- Glycoconjugate Oxime Formation Catalyzed at Neutral pH: Mechanistic Insights and Applications of 1,4-Diaminobenzene as a Superior Catalyst for Complex Carbohydrates
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The reaction of unprotected carbohydrates with aminooxy reagents to provide oximes is a key method for the construction of glycoconjugates. Aniline and derivatives serve as organocatalysts for the formation of oximes from simple aldehydes, and we have previously reported that aniline also catalyzes the formation of oximes from the more complex aldehydes, carbohydrates. Here, we present a comprehensive study of the effect of aniline analogues on the formation of carbohydrate oximes and related glycoconjugates depending on organocatalyst structure, pH, nucleophile, and carbohydrate, covering more than 150 different reaction conditions. The observed superiority of the 1,4-diaminobenzene (PDA) catalyst at neutral pH is rationalized by NMR analyses and DFT studies of reaction intermediates. Carbohydrate oxime formation at pH 7 is demonstrated by the formation of a bioactive glycoconjugate from a labile, decorated octasaccharide originating from exopolysaccharides of the soil bacterium Mesorhizobium loti. This study of glycoconjugate formation includes the first direct comparison of aniline-catalyzed reaction rates and equilibrium constants for different classes of nucleophiles, including primary oxyamines, secondary N-alkyl oxyamines, as well as aryl and arylsulfonyl hydrazides. We identified 1,4-diaminobenzene as a superior catalyst for the construction of oxime-linked glycoconjugates under mild conditions.
- ?stergaard, Mads,Christensen, Niels Johan,Hjuler, Christian T.,Jensen, Knud J.,Thygesen, Mikkel B.
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- Iridium-Catalyzed Acid-Assisted Hydrogenation of Oximes to Hydroxylamines
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We found that cyclometalated cyclopentadienyl iridium(III) complexes are uniquely efficient catalysts in homogeneous hydrogenation of oximes to hydroxylamine products. A stable iridium C,N-chelation is crucial, with alkoxy-substituted aryl ketimine ligand
- Cope, Christopher J.,Cramer, Nicolai,Mas-Roselló, Josep,Pinson, Benjamin,Robinson, Alan,Smejkal, Tomas,Tan, Eric
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supporting information
p. 15524 - 15532
(2021/06/11)
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- Deoxyalkoxyamination of Alcohols for the Synthesis of N-Alkoxy-N-alkylbenzenesulfonamides
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A novel protocol for the deoxyalkoxyamination of alcohols has been developed, using N-alkoxybenzenesulfonimide (NOSI) as both a sulfonyl transfer reagent and an alkoxyamine source, accessing a diverse range of N-alkoxy-N-alkylbenzenesulfonamides with excellent isolated yields. This method is characterized by metal-free reaction, scalability, and waste-balance. Chiral substrates are converted with excellent levels of stereochemical inversion. NOSI could be generated in situ during the reaction as a stable reagent if a three-component one-pot reaction was designed. Exploiting this approach to run intramolecular reactions offered various N-protected isoxazolidines. In addition, valuable O-alkyl hydroxylamines (or isoxazolidines) were obtained through a neutral strategy of desulfonylation of the products.
- Sun, Qi-An,Lu, Ze-Hai,Pu, Xiao-Qiu,Hu, Hui-Lian,Zhang, Jia-heng,Yang, Xian-Jin
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supporting information
p. 3920 - 3927
(2018/07/31)
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- One-pot synthesis of alkoxyamine derivatives by reductive alkoxyamination with a 2-picoline-borane complex
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Reduction of oxime ethers with a 2-picoline-borane complex was examined to give alkoxyamine derivatives. The reduction was found to proceed in the presence of aqueous HCl in MeOH-AcOH. The method was extended to one-pot synthesis of alkoxyamine derivative
- Kawase, Yasushi,Yamagishi, Takehiro,Kutsuma, Teruo,Ueda, Kimio,Iwakuma, Takeo,Nakata, Tadashi,Yokomatsu, Tsutomu
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experimental part
p. 463 - 470
(2009/06/08)
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- Probing the aglycon promiscuity of an engineered glycosyltransferase
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(Figure Presented) A sweet library: Two variants (wild-type (WT) and a triple mutant) of glycosyltransferase (GT) OleD have been shown to catalyze glycosylation of over 70 substrates, formation of O-, S- and N-glycosidic bonds, and iterative glycosylation (see scheme). Identified substrates include nucleophiles not previously known to act in GT reactions and span numerous natural product and therapeutic drug classes.
- Gantt, Richard W.,Goff, Randal D.,Williams, Gavin J.,Thorson, Jon S.
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supporting information; experimental part
p. 8889 - 8892
(2009/05/26)
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- Intramolecular catalytic Friedel-Crafts reactions with allenyl cations for the synthesis of quinolines and their analogues
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(Equation Presented) This paper describes a novel method to synthesize a quinoline backbone by incorporating allenyl cations into a catalytic intramolecular Friedel-Crafts reaction. The initial products were isomerized and aromatized upon treatment with acid and base, respectively, to give quinolines. The basic concept also proved to be promising for 1-benzazepine, 1-benzazocine, or isoquinoline synthesis.
- Ishikawa, Teruhiko,Manabe, Shinobu,Aikawa, Toshiaki,Kudo, Takayuki,Saito, Seiki
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p. 2361 - 2364
(2007/10/03)
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- N-nitroso-N,O-dialkylhydroxylamines: Preparation, structure, and mechanism of the hydronium ion catalysed solvolytic nitrous oxide extrusion reaction
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Eleven N-nitroso-N,O-dialkylhydroxylamines, RN(NO)OR′, have been prepared and the mechanisms of their hydronium ion catalysed solvolyses in aqueous solution which liberate nitrous oxide have been investigated. All reactions are first-order in substrate and first-order in hydronium ion, and the second-order rate constants at 25°C vary over a range of less than 140 in spite of considerable variation in substrate structure (R ranges from methyl to 4-methoxybenzyl to 2-adamantyl, for example) and changes in solvent composition (water with up to 50% methanol or 66% acetonitrile). Enthalpies and entropies of activation are qualitatively similar throughout the range (ΔH?= 72-93 kJ mol-1 and ΔS? = -19 to -57 J K-1 mol-1) which, with the product analyses, are accommodated by a mechanism involving pre-equilibrium protonation of the substrates followed by rate-limiting dissociation to give RN2O+ and HOR′. The oxodiazonium ion intermediate, RN2O+, then dissociates further to give the carbenium ion intermediate, R+, or suffers direct nucleophilic displacement of N2O by solvent (the external nucleophile) or by R′OH (the internal nucleophile liberated in the initial fragmentation). The carbenium ion, R+ (if formed), suffers nucleophilic capture either by solvent or by R′OH. When acetonitrile is the co-solvent (rather than methanol) for the N-(2-adamantyl) substrate 3g, the product of the Ritter reaction, 2-acetamidoadamantane, is detected. These nitrous oxide liberating reactions are compared with the nitric oxide liberating reactions of related N-nitrosohydroxylamines, and the origin of the difference between them is identified. The N(1)-nitroso group in the N,O-dibenzyl compound 3c is shown by X-ray crystallography to be essentially coplanar with the C and O atoms also bonded to N(1).
- Bhat, J. Ishwara,Clegg, William,Maskill, Howard,Elsegood, Mark R.J.,Menneer, Iain D.,Miatt, Peter C.
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p. 1435 - 1446
(2007/10/03)
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- Reductive cleavage of N-O bonds in hydroxylamines and hydroxamic acid derivatives using samarium diiodide
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An efficient process for the reductive cleavage of N-O bonds using samarium diiodide is detailed for a variety of structural types to define the scope and limitations of the method. The reduction is shown to be compatible with base sensitive substrates such as trifluoroacetamide derivatives, which cannot be reduced satisfactorily using aluminum amalgam or sodium amalgam. Direct quenching of the reduction mixture with acylating agents is demonstrated to provide high yields of protected amines in a one-pot process from the N-O derivatives.
- Keck, Gary E.,Wager, Travis T.,McHardy, Stanton F.
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p. 11755 - 11772
(2007/10/03)
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- Stereoselective pinacol coupling of planar chiral (benzaldehyde)Cr(Co)3, (benzaldimine)Cr(CO)3, ferrocenecarboxaldehyde and (dienal)Fe(CO)3 complexes with samarium diiodide
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An intermolecular pinacol coupling of the Planar chiral tricarbonylchromium complexes of o-substituted benzaldehydes or benzaldimines with samarium(II) diiodide in THF produces exclusively threo 1.2-diols or 1,2-diamines in an optically pure form, while the corresponding racemic o- substituted benzaldehyde or benzaldimine chromium complexes give a mixture of threo and erythro pinacol coupling products in a various ratio depending upon the nature of o-substituent. Similarly, planar chiral 2-substituted ferrocenecarboxaldehydes and (dienal)Fe(CO)3 produce the corresponding 1.2- diols with high stereoselectivity. The generated transition metal-complexed ketyl radical intermediates are configurationally stable with restriction to a rotation about C(α)-C(ipso) bond.
- Taniguchi, Nobukazu,Uemura, Motokazu
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p. 12775 - 12788
(2007/10/03)
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- A convenient method for the preparation of N-aryl and N-alkyl-O-methyl hydroxylamines
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Trifluoroaceto or p-nitrobenzo-N-substituted hydroxamic acids are smoothly methylated with diazomethane and the products cleanly cleaved by hydrazine to provide the title compounds.
- Santos,Lobo,Prabhakar
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p. 3509 - 3518
(2007/10/03)
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- Compositions stabilized with ethers of di- and tri-substituted hydroxylamines
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Various di- and tri-substituted hydroxylamine derivatives are effective in stabilizing organic materials against oxidative, thermal and actinic degradation, said derivatives being particularly effective as color improvers and process stabilizers in organi
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