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A catalytic system for a phosphorus ligand-free Suzuki-Miyaura reaction in water at room temperature was disclosed. Ammonium 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonate) (ABTS) was an efficient promoterand actedboth asa ligand and as a surfactant for the synthesis of biaryl compounds via the Suzuki-Miyaura reaction in water. The targeted biaryl architectures were achieved under mild conditions with high efficiency and good functional group tolerance. Key words: Suzuki-Miyaura reaction, biaryl, ligand free, 22'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), water. Nous presentons un systeme catalytique sans ligand phosphore pour la reaction de SuzukiMiyaura dans l'eau a temperature ambiante. Le 2,2'azino-bis(3-ethylbenzohiazoline-6-sulfonate) d'ammonium (ABTS) s'est revele etre un promoteur efficace, agissant a la fois comme ligand et comme tensioactif dans la synthese de composes biaryliques par couplage de SuzukiMiyaura dans l'eau. Ce systeme catalytique a permis de former les structures biaryliques ciblees dans des conditions douces avec une grande efficacite et une bonne tolerance aux groupements fonctionnels. [Traduit par la Redaction] Mots-cles: reaction de Suzuki-Miyaura, biaryle, sans ligand, 22'-azino-bis(acide 3ethylbenzohiazoline-6-sulfonique), eau., Introduction As a versatile alternative to the formation of C-C bonds, (1,2) the Suzuki-Miyaura coupling reaction has found extensive use in the synthesis of natural products, pharmaceuticals, and advanced materials [...]

Author(s): Rutger D. Luteijn [sup.1] , Shivam A. Zaver [sup.2] , Benjamin G. Gowen [sup.3] [sup.4] , Stacia K. Wyman [sup.3] , Nick E. Garelis [sup.1] , Liberty Onia [sup.1] [...], The accumulation of DNA in the cytosol serves as a key immunostimulatory signal associated with infections, cancer and genomic damage.sup.1,2. Cytosolic DNA triggers immune responses by activating the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway.sup.3. The binding of DNA to cGAS activates its enzymatic activity, leading to the synthesis of a second messenger, cyclic guanosine monophosphate-adenosine monophosphate (2'3'-cGAMP).sup.4-7. This cyclic dinucleotide (CDN) activates STING.sup.8, which in turn activates the transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor [kappa]-light-chain-enhancer of activated B cells (NF-[kappa]B), promoting the transcription of genes encoding type I interferons and other cytokines and mediators that stimulate a broader immune response. Exogenous 2'3'-cGAMP produced by malignant cells.sup.9 and other CDNs, including those produced by bacteria.sup.10-12 and synthetic CDNs used in cancer immunotherapy.sup.13,14, must traverse the cell membrane to activate STING in target cells. How these charged CDNs pass through the lipid bilayer is unknown. Here we used a genome-wide CRISPR-interference screen to identify the reduced folate carrier SLC19A1, a folate-organic phosphate antiporter, as the major transporter of CDNs. Depleting SLC19A1 in human cells inhibits CDN uptake and functional responses, and overexpressing SLC19A1 increases both uptake and functional responses. In human cell lines and primary cells ex vivo, CDN uptake is inhibited by folates as well as two medications approved for treatment of inflammatory diseases, sulfasalazine and the antifolate methotrexate. The identification of SLC19A1 as the major transporter of CDNs into cells has implications for the immunotherapeutic treatment of cancer.sup.13, host responsiveness to CDN-producing pathogenic microorganisms.sup.11 and--potentially--for some inflammatory diseases. A genome-wide CRISPR-interference screen is used to identify the reduced folate carrier SLC19A1 as the major transporter of cyclic dinucleotides in human cells, with potential roles in immunotherapeutic treatment of cancer, immune responses to pathogens and inflammatory diseases.

G protein-coupled receptors (GPCRs) are physiologically important transmembrane signalling proteins that trigger intracellular responses upon binding of extracellular ligands. Despite recent breakthroughs in GPCR crystallography (1-3), the details of ligand-induced [...]

The low-molecular-mass organic acid anion 2-ketogluconate (kG) is produced via microbial activity in rhizosphere soils. One of the mechanisms by which this organic ligand may influence the chemistry of soil systems is through adsorption by constant-potential minerals. This study examined the adsorption of kG onto gibbsite and kaolinite in the presence or absence of P[O.sub.4], As[O.sub.4], and S[O.sub.4] as a function of pH and ionic strength. The adsorption edge studies were performed in the pH 3 to 10 range and at ambient (20-22[degrees]C) temperatures. The adsorption of kG is a function of solution pH (decreasing with increasing pH) and independent of solution ionic strength, supporting the conclusion that kG is adsorbed by ligand exchange mechanisms. The adsorption of kG was decreased at all pH values in the presence of P[O.sub.4] and As[O.sub.4], and was not significantly affected by the presence of S[O.sub.4] at pH values >5. The decrease in kG adsorption in the presence of As[O.sub.4] and P[O.sub.4] is further evidence that kG is adsorbed via specific retention mechanisms. The addition of kG to gibbsite containing readsorbed P[O.sub.4] did not result in P[O.sub.4] displacement, regardless of the concentration of kG. Ligand adsorption was modeled using the adsorption edge data and the 1-pK basic Stern surface complexation model. The kG adsorption data was described by the formation of two inner-sphere surface species: mononuclear monodentate and binuclear bidentate. The chemical models and associated intrinsic equilibrium constants developed to describe ligand adsorption in single-adsorbate gibbsite systems were used to predict ligand retention in the kaolinite and binary-adsorbate systems. In this manner, the competitive adsorption of all ligands as a function of pH was adequately described. The findings of this study indicate that kG is specifically retained by common soil minerals and may impact the availability of P[O.sub.4] and other specifically retained ligands in the rhizosphere. Abbreviations: kG, 2-ketogluconate; LMMOA, low-molecular-mass organic acid; WSOS/DF, weighted sum of squares of residuals divided by the degrees of freedom.

The nuclear receptor PXR (pregnane X receptor) is a broad-specificity sensor that recognizes a wide variety of synthetic drugs and xenobiotic agents. On activation by these compounds, PXR coordinately induces a network of transporters, cytochrome P450 enzymes, and other genes that effectively clear xenobiotics from the liver and intestine. Like PXR, the majority of its target genes also possess a broad specificity for exogenous compounds. Thus, PXR is both a sensor and effector in a well integrated and generalized pathway for chemical immunity. Although it is clear that PXR responds to numerous foreign compounds, it is unclear whether it possesses an endogenous ligand. To address this issue, we noted that there is substantial overlap in the substrate specificities of PXR and its critical CYP3A target gene. This prompted us to ask whether endogenous CYP3A substrates also serve as PXR ligands. We demonstrate that 5[beta]-cholestane-3[alpha], 7[alpha], 12[alpha]-triol (triol), a cholesterol-derived CYP3A substrate, is a potent PXR agonist that effectively induces cyp3a expression in mice. This defines a critical salvage pathway that can be autoinduced to minimize triol accumulation. In contrast, triol can accumulate to very high levels in humans, and unlike mice, these people develop the severe clinical manifestations of cerebrotendinous xanthomatosis. The reason for these dramatic species differences has remained unclear. We now demonstrate that triol fails to activate human PXR or induce the CYP3A-salvage pathway. This explains why humans are more susceptible to sterol accumulation and suggests that synthetic ligands for human PXR could be used to treat cerebrotendinous xanthomatosis and other disorders of cholesterol excess.

Cysteine scanning mutagenesis of the transmembrane domains 5 and 6 reveal that phenylalanine204 and tyrosine266 are important for receptor signaling. Data are consistent with the role of these aromatic residues near the ends of the transmembrane segments in the alpha-receptor promoting ligand activation.

The X-ray crystallographic analysis of an apo, a binary complex, and a tertiary complex of human formaldehyde dehydrogenase, with the respective substrates bound, show that the binding of the first substrate, alcohol or enzyme, leads to only minor changes in the enzyme structure. Data suggest that the substrate binding follows a random mechanism.

Research discusses the binding of europium(III), magnesium(II), and manganese(II) to an RNA tetraloop of the GNRA family. The binding events are driven by separate pathways. The solution structure of the GAAA tetraloop indicates that 5' side of the loop contains ligands to encapsulate the europium(II) ion with specificity.

Site-directed mutagenesis of cystathionine beta-synthase demonstrates that heme saturation does not lead to pyridoxal phosphate saturation, as shown by mutant enzymes. Data reveal that both H65 and C52 enzyme variants exhibit low catalytic activity and are modulated by the changes in the heme binding domain.

Results demonstrate that both the RNA-dependent protein kinase double-stranded RNA binding motifs simultaneously bind to kinase activating ligands. The RNAs that do not participate in this binding function act as antagonists of kinase activation. The binding sites for the individual double-stranded RNA binding motifs on RNA ligands are described.

The crystal structure of the periplasmic penta-heme cytochrome c nitrite reductase of Escherichia coli shows that four hemes of the enzyme exhibit bis-histidine axial heme-iron ligation with the catalytic heme-iron showing a distal lysine ligand and a proximal oxygen ligand. The spectroscopic signals and redox potentials of individual hemes are discussed.

Combinatorial small molecule growth algorithm was used to design inhibitors for human carbonic anhydrase II. Two enantiomeric candidate molecules were predicted to bind with high potency (with R isomer binding stronger than S), but in two distinct conformations. The experiments verified that computational predictions concerning the binding affinities and the binding modes were correct for both isomers. The designed R isomer is the best-known inhibitor ([K.sub.d] ~ 30 pM) of human carbonic anhydrase II.

Results reveal that the ligands for the catalytically active zinc metal ion of the gamma subunit of the oxaloacetate decarboxylase sodium pump are aspartate 62, histidine 77, and histidine 82. Data indicate that the catalytic rate of the enzyme subunit is dependent on the amount of zinc present in the protein subunit.

Protein-protein interactions are mediated by PDZ domains, which recognize specific peptide motifs. Data indicate that internal motif of the neuronal nitric oxide synthase of beta-hairpin conformation mediates the binding of peptide motifs.

Results demonstrate that high stability of the mixed copper ternary complex systems is not due to the global hardness. Data suggest that local softness and electron affinity influence their formation constants and reactivity behavior as revealed by density functional analysis.

Results show that zinc cofactor is a structural component of the McbB subunit of the purified multimeric enzyme, the microcin B17 synthetase. Data indicate cysteine residue serves as the metal ligand.

Research describes structural and magnetic properties of six chiroporphyrins. Results show bond-stretch isomerism exists in the form of hydrogen bonding from an aqua ligand of iron(III) extending to ethanol or water molecule, which may be involved in the regulation of hemoprotein structure and function.

Organic synthesis of cyclohexadiene ligands starting from tricarbonyliron-diene complexes is presented. Recent developments in the methodologies for the synthesis of tricarbonyliron transfer reagents and the catalytic complexation of dienes by the tricarbonyliron together with the asymmetric catalytic complexation of cyclohexa-1,3-dienes are discussed.

This paper examines the various steps involved in the organic synthesis involving monocarbanionic organometallic reagents. Research reveals that these compounds in the presence of titanium derivatives behave as dicarbanionics when reacting with electrophiles.

This review discusses the rate and selectivity of metal-catalyzed reactions as influenced by the bite angle of the bidentate ligands. Data reveal that ligands are involved in the stabilization or destabilization of the reaction intermediates and the bite angle brings about the steric hindrance between the ligand and the substrate.

Research demonstrates the synthesis of the chelating ligand enantiopure (plus)- and (minus)- 2,2',5,5'-tetramethyl-4,4'-bis(diphenylphosphino)-3,3'-bithiophene exhibiting a C(sub)2-symmetry. The electron rich metal associated diphosphine serves as catalysts in homogeneous hydrogenation of prostereogenic carbonyl functions.

Research demonstrates that the peptidosulfonamide tweezers are prepared by the solid-phase synthetic approach. Results show that the solid-phase tweeezer ligand functions in solution-phase catalysis as well and the methodology is useful in the optimization of the tweezer and determination of substrate range.

Research was conducted to determine the role of an amphipathic alpha helix 9 in conferring stability upon glutathione transferease. Mutational analysis indicate an interaction between helix 9 and enzyme leads to stability which in turn increases enzyme's affinity to bind ligands at noncatalytic binding sites.

In this paper, we describe a general procedure to evaluate the thermodynamics of the interaction between polypeptides and hydrophobic ligands in the presence of aquo-organic solvent mixtures. These studies address experimental requirements for the determination of the linear free energy relationships, derivation of partition coefficients or other extrathermodynamic parameters such as contact areas, or assessment of the conformational changes that may occur when polypeptides or proteins interact with immobilized nonpolar ligands. Not unexpectedly from thermodynamic arguments, the trends and magnitudes of free energy parameters, such as the enthalpy of association, as previously derived in many studies from gradient elution reversed-phase high-performance liquid chromatographic (RP-HPLC) measurements are often different from the data for the same parameters derived from equilibrium binding or microcalorimetric determinations. To reconcile these divergencies and to more closely examine the thermodynamic basis of the interaction of polypeptides with nonpolar ligands, the dependency of the logarithmic capacity factor, ln (mathematical expression not reproducible in ASCII)', on temperature, T, for several polypeptides (bombesin, (Beta)-endorphin, glucagon) have been investigated using a n-butylsilica and acetonitrile - water or methanol - water mixtures of defined solvent compositions. With low-pH, acetonitrile - water mixtures, the van't Hoffplots, i.e., the plots of ln (mathematical expression not reproducible in ASCII)' versus 1/T, were nonlinear over the range of T = 278-358 K, although within a narrow temperature range, e.g., from T = 278-308 K, the experimental data for these polypeptides could be approximated by a linear relationship. This nonclassical van't Hoff behavior was associated with interactive processes that involved temperature-dependent enthalpic, entropic, and heat capacity changes. In contrast, with low-pH, methanol-water mixtures, the van't Hoff plots showed dependencies that were essentially linear over the range of T = 278-358 K. The slopes of the van't Hoff plots with acetonitrile-water and methanolwater mixtures at a defined T value and solvent composition were significantly larger than those found for the corresponding experiments carried out under gradient elution RP-HPLC conditions. From these plots of ln k' versus 1/T, the changes in the apparent enthalpy of association ((Delta)H(super +/-)(sub assoc)) and the apparent entropy of association ((Delta)S(super +/-)(sub asso)) for the interaction of these polypeptides with the solvated n-butyl ligands at different T and solvent compositions have been determined. For these polypeptides, both (Delta)H(super +/-)(sub assoc) and (Delta)S(super +/-)(sub assoc) exhibited linear dependencies on the volume fraction, (mathematical expression not reproducible in ASCII), of the organic solvent over a narrow range of T, but the slopes of these plots were dependent on the T range examined. The dependencies of the slope term, S, and the intercept term, ln (mathematical expression not reproducible in ASCII)(sub 0), derived from the plots of In (mathematical expression not reproducible in ASCII)' versus (mathematical expression not reproducible in ASCII) as a function of T, have also been investigated. A new relationship linking the S values with(Delta)H(super +/-)(sub assoc) and (Delta)S(super +/-)(sub assoc) as a function of T and (mathematical expression not reproducible in ASCII) has been derived and validated. In addition, the relationship between S, (Delta)H(super +/-)(sub assoc) and (Delta)S(super +/-)(sub assoc), the apparent change in heat capacity, (Delta)C(super +/-)(sub assoc), and the accessible surface area, (Delta)A(sub tot), of these polypeptides has been examined, thus providing a linkage of these thermodynamic and extrathermodynamic parameters to the partition coefficient, P, and the molecular properties of these polypeptides. The results confirm that entropy - enthalpy compensation effects participate in the interaction of polypeptides with hydrophobic ligands. This investigation has confirmed that the use of solvent - water mixtures of defined composition, rather than the more convenient practice of using gradient elution methods, is essential if thermodynamically consistent values of the binding affinities and partition coefficients are to be quantitatively derived. Similar considerations apply to the derivation of extrathermodynamic parameters associated with the conformational transitions of polypeptides (or proteins) when they interact with nonpolar n-alkyl ligands. This study thus provides a general approach to evaluate the interaction thermodynamics of polypeptides or proteins in these and similar lipophilic systems.

A study successfully applied electron spin-echo envelope modulation (ESEEM) spectroscopy to the detection of a guanosine-derived nitrogen ligand to Mn2+ in the hammerhead ribozyme, which is a chemically active RNA molecule. The three-pulse ESEEM spectrum obtained for Mn2+ bound to hammerhead ribozyme complex, which consists of an RNA 'enzyme' and DNA 'substrate' strand, exhibits significant modulation. Experimental methods and results are presented.

This article discusses defining selectin ligands and their analogues for three selectins, E-, L- and P-selectin. Results demonstrate that lectin-like domains in selectins have led to designing carbohydrate based ligands for human E- and P-selectins and their sulfated variants for L-selectins.

We demonstrate that binding of mixtures of aminoglycosides can be measured simultaneously against multiple RNA targets of identical length and similar (or identical) molecular weight. Addition of a neutral mass tag to one of the RNA targets shifts the detected peaks to a higher mass/charge ratio, where complexes with small molecules can be identified unambiguously. An appropriately placed neutral mass tag does not alter RNA-ligand binding. The utility of this strategy is demonstrated with model RNAs corresponding to the decoding region of the prokaryotic and eukaryotic rRNAs and a mixture of five aminoglycosides. Complexes are observed between the aminoglycoside library and the prokaryotic rRNA model, while no aminoglycoside was observed to bind to the mass-tagged eukaryotic rRNA model. The differential binding data is consistent with the eukaryotic A-site rRNA having a different conformation compared with the prokaryotic A-site that prevents entry and binding of neomycin-class aminoglycosides. Mass spectrometric analysis of neutral mass-tagged macromolecular targets represents a new high-throughput screening paradigm in which the interaction of multiple targets against a collection of small molecules can be evaluated in parallel.

UV-vis spectroscopy, isothermal titration calorimetry and vapor pressure osmometry reveals that SmI2 is monomeric. Analysis shows that the aggregation number for SmI2 in THF over the entire concentration range studied is 0.98 +/- 0.09. THF is displaced to the Sm metal when hexamethylphosphoramide (HMPA) cosolvent is added to a solution of SMI2. Calorimetry data reveals the tightly bound relationship of four HMPA ligands to SmI2 in THF.

The function of CD48 is determined by generating mice deficient in CD48 expression. The results of the experiment show that CD48 plays a crucial role in T cell activation through the T receptor cell/CD3 complex. Reduced proliferation in response to stimulation with lectins, alloantigen and anti-CD3 mAb were observed from the T cells of CD48-deficient mice. The use of phorbol ester phorbol 12-Myristate 13-Acetate as a costimulatory signal instead of antigen-presenting cells resulted in impairments. T cell responses were reconstituted with the addition of irradiated APCs.

The affinity labeling was used to investigate the origin of carbohydrate recognition specificity of human lysozyme by employing the three types of the 2',3'-epoxypropyl beta-glycoside of disaccharides. The human lysozyme labeled with two Gal-beta1,4-GlcNAc-epo was separated and crystallized. X-ray analysis showed the presence of both Gal-beta1,4-GlcNAc-epo moieties within the catalytic cleft. In addition to the protein-carbohydrate interaction, the results proved the recognition of the second ligand through the carbohydrate-carbohydrate interaction.

[LXR.sub.[Alpha]] and -[Beta] are nuclear receptors that regulate the metabolism of several important lipids, including cholesterol and bile acids. Previously, we have proposed that LXRs regulate these pathways through their interaction with specific, naturally occurring oxysterols, including 22(R)-hydroxycholesterol, 24(S)-hydroxycholesterol, and 24(S),25-epoxycholesterol. Using a ligand binding assay that incorporates scintillation proximity technology to circumvent many of the problems associated with assaying extremely hydrophobic ligands, we now demonstrate that these oxysterols bind directly to LXRs at concentrations that occur in vivo. To characterize further the structural determinants required for potent LXR ligands, we synthesized and tested a series of related compounds for binding to LXRs and activation of transcription. These studies revealed that position-specific monooxidation of the sterol side chain is requisite for LXR high-affinity binding and activation. Enhanced binding and activation can also be achieved through the use of 24-oxo ligands that act as hydrogen bond acceptors in the side chain. In addition, introduction of an oxygen on the sterol B-ring results in a ligand with LXR[Alpha]-subtype selectivity. These results support the hypothesis that naturally occurring oxysterols are physiological ligands for LXRs and show that a rational, structure-based approach can be used to design potent LXR ligands for pharmacologic use.

A study on the binding of ethidium and netrospin binding to chromatin from chicken erythrocytes using isothermal titration calorimetry is presented. Ethidium is a well-known intercalator with antibactericidal and carcinogenic properties. Netropsin is an oligopeptide with antibiotic properties against bacteria, fungi and viruses. Results show that enthalpy causes the binding of ethidium and netropsin to chromatin. The binding is relatively weak and with more ligands scattered than on DNA.

Perturbation theory and density functional theory were used to determine the thermodynamic and kinetic enthalpies for the introduction of H2 into IrXH2(PR3)2 (X = Cl, Br, I; R = H, Me). The two methods were compared to determine their individual capacity to perform in weakly bound complexes. Findings revealed that the calculations conformed to experimental results for IrClH2(P(super t)Bu2Me)2 and IrIH2(H2)(P(super i)Pr3)2. The density functional method underestimated the binding energy of H2 while the perturbation theory overestimated it. Modeling of the phosphine with PMe3 in place of PH3 enhanced the results.

The screening of ligands for membrane receptor proteins is central to the discovery of new pharmaceutical drugs. We present a general method to reversibly attach receptor proteins via an affinity tag to a quartz surface and subsequently detect with high sensitivity the real-time binding of ligands by total internal reflection fluorescence. A serotonin-gated ion channel protein was immobilized, and the binding of a fluorescent ligand was investigated. The affinity and the kinetic parameters of binding were measured, and the effect of unlabeled compounds was determined by competition. The pharmacology of the immobilized receptor was identical to that of the native receptor. The affinity of unlabeled ligands was rapidly and effectively determined. The method described here is generally applicable for membrane proteins and opens new ways for the discovery of pharmacologically active compounds.

An experiment was conducted to investigate the binding of octenoyl-CoA to pig kidney medium-chain acyl-coenzyme-A dehydrogenase (MCAD) through isothermal titration microcalorimetry. The experiment was performed in 50 mM potassium phosphate buffer. Results revealed that the overall binding occurred through formation of a MCAD-trans-3-indoleacryloyl-CoA collision complex in which the electronic structure of trans-3-indoleacryloyl-CoA remained unchanged and through slow isomerization step with a concomitant red-shift in the trans-3-indoleacryloyl-CoA spectrum.

A study was conducted to determine the roles of specific ligand-DNA interactions of terbenzimidazole in the DNA topoisomerase I poisoning. Spectroscopic, calorimetric, DNA cleavage and DNA winding/unwinding measurements were utilized to characterize the DNA binding and topoisomerase I poisoning properties of three terbenzimidazoles. Results suggested that DNA minor groove binding was vital to the topoisomerase I poisoning capabilities of terbenzimidazole.

The inhibition of selectin-ligand binding is necessary to disrupt the over recruitment of lymphocytes from the vasculature to the site of injury because over recruitment of lymphocytes results to chronic inflammatory diseases. Despite the importance of selectins in inflammation for they function as cell-surface receptor, selectin antagonists are necessary to avoid abnormal function of the receptor. These antagonists may help in regulating abnormal adhesion and recruitment of lymphocytes.

The amination of olefins can be done through direct addition of nucleophiles to activate alkenes. The activation of alkenes is accomplished with late-transition-metal catalysts which allows the olefins to become susceptible to attack by amido species. The other alternative for amine activation route utilizes N-H oxidative addition to electron rich metal centers. If the oxidative addition would be coupled to an alkene/alkyne insertion process and reductive elimination, catalytic cycle for olefin can be achieved.

An experiment evaluated the basic transmutations of eta2-coordinated furan complexes of pentaammineosmium(II). Coordination of the electron-rich pentaammineosmium(II) moiety to a furan significantly changes the structural and chemical character of the ligand, with the generated complexed ligands easily experiencing different electrophilic addition reactions that feature two reactive species. These species are the apparently interchangeable open-chain eta2-vinyl cation species and eta2-3H-furanium species.