Proteome‐Wide Profiling of Targets of Cysteine reactive Small Molecules by Using Ethynyl Benziodoxolone Reagents

In this study, we present a highly efficient method for proteomic profiling of cysteine residues in complex proteomes and in living cells. Our method is based on alkynylation of cysteines in complex proteomes using a “clickable” alkynyl benziodoxolone bearing an azide group. This reaction proceeds fast, under mild physiological conditions, and with a very high degree of chemoselectivity. The formed azide‐capped alkynyl–cysteine adducts are readily detectable by LC‐MS/MS, and can be further functionalized with TAMRA or biotin alkyne via CuAAC. We demonstrate the utility of alkynyl benziodoxolones for chemical proteomics applications by identifying the proteomic targets of curcumin, a diarylheptanoid natural product that was and still is part of multiple human clinical trials as anticancer agent. Our results demonstrate that curcumin covalently modifies several key players of cellular signaling and metabolism, most notably the enzyme casein kinase I gamma. We anticipate that this new method for cysteine profiling will find broad application in chemical proteomics and drug discovery.     

Fast, ligand- and solvent-free synthesis of 1,4-substituted buta-1,3-diynes by Cu-catalyzed homocoupling of terminal alkynes in a ball mill

A method for the Glaser coupling reaction of alkynes by using a vibration ball mill has been developed. The procedure avoids the use of ligands and solvents during the reaction. Aryl- and alkyl-substituted terminal alkynes undergo homocoupling if coground with KF-Al(2)O(3) and CuI as a milling auxiliary and catalyst. Furthermore, an alternative protocol has been developed incorporating 1,4-diazabicyclo[2.2.2]octane (DABCO) as an additional base allowing the use of KF-Al(2)O(3) with a lower KF loading. Besides Cu salts, the homocoupling of phenylacetylene is also catalyzed by Ni or Co salts, as well as by PdCl(2). TMS-protected phenylacetylene could be directly converted into the homocoupling product after in situ deprotection of the alkyne by fluoride-initiated removal of the trimethylsilyl group.     

NHC–Pd(II) complex–Cu(I) co‐catalyzed homocoupling reaction of terminal alkynes

Two NHC–Pd(II) complexes synthesized from trans‐cyclohexane‐1,2‐diamine were fairly effective in the NHC–Pd(II) complex/Cu co‐catalyzed terminal alkyne homocoupling reaction to give the corresponding symmetrical 1,4‐disubstituted 1,3‐diynes in good yields under mild conditions. Copyright © 2006 John Wiley & Sons, Ltd.     

Development and Optimization of Glaser–Hay Bioconjugations

The prevalence of bioconjugates in the biomedical sciences necessitates the development of novel mechanisms to facilitate their preparation. Towards this end, the translation of the Glaser–Hay coupling to an aqueous environment is examined, and its potential as a bioorthogonal conjugation reaction is demonstrated. This optimized, novel, and aqueous Glaser–Hay reaction is applied towards the development of bioconjugates utilizing protein expressed with an alkynyl unnatural amino acid. Unnatural amino acid technology provides a degree of bioorthognality and specificity not feasible with other methods. Moreover, the scope of the reaction is demonstrated through protein–small molecule couplings, small‐molecule–solid‐support couplings, and protein–solid‐support immobilizations.     

Click Synthesis of Triazolyl Phenylalaninyl and Tyrosinyl Derivatives as New Protein Tyrosine Phosphatase Inhibitors

The efficient construction of triazolyl peptidomimetics via the powerful click chemistry for the discovery of small molecule‐based chemotherapeutic agents represents a promising strategy in drug development today. Herein, the synthesis of novel mono‐triazolyl or bis‐triazolyl amino acid derivatives was rapidly achieved via microwave‐assisted Cu(I)‐catalyzed azide‐alkyne 1,3‐dipolar cycloaddition (CuAAC). Subsequent in vitro enzymatic assay on several homologous protein tyrosine phosphatases (PTPs) identified the triazolyl dimers as new specific inhibitors of Cell Cycle Division 25B (CDC25B) phosphatase and Protein Tyrosine Phosphatase 1B (PTP1B).     

Recyclable clay supported Cu (II) catalyzed tandem one-pot synthesis of 1-aryl-1,2,3-triazoles

Montmorillonite KSF clay supported CuO nanoparticles efficiently catalyzes one-pot aromatic azidonation of aryl boronic acids followed by regioselective azide–alkyne 1,3-dipolar cycloaddition (CuAAC) reaction producing corresponding 1-aryl-1,2,3-triazole derivatives at room temperature in excellent yields without use of any additives. Investigations on mechanism of CuAAC revealed that sodium azide, which is used as azidonating reagent in one-pot protocol reduces Cu(II) to click-active Cu(I). The catalytic efficiency of another Cu(II) source CuSO₄ in combination with NaN₃ for this one-pot CuAAC protocol, further supported our mechanism. This is the first report for use of Cu(II)/NaN₃ catalytic system for CuAAC protocol. The clay–Cu(II) catalyst being ligand-free, leaching-free, easy to synthesize from inexpensive commercially available precursors, recyclable, and environmentally friendly will be highly useful for economical synthesis of 1,4-disubstituted 1,2,3-triazoles.     

Requirement for an oxidant in Pd/Cu co-catalyzed terminal alkyne homocoupling to give symmetrical 1,4-disubstituted 1,3-diynes

Palladium-catalyzed terminal alkyne dimerization, through oxidative homocoupling, is a useful approach to the synthesis of symmetrical 1,4-diynes. Recent investigations have suggested that this reaction might be accomplished in the absence of intentionally added stoichiometric oxidants (to reoxidize Pd(0) to Pd(II)). In this paper, we have fully addressed the question of whether oxygen (or added oxidant) is required to facilitate this process. The presence of a stoichiometric quantity of air (or added oxidant such as I2) is essential for alkyne dimerization. Excess PPh3 inhibits alkyne dimerization to enyne, which only occurs to a significant extent when the reaction is starved of oxidant. Theoretical studies shed more light on the requirement for an oxidant in the homocoupling reaction in order for the process to be theromodynamically favorable. The employment of I2 as the stoichiometric oxidant appears to be the method of choice. The dual role of Cu both in transmetalation of alkynyl units to Pd(II) and in assisting reoxidation of Pd(0) to Pd(II) is suggested.     

Single‐step oxidative homocoupling of aryl Grignard reagents via Co(II), Ni(II) and Cu(II) Complexes under air

A simple catalytic system of direct synthesis for the symmetrical biaryls using catalytic amounts of Co(II), Ni(II) and Cu(II) complexes has been developed. The reaction system involves in situ synthesis of Grignard reagents. The complexes, containing bidentate Schiff base and dmit (2‐thioxo‐1,3‐dithiole‐4,5‐dithiolate) ligands, were compatible with diverse functionalities and afford a high yield of biaryls in a single step, proving to be promising catalysts in homocoupling reactions. Atmospheric oxygen is used as an oxidant which renders a green, simple and economical catalytic route. Copyright © 2014 John Wiley & Sons, Ltd.     

On‐Surface Domino Reactions: Glaser Coupling and Dehydrogenative Coupling of a Biscarboxylic Acid To Form Polymeric Bisacylperoxides

Herein we report the on‐surface oxidative homocoupling of 6,6′‐(1,4‐buta‐1,3‐diynyl)bis(2‐naphthoic acid) (BDNA) via bisacylperoxide formation on different Au substrates. By using this unprecedented dehydrogenative polymerization of a biscarboxylic acid, linear poly‐BDNA with a chain length of over 100 nm was prepared. It is shown that the monomer BDNA can be prepared in situ at the surface via on‐surface Glaser coupling of 6‐ethynyl‐2‐naphthoic acid (ENA). Under the Glaser coupling conditions, BDNA directly undergoes polymerization to give the polymeric peroxide (poly‐BDNA) representing a first example of an on‐surface domino reaction. It is shown that the reaction outcome varies as a function of surface topography (Au(111) or Au(100)) and also of the surface coverage, to give branched polymers, linear polymers, or 2D metal–organic networks.     

Efficient Atropodiastereoselective Access to 5,5′‐Bis‐1,2,3‐triazoles: Studies on 1‐Glucosylated 5‐Halogeno 1,2,3‐Triazoles and Their 5‐Substituted Derivatives as Glycogen Phosphorylase Inhibitors

Whereas copper‐catalyzed azide–alkyne cycloaddition (CuAAC) between acetylated β‐D ‐glucosyl azide and alkyl or phenyl acetylenes led to the corresponding 4‐substituted 1‐glucosyl‐1,2,3‐triazoles in good yields, use of similar conditions but with 2 equiv CuI or CuBr led to the 5‐halogeno analogues (>71 %). In contrast, with 2 equiv CuCl and either propargyl acetate or phenyl acetylene, the major products (>56 %) displayed two 5,5′‐linked triazole rings resulting from homocoupling of the 1‐glucosyl‐4‐substituted 1,2,3‐triazoles. The 4‐phenyl substituted compounds (acetylated, O‐unprotected) and the acetylated 4‐acetoxymethyl derivative existed in solution as a single form (d.r.>95:5), as shown by NMR spectroscopic analysis. The two 4‐phenyl substituted structures were unambiguously identified for the first time by X‐ray diffraction analysis, as atropisomers with aR stereochemistry. This represents one of the first efficient and highly atropodiastereoselective approaches to glucose‐based bis‐triazoles as single atropisomers. The products were purified by standard silica gel chromatography. Through Sonogashira or Suzuki cross‐couplings, the 1‐glucosyl‐5‐halogeno‐1,2,3‐triazoles were efficiently converted into a library of 1,2,3‐triazoles of the 1‐glucosyl‐5‐substituted (alkynyl, aryl) type. Attempts to achieve Heck coupling to methyl acrylate failed, but a stable palladium‐associated triazole was isolated and analyzed by ¹H NMR and MS. O‐Unprotected derivatives were tested as inhibitors of glycogen phosphorylase. The modest inhibition activities measured showed that 4,5‐disubstituted 1‐glucosyl‐1,2,3‐triazoles bind weakly to the enzyme. This suggests that such ligands do not fit the catalytic site or any other binding site of the enzyme.     

2,4‐Dinitrophenol‐Catalyzed α‐C(sp3)−H and C(sp)−H Bond Functionalization of Cyclic Amines and Alkynes: Highly Regio‐/Diastereoselective Synthesis of α‐Alkynyl‐3‐Amino‐2‐Oxindoles

A transition‐metal‐ and oxidant‐free DNP (2,4‐dinitrophenol)‐catalyzed atom‐economical regio‐ and diastereoselective synthesis of monofunctionalized α‐alkynyl‐3‐amino‐2‐oxindole derivatives by C?H bond functionalization of cyclic amines and alkynes with indoline‐2,3‐diones has been developed. This cascade event sequentially involves the reductive amination of indoline‐2,3‐dione by imine formation and cross coupling between C(sp³)?H and C(sp)?H of the cyclic amines and alkynes. This reaction offers an efficient and attractive pathway to different types of α‐alkynyl‐3‐amino‐2‐oxindole derivatives in good yields with a wide tolerance of functional groups. The salient feature of this methodology is that it completely suppresses the homocoupling of alkynes. To the best of our knowledge, this is the first example of a DNP‐catalyzed metal‐free direct C(sp³)?H and C(sp)?H bond functionalization providing biologically active α‐alkynyl‐3‐amino‐2‐oxindole scaffolds.     

介孔TiO2担载Cu（OH）2及其催化炔烃氧化偶联反应

在有序介孔TiO₂中原位担载了高分散的Cu（OH）₂,并将其应用于炔烃的氧化偶联（Glaser）多相催化反应,该催化剂表现出很高的催化活性.Cu（OH）₂为催化剂的主要活性组分,TiO₂的有序介孔和较大的比表面积有利于Cu（OH）₂的分散以及反应物和产物的扩散,具有重要的应用前景.     

Metal‐Free Reaction of ortho‐Carbonylated Alkynyl‐Substituted Arylaldehydes with Common Amines: Selective Access to Functionalized Isoindolinone and Indenamine Derivatives

Herein we describe a reaction of ortho‐carbonylated alkynyl‐substituted arylaldehydes with common primary amines that can provide functionalized isoindolinone and 3‐hydroxylindenamine products in high yields. Depending on the substituent size of primary amines, two distinct reaction pathways were exploited selectively, that are, an initial aza‐conjugate addition followed by hydrogen transfer to access isoindolinone framework and a unique oxa‐conjugate addition followed by Petasis–Ferrier rearrangement to afford indenamine derivatives. In the presence of Et₃N, the reaction property of small primary amines was changed, proceeding to afford 3‐hydroxylindenamine derivatives efficiently. These products contain interesting substructures that exist in many natural products and bioactive molecules. The reaction features contain the use of transition‐metal‐free catalysts, simple operation, broad substrate scope, and product diversity.     

A Practical Guide on the Synthesis of Metal Chelates for Molecular Imaging and Therapy by Means of Click Chemistry

The copper‐catalyzed cycloaddition of organic azides and alkynes (CuAAC) is one of the most popular reactions for rapid assembly of multifunctional molecular frameworks from commercially available building blocks. It is also attractive for synthesis of conjugates of multidentate chelate ligands (chelators) with molecular targeting vectors, such as peptides or proteins, which serve as precursors for labeling with metal radionuclides or are useful as MRI contrast agents after Gd^III complexation. However, applicability of CuAAC for such purposes is complicated by formation of unwanted copper chelates. The alternative use of copper‐free click chemistry, for example, the strain‐promoted alkyne‐azide cycloaddition (SPAAC) or the Diels–Alder reaction of tetrazines and strained alkenes, entails other specific challenges: Introduction of large, isomerically non‐homogeneous and hydrophobic linker groups affects product homogeneity and can severely change pharmacokinetic profiles. Against this background, this review elucidates scope and applicability of both Cu‐catalyzed and Cu‐free alkyne‐azide cycloadditions pertinent to the elaboration of radiometal chelates and MRI contrast agents, with an emphasis on strategies to tackle the problem of copper complexation during CuAAC.     

A reusable polymer‐supported copper(I) catalyst for triazole click reaction on water: An experimental and computational study

In the search for establishing a clickable copper‐catalysed (3 + 2) Huisgen azide–alkyne cycloaddition (CuAAC) reaction under strict conditions, in particular in terms of preventing the presence of copper particles/traces in reaction products and using an environmentally benign medium such as water, we describe here the synthesis of an aminomethyl polystyrene‐supported copper(I) catalyst (Cu(I)‐AMPS) and its characterization by means of Fourier transform infrared and energy‐dispersive X‐ray spectroscopies and scanning electron microscopy. Cu(I)‐AMPS was found to be highly active in the CuAAC reaction of various organic azides with alkynes affording the corresponding 1,4‐disubstituted 1,2,3‐triazoles in a regioselective manner in air at room temperature and using water as solvent. The insolubility and/or partial solubility of the organic azide and alkyne precursors as well as the heterogeneous Cu(I)‐AMPS catalytic system points to the occurrence of the cycloaddition at the organic–water interface ‘on water’ affording quantitative yields of water‐insoluble 1,2,3‐triazoles. A mechanistic study was performed using density functional theory aiming at explaining the observed reactivity and selectivity of the Cu (I)‐AMPS catalyst in CuAAC reactions.     

Sunlight‐Driven Copper‐Catalyst Activation Applied to Photolatent Click Chemistry

The synthesis, full characterization, photoreduction properties, and catalytic activity for the copper(I)‐catalyzed alkyne‐azide cycloaddition (CuAAC) reaction of a copper(II)–DMEDA (N,N′‐dimethylethylendiamine) complex is reported. Spectroscopic studies (UV/Vis, EPR) demonstrated that under daylight illumination highly effective copper(II) to copper(I) reduction occurs in this complex. These findings are in agreement with a high photoreduction quantum yield value of 0.22 in MeOH, and a value approaching unity as determined in THF. The reduction process, which can also be conducted by irradiation at 365 nm by using a standard TLC (thin layer chromatography) lamp, is ascribed to a highly efficient photoinduced electron transfer (PET) process mediated by the benzophenone photosensitizer present in the carboxylate counterion. Having deaerated the reaction mixture, the photogenerated copper(I) species proved to be highly active for the CuAAC reaction, demonstrated by reactions conducted with low catalyst loading (0.5 mol %) on a range of clickable protected and non‐protected mono‐ and disaccharides. Once initiated, the reaction can be stopped at any time on introducing air into the reaction medium. Deoxygenation followed by irradiation restores the activity, making the copper(II)–DMEDA complex a switchable catalyst of practical value.     

Biofunctionalization on alkylated silicon substrate surfaces via "click" chemistry

Biofunctionalization of silicon substrates is important to the development of silicon-based biosensors and devices. Compared to conventional organosiloxane films on silicon oxide intermediate layers, organic monolayers directly bound to the nonoxidized silicon substrates via Si-C bonds enhance the sensitivity of detection and the stability against hydrolytic cleavage. Such monolayers presenting a high density of terminal alkynyl groups for bioconjugation via copper-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC, a "click" reaction) were reported. However, yields of the CuAAC reactions on these monolayer platforms were low. Also, the nonspecific adsorption of proteins on the resultant surfaces remained a major obstacle for many potential biological applications. Herein, we report a new type of "clickable" monolayers grown by selective, photoactivated surface hydrosilylation of α,ω-alkenynes, where the alkynyl terminal is protected with a trimethylgermanyl (TMG) group, on hydrogen-terminated silicon substrates. The TMG groups on the film are readily removed in aqueous solutions in the presence of Cu(I). Significantly, the degermanylation and the subsequent CuAAC reaction with various azides could be combined into a single step in good yields. Thus, oligo(ethylene glycol) (OEG) with an azido tag was attached to the TMG-alkyne surfaces, leading to OEG-terminated surfaces that reduced the nonspecific adsorption of protein (fibrinogen) by >98%. The CuAAC reaction could be performed in microarray format to generate arrays of mannose and biotin with varied densities on the protein-resistant OEG background. We also demonstrated that the monolayer platform could be functionalized with mannose for highly specific capturing of living targets (Escherichia coli expressing fimbriae) onto the silicon substrates.     

Copper‐Catalyzed Amine–Alkyne–Alkyne Addition Reaction: An Efficient Method For the Synthesis of γ,δ‐Alkynyl‐β‐amino Acid Derivatives

A simple and efficient method for the synthesis of γ,δ‐alkynyl‐β‐amino acid derivatives by a copper‐catalyzed three‐component amine–alkyne–alkyne addition reaction was developed. Various γ,δ‐alkynyl‐β‐amino acid derivatives were synthesized in moderate to good yields in one step. With chiral prolinol derivatives employed as the amine component, excellent diastereoselectivities (up to >99:1 diastereomeric ratio (dr)) were obtained. The scope of the reaction and further transformations of the resulting amino acid derivatives, such as deprotection and cyclization are also described.     

Efficient alkyne homocoupling catalysed by copper immobilized on functionalized silica

Copper immobilized on a functionalized silica support is a good catalyst for the homocoupling of terminal alkynes. The so‐called Glaser–Hay coupling reaction can be run in air with catalytic amounts of base. The copper catalyst is active for multiple substituted alkynes, in both polar and non‐polar solvents, with good to excellent yields (75–95%). Depending on the alkyne, full conversion can be achieved within 3–24 h. The catalyst was characterized by TGA, inductively coupled plasma and X‐ray photoelectron spectroscopy. Leaching tests confirm that the catalyst is and remains heterogeneous. Importantly, the overall reaction requires only alkyne and oxygen (in this case, air) as reagents, making this a clean catalytic oxidative coupling reaction. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly reusable support‐free copper(II) complex of para‐hydroxy‐substituted salen: Novel,efficient and versatile catalyst for C─N bond forming reactions

An air‐stable, highly active and versatile method for C─N bond forming reactions is reported. Under mild conditions using a highly reusable support‐free Cu(II)–salen complex, structurally diverse N ‐aryl‐substituted compounds were obtained via direct C─N bond forming reaction of HN‐heterocycles with aryl iodides or three‐component C─N bond forming reaction of 2‐bromobenzaldehyde, aniline derivatives and sodium azide in good to excellent yields. C─N bond forming reaction for benzimidazole derivatives was also performed in the presence of the catalyst under ambient conditions. A series of hybrid benzimidazoles bearing morpholine, tetrazole and quinoxaline backbones were produced using this method. All reactions were performed in short times under air. The Cu(II) catalyst could be reused up to eight times in the direct cross‐coupling reaction of 9H –carbazole with iodobenzene without any decrease in its catalytic activity.