Inhibition mechanism of urease by Au(III) compounds unveiled by x-ray diffraction analysis

The nickel-dependent enzyme urease is a virulence factor for a large number of critical human pathogens, making this enzyme a potential target of therapeutics for the treatment of resistant bacterial infections. In the search for novel urease inhibitors, five selected coordination and organometallic Au(III) compounds containing N∧N or C∧N and C∧N∧N ligands were tested for their inhibitory effects against Canavalia ensiformis (jack bean) urease. The results showed potent inhibition effects with IC50 values in the nanomolar range. The 2.14 Å resolution crystal structure of Sporosarcina pasteurii urease inhibited by the most effective Au(III) compound [Au(PbImMe)Cl2]PF6 (PbImMe = 1-methyl-2-(pyridin-2-yl)-benzimidazole) reveals the presence of two Au ions bound to the conserved triad αCys322/αHis323/αMet367. The binding of the Au ions to these residues blocks the movement of a flap, located at the edge of the active site channel and essential for enzyme catalysis, completely obliterating the catalytic activity of urease. Overall, the obtained results constitute the basis for the design of new gold complexes as selective urease inhibitors with future antibacterial applications

Exo-functionalized metallacages as host-guest systems for the anticancer drug Cisplatin

Within the framework of designing new self-assembled metallosupramolecular architectures for drug delivery, seven [Pd2L4]4+ metallacages (L = 2,6-bis(pyridine-3-ylethynyl)pyridine) featuring different groups in exo-position, selected to enhance the cage solubility in aqueous environment, were synthesized. Thus, carboxylic acids, sugars, and PEG groups were tethered to the bispyridyl ligands directly or via disulfide bond formation, as well as via click chemistry. The ligands and respective cages were characterized by different methods, including NMR spectroscopy and high-resolution electrospray mass spectrometry (HR-ESI-MS). While the two ligands featuring carboxylic acid-functionalized groups showed improved solubility in water, the other ligands were soluble only in organic solvents. Unfortunately, all the respective self-assembled cages were also insoluble in water. Afterwards, the encapsulation properties of the anticancer drug cisplatin in selected [Pd2L4]X4 cages (X = NO−3, BF−4) were studied by 1H, 1H DOSY, and 195Pt NMR spectroscopy. The effect of the counter ions as well as of the polarity of the solvent in the drug encapsulation process were also investigated, and provided useful information on the host-guest properties of these experimental drug delivery systems. Our results provide further experimental support for previous studies that suggest the desolvation of guests from surrounding solvent molecules and the resulting solvent rearrangement may actually be the primary driving force for determining guest binding affinities in metallacages, in the absence of specific functional group interactions

Polymer masked-unmasked protein therapy: Identification of the active species after amylase-activation of dextrin-colistin conjugates.

Polymer masked–unmasked protein therapy (PUMPT) uses conjugation of a biodegradable polymer, such as dextrin, hyaluronic acid, or poly(l-glutamic acid), to mask a protein or peptide’s activity; subsequent locally triggered degradation of the polymer at the target site regenerates bioactivity in a controllable fashion. Although the concept of PUMPT is well established, the relationship between protein unmasking and reinstatement of bioactivity is unclear. Here, we used dextrin–colistin conjugates to study the relationship between the molecular structure (degree of unmasking) and biological activity. Size exclusion chromatography was employed to collect fractions of differentially degraded conjugates and ultraperformance liquid chromatography–mass spectrometry (UPLC–MS) employed to characterize the corresponding structures. Antimicrobial activity was studied using a minimum inhibitory concentration (MIC) assay and confocal laser scanning microscopy of LIVE/DEAD-stained biofilms with COMSTAT analysis. In vitro toxicity of the degraded conjugate was assessed using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. UPLC–MS revealed that the fully “unmasked” dextrin–colistin conjugate composed of colistin bound to at least one linker, whereas larger species were composed of colistin with varying lengths of glucose units attached. Increasing the degree of dextrin modification by succinoylation typically led to a greater number of linkers bound to colistin. Greater antimicrobial and antibiofilm activity were observed for the fully “unmasked” conjugate compared to the partially degraded species (MIC = 0.25 and 2–8 μg/mL, respectively), whereas dextrin conjugation reduced colistin’s in vitro toxicity toward kidney cells, even after complete unmasking. This study highlights the importance of defining the structure–antimicrobial activity relationship for novel antibiotic derivatives and demonstrates the suitability of LC–MS to aid the design of biodegradable polymer–antibiotic conjugates

Construçao do masculino na Curitiba das décadas de 1940 e 1950 tornar-se homem

Orientadora : Maria Luiza AndreazzaAutor não autorizou a divulgação do arquivo digitalDissertaçao (mestrado) - Universidade Federal do Paraná, Setor de Ciencias Humanas, Letras e ArtesInclui referência

Insights into the mechanisms of aquaporin-3 inhibition by gold(III) complexes: the importance of non-coordinative adduct formation

A series of six new Au(III) coordination compounds with phenanthroline ligands have been synthesized and studied for the inhibition of the water and glycerol channel aquaporin-3 (AQP3). From a combination of different experimental and computational approaches, further insights into the mechanisms of AQP3 inhibition by gold compounds at a molecular level have been gained. The results evidence the importance of noncoordinative adduct formation, prior to “covalent” protein binding, to achieve selective AQP3 inhibition

Supramolecular metal-based structures for applications in cancer therapy [Chapter 9]

Discrete supramolecular constructs continue to attract important research interest because of their myriad of applications, including in biology. The biomedical application of supramolecular coordination complexes (SCCs) is still an emergent field of study, but the pioneering examples discussed in this chapter confirm that these scaffolds hold promise as novel anticancer drugs, endowed with different mechanisms of action compared to classical small-molecule and metal-based cytotoxic agents, often linked to their peculiar molecular recognition properties. Moreover, the host–guest chemistry of SCCs can also be exploited to design a new generation of drug delivery systems for anticancer chemotherapeutics. In fact, the robustness of supramolecular metal-based complexes allows incorporation of different functionalities in the same scaffold to enable imaging in cells, as well as targeting and stimuli responsiveness. Certainly, the myriad of possible SCCs and their almost limitless modularity and tunability, without significant synthetic penalty, suggests that the biomedical applications of such species will continue along this already promising path. In this chapter, we aim to summarize the main concepts in this fascinating research area, illustrating representative examples and providing a critical discussion of the state-of-the-art

Selective targeting of PARP-1 zinc finger recognition domains with Au(III) organometallics

The binding of Au(iii) complexes to the zinc finger domain of the anticancer drug target PARP-1 was studied using a hyphenated mass spectrometry approach combined with quantum mechanics/molecular mechanics (QM/MM) studies. Competition experiments were carried out, whereby each Au complex was exposed to two types of zinc fingers. Notably, the cyclometallated Au-C^N complex was identified as the most selective candidate to disrupt the PARP-1 zinc finger domain, forming distinct adducts compared to the coordination compound Auphen

Redox Couple Involving NO_<i>x</i> in Aerobic Pd-Catalyzed Oxidation of sp³‑C–H Bonds: Direct Evidence for Pd–NO₃^–/NO₂^– Interactions Involved in Oxidation and Reductive Elimination

NaNO₃ is used in oxidative Pd-catalyzed processes as a complementary co-catalyst to common oxidants, e.g., Cu^II salts, in C–H bond activation and Wacker oxidation processes. NaNO₃ and NaNO₂ (with air or O₂) assist the sp³-C–H bond acetoxylation of substrates bearing an N-directing group. It has been proposed previously that a redox couple is operative. The role played by NO_<i>x</i> anions is examined in this investigation. Evidence for an NO_<i>x</i> anion interaction at Pd^II is presented. Palladacyclic complexes containing NO_<i>x</i> anions are competent catalysts for acetoxylation of 8-methylquinoline, with and without exogenous NaNO₃. The oxidation of 8-methylquinoline to the corresponding carboxylic acid has also been noted at Pd^II. ¹⁸O-Labeling studies indicate that oxygen derived from nitrate appears in the acetoxylation product, the transfer of which can only occur by interaction of ¹⁸O at Pd with a coordinating-acetate ligand. Nitrated organic intermediates are formed under catalytic conditions, which are converted to acetoxylation products, a process that occurs with (50 °C) and without Pd (110 °C). A catalytically competent palladacyclic dimer intermediate has been identified. Head-space analysis measurements show that NO and NO₂ gases are formed within minutes on heating catalytic mixtures to 110 °C from room temperature. Measurements by in situ infrared spectroscopy show that N₂O is formed in sp³-C–H acetoxylation reactions at 80 °C. Studies confirm that cyclopalladated NO₂ complexes are rapidly oxidized to the corresponding NO₃ adducts on exposure to NO₂(g). The investigation shows that NO_<i>x</i> anions act as participating ligands at Pd^II in aerobic sp³-C–H bond acetoxylation processes and are involved in redox processes