Staudinger Reaction Research Articles

Electrocatalytic hydrogen evolution of a cobalt A2B triaryl corrole complex containing –N=PPh3 group

A new cobalt 5,15-bis(perfluorophenyl)-10-(4-N-(triphenylphosphoranylidene)-2,3,5,6-tetrafluorophenyl) corrole complex (Co-BPNC-PPh3) containing –N=PPh3 group has been prepared by Staudinger reaction and characterized by the single-crystal X-ray structure determination. The electrocatalytic hydrogen evolution reaction (HER) of Co-BPNC-PPh3 by using acetic acid (AcOH), trifluoroacetic acid (TFA) and p-toluenesulfonic acid (TsOH) as proton sources in N, N-dimethylformamide (DMF) solvent had been investigated. The turn-over frequency (TOF) value of Co-BPNC-PPh3 was observed 450 h−1 at an overpotential of 838 mV in neutral aqueous solution, showing excellent electrocatalytic HER activity. This Co-BPNC-PPh3 exhibited excellent durability and stability in the 5-hours electrolysis. Its activity is also better than cobalt 5, 10, 15-(tris-pentatfulorophenyl) corrole (Co-TPFC-PPh3), which may be ascribed to the –N=PPh3 proton relay effect in the electrocatalytic HER.

P-052 - Perfluoroaryl azide staudinger reaction combined with sulfur [18F]Fluoride exchange click chemistry for live cell radiolabeling

P-052 - Perfluoroaryl azide staudinger reaction combined with sulfur [18F]Fluoride exchange click chemistry for live cell radiolabeling

Cell-Free Systems Enable the Production of AB5 Toxins for Diagnostic Applications.

Cell-free protein synthesis (CFPS) represents a versatile key technology for the production of toxic proteins. As a cell lysate, rather than viable cells, is used, the toxic effects on the host organism can be circumvented. The open nature of cell-free systems allows for the addition of supplements affecting protein concentration and folding. Here, we present the cell-free synthesis and functional characterization of two AB5 toxins, namely the cholera toxin (Ctx) and the heat-labile enterotoxin (LT), using two eukaryotic cell-free systems based on Chinese hamster ovary (CHO) and Spodoptera frugiperda (Sf21) cells. Through an iterative optimization procedure, the synthesis of the individual AB5 toxins was established, and the formation of multimeric structures could be shown by autoradiography. A functional analysis was performed using cell-based assays, thereby demonstrating that the LT complex induced the characteristic cell elongation of target cells after 24 h. The LT complex induced cell death at higher concentrations, starting at an initial concentration of 5 nM. The initial toxic effects of the Ctx multimer could already be detected at 4 nM. The detection and characterization of such AB5 toxins is of utmost importance, and the monitoring of intracellular trafficking facilitates the further identification of the mechanism of action of these toxins. We showed that the B-subunit of LT (LTB) could be fluorescently labeled using an LTB-Strep fusion protein, which is a proof-of-concept for future Trojan horse applications. Further, we performed a mutational analysis of the CtxA subunit as its template was modified, and an amber stop codon was inserted into CtxA’s active site. Subsequently, a non-canonical amino acid was site-specifically incorporated using bio-orthogonal systems. Finally, a fluorescently labeled CtxA protein was produced using copper-catalyzed click reactions as well as a Staudinger ligation. As expected, the modified Ctx multimer no longer induced toxic effects. In our study, we showed that CFPS could be used to study the active centers of toxins by inserting mutations. Additionally, this methodology can be applied for the design of Trojan horses and targeted toxins, as well as enabling the intracellular trafficking of toxins as a prerequisite for the analysis of the toxin’s mechanism of action.

An ESIPT fluorescent probe based on Staudinger reaction for detection of triphenylphosphine and tetrakis(triphenyl-phosphine)palladium

Triphenylphosphine (PPh3) and tetrakis(triphenylphosphine)palladium (Pd(PPh3)4) are harmful at extremely low concentration, thus it is essential to explore selective and sensitive method to detect them. Based on Staudinger reaction mechanism, here we present a simple excited-state intramolecular proton transfer (ESIPT) fluorescent probe (HBTN) for detection of PPh3 and Pd(PPh3)4 over other phosphine derivatives with differential channel fluorescence (enol and keto emission). The reaction-typed fluorescence probe with novel Staudinger reaction mechanism offers very low autofluorescence and a large signal-to-noise response signal, which is beneficial for the sensitive detection of PPh3 and Pd(PPh3)4. Moreover, HBTN can be used for efficiently detecting Pd(PPh3)4 residues in highly purified products and imaging PPh3 in living cells.

Synthesis of the New Nucleoside 5'-Alpha-Iminophosphates Using Staudinger Reaction

Synthesis of the New Nucleoside 5'-Alpha-Iminophosphates Using Staudinger Reaction

Green light enabled Staudinger-Bertozzi ligation.

We introduce a visible light-induced Staudinger-Bertozzi ligation via photo-uncaging of a triphenylphosphine moiety with a photolabile coumarin derivative. Our action plot study examines the conversion as the function of wavelength, revealing that the uncaging process and Staudinger reaction can be triggered by green light (λ < 550 nm). We further demonstrate the applicability of our approach in materials science via endgroup modification of water soluble poly(ethylene glycol) and green light-induced patterning of a solid substrate.

Role of imine isomerization in the stereocontrol of the Staudinger reaction between ketenes and imines.

Computational–experimental analysis has allowed determining that the stereochemistry of the Staudinger reaction between ketenes and imines is strongly associated with the nature of the imine, which affects the two steps of the reaction. The first step, namely the nucleophilic attack of the sp2-hybridized nitrogen atom of the imine on the sp-hybridized carbon atom of the ketene, is affected by the energetically accessible in situ isomerization patterns of the imine. The second step consists of a conrotatory electrocyclization of the zwitterionic intermediate formed in the previous step. This latter pericyclic step depends on the inward/outward torquoelectronic effects generated by the substituents of the imine. The impact of these factors on the stereochemistry of this reaction has been analyzed kinetically by numerical methods. The results of these simulations are compatible with the experimental results and support these conclusions.

Synthesis and Applications of Porphyrin-Biomacromolecule Conjugates.

With potential applications in materials and especially in light-responsive biomedicine that targets cancer tissue selectively, much research has focused on developing covalent conjugation techniques to tether porphyrinoid units to various biomacromolecules. This review details the key synthetic approaches that have been employed in the recent decades to conjugate porphyrinoids with oligonucleotides and peptides/proteins. In addition, we provide succinct discussions on the subsequent applications of such hybrid systems and also give a brief overview of the rapidly progressing field of porphyrin-antibody conjugates. Since nucleic acid and peptide systems vary in structure, connectivity, functional group availability and placement, as well as stability and solubility, tailored synthetic approaches are needed for conjugating to each of these biomacromolecule types. In terms of tethering to ONs, porphyrins are typically attached by employing bioorthogonal chemistry (e.g., using phosphoramidites) that drive solid-phase ON synthesis or by conducting post-synthesis modifications and subsequent reactions (such as amide couplings, hydrazide-carbonyl reactions, and click chemistry). In contrast, peptides and proteins are typically conjugated to porphyrinoids using their native functional groups, especially the thiol and amine side chains. However, bioorthogonal reactions (e.g., Staudinger ligations, and copper or strain promoted alkyne-azide cycloadditions) that utilize de novo introduced functional groups onto peptides/proteins have seen vigorous development, especially for site-specific peptide-porphyrin tethering. While the ON-porphyrin conjugates have largely been explored for programmed nanostructure self-assembly and artificial light-harvesting applications, there are some reports of ON-porphyrin systems targeting clinically translational applications (e.g., antimicrobial biomaterials and site-specific nucleic acid cleavage). Conjugates of porphyrins with proteinaceous moieties, on the other hand, have been predominantly used for therapeutic and diagnostic applications (especially in photodynamic therapy, photodynamic antimicrobial chemotherapy, and photothermal therapy). The advancement of the field of porphyrinoid-bioconjugation chemistry from basic academic research to more clinically targeted applications require continuous fine-tuning in terms of synthetic strategies and hence there will continue to be much exciting work on porphyrinoid-biomacromolecule conjugation.

Strategic Evaluation of the Traceless Staudinger Ligation for Radiolabeling with the Tricarbonyl Core.

The traceless Staudinger ligation with its two variants is a powerful biorthogonal conjugation method not only for the connection of biomolecules, but also for the introduction of fluorescence- or radiolabels under mild reaction conditions. Herein, the strategic evaluation of the traceless Staudinger ligation for radiolabeling 99mTc using the fac-[Tc(CO)3]+ core is presented. A convenient and high-yielding three-step synthetic procedure of dipicolylamine-based phosphanols as ligands for the mild radiolabeling was developed. The labeling was accomplished using a tricarbonyl kit and a 99mTc-pertechnetate generator eluate showing 87% radiochemical conversion. The respective rhenium-based, non-radioactive reference compounds were synthesized using (Et4N)2[Re(CO)3Br3] as precursor. All products were analyzed by NMR, MS, and elemental analysis. Additional XRD analyses were performed.

Small Molecule Control of Morpholino Antisense Oligonucleotide Function through Staudinger Reduction.

Conditionally activated, caged morpholino antisense agents (cMOs) are tools that enable the temporal and spatial investigation of gene expression, regulation, and function during embryonic development. Cyclic MOs are conformationally gated oligonucleotide analogs that do not block gene expression until they are linearized through the application of an external trigger, such as light or enzyme activity. Here, we describe the first examples of small molecule-responsive cMOs, which undergo rapid and efficient decaging via a Staudinger reduction. This is enabled by a highly flexible linker design that offers opportunities for the installation of chemically activated, self-immolative motifs. We synthesized cyclic cMOs against two distinct, developmentally relevant genes and demonstrated phosphine-triggered knockdown of gene expression in zebrafish embryos. This represents the first report of a small molecule-triggered antisense agent for gene knockdown, adding another bioorthogonal entry to the growing arsenal of gene knockdown tools.

Total Synthesis of a Chimeric Glycolipid Bearing the Partially Acetylated Backbone of Sponge-Derived Agminoside E.

We describe the total synthesis of a chimeric glycolipid bearing both the partially acetylated backbone of sponge-derived agminoside E and the (R)-3-hydroxydecanoic acid chain of bacterial rhamnolipids. The branched pentaglucolipid skeleton was achieved using a [3 + 2] disconnection approach. The β-(1 → 2) and β-(1 → 4)-glycosidic bonds were synthesized through a combination of NIS/Yb(OTf)3- and TMSOTf-mediated stereoselective glycosylations of thiotolyl, N-phenyltrifluoroacetimidate, and trichloroacetimidate donors. Late-stage pentaacetylation, Staudinger reduction of a (2-azidomethyl)benzoyl group, followed by continuous-flow microfluidic hydrogenolysis completed the total synthesis of the structurally simplified glycolipid, whose partial acetylation pattern on the glycan part was identical to agminoside E. Our study lays the foundation for the total synthesis of sponge-derived agminosides and the understanding of their biological functions in sponges.

Traceless Staudinger Ligation To Introduce Chemical Diversity on β-Lactamase Inhibitors of Second Generation.

We explored the traceless Staudinger ligation for the functionalization of the C2 position of second generation β-lactamase inhibitors based on a diazabicyclooctane (DBO) scaffold. Our strategy is based on the synthesis of phosphine phenol esters and their ligation to an azido-containing precursor. Biological evaluation showed that this route provided access to a DBO that proved to be superior to commercial relebactam for inhibition of two of the five β-lactamases that were tested.

Research Progress and Application of Bioorthogonal Reactions in Biomolecular Analysis and Disease Diagnosis.

Bioorthogonal reactions are rapid, specific and high yield reactions that can be performed in in vivo microenvironments or simulated microenvironments. At present, the main biorthogonal reactions include Staudinger ligation, copper-catalyzed azide alkyne cycloaddition, strain-promoted [3 + 2] reaction, tetrazine ligation, metal-catalyzed coupling reaction and photo-induced biorthogonal reactions. To date, many reviews have reported that bioorthogonal reactions have been used widely as a powerful tool in the field of life sciences, such as in target recognition, drug discovery, drug activation, omics research, visualization of life processes or exogenous bacterial infection processes, signal transduction pathway research, chemical reaction dynamics analysis, disease diagnosis and treatment. In contrast, to date, few studies have investigated the application of bioorthogonal reactions in the analysis of biomacromolecules in vivo. Therefore, the application of bioorthogonal reactions in the analysis of proteins, nucleic acids, metabolites, enzyme activities and other endogenous molecules, and the determination of disease-related targets is reviewed. In addition, this review discusses the future development opportunities and challenges of biorthogonal reactions. This review presents an overview of recent advances for application in biomolecular analysis and disease diagnosis, with a focus on proteins, metabolites and RNA detection.

One-Carbon Insertion and Polarity Inversion Enabled a Pyrrole Strategy to the Total Syntheses of Pyridine-Containing Lycopodium Alkaloids: Complanadine A and Lycodine.

Complanadine A and lycodine are representative members of the Lycopodium alkaloids with a characteristic pyridine-containing tetracyclic skeleton. Complanadine A has demonstrated promising neurotrophic activity and potential for persistent pain management. Herein we report a pyrrole strategy enabled by one-carbon insertion and polarity inversion for concise total syntheses of complanadine A and lycodine. The use of a pyrrole as the pyridine precursor allowed the rapid construction of their tetracyclic skeleton via a one-pot Staudinger reduction, amine-ketone condensation, and Mannich-type cyclization. The pyrrole group was then converted to the desired pyridine by the Ciamician-Dennstedt rearrangement via a one-carbon insertion process, which also simultaneously introduced a chloride at C3 for the next C-H arylation. Other key steps include a direct anti-Markovnikov hydroazidation, a Mukaiyama-Michael addition, and a Paal-Knorr pyrrole synthesis. Lycodine and complanadine A were prepared in 8 and 11 steps, respectively, from a readily available known compound.

Time‐Dependent Diastereodivergent Michael Addition Enabled by Phosphazenes Acting as Catalysts and Reactants

AbstractA switching of the step order within cascade process enabled design of a diastereodivergent approach to phosphazenopyrrolines with a 1,3‐relationship of stereocenters. The approach is based on a cascade transformation of readily accessible γ‐azidobutyronitriles that includes Staudinger, aza‐Wittig and Michael steps. Stereodivergence is achieved at the Michael step that is self‐catalyzed by phosphazene intermediates and provides construction of quaternary stereocenter. Depending on the type of phosphazene intermediates, generating either via Staudinger reaction or via subsequent intramolecular aza‐Wittig reaction with nitrile and then reacting with a Michael acceptor, either trans‐ or cis‐isomers of the target product can be produced. Thus, diastereoselectivity can be achieved by varying the time of addition for the Michael acceptor. Therefore, three distinct roles were revealed for phosphazenes in this process: catalysts, reactants and stereoselectivity controllers. This stereodivergent strategy was applied for the synthesis of all stereoisomers of the biorelevant tetrahydro‐7‐aza‐indoles.magnified image

Polymorphism of Kdo-Based Glycolipids: The Elaborately Determined Stable and Dynamic Bicelles

Polymorphism of Kdo-Based Glycolipids: The Elaborately Determined Stable and Dynamic Bicelles

Synthesis and 1H NMR data assignment of 3-acetamido-4-amino-3,4-dihydro-2H-pyran-6-carboxylates and their acetyl-migrated isomers

An unexpected acetyl migration is found in the product of Staudinger reduction to prepare the 4(R)-epimer of zanamivir and laninamivir octanoate as the impurity of drug substance. The synthesis and 1H NMR data assignment of (3 R,4R) or (3 R,4S)-3-acetamido-4-amino-3,4-dihydro-2H-pyran-6-carboxylates and the acetyl-migrated isomers (3 R,4R)- 3-amino-4-acetamido-3,4-dihydro-2H-pyran-6-carboxylates are herein described. Additionally, the experiments show that the acetyl migration tends to occur under neutral or acidic conditions, but not under alkalic conditions. Some organic bases are screened to block the migration during the Staudinger reduction, and the best (DBU) is identified.

IEDDA: An Attractive Bioorthogonal Reaction for Biomedical Applications.

The pretargeting strategy has recently emerged in order to overcome the limitations of direct targeting, mainly in the field of radioimmunotherapy (RIT). This strategy is directly dependent on chemical reactions, namely bioorthogonal reactions, which have been developed for their ability to occur under physiological conditions. The Staudinger ligation, the copper catalyzed azide-alkyne cycloaddition (CuAAC) and the strain-promoted [3 + 2] azide–alkyne cycloaddition (SPAAC) were the first bioorthogonal reactions introduced in the literature. However, due to their incomplete biocompatibility and slow kinetics, the inverse-electron demand Diels-Alder (IEDDA) reaction was advanced in 2008 by Blackman et al. as an optimal bioorthogonal reaction. The IEDDA is the fastest bioorthogonal reaction known so far. Its biocompatibility and ideal kinetics are very appealing for pretargeting applications. The use of a trans-cyclooctene (TCO) and a tetrazine (Tz) in the reaction encouraged researchers to study them deeply. It was found that both reagents are sensitive to acidic or basic conditions. Furthermore, TCO is photosensitive and can be isomerized to its cis-conformation via a radical catalyzed reaction. Unfortunately, the cis-conformer is significantly less reactive toward tetrazine than the trans-conformation. Therefore, extensive research has been carried out to optimize both click reagents and to employ the IEDDA bioorthogonal reaction in biomedical applications.

Stereoselective synthesis and characterization of monocyclic cis‐β‐lactams containing 5‐methyl‐1,3,4‐thiadiazole‐2‐thiol moiety

AbstractThis article describes the stereoselective synthesis of monocyclic cis‐β‐lactams. The 2‐(4‐chlorophenoxy)‐acetic acid or 2‐phenoxy‐acetic acid with a carboxylic acid activator 2‐ethoxy carbonyl DCPN generate ketene in situ, which reacts with imines derived from substituted tetralone carbaldehyde yielded monocyclic cis‐β‐lactams having 5‐methyl‐1,3,4‐thiadiazole‐2‐thiol moiety through [2+2] cyclo‐addition reaction (Staudinger reaction). All structures of cis‐β‐lactams were elucidated by a spectral technique like FT‐IR, 1H and 13C NMR spectra, HRMS, and single X‐ray crystallography. The cis configuration of the β‐lactams was determined based on coupling constant (J) value using 1H NMR for hydrogens H‐3 and H‐4 of the β‐lactams ring. This work presents the synthesis of β‐lactams more simply with high yields. The products were simply purified by crystallization technique.

Toward conditional control of Smac mimetic activity by RNA-templated reduction of azidopeptides on PNA or 2'-OMe-RNA.

Oligonucleotide templated reactions can be used to control the activity of functional molecules based on the presence of a specific trigger sequence. We report an RNA-controlled reaction system to conditionally restore the N-terminal amino group and thus binding affinity of azide-modified Smac mimetic compounds (SMCs) for their target protein X-linked Inhibitor of Apoptosis Protein (XIAP). Two templated reactions were compared: Staudinger reduction with phosphines and a photocatalytic reaction with Ru(bpy)2 (mcbpy). The latter proved faster and more efficient, especially for the activation of a bivalent SMC, which requires two consecutive reduction steps. The templated reaction proceeds with turnover when 2'-OMe-RNA probes are used, but is significantly more efficient with PNA, catalyzing a reaction in the presence of low, substoichiometric amounts (1%-3%, 10nM) of target RNA.