Peroxidase-like catalytic activity of copper ions and its application for highly sensitive detection of glypican-3

Glypican-3 (GPC3) might be used as new biomarker of liver cancer for the development of new diagnostic methods. The most commonly used methods for protein detection are based on natural enzymes, which are easily affected by environmental conditions and suffer from the rigorous preparation conditions. Thus, the development of new enzyme mimetics with high and stable catalytic activity is of great significance in diagnostic applications. In this paper, copper ions (Cu²⁺) was found to possess the peroxidase-like catalytic activity, which can catalyze H₂O₂-mediated oxidation of peroxidase substrate and obtain the oxidation product with color change. This catalytic activity is much more stable than other nanomaterials based peroxidase mimetics, and can significantly increase by increasing the concentration of H₂O₂. It is worth mentioning that the absorbance signal induced by 5 nM Cu²⁺ can be easily detected. This Cu²⁺-catalyzed reaction can be also applied in the detection of GPC3 by using the anti-GPC3 antibody functionalized CuO NPs, which can release the Cu²⁺ by dissolved in HCl solution. This method permits detection of as low as 0.26 pg mL⁻¹ GPC3. This sensitivity is about one or several magnitudes higher than that of ELISA or other peroxidase mimetics based methods. The high catalytic activity of Cu²⁺ and the signal amplification process of CuO NPs into high amount of Cu²⁺ also make this method more simple and effective.     

Microfluidic paper-based multiplex colorimetric immunodevice based on the catalytic effect of Pd/Fe3O4@C peroxidase mimetics on multiple chromogenic reactions

In this report, a non-toxic method was proposed for the simple synthesis of palladium nanoparticles (Pd)/Fe₃O₄@C peroxidase mimetics by virtue of in situ growth of Pd nanoparticles on Fe₃O₄@C magnetic nanoparticles. And a microfluidic paper-based multiplex colorimetric immunodevice (named α-sheet) was developed by site-selectively immobilizing multiple antigens owing to its intrinsic high-efficiency catalytic activity of peroxidase mimetics to multiple chromogenic reactions. The immunosensor platform was prepared by growing a layer of flower-like gold nanoparticles which could entrap the primary antibodies onto paper sensing zones, and the as-prepared Pd/Fe₃O₄@C peroxidase mimetics was used to label secondary antibodies. In the presence of 3,3′,5,5′-tetramethylbenzidine and o-phenylenediamine chromogenic substrates, Pd/Fe₃O₄@C peroxidase mimetics catalyzed chromogenic reactions and showed different colors with respective intensity. To precisely identify the intensity, a piece of black wax printed chromatographic paper with three observing windows (named β-sheet) was flatted on α-sheet. Under the optimal condition, the proposed multiplex colorimetric immunodevice displayed wide linear ranges from 0.005 to 30 ng mL⁻¹ with low detection limits of 1.7 pg mL⁻¹ for carcinoembryonic antigen (CEA) and α-fetoprotein (α-AFP). Meanwhile, the proposed method provided provided a non-toxic, low-cost and promising tool for point-of-care diagnosis.     

Synthesis of new sulfonic acid-containing oligosaccharide mimetics of sialyl Lewis A

Two trisaccharides as new sulfonic acid mimetics of the sialyl Lewis A tetrasaccharide were synthesized. The natural sialic acid residue is replaced by a C-sulfonic acid moiety attached to position C-3′ of the lactosamine unit of the mimetics. The l-fucose unit was also replaced by a d-arabinose ring in one of the analogues. Formation of the sulfonic acid moiety on the trisaccharide level could be successfully achieved by means of introduction of an acetylthio moiety into the galactose skeleton and subsequent oxidation. The equatorial arrangement of the acetylthio group linked to C-3 of the galactose ring could be achieved by double nucleophilic substitution; efficient formation of the gulo-triflate derivatives required low-power microwave activation. Oxidation of the acetylthio group was carried out using Oxone in acetic acid.     

Reactivity Tournament of Isothiocyanato-Functionalized Saccharides with 1,6-Diamino-3,6-oxaoctane

Summary.  Thiourea-bridged glycoclusters and glycodendrimers are described in the literature as mimetics of (oligoantennary) oligosaccharides to serve as high-affinity lectin ligands. In extension of this concept, the assembly of different, structurally varied isothiocyanato-functionalized sugar derivatives on an oligoamine scaffold would lead to novel mixed glycoclusters. To control this approach, the relative reactivities of the isothiocyanates used in the thiourea-bridging reaction have to be known. Therefore, competition experiments with six different sugar isothiocyanates were carried out using 1,8-diamino-3,6-dioxaoctane as a symmetrical difunctionalized core molecule. Reactivities were ranked on the basis of integration ratios in the ¹H NMR spectra. A first mixed thiourea-bridged glycocluster was successfully prepared. Received June 13, 2001. Accepted October 31, 2001     

2,4‐Dioxa‐7‐aza‐, 2,4‐Dioxa‐8‐aza‐, and 2,4‐Dioxa‐9‐aza‐3‐phosphadecalins as Rigid Acetylcholine Mimetics: Syntheses and Characterization

Phosphorylation of suitable piperidine precursors yielded a series of novel decalin‐type O,N,P‐heterocycles. The title compounds, P(3)‐axially and P(3)‐equatorially X‐substituted, cis‐ and trans‐configurated 2,4‐dioxa‐7‐aza‐, 2,4‐dioxa‐8‐aza‐, and 2,4‐dioxa‐9‐aza‐3‐phosphabicyclo[4.4.0]decane 3‐oxides (X=Cl, F, 4‐nitrophenoxy, and 2,4‐dinitrophenoxy), are configuratively fixed and conformationally constrained P‐analogues of acetylcholine and as such represent acetylcholine (7‐aza and 9‐aza isomers) or γ‐homo‐acetylcholine mimetics (8‐aza isomers). Being irreversible inhibitors of acetylcholinesterase (AChE), the compounds are considered to be suitable probes for the investigation of the stereochemical course of the inhibition reaction by ³¹P‐NMR spectroscopy. Moreover, the design of these mimetics will enable studies of molecular interactions with AChE, in particular, the recognition conformation of acetylcholine.     

Phosphono Bisbenzguanidines as Irreversible Dipeptidomimetic Inhibitors and Activity‐Based Probes of Matriptase‐2

Matriptase‐2, a type II transmembrane serine protease, plays a key role in human iron homeostasis. Inhibition of matriptase‐2 is considered as an attractive strategy for the treatment of iron‐overload diseases, such as hemochromatosis and β‐thalassemia. In the present study, synthetic routes to nine dipeptidomimetic inactivators were developed. Five active compounds ( 41 – 45 ) were identified and characterized kinetically as irreversible inhibitors of matriptase‐2. In addition to a phosphonate warhead, these dipeptides possess two benzguanidine moieties as arginine mimetics to provide affinity for matriptase‐2 by binding to the S1 and S3/S4 subpockets, respectively. This binding mode was strongly supported by covalent docking analysis. Compounds 41 – 45 were obtained as mixtures of two diastereomers and were therefore separated into the single epimers. Compound 45 A , with S configuration at the N‐terminal amino acid and R configuration at the phosphonate carbon atom, was the most potent matriptase‐2 inactivator with a rate constant of inactivation of 2790 m ^?1 s^?1 and abolished the activity of membrane‐bound matriptase‐2 on the surface of intact cells. Based on the chemotyp of phosphono bisbenzguanidines, the design and synthesis of a fluorescent probe ( 51 A ) by insertion of a coumarin label is described. The in‐gel fluorescence detection of matriptase‐2 was demonstrated by applying 51 A as the first activity‐based probe for this enzyme.     

An efficient synthesis of triazolo-carbohydrate mimetics and their conformational analysis

A chemical library of 1,2,3-triazole fused carbohydrate mimetics was constructed. To synthesize enantiomerically pure mimetics, we developed a stereo- or diastereodivergent synthetic route from D-glucose, D-mannose and D-galactose as chiral sources. In this synthesis, an In(OTf)(3)-catalyzed tandem azidation-1,3-dipolar cycloaddition reaction of 1,1-dimethoxyhex-5-yne derivatives with TMSN(3) was used as the key step to construct the 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyridine framework. Additionally, NMR was used to carry out a conformational analysis of the synthesized mimetics, which are of structural interest since they have an N,O-acetal moiety in place of the anomeric position of normal pyranosides.     

Mimetics of the Selenoenzyme Glutathione Peroxidase: Novel Structures and Unusual Catalytic Mechanisms

Glutathione peroxidase (GPx) mimetics comprise an important class of selenium-containing antioxidants that catalyze the destruction of biologically harmful peroxides in the presence of stoichiometric thiol reductants. The synthesis of two novel cyclic selenium compounds and their evaluation as GPx mimetics was achieved. The first is a cyclic seleninate ester that is formed in situ from the oxidation of allyl 3-hydroxypropyl selenide. The second is a spirodioxyselenurane that is similarly formed from di(3-hydroxypropyl) selenide. Both compounds were shown to be remarkably active catalysts in an assay based on the reduction of t-butyl hydroperoxide with benzyl thiol. The mechanisms of the catalytic cycles of the two novel selenium compounds were elucidated and were found to be distinct from each other and from that of GPx.     

An ‘Umpolung’ Route to Peptide Mimetics of Thyrotropin-Releasing Hormone based on a cyclohexane framework

Peptide mimetics of thyrotropin-releasing hormone (TRH) in which the peptide backbone is replaced by cyclohexane were synthesized from the cyclohexenone precursor 7 . The aromatic side chains of the mimetics were derived from the corresponding aldehydes which were attached to the cyclohexenone via the Wittig reagent 8 . The TRH mimetics are active in a mouse model of cognitive performance.     

Modular alpha-helical mimetics with antiviral activity against respiratory syncitial virus

A 13-residue peptide sequence from a respiratory syncitial virus fusion protein was constrained in an alpha-helical conformation by fusing two back-to-back cyclic alpha-turn mimetics. The resulting peptide, Ac-(3-->7; 8-->12)-bicyclo-FP[KDEFD][KSIRD]V-NH(2), was highly alpha-helical in water by CD and NMR spectroscopy, correctly positioning crucial binding residues (F488, I491, V493) on one face of the helix and side chain-side chain linkers on a noninteracting face of the helix. This compound displayed potent activity in both a recombinant fusion assay and an RSV antiviral assay (IC(50) = 36 nM) and demonstrates for the first time that back-to-back modular alpha-helix mimetics can produce functional antagonists of important protein-protein interactions.     

Stereoisomers of 4-amino-3-hydroxy-1-cyclohexanecarboxylic acid and 4-amino-3-oxo-1-cyclohexanecarboxylic acid as mimetics of a twisted cis-amide bond

Stereoselective synthesis of the title compounds was performed. The relative configuration of methyl t-4-(tert-butoxycarbonylamino)-c-3-hydroxy-r-1-cyclohexanecarboxylate and methyl trans-4-(tert-butoxycarbonylamino)-3-oxo-r-1-cyclohexanecarboxylate was confirmed by X-ray diffraction methods. Analogues of cyclolinopeptide A (CLA) containing these twisted cis-amide bond mimetics were then synthesised.     

Parallel Synthesis of Sialyl Lewis X Mimetics on a Solid Phase: Access to a Library of Fucopeptides

A novel anchoring group p-(acyloxymethyl)benzylidene acetal (p-AMBA) enables the bidirectional functionalization of glycosylated amino acid derivatives and thus the rapid parallel synthesis of fucopeptides as sialyl Lewis X mimetics on a solid phase [Eq. (a), PEG-PS=poly(ethylene glycol) graft copolymer]. This led to the discovery of new mimetics against P-selectin with IC₅₀ values in the low μM range.     

Azabicycloalkenes as synthetic intermediates: application to the preparation of diazabicycloalkane scaffolds

[reaction: see text] A general method to synthesize bicyclic dipeptide mimetics is reported. Key intermediates are azabicycloalkenes 9 and 17, which are prepared via Diels-Alder reactions and subsequent mild deprotection. These unsaturated bicyclic heterocycles are versatile intermediates for different dipeptide mimetics of the aza- and diazabicycloalkane type, which is demonstrated by the synthesis of diazabicycloalkanes 11 and 19 in only 3-6 steps and good overall yield.     

Vacancy‐Engineered Nanoceria: Enzyme Mimetic Hotspots for the Degradation of Nerve Agents

Organophosphorus‐based nerve agents, such as paraoxon, parathion, and malathion, inhibit acetylcholinesterase, which results in paralysis, respiratory failure, and death. Bacteria are known to use the enzyme phosphotriesterase (PTE) to break down these compounds. In this work, we designed vacancy‐engineered nanoceria (VE CeO₂ NPs) as PTE mimetic hotspots for the rapid degradation of nerve agents. We observed that the hydrolytic effect of the nanomaterial is due to the synergistic activity between both Ce³⁺ and Ce⁴⁺ ions located in the active site‐like hotspots. Furthermore, the catalysis by nanoceria overcomes the product inhibition generally observed for PTE and small molecule‐based PTE mimetics.     

Structure-based design of potent, conformationally constrained Smac mimetics

A successful structure-based design and synthesis of a class of highly potent conformationally constrained Smac mimetics is described. The most potent compound has a Ki value of 25 nM binding to the XIAP BIR3 protein and is 23 times more potent than natural Smac peptides. These potent Smac mimetics can serve as powerful chemical and pharmacological tools to further elucidate the role of Smac and its cellular binding partners in apoptosis regulation and may be developed as a new class of anti-cancer drugs.     

Discovery of aminoglycoside mimetics by NMR-based screening of Escherichia coli A-site RNA

A method is described for the NMR-based screening for the discovery of aminoglycoside mimetics that bind to Escherichia coli A-site RNA. Although aminoglycosides are clinically useful, they exhibit high nephrotoxicity and ototoxicity, and their overuse has led to the development of resistance to important microbial pathogens. To identify a new series of aminoglycoside mimetics that could potentially overcome the problems associated with toxicities and resistance development observed with the aminoglycosides, we have prepared large quantities of E. coli 16 S A-site RNA and conducted an NMR-based screening of our compound library in search for small-molecule RNA binders against this RNA target. From these studies, several classes of compounds were identified as initial hits with binding affinities in the range of 70 microM to 3 mM. Lead optimization through synthetic modifications of these initial hits led to the discovery of several small-molecule aminoglycoside mimetics that are structurally very different from the known aminoglycosides. Structural models of the A-site RNA/ligand complexes were prepared and compared to the three-dimensional structures of the RNA/aminoglycoside complexes.     

New cytotoxic annonaceous acetogenin mimetics having a nitrogen-heterocyclic terminal and their application to cell imaging

A terminal unsaturated lactone or its equivalent is commonly believed to be essential for the cytotoxicity of natural annonaceous acetogenins and their artificial mimetics. In this work, we discovered a series of new cytotoxic ethylene glycol ether-containing mimetics, in which a variety of simple aliphatic nitrogen-heterocycles were introduced to replace the lactone terminal of AA005 (1), a representative bioactive polyether mimic identified from our previous research, for the first time. Among these, mimic 4 bearing a terminal piperazine was found to be the most potent compound against the proliferation of three cancer cells. Based on our new findings, a fluorescent probe 7 was also developed and successfully applied to the imaging of cancer cells. This work provides a new strategy for developing simpler cytotoxic mimetics of natural annonaceous acetogenins and molecular tools for biological imaging.     

Improved synthesis of the valuable peptidomimetic intermediate 3-azido-4-hydroxy cyclopentanoic acid

An improved synthesis of 3-azido-4-hydroxy cyclopentanoic acid 2 is presented. This molecule is useful as a synthetic scaffold for β-turn mimetics on solid phase, with the selectivity of the turns being dependent on the diastereomer employed. A high diastereoselectivity in the synthesis of this molecule in solution is reported, which may then be attached to the solid phase for the synthesis of peptidomimetic libraries.     

A simple and efficient synthesis of an Asp-Gly dipeptide mimetic

Alkylation of N^α-Boc protected aspartic acid with allyl bromide in the presence of lithium bis(trimethylsilyl)amide (LHMDS) and hexamethylphosphoramide (HMPA) afforded chiral β-allyl substituted aspartic acid in good yields. After deprotection of the N^α-Boc group and reprotection as a trifluoroacetamide, the terminal alkene was oxidized to an aldehyde. The aldehyde was then coupled with l-cysteine through a cascade three-bond formation process to afford aspartic acid-glycine bicyclic dipeptide mimetics.