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Oxidation Steps (oxidation + step)
Selected AbstractsPermanganate Oxidation Revisited: Synthesis of 3-Deoxy-2-uloses via Indium-Mediated Chain Elongation of CarbohydratesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Christoph Schmölzer Abstract Application of the Barbier-type indium-mediated allylation method to suitable substrates offers access to carbohydrates bearing a terminal olefin moiety. The C,C bond forming reaction generates a defined stereochemistry of the new chiral center and tolerates a wide variety of starting aldehydes thus allowing modifications in the carbohydrate backbone. Further transformations of the alkene moiety via an environmentally benign and subtle controlled protocol using potassium permanganate gives rise to the structural motif of 3-deoxy-2-uloses in good yields. The final part of the reaction sequence focuses on the deprotection of the acetyl groups essential for the success of the oxidation step. The acidic and labile 3-deoxy position of the target molecule is prone to elimination applying standard deacetylation conditions and therefore demands derivatisation of the molecule. The introduction of a thioketal moiety using microwave conditions shows promising results and subsequent standard transformations are applicable leading to the desired products. [source] Exploring the Biocatalytic Scope of Alditol Oxidase from Streptomyces coelicolorADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009W. van Hellemond Abstract The substrate scope of the flavoprotein alditol oxidase (AldO) from Streptomyces coelicolor A3(2), recombinantly produced in Escherichia coli, was explored. While it has been established that AldO efficiently oxidizes alditols to D -aldoses, this study revealed that the enzyme is also active with a broad range of aliphatic and aromatic alcohols. Alcohols containing hydroxy groups at the C-1 and C-2 positions like 1,2,4-butanetriol (Km=170,mM, kcat=4.4,s,1), 1,2-pentanediol (Km=52,mM, kcat=0.85,s,1) and 1,2-hexanediol (Km=97,mM, kcat=2.0,s,1) were readily accepted by AldO. Furthermore, the enzyme was highly enantioselective for the oxidation of 1,2-diols [e.g., for 1-phenyl-1,2-ethanediol the (R)-enantiomer was preferred with an E -value of 74]. For several diols the oxidation products were determined by GC-MS and NMR. Interestingly, for all tested 1,2-diols the products were found to be the ,-hydroxy acids instead of the expected ,-hydroxy aldehydes. Incubation of (R)-1-phenyl-1,2-ethanediol with 18O-labelled water (H218O) revealed that a second enzymatic oxidation step occurs via the hydrate product intermediate. The relaxed substrate specificity, excellent enantioselectivity, and independence of coenzymes make AldO an attractive enzyme for the preparation of optically pure 1,2-diols and ,-hydroxy acids. [source] Sodium Perborate,A Convenient Baeyer,Villiger Oxidation Reagent in the Synthesis of the Corey AldehydeADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2003Maria Espiritu Abstract Sodium perborate tetrahydrate is a cheap, safe and readily available alternative to the commonly used peracetic acid for the Baeyer,Villiger oxidation step of the Corey aldehyde synthesis. Chloroketo acid 1 is smoothly converted by sodium perborate tetrahydrate in formic acid to the chloroketolactone 2 in 66% isolated yield. In contrast to previously reported reactions using other oxidants, the formation of the lactone is completely regioselective in favour of the "bridgehead-migrated" isomer 2. [source] Measurement of inhibin A: a modification to an enzyme-linked immunosorbent assayPRENATAL DIAGNOSIS, Issue 8 2001Prema P. Thirunavukarasu Abstract Inhibin A is a useful prenatal marker of Down syndrome. Currently, the available enzyme-linked immunosorbent assays (ELISAs) for inhibin A are based upon the same paired monoclonal antibodies. In the present study we have confirmed for one of those ELISAs that short-term sample storage as whole blood leads to a significant decline in detectable inhibin A and that this is most likely due to erythrocyte catalase interference with a critical oxidation step in the assay. While this interference can be eliminated by heating the samples pre-assay, this process is labour intensive. In the present study we have demonstrated that the addition of 3-amino-1,2,4-triazole (AT), a catalase ,suicide' inhibitor, also prevents the decline of inhibin A levels in samples stored as whole blood. We suggest that the addition of AT to samples prior to assay is a simple modification to the inhibin A ELISA that affords optimum performance. Copyright © 2001 John Wiley & Sons, Ltd. [source] Redox Active Two-Component Films of Palladium and Covalently Linked Zinc Porphyrin,Fullerene DyadELECTROANALYSIS, Issue 9 2006Marta Plonska Abstract Redox active films have been generated electrochemically by the reduction of dyads consisting of fullerene C60 covalently linked to zinc meso -tetraphenyloporphyrin, ZnPC60, and palladium acetate. The films are believed to consist of a polymeric network formed via covalent bonds between the palladium atoms and the fullerene moieties. In these films, the zinc porphyrin moiety is covalently linked to the polymeric chains through the pyrrolidine ring of the fullerene. The ZnPC60/Pt films are electrochemically active in both positive and negative potential excursions. At positive potentials, two oxidation steps for the zinc porphyrin are observed. In the negative potential range, electron transfer processes involving the zinc porphyrin and the fullerene entities are observed. Film formation is also accompanied by palladium deposition on the electrode surface. The presence of a metallic phase in the film influences its morphology, structure and electrochemical properties. [source] Catalytic Effect on Silver Electrodeposition of Gold Deposited on Carbon ElectrodesELECTROANALYSIS, Issue 19 2004Alfredo de, Escosura-Muñiz Abstract A new methodology, based on silver electrocatalytic deposition and designed to quantify gold deposited onto carbon paste electrode (CPE) and glassy carbon electrode (GCE), has been developed in this work. Silver (prepared in 1.0,M NH3) electrodeposition at ,0.13,V occurs only when gold is previously deposited at an adequate potential on the electrode surface for a fixed period of time. When a CPE is used as working electrode, an adequate oxidation of gold is necessary. This oxidation is carried out in both 0.1,M NaOH and 0.1,M H2SO4 at oxidation potentials. When a GCE is used as working electrode, the oxidation steps are not necessary. Moreover, a cleaning step in KCN, which removes gold from electrode surface, is included. To obtain reproducibility in the analytical signal, the surface of the electrodes must be suitably pretreated; this electrodic pretreatment depends on the kind of electrode used as working electrode. Low detection limits (5.0×10,10,M) for short gold deposition times (10,min for CPE and 5,min for GCE) were achieved with this novel methodology. Finally, sodium aurothiomalate can be quantified using silver electrocatalytic deposition and GCE as working electrode. Good linear relationship between silver anodic stripping peak and aurothiomalate concentration was found from 5.0×10,10,M to 1.0×10,8,M. [source] Flexible Route to Palmarumycin CP1 and CP2 and CJ-12.371 Methyl EtherEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2010Karsten Krohn Abstract The total synthesis of palmarumycin CP1 (4) and CP2 (5) and racemic CJ-12.371 methyl ether (17) is described using the Diels,Alder reaction of benzoquinone 1,8-dihydroxynaphthalene acetal (10) with 1-methoxy-1,3-butadiene under neat reaction conditions. The stereochemistry of adduct 15 was confirmed by single-crystal X-ray analysis. The transformation of 15 into target products 4, 5, and 17 involved dehydrogenation, methyl ether cleavage, and reduction and oxidation steps. [source] [1.1]Ferrocenophane-1,12-dione as a Precursor of 1,12-Di(cyclopenta-2,4-dienylidene)-[1.1]ferrocenophane, a Doubly Bridged DifulveneADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 7-8 2009José Ramon Garabatos-Perera Abstract An improved synthesis of [1.1]ferrocenophane-1,12-dione (2) by oxidation of [1.1]ferrocenophane with 2,3-dichloro-5,6-dicyano- p -benzoquinone (DDQ) is presented. The syn conformer of dione 2 is structurally characterized. The compound undergoes various addition reactions at the bridging carbonyl groups. Attempts to add 1,1,-dilithioferrocene result, however, in the diadduct 9, not in the symmetric trinuclear diol 8. Reaction of 2 with sodium cyclopentadienide in the presence of aluminium trichloride (AlCl3) gives the respective difulvene 11 in excellent yield. The dynamic behavior of 11 is investigated by variable temperature 1H,NMR measurements (VT-NMR). The cyclovoltammogram of 11 indicates two reversible oxidation steps. Reduction of difulvene 11 with lithium aluminium hydride (LiAlH4) results in the formation of [1.1]ferrocenophane 12 with cyclopentadienyl anion substituents at either one of the two bridges. While attempts to generate a third ferrocene moiety by reaction with iron(II) choride (FeCl2) have failed so far, the formation of 12 is established by protonolysis and methylation reactions. [source] Thin-film (25.5,,m) solar cells from layer transfer using porous silicon with 32.7,mA/cm2 short-circuit current densityPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2 2003Karlheinz Feldrapp Abstract We fabricate a 25.5-,m-thick monocrystalline Si solar cell with a confirmed power conversion efficiency of 15.4% and an area of 3.88,cm2 using a layer transfer process with porous Si. The process is free of photolithography and contains no high-temperature oxidation steps. We investigate three design features that improve the short-circuit current density to a value of 32.7,mA/cm2 under AM1.5 illumination. The detached back reflector contributes 2,mA/cm2, a reduced front-surface reflectance accounts for an additional 2,mA/cm2 and a reduced base doping increases the current density by 1,mA/cm2. Copyright © 2002 John Wiley & Sons, Ltd. [source] From Metacyclophanes to Cyclacenes: Synthesis and Properties of [6.8]3CyclaceneCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2009Birgit Esser Dr. Abstract Conjugated belts: [6.8]3cyclacene as the first hydrocarbon cyclacene was synthesized in a de novo strategy. Various [23]metacyclophanes are described as intermediates. The synthetic approach was extended to larger cyclacenes, and [24]metacyclophanes as precursors of [6.8]4cyclacene were synthesized. In this article we show synthetic pathways to [6.8]ncyclacenes demonstrated by the de novo synthesis of [6.8]3cyclacene as the first purely hydrocarbon cyclacene and of precursors for [6.8]4cyclacene. The design of the de novo synthesis by exploring alternative pathways is discussed and various precursors are shown. Crucial to the synthesis of [6.8]3cyclacene were two cyclization steps. The first is a Wittig trimerization reaction which yielded the hexamethyl substituted all - cis -[23]metacyclophanetriene. For the second cyclization step the methyl groups were converted to aldehyde functionalities by two subsequent oxidation steps of N-bromosuccinimide (NBS) bromination and oxidation with 2-iodoxybenzoic acid (IBX). The final cyclization of the second set of double bonds was achieved by a McMurry-coupling reaction. Towards the synthesis of [6.8]4cyclacene different synthetic pathways to methyl substituted all - cis -[24]metacyclophanetetraenes were explored. Insights into the structures of [23]metacyclophanetri- and [24]metacyclophanetetraenes were gained by X-ray crystallographic investigations on various intermediates. A crystallographic analysis of [6.8]3cyclacene revealed a D3h symmetrical structure with planar benzene rings and a formation of tubular structures in the solid state. [source] | ||||||||||