High Binding Selectivity Research Articles

Analysis of Flexibility and Hotspots in Bcl-xL and Mcl-1 Proteins for the Design of Selective Small-Molecule Inhibitors.

Although Bcl-xL and Mcl-1, two antideath Bcl-2 members, have similar, flexible binding sites, they can achieve high binding selectivity to endogenous binding partners and synthetic small-molecule inhibitors. Here, we employed molecular dynamic (MD) simulations and hotspot analysis to investigate the conformational flexibility of these proteins and their binding hotspots at the binding sites. Backbone flexibility analyses indicate that the highest degree of flexibility in Mcl-1 is the α4 helical segment as opposed to the α3 helix in Bcl-xL among four helical segments in their binding sites. Furthermore, common and unique binding hotspots at both proteins were identified using small-molecule probes. These analyses can aid the design of potent and specific small-molecule inhibitors for these proteins.

Highly selective and sensitive fluorescent sensing of oxalate in water

Effective fluorescent sensing of oxalate in water is significant but still remains a challenge. By using indicator-displacement assays, a readily available macrocyclic copper(II) complex was found to show a sensitive off-on fluorescent sensing for oxalate with high selectivity and high binding affinity (>10(7) M(-1)) in water at neutral pH.

A Ag+-selective “off–on” probe based on a naphthalimide derivative

A new naphthalimide-based derivative L bearing an S-benzyldithiocarbazate moiety was synthesized as an “off–on” probe for Ag+. The new probe has high binding selectivity for Ag+ in water media with a detection limit of Ag+ down to 270 nM. Based on the Ag+-induced inhibition of a PET process and restriction of CN rotation, the coordination mode of 1 : 1 between L and Ag+ was proposed.

Evaluation of 18F-Labeled Benzodioxine Piperazine-Based Dopamine D4 Receptor Ligands: Lipophilicity as a Determinate of Nonspecific Binding

Derivatization of the putative neuroleptic 1-(2,3-dihydrobenzo[1,4]dioxin-6-yl)-4-(4-fluorobenzyl)piperazine (3a) led to a series of new dopamine receptor D4 ligands displaying high affinity (Ki=1.1-15 nM) and D2/D4 subtype selectivities of about 800-6700. These ligands were labeled with the short-lived positron emitter fluorine-18 and analyzed for their potential application for imaging studies by positron emission tomography (PET). In vitro autoradiography was used to determine their nonspecific binding behavior as a result of their structural and thus physicochemical properties. The biodistribution, in vivo stability, and brain uptake of the most promising D4 radioligand candidate were determined. This proved to be 1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-4-((6-fluoropyridin-3-yl)methyl)piperazine ([18F]3d), which revealed an excellent binding pattern with a high selectivity and limited nonspecific binding in vitro. This analogue also exhibited a high stability and an extremely high brain uptake in vivo with specific binding in hippocampus, cortex, colliculus, and cerebellum as determined by ex vivo autoradiography. Thus, [18F]3d appears as a suitable D4 radioligand for in vivo imaging, encouraging continued evaluation by PET studies.

Self-assembly molecularly imprinted polymers of 17β-estradiol on the surface of magnetic nanoparticles for selective separation and detection of estrogenic hormones in feeds

This paper reports a surface molecular self-assembly strategy for molecular imprinting on magnetic nanoparticles for selective separation and detection of estrogens in feeds. First, γ-methacryloxypropyltrimethoxysilane (MEMO) was successfully assembled at the surface magnetic nanoparticles through simple free radical polymerization, and subsequently, the copolymerization was further assembled between methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) in the presence of templates 17β-estradiol (E2). The synthesized magnetic molecularly imprinted polymers for E2 (E2-MMIPs) showed quick separation, large adsorption capacity, high selectivity and fast binding kinetics for E2. Meanwhile, a dispersive solid-phase extraction (DSPE) based on E2-MMIPs has been established for efficient separation and fast enrichment of estrogens from the feeds. The assay exhibited a linear range of 0.1–4 μM for E2 and estriol (E3) with the correlation coefficient above 0.9996 and 0.9994, respectively. Recoveries of E2 from three kinds of feeds spiked at different concentration levels ranged from 92.7% to 97.0% with RSD < 4.7%, and recoveries of E3 ranged from 71.9% to 83.1% with RSD < 4.9%, respectively. The method is simple and sensitive, and can be used as an alternative tool to effectively separate and enrich the trace of estrogens in agricultural products by HPLC–UV.

Molecularly Imprinted Membrane Applied for Selective Separation

Molecular Imprinting Polymer (VHP) technique is well known for creating polymer materials with molecule selectivity in adsorption and separation. MIPs have mostly been prepared by bulk polymerization and grinding the resulting brittle polymer to prepare particles of the desired dimensions. However, this technique also suffered some backdrops such as limitation in its application due to powder shape and limitation in binding ability. To circumvent these problems, we had extended such technique on formation of membrane adsorbents using phase inversion imprinting technique. Namely, copolymerization of a template-containing monomers with commercial scaffold monomer was achieved such membranes in order to selectively separate the target molecules. One main feature of this system is the imprinted polymer forming film which is possible to be use as filtration materials for selective separation. In the present study, we prepared the imprinted membranes by copolymerization of covalently linked tocopherol methacrylate (α-TMA) monomer and acrylonitrile (AN) followed by phase inversion in water non-solvent for membrane formation. Herein, the evidence included advantage in phase inversion covalently imprinting technique in their binding natures to tocopherol (Toe) and phenol derivatives and was studied on basis of selectivity of the imprinted membrane. Scatchard analysis indicated that the imprinted membranes exhibited high affinity and good selective binding of α-Toc relative to its analogs, δ-Toc and 4-chromanol (4-Chr). Results of permeation of Toes and phenol mixture showed that the imprinted membranes were achieved higher separation factor of α-Toc and 4-Chr as compared to the non-imprinted membrane. This indicated that the covalent imprinting of α-Toc in AN segment scaffold was able to recognize both chemical structures with or without methyl group in the Toe derivatives. © 2011 Asian Network for Scientific Information.

Characterization of 6α- and 6β-N-Heterocyclic Substituted Naltrexamine Derivatives as Novel Leads to Development of Mu Opioid Receptor Selective Antagonists

As important pharmacological probes, highly selective opioid receptor antagonists are essential in opioid receptor structural characterization and opioid agonist functional studies. At present, a nonpeptidyl, highly selective, and reversible mu opioid receptor antagonist is still not available. Among a series of novel naltrexamine derivatives that have been designed and synthesized following molecular modeling studies, two compounds, NAP and NAQ, were identified as leads based on the results of in vitro and in vivo pharmacological assays. Both of them displayed high binding affinity and selectivity to the mu opioid receptor. Further pharmacokinetic and functional characterization revealed that NAP seems to be a peripheral nervous system agent while NAQ seems to be a central one. Such characteristics provide two distinguished potential application routes for these two agents and their derivatives. These results also supported our hypothesis that they may serve as leads to develop more potent and selective antagonists for the mu opioid receptor.

Novel amperometric sensor using metolcarb-imprinted film as the recognition element on a gold electrode and its application

A molecularly imprinted film is electrochemically synthesized on a gold electrode using cyclic voltammetry to electropolymerize o-aminothiophenol in the presence of metolcarb (MTMC). The mechanism of the imprinting process and a number of factors affecting the activity of the imprinted film are discussed and optimized. Scanning electron microscope observations and binding measurements have proved that an MTMC-imprinted film (with a thickness of nearly 100 nm) was formed on the surface of the gold electrode. The film exhibited high binding affinity and selectivity towards the template MTMC, as well as good penetrability, reproducibility and stability. A novel amperometry sensor using the imprinted film as recognition element was developed for MTMC determination in food samples. Under the experimental conditions, the MTMC standard is linear within the concentration range studied ( r 2 = 0.9906). The limit of detection ( S/ N = 3) of the modified electrode was achieved to 1.34 × 10 −8 mol L −1. Recoveries of MTMC from spiked apple juice, cabbage and cucumber samples for the developed electrochemical assay ranged from 94.80% to 102.43%, which was with great correlation coefficient (0.9929) with results from high-performance liquid chromatography. In practical application, the prepared amperometric sensor also showed good reproducibility and long lifetime for storage. The research in this study has offered a rapid, accurate and sensitive electrochemical method for quantitative determination of MTMC in food products.

Discovery and evaluation of pyrazolo[1,5-a]pyrimidines as neuropeptide Y1 receptor antagonists

A novel series of pyrazolo[1,5-a]pyrimidine derivatives was synthesized and evaluated as NPY Y1R antagonists. High binding affinity and selectivity were achieved with C3 trisubstituted aryl groups and C7 substituted 2-(tetrahydro-2H-pyran-4-ylamino)ethylamine moieties. Efforts to find close analogs with low plasma clearance in the rat and minimal p-glycoprotein efflux in the mouse were unsuccessful. Compound 2f (CP-671906) inhibited NPY-induced increases in blood pressure and food intake after iv and icv administration, respectively, in Sprague-Dawley (SD) rat models. Oral administration of compound 2f resulted in a modest, but statistically significant, reduction in food intake in a Wistar rat model of feeding behavior. Small inhibitions of food intake were also observed in an overnight fasting/refeeding model in SD rats. These data suggest a potential role for Y1R in the regulation of food intake in rodents.

Colorimetric ‘naked-eye’ sensor for anions based on conformational flexible tripodal receptor

A new tripodal receptor for anion sensing based on amide-pyridinium as recognition site and nitro-benzene as signaling unit was designed and successfully synthesized. This receptor showed high selectivity and strong binding affinity toward AcO− over the investigated anions, especially over H2PO4−. Addition of AcO− induced clear color change of solution from colorless to yellow, realizing the “naked-eye” detection. UV–Vis and 1H NMR experiments indicated the selectivity might origin from the synergistic effects arising from hydrogen bonding, electrostatic interactions and conformational change.

Chemistry and Pharmacological Characterization of Novel Nitrogen Analogues of AMOP-H-OH (Sazetidine-A, 6-[5-(Azetidin-2-ylmethoxy)pyridin-3-yl]hex-5-yn-1-ol) as α4β2-Nicotinic Acetylcholine Receptor-Selective Partial Agonists

In order to advance therapeutic applications of nicotinic ligands, continuing research efforts are being directed toward the identification and characterization of novel nicotinic acetylcholine receptor (nAChR) ligands that are both potent and subtype selective. Herein we report the synthesis and pharmacological evaluation of members of a new series of 3-alkoxy-5-aminopyridine derivatives that display good selectivity for the α4β2-nAChR subtype based on ligand binding and functional evaluations. The most potent ligand in this series, compound 64, showed high radioligand binding affinity and selectivity for rat α4β2-nAChR with a K(i) value of 1.2 nM and 4700-fold selectivity for α4β2- over α3β4-nAChR, and ∼100-fold selectivity for functional, high-sensitivity, human α4β2-nAChR over α3β4*-nAChR. In the mouse forced swim test, compound 64 exhibited antidepressant-like effects. Structure-activity relationship (SAR) analyses suggest that the introduction of additional substituents to the amino group present on the pyridine ring of the N-demethylated analogue of compound 17 can provide potent α4β2-nAChR-selective ligands for possible use in treatment of neurological and psychiatric disorders including depression.

Pyrazolo[1,5- a]pyrimidine acetamides: 4-Phenyl alkyl ether derivatives as potent ligands for the 18 kDa translocator protein (TSPO)

Herein, we report the synthesis of four new phenyl alkyl ether derivatives ( 7, 9– 11) of the pyrazolo[1,5- a]pyrimidine acetamide class, all of which showed high binding affinity and selectivity for the TSPO and, in the case of the propyl, propargyl, and butyl ether derivatives, the ability to increase pregnenolone biosynthesis by 80–175% over baseline in rat C6 glioma cells. While these compounds fit our in silico generated pharmacophore for TSPO binding the current model does not account for the observed functional activity.

Structure−Activity Relationships for a Novel Series of Citalopram (1-(3-(Dimethylamino)propyl)-1-(4-fluorophenyl)-1,3-dihydroisobenzofuran-5-carbonitrile) Analogues at Monoamine Transporters

(+/-)-Citalopram (1, 1-(3-(dimethylamino)propyl)-1-(4-fluorophenyl)-1,3-dihydroisobenzofuran-5-carbonitrile), and its eutomer, escitalopram (S-(+)-1) are selective serotonin reuptake inhibitors (SSRIs) that are used clinically to treat anxiety and depression. To further explore structure-activity relationships at the serotonin transporter (SERT), a series of (+/-)-4- and 5-substituted citalopram analogues were designed, synthesized, and evaluated for binding at the SERT, dopamine transporter (DAT) and norepinephrine transporter (NET) in native rodent tissue. Many of these analogues showed high SERT binding affinities (Ki=1-40 nM) and selectivities over both NET and DAT. Selected enantiomeric pairs of analogues were synthesized and both retained enantioselectivity as with S- and R-1, wherein S>R at the SERT. In addition, the enantiomeric pairs of 1 and 5 were tested for binding at the homologous bacterial leucine transporter (LeuT), wherein low affinities and the absence of enantioselectivity suggested distinctive binding sites for these compounds at SERT as compared to LeuT. These novel ligands will provide molecular tools to elucidate drug-protein interactions at the SERT and to relate those to behavioral actions in vivo.

Carrageenans as a New Source of Drugs with Metal Binding Properties

Carrageenans are abundant and safe non-starch polysaccharides exerting their biological effects in living organisms. Apart from their known pro-inflammation properties and some pharmacological activity, carrageenans can also strongly bind and hold metal ions. This property can be used for creation of the new drugs for elimination of metals from the body or targeted delivery of these metal ions for healing purposes. Metal binding activity of different carrageenans in aqueous solutions containing Y3+ or Pb2+ ions was studied in a batch sorption system. The metal uptake by carrageenans is not affected by the change of the pH within the range from 2.0 to 6.0. The rates and binding capacities of carrageenans regarding metal ions were evaluated. The Langmuir, Freundlich and BET sorption models were applied to describe the isotherms and constants, and the sorption isothermal data could be explained well by the Langmuir equation. The results obtained through the study suggest that κ-, ι-, and λ-carrageenans are favorable sorbents. The largest amount of Y3+ and Pb2+ ions are bound by ι-carrageenan. Therefore, it can be concluded that this type of polysaccharide is the more appropriate substance for elaboration of the drugs with high selective metal binding properties.

Two-step on-particle ionization/enrichment via a washing- and separation-free approach: multifunctional TiO2 nanoparticles as desalting, accelerating, and affinity probes for microwave-assisted tryptic digestion of phosphoproteins in ESI-MS and MALDI-MS: comparison with microscale TiO2

We introduce a simplified sample preparation method using bare TiO(2) nanoparticles (NPs) to serve as multifunctional nanoprobes (desalting, accelerating, and affinity probes) for effective enrichment of phosphopeptides from microwave-assisted tryptic digestion of phosphoproteins (alpha-casein, beta-casein and milk) in Electrospray Ionization Mass Spectrometry (ESI-MS) and Matrix Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS). The results demonstrate that TiO(2) NPs can effectively enrich and accelerate the digestion reactions of phosphoproteins in aqueous solutions and also from complex real samples. After the microwave experiments, we directly injected the resulting solutions into the ESI-MS and MALDI-MS systems for analysis, and excellent sensitivity was achieved without the need for any washing procedure or separation process. The reasons are attributed to the high binding affinity and selectivity of TiO(2) NPs toward phosphopeptides. Thus, phosphopeptides can be adsorbed onto the TiO(2) NP surface. The digested or partially digested phosphoproteins can be concentrated onto the TiO(2) NP surface. This results in the effective or complete digestion of phosphoproteins in a short period of time (45 s). In addition, high sensitivity and sequence coverage of phosphopeptide can be obtained using TiO(2) NPs as microwave absorbers and affinity probes in MALDI-MS and ESI-MS. This is due to the photocatalytic nature of the TiO(2) NPs because the absorption of microwave radiation that can accelerate the activation of trypsin for efficient digestion of phosphoproteins and enhances the ionization of phosphopeptides. The lowest concentrations detected for ESI-MS and MALDI-MS were 0.1 microM and 10 fmol, respectively, for alpha-casein. Comparing the two-step approach of TiO(2) NPs with microscale TiO(2) particles, the microscale TiO(2) particles shows no effect on the microwave-assisted tryptic digestion of phosphoproteins. The current approach offers multiple advantages, such as great simplicity, high sensitivity and selectivity, straightforward and separation/washing-free technique for phosphopeptide enrichment analysis.

Molecularly Imprinted PHEMA‐Based Cryogel for Depletion of Hemoglobin from Human Blood

AbstractA new generation of molecularly imprinted macroporous hydrogels, so‐called cryogels, were prepared for depletion of hemoglobin from human blood. Hb‐PHEMAH cryogels were prepared with gel fraction yields up to 90%, and its morphology and porosity were characterized by FTIR, SEM, swelling studies, flow dynamics and surface area measurements. Selective binding experiments were performed in the presence of competitive proteins Myb and BSA. Hb‐PHEMAH cryogel exhibited a high binding capacity and selectivity for Hb in the presence of Myb and BSA. The selectivity of Hb‐PHEMAH cryogel for Hb was confirmed by HPLC. Hb depletion from blood hemolysate was also studied using SDS‐PAGE. Hb‐PHEMAH cryogel can be reused many times with no apparent decrease in Hb adsorption capacity.magnified image

Discovery of a highly selective turn-on fluorescent probe for Ag+

An ideal fluorescent probe should show the strongest affinity with the relevant target (binding-selectivity) by means of a selective fluorescence change (signal-selectivity). [15]aneNO(2)S(2) (1,4-dioxa-7,13-dithia-10-azacyclopentadecane) based probes usually show high binding selectivity for Ag(+) but signal selectivity for Hg(2+), because Ag(+) can quench or silence the fluorescence. To amplify the Ag(+) binding to the greatest extent, a carbonyl group was positioned between 1,8-naphthalimide and [15]aneNO(2)S(2) which played a key role of displaying selective fluorescence enhancements with Ag(+) through increasing the oxidation potential of the fluorophore, blocking Ag(+) from sterically interacting with the naphthalimide fluorophore, and by acting as a sacrificial donor. Probe 2 can detect Ag(+) with a selective fluorescence enhancement (∼14 fold) and high affinity (K(a) = 1.64 × 10(5) M(-1)).

Synthesis of Molecularly Imprinted Polymers for Nevirapine by Dummy Template Imprinting Approach

Nevirapine (NVP) and its structurally related analogs including nicotinamide (NAM), benzamide (BZM) and benzophenone (BZP) were used as templates in the synthesis of molecularly imprinted polymers for NVP. Molecular modeling was used to estimate binding energy of the complex formation between methacrylic acid (MAA) monomer and the selected templates, while equilibrium binding studies were applied to evaluate the polymer binding efficiency. The data indicated that NAM is the best candidate to prepare MIPs for retaining NVP due to a relatively similar binding energy between the NVP–MAA and NAM–MAA complex. The NAM-imprinted polymer showed a high binding affinity and selectivity toward NVP. When the polymer was applied as a sorbent in solid-phase extraction of NVP from human plasma, high recovery and reproducibility were obtained.

Tetrapyrrolic compounds as hosts for binding of halides and alkali metal cations

In this paper the binding of halides and alkali metal cations with porphyrin hosts is reported. The halide ions are complexed with diprotonated porphyrin macrocycle with high affinity and stable complexes of 1:1 and 1:2 structures with halide ions are formed. Strong (up to 300 times) quenching of the porphyrin fluorescence has been found upon the titration of porphyrin solutions with iodide ions. It was established that both static quenching upon formation of the non-fluorescent complex and dynamic diffusion-controlled quenching took place. It is shown that the halide ions binding isotherms can be linearized with double-logarithmic plots. The alkali metal cations are trapped with mono-meso-arylporphyrins containing a conformationally mobile complexing polyether fragment on the benzene ring with a terminal pyridine ring. The alkali metal cation binding constant depends on the polyether chain length. The five-membered (n = 5) polyether chain provides very high binding selectivity for potassium over lithium or sodium. The potassium complexation constants 3.6 × 105and 7.2 × 104M-1have been obtained for Zn2+complex and diprotonated porphyrin, respectively. For signaling of the alkali cation complexation, it is proposed to use the binding between the terminal pyridine ring with either the Lewis acidic site (chelated Zn2+ion) or the diprotonated macrocycle core ( H4P2+) acting as salt bridging site.

Cucurbit[7]uril Complexation Drives Thermal trans–cis‐Azobenzene Isomerization and Enables Colorimetric Amine Detection

Complexation of yellow diaminoazobenzenes 1 and 3 inside cucurbit[7]uril (CB[7]) results in the formation of purple-colored CB[7].cis-1.2H+ and CB[7].cis-3.2H+ complexes, respectively. The high binding affinity and selectivity displayed by CB[7] toward 1 and 3 pays the >10 kcal mol(-1) thermodynamic cost for this isomerization. We investigated the behavior of these complexes as a function of pH and observed large pK(a) shifts and high pH responsiveness, which are characteristic of cucurbit[n]uril molecular containers. The remarkable yellow to purple color change was utilized in the construction of an indicator displacement assay for biologically active amines 4-10. This indicator displacement assay is capable of quantifying the pseudoephedrine (5) content in Sudafed tablets over the 5-350 microM range.