- Bioinspired Radical Stetter Reaction: Radical Umpolung Enabled by Ion-Pair Photocatalysis
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A bioinspired, intermolecular radical Stetter reaction of α-keto acids and aldehydes is disclosed that is contingent on a formal “radical umpolung” concept. Enabled by secondary amine activation, electrostatic recognition ensures that the α-ketocarboxylic acids, which function as latent acyl radicals, are proximal to the in situ generated iminium salts. This photoactive contact ion pair is an electron donor–acceptor (EDA) complex, and undergoes facile single electron transfer (SET) and rapid decarboxylation prior to radical–radical recombination. Importantly, decarbonylation is mitigated by this strategy. The initial computational validation on which the process is predicated matches closely with experiment. Synergising organo- and photocatalysis activation principles finally expands the mechanistic and synthetic scope of the classic Stetter reaction to include α,β-unsaturated aldehydes as acceptors.
- Morack, Tobias,Mück-Lichtenfeld, Christian,Gilmour, Ryan
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supporting information
p. 1208 - 1212
(2019/01/04)
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- Effect of Monoelectronic Oxidation of an Unsymmetrical Phenoxido-Hydroxido Bridged Dicopper(II) Complex
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A (μ-hydroxido, μ-phenoxido)CuIICuII complex 1 has been synthesized using an unsymmetrical ligand bearing an N,N-bis(2-pyridyl)methylamine (BPA) moiety coordinating one copper and a dianionic bis-amide moiety coordinating the other copper(II) ion. Electrochemical mono-oxidation of the complex in DMF occurs reversibly at 213 K at E1/2 = 0.12 V vs Fc+/Fc through a metal-centered process. The resulting species (complex 1+) is only stable at low temperature and has been spectroscopically characterized by UV-vis-NIR cryo-spectroelectrochemical and EPR methods. DFT and TD-DFT calculations, consistent with experimental data, support the formation of a CuIICuIII phenoxido-hydroxido complex. Low-temperature chemical oxidation of 1 by NOSbF6 yields a tetranuclear complex 2(SbF6)(NO2) which displays two binuclear CuIICuII subunits. The X-ray crystal structure of 2(SbF6)(NO2) evidences that the nitrogen of the terminal amide group is protonated and the coordination of the amide occurs via the O atom. The bis-amide moiety appears to be a non-innocent proton acceptor along the redox process. Alternatively, protonation of complex 1 leads to the complex 2(ClO4)2, as evidenced by X-ray crystallography, cyclic voltammetry, and 1H NMR.
- Thibon-Pourret, Aurore,Gennarini, Federica,David, Rolf,Isaac, James A.,Lopez, Isidoro,Gellon, Gisèle,Molton, Florian,Wojcik, Laurianne,Philouze, Christian,Flot, David,Le Mest, Yves,Réglier, Marius,Le Poul, Nicolas,Jamet, Hélène,Belle, Catherine
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p. 12364 - 12375
(2018/09/27)
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- Imidazolidinone nitroxides as catalysts in the aerobic oxidation of alcohols, en route to atroposelective oxidative desymmetrization
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New chiral nitroxides based on the imidazolidin-4-one skeleton, and the corresponding hydroxylamines, have been prepared from cyclic nitrones by a straightforward reaction sequence. They were evaluated as catalysts in the aerobic oxidation of benzyl alcohol using different co-catalysts. Both the imidazolidinone nitroxides and hydroxylamines were proven to catalyze the reaction, with the ring substituent having an effect depending on the co-catalytic system. In some cases, rapid oxidation to benzaldehyde was accomplished at room temperature under an atmospheric O2 pressure. Moreover, atroposelective desymmetrization was achieved during the aerobic oxidation of a diol catalyzed by an enantiopure imidazolidinone nitroxide. Finally, the electrochemical behavior of the new hydroxylamines and nitroxides was investigated by cyclic voltammetry, which gave insights into the observed catalytic properties.
- Carbo Lopez, Marta,Royal, Guy,Philouze, Christian,Chavant, Pierre Y.,Blandin, Veronique
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p. 4884 - 4896
(2014/08/05)
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- Readily accessible chiral at nitrogen cage structures
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The reaction of glycine-N-methyl amide with paraformaldehyde in the presence of ytterbium triflate (1 mol%) leads to a novel cage structure 6 which is chiral at nitrogen. Single crystal X-ray analysis and DFT calculations suggest this cage structure is rigid and adopts a single low energy conformation. Use of single enantiomer α-amino amides results in two diastereomeric tertiary amines that differ in their absolute configuration at nitrogen. These diastereoisomers interconvert under acidic conditions but are configurationally stable under basic conditions and can be readily separated by either crystallisation or column chromatography. By reacting racemic chiral α-amino amides a third diastereomeric cage can also be isolated through this reaction protocol. Preparation of mixed cages by reacting two different α-amino amides is also possible allowing for greater structural diversity in the products to be attained. Preliminary mechanistic studies show that all three methylene units in the cage structure are labile and can be replaced under acidic reaction conditions. The Royal Society of Chemistry 2013.
- Rowley, Julian H.,Yau, Sze Chak,Kariuki, Benson M.,Kennedy, Alan R.,Tomkinson, Nicholas C. O.
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p. 2198 - 2205
(2013/05/09)
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- Synthesis, physical-chemical characterisation and biological evaluation of novel 2-amido-3-hydroxypyridin-4(1H)-ones: Iron chelators with the potential for treating Alzheimer's disease
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A novel class of 2-amido-3-hydroxypyridin-4-one iron chelators is described. These compounds have been designed to behave as suitable molecular probes which will improve our knowledge of the role of iron in neurodegenerative conditions. Neurodegenerative disorders, such as Alzheimer's disease (AD) and Parkinson disease (PD), can be considered as diverse pathological conditions sharing critical metabolic processes such as protein aggregation and oxidative stress. Interestingly, both these metabolic alterations seem to be associated with the involvement of metal ions, including iron. Iron chelation is therefore a potential therapeutic approach. The physico-chemical (pKa, pFe 3+ and log P) and biological properties (inhibition of iron-containing enzymes) of these chelators have been investigated in order to obtain a suitable profile for the treatment of neurodegenerative conditions. Studies with neuronal cell cultures confirm that the new iron chelators are neuroprotective against β-amyloid-induced toxicity.
- Gaeta, Alessandra,Molina-Holgado, Francisco,Kong, Xiao L.,Salvage, Sarah,Fakih, Sarah,Francis, Paul T.,Williams, Robert J.,Hider, Robert C.
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experimental part
p. 1285 - 1297
(2011/03/23)
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- Preparation of the MacMillan imidazolidinones
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A general method for the preparation of the MacMillan imidazolidinones is described. Treatment of an α-amino amide with a carbonyl compound in refluxing chloroform in the presence of Yb(OTf)3 (1 mol %) provides convenient access to the corresponding imidazolidinones.
- Samulis, Leopold,Tomkinson, Nicholas C.O.
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supporting information; experimental part
p. 4263 - 4267
(2011/06/26)
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- IRON MODULATORS
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Iron modulator compounds of formula (I) are provided for treating amyloidoses wherein R1 is selected from H, C1-6 alkyl, C1-6 alkenyl, C1-6 hydroxyalkyl, C1-6 hydroxyalkenyl, R2 is selected from H, C1-6 alkyl, C1-6 alkenyl, C1-6 hydroxyalkyl, C1-6 hydroxyalkenyl and C6-10 aralykyl in which the aryl group of the aralkyl group is optionally substituted by hydroxy, halo or C1-4 alkyl R3 is selected from H, C1-6 alkyl, C1-6 alkenyl and C1-12 acyl; R4 is selected from H and C1-3 alkyl R5, R6 and R7 are independently selected from H, C1-6 alkyl, C3-7 aryl, and C1-10 aralkyl; the alkyl, aryl and aralkyl groups being optionally substituted by one or more halo, hydroxy and nitro groups or R5 and R7 together with the nitrogen atom to which they are bonded form a heterocyclic ring optionally substituted by one or more hydroxyl groups or a pharmaceutically acceptable tautomer, ester or addition salt thereof.
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Page/Page column 15; Figure 3
(2010/11/24)
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- The photochemistry of N-p-toluenesulfonyl peptides: The peptide bond as an electron donor
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The scope of photobiological processes that involve absorbers within a protein matrix may be limited by the vulnerability of the peptide group to attack by highly reactive redox centers consequent upon electronic excitation. We have explored the nature of this vulnerability by undertaking comprehensive product analyses of aqueous photolysates of 12 N-p-toluene-sulfonyl peptides with systematically selected structures. The results indicate that degradation includes a major pathway that is initiated by intramolecular electron transfer in which the peptide bond serves as electron donor, and the data support the likelihood' of a relay process in dipeptide derivatives.
- Hill, Roger R.,Moore, Sharon A.,Roberts, David R.
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p. 1439 - 1446
(2008/02/01)
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- Competitive electron transfers from a tyrosyl side-chain and peptide bond in the photodegradation of N-tosyl α-aminomethylamides: An insight into photosynthesis and photodamage in the biological oxidation of water?
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Photo-excited N-tosyl derivatives of phenylalanyl- and, more particularly, O-methyltyrosylmethylamides undergo electron transfer from aryl to tosyl groups whereas the photo-degradation of aliphatic analogues is initiated by electron transfer from the peptide bond, suggesting the latter as one possible reason for the rapid turnover of the D1 protein in biological water oxidation when the essential mediating role of tyrosine 116 in the PSII complex is inhibited.
- Hill, Roger R.,Moore, Sharon A.,Roberts, David R.
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p. 2838 - 2839
(2007/10/03)
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- Rates of uncatalyzed peptide bond hydrolysis in neutral solution and the transition state affinities of proteases
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To assess the relative proficiencies of enzymes that catalyze the hydrolysis of internal and C-terminal peptide bonds, the rates of the corresponding nonenzymatic reactions were examined at elevated temperatures in sealed quartz tubes, yielding linear Arrhenius plots. The results indicate that in neutral solution at 25°C, peptide bonds are hydrolyzed with half-times of approximately 500 years for the C-terminal bond of acetylglycylglycine, 600 years for the internal peptide bond of acetylglycylglycine N-methylamide, and 350 years for the dipeptide glycylglycine. These reactions, insensitive to changing pH or ionic strength, appear to represent uncatalyzed attack by water on the peptide bond. Comparison of rate constants indicates very strong binding of the altered substrate in the transition states for the corresponding enzyme reactions, K(tx) attaining a value of less than 10-17 M in carboxypeptidase B. The half-life of the N-terminal peptide bond in glycylglycine N-methylamide, whose hydrolysis might have provided a reference for assessing the catalytic proficiency of an aminopeptidase, could not be determined because this compound undergoes relatively rapid intramolecular displacement to form diketopiperazine (t( 1/4 ) ~ 35 days at pH 7 and 37°C). The speed of this latter process suggests an evolutionary rationale for posttranslational N-acetylation of proteins in higher organisms, as a protection against rapid degradation.
- Radzicka,Wolfenden
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p. 6105 - 6109
(2007/10/03)
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- Synthesis of peptides containing a sulfinamide or a sulfonamide transition-state isostere
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A versatile synthesis of peptides incorporating the sulfinamide or sulfonamide transition-state analogue is described. Apart from the easily accessible Gly-Xxx isosteres used as haptens to elicit catalytic antibodies, other amino acids than Gly can be prepared by α-alkylation of the sulfonamide containing peptides. This is illustrated with the synthesis of a potential HIV-protease inhibitor 27.
- Moree, Wilna J.,Van Gent, Liesbeth C.,Van Der Marel, Gijs A.,Liskamp, Rob M. J.
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p. 1133 - 1150
(2007/10/02)
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- PREPARATION, SPECTRAL AND PHYSICOCHEMICAL CHARACTERISTICS OF METHYLAMIDE Nα-PHENYLTHIOCARBAMOYL DERIVATIVES OF NATURALLY OCCURING AMINO ACIDS
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The methylamide Nα-phenylthiocarbamoyl derivatives of encoded amino acids II were prepared either by the addition of phenylisothiocyanate to amino acid methylamides or by the treatment of amino acid phenylthiohydantoins (5-alkyl-3-phenyl-2-thioxo-4-imidazolinones) I with methylamine.The derivatives were prepared of 19 amino acids and their melting points, 1H NMR, 13C NMR, mass, ultraviolet and infrared spectra were measured.
- Pavlik, Manfred,Kluh, Ivan,Pavlikova, Frantiska,Vasickova, Sona,Kostka, Vladimir
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p. 1940 - 1954
(2007/10/02)
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- Photoinduced Electron Transfer in Aliphatic Peptides
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Product analysis in the photolysis of triglycine in neutral aqueous solution suggests that the initial intramolecular electron transfer from the carboxylate to the peptide group, shown to lead to efficient (φ 0.44 +/- 0.11) photodegradation for glycylglycine, may be followed by transfer to the second peptide group.
- Birch, David,Coyle, John D.,Hill, Roger R.,Jeffs, Graham E.
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p. 293 - 295
(2007/10/02)
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- Herstellung enantiomerenreiner cis- oder trans-konfigurierter 2-(tert-Butyl)-3-methylimidazolidin-4-one aus den Aminosaeuren (S)-Alanin, (S)-Phenylalanin, (R)-Phenylglycin, (S)-Methionin und (S)-Valin.
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In contrast to α-hydroxy and α-mercapto carboxylic acids, simple α-amino acids do not form acetal-type derivatives (2, X=NH) with pivalaldehyde.For the generation of amino-acid-derived chiral, nonracemic enolates (cf.3), and hence, for the α-alkylation of amino acids without racemization and without an external chiral auxiliary, the imidazolidinones 12-14 were prepared diastereoselectively.To this end, the methyl or ethyl esters of amino-acid hydrochlorides were first converted to N-methylamides of amino acids which in turn were condensed with pivalaldehyde to give (neopentylidenamino)amides (11).These Schiff bases could be cyclized either to trans- or to cis-imidazolidinones (12, 14 and 13, respectively), which were obtained in enantiomerically pure form after recrystallization.The enantiomeric purities were confirmed by HPLC with chiral stationary phases or by 1H-NMR spectroscopy in the presence of chiral shift reagents.The configurations (cis, trans) were assigned by NOE measurements on 300- or 360-MHz 1H-NMR spectrometers.
- Naef, Reto,Seebach, Dieter
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p. 135 - 143
(2007/10/02)
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