Nitroxide: Anwendungen in der Synthese und in der Polymerchemie

Tebben, Ludger; Studer, Armido

doi:10.1002/ange.201002547

Cited by 171 publications

(43 citation statements)

References 575 publications

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“…Isomerization as a potential link to join nucleophilic addition with enolate chemistry. With optimal conditions for the isomerization of alkoxides to enolates established, the tandem sequence was elaborated; it consists of: 1) nucleophilic addition of several aryllithium reagents 1 to a,b-unsaturated aldehydes 2, 2) isomerization catalyzed by Cat-1, 3) Michael addition of the resulting enolates to acceptors 6, 4) SET oxidation to the corresponding radicals by selective SET oxidant ferrocenium hexafluorophosphate 7, [16] 5) radical cyclizations to construct a fivemembered ring, and finally 6) CÀO bond formation by reaction with persistent radical TEMPO 8 [17] (Scheme 3). The substrate scope is broad and only two, often partly separable anti and syn diastereomers of cyclic oxygenated products 9 a-m, both having exclusive trans stereochemistry at the cyclopentane ring, were isolated.…”

Section: Resultsmentioning

confidence: 99%

Highly Functionalized and Potent Antiviral Cyclopentane Derivatives Formed by a Tandem Process Consisting of Organometallic, Transition‐Metal‐Catalyzed, and Radical Reaction Steps

Jagtap

Ford

Deister

et al. 2014

Chemistry A European J

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A simple modular tandem approach to multiply substituted cyclopentane derivatives is reported, which succeeds by joining organometallic addition, conjugate addition, radical cyclization, and oxygenation steps. The key steps enabling this tandem process are the thus far rarely used isomerization of allylic alkoxides to enolates and single-electron transfer to merge the organometallic step with the radical and oxygenation chemistry. This controlled lineup of multiple electronically contrasting reactive intermediates provides versatile access to highly functionalized cyclopentane derivatives from very simple and readily available commodity precursors. The antiviral activity of the synthesized compounds was screened and a number of compounds showed potent activity against hepatitis C and dengue viruses.

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Section: Resultsmentioning

confidence: 99%

Highly Functionalized and Potent Antiviral Cyclopentane Derivatives Formed by a Tandem Process Consisting of Organometallic, Transition‐Metal‐Catalyzed, and Radical Reaction Steps

Jagtap

Ford

Deister

et al. 2014

Chemistry A European J

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“…We turned to the persistent radical effect (PRE) for an alternative means of equilibration at the anomeric center, thus avoiding any ring-opened species. [8] Anomeric radical reactions are well known to give rise to axially quenched products under kinetic conditions, [9] with the notable exception of the sialic acids wherein poor selectivity is found. [10] Conversely, the equilibration of anomeric stereochemistry via radical intermediates is rare [11] and has not been applied explicitly to the study of the anomeric effect.…”

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confidence: 99%

Dissecting the Influence of Oxazolidinones and Cyclic Carbonates in Sialic Acid Chemistry

2012

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Polarisierende Wirkung: Die thermische Gleichgewichtseinstellung für 1 und eine massenspektrometrische Analyse von Sialylphosphaten sprechen dafür, dass das 4O,5N‐Oxazolidinon‐ und das 4,5‐O‐Carbonat‐System den anomeren Effekt und den Sialidierungsmechanismus durch ihr Dipolmoment in der Ebene des Pyranoserings beeinflussen. Die elektronenziehende Wirkung destabilisiert 2 und begünstigt assoziative Glycosylierungsmechanismen. TEMPO=2,2,6,6‐Tetramethylpiperidin‐N‐oxid.

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“…[14] To realize the designed reaction, we focused on an oxidation of a Ser hydroxymethyl moiety with molecular oxygen catalyzed by a Cu/N-oxyl radical. [15][16][17] This catalysis is tolerant to water and Lewis basic functionalities. [16b] The initial optimization was conducted using N-Cbz-serine tertbutylamide as a model substrate (0.1-0.2 m, see Tables S1 and S2 in the Supporting Information for details).…”

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confidence: 99%

Serine‐Selective Aerobic Cleavage of Peptides and a Protein Using a Water‐Soluble Copper–Organoradical Conjugate

et al. 2014

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The site-specific cleavage of peptide bonds is an important chemical modification of biologically relevant macromolecules. The reaction is not only used for routine structural determination of peptides, but is also a potential artificial modulator of protein function. Realizing the substrate scope beyond the conventional chemical or enzymatic cleavage of peptide bonds is, however, a formidable challenge. Here we report a serine-selective peptide-cleavage protocol that proceeds at room temperature and near neutral pH value, through mild aerobic oxidation promoted by a water-soluble copperorganoradical conjugate. The method is applicable to the siteselective cleavage of polypeptides that possess various functional groups. Peptides comprising d-amino acids or sensitive disulfide pairs are competent substrates. The system is extendable to the site-selective cleavage of a native protein, ubiquitin, which comprises more than 70 amino acid residues.Chemical modifications of proteins [1,2] have a great impact on a broad range of research fields, such as chemical biology, [3] chemical genetics, [4] protein engineering, [5] proteomics, [6] and drug discovery. [7] Site-specific cleaving reactions of peptide bond are among such important chemical modifications. The method is routinely used when structural determination or fragmentation of peptides plays a pivotal role, [8] and it is also regarded as a new strategy for modulating the physiological functions of proteins for medical applications. [9,10] Although peptidases hydrolyze peptide bonds at specific sites under mild conditions with high fidelity, [11] the scope of the scissile substrates is restricted in principle to genetically encoded amino acid sequences. Unnatural or structurally modified peptides and proteins are out of the scope of peptidase digestion. Metal-catalyzed site-selective hydrolysis of pep-tides [12] has been intensively studied as a potential alternative to the enzymatic method. The establishment of practical protocols and generalization to protein cleavage, however, remain challenging because of the chemical robustness of amides. [13] Herein we report a serine (Ser)-selective cleavage of peptides (including a native protein) through mild aerobic oxidation of the hydroxymethyl group of Ser, promoted by a water-soluble Cu/N-oxyl radical system.We envisioned a Ser-selective cleavage of the peptide bond initiated by aerobic chemoselective oxidation of its hydroxymethyl moiety (see Scheme 1). [8c,d] Oxidation of the hydroxymethyl moiety of a Ser residue (A) to a formyl group would produce an a-formylglycineamide intermediate B.Further oxidation of B would produce oxalimide C through oxidative deformylation. Hydrolysis of the latent precursor C under mild conditions should then be possible, because the carbonyl groups of the oxalimide are more electrophilic than those of simple amides, giving peptide bond cleaved fragments D and D'. Using molecular oxygen as a terminal oxidant, water and a C 1 molecule (possibly HCO 2 H) are stoichiometric side product...

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Nitroxide: Anwendungen in der Synthese und in der Polymerchemie

Cited by 171 publications

References 575 publications

Highly Functionalized and Potent Antiviral Cyclopentane Derivatives Formed by a Tandem Process Consisting of Organometallic, Transition‐Metal‐Catalyzed, and Radical Reaction Steps

Highly Functionalized and Potent Antiviral Cyclopentane Derivatives Formed by a Tandem Process Consisting of Organometallic, Transition‐Metal‐Catalyzed, and Radical Reaction Steps

Dissecting the Influence of Oxazolidinones and Cyclic Carbonates in Sialic Acid Chemistry

Serine‐Selective Aerobic Cleavage of Peptides and a Protein Using a Water‐Soluble Copper–Organoradical Conjugate

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