{Au(IPr)}2(μ-OH)]X complexes: synthetic, structural and catalytic studies

The synthesis of a series of dinuclear gold hydroxide complexes has been achieved. These complexes of type [{Au(IPr)}(2)(μ-OH)]X (X=BF(4), NTf(2), OTf, FABA, SbF(6); IPr=2,6-bis(disopropylphenyl)imidazol-2-ylidene; NTf(2)=bis(trifluoromethanesulfonyl)imidate; OTf=trifluoromethanesulfonate; FABA=tetrakis(pentafluorophenyl)borate) are easily formed in the presence of water and prove highly efficient in the catalytic hydration of nitriles. Their facile formation in aqueous media suggests they are of relevance in gold-catalyzed reactions involving water. Additionally, a series of [Au(IPr)(NCR)][BF(4)] (R=alkyl, aryl) complexes was synthesized as they possibly occur as intermediates in the catalytic reaction mechanism. (1)H and (13)C NMR data as well as key bond lengths obtained by X-ray diffraction studies are compared and reveal an interesting structure-activity relationship. The collected data indicate a negligible effect of the nature of the nitrile on the reactivity of [Au(L)(NCR)][X] complexes in catalysis.