NMR Spectroscopic Analysis (nmr + spectroscopic_analysis)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Lewis Acid Catalyzed, Selective Cyclopropane-Ring Opening in Ingol Diterpene Derivatives

HELVETICA CHIMICA ACTA, Issue 9 2005
Masuna Srinivasulu
Lewis acid mediated skeletal rearrangement of the ingol diterpenoids 1 and 4via regio- and stereospecific cyclopropane-ring opening afforded the four new compounds 2, 3, 5, and 6, named nivulianol A,D (Scheme,1). Their structures were established by means of IR, MS, and in-depth NMR spectroscopic analyses. The rearranged congeners were tested for lipopolysaccharide (LPS)-induced prostaglandin (PG) E2 (cyclooxygenase-2) inhibition. Thereby, nivulianol B (=(1S*,2E,4R*,5S*,7Z,9S*,11R,13S*,14S*)-14-acetoxy-5-methoxy-3,9,13-trimethyl-6-(1-methylethenyl)-10-oxo-15-oxatricyclo[9.3.1.01,11]pentadeca-2,7-dien-4-yl (2Z)-2-methylbut-2-enoate; 3) was found to be significantly active, with an IC50 value of 36.3,,g/ml. [source]


Substitution- and Elimination-Free Phosphorylation of Functionalized Alcohols Catalyzed by Oxidomolybdenum Tetrachloride

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010
Cheng-Yuan Liu
Abstract Among 14 oxidometallic species examined for catalytic phosphorylation of the tested alcohols, oxidomolybdenum tetrachloride (MoOCl4) was found to be the most efficient with a negligible background reaction mediated by triethylamine (Et3N). The new catalytic protocol can be applied to the chemoselective phosphorylations of primary, secondary and tertiary alcohols as well as the substitution-free phosphorylations of allylic, propargylic, and benzylic alcohols. Functionalized alcohols bearing acetonide, tetrahydropyranyl ether, tert -butyldimethylsilyl ether, or ester group are also amenable to the new catalytic protocol. The most difficult scenarios involve substitution-free phosphorylations of 1-phenylethanol and 1-(2-naphthyl)ethanol which can be effected in 95 and 90% yields, respectively. ESI-MS, IR, 1H, and 31P,NMR spectroscopic analyses of the reaction progress suggest the intermediacy of an alkoxyoxidomolybdenum trichloride-triethylamine adduct such as [(RO)Mo(O)Cl3 -Et3N] to be responsible for the catalytic turnover. [source]


Structural determination of seven new triterpenoids from Kadsura heteroclita by NMR techniques

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2007
Wei Wang
Abstract Seven new triterpenoids, namely heteroclitalactones G,M (1,7), were isolated from the ethanol extract of the stems of Kadsura heteroclita. Structures of these compounds were characterized by extensive 1D and 2D NMR spectroscopic analyses. Copyright © 2007 John Wiley & Sons, Ltd. [source]


Bifunctional Heterogeneous Catalysis of Silica,Alumina-Supported Tertiary Amines with Controlled Acid,Base Interactions for Efficient 1,4-Addition Reactions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009
Ken Motokura Dr.
Abstract We report the first tunable bifunctional surface of silica,alumina-supported tertiary amines (SA,NEt2) active for catalytic 1,4-addition reactions of nitroalkanes and thiols to electron-deficient alkenes. The 1,4-addition reaction of nitroalkanes to electron-deficient alkenes is one of the most useful carbon,carbon bond-forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA-supported amine (SA,NEt2) catalyst enabled selective formation of a double-alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA,NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA,NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron-deficient alkenes. The solid-state magic-angle spinning (MAS) NMR spectroscopic analyses, including variable-contact-time 13C cross-polarization (CP)/MAS NMR spectroscopy, revealed that acid,base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid,base interactions. [source]


Synthesis and Characterisation of a New Cu(O2CNAllyl2)2 Carbamato Complex and an Unusual Polymeric CuI Complex [CuI4Cl4(NHAllyl2)4]n: New Insights into Metal Carbamato Chemistry

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009
Alberto Albinati
Abstract Transition-metal N,N -dialkylcarbamato complexes represent an interesting class of compounds that can be conveniently used as precursors for the controlled formation of inorganic compounds, typically oxides. They can also be used as convenient precursors for chemical grafting of metal oxides on oxide surfaces as well as for the synthesis of inorganic,organic hybrid materials. In this last case, the presence of double bonds on the complex would enable its covalent embedding into a polymer matrix through reaction with suitable monomers. To this aim, we addressed the synthesis of an allyl-functionalised copper carbamato complex. During the synthesis of the N,N -diallylcarbamato complex Cu(O2CNAllyl2)2 (Cu1), the formation of the crystalline and unusual polymeric CuI complex [CuI4Cl4(NHAllyl2)4]n (Cu2) was observed. The new compound was characterised by X-ray single crystal diffraction and FTIR, 1H and 13C NMR spectroscopic analysis. In an attempt to investigate the redox mechanism and the equilibria leading to the formation of the observed unusual CuI polymeric complex, gas chromatography coupled with mass spectrometry (GC,MS) experiments were carried out, which allowed us to identify 3,4-dimethylpyrrole as the oxidation product of the reaction, leading to the reduction of CuII to CuI.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Hydrosilanes Are Not Always Reducing Agents for Carbonyl Compounds, II: Ruthenium-Catalyzed Deprotection of tert -Butyl Groups in Carbamates, Carbonates, Esters, and Ethers

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2010
Shiori Hanada
Abstract Hydrosilanes act as a reagent to cleave the C,O bond of OtBu groups in carbamates, carbonates, esters, and ethers by catalysis of a triruthenium cluster. The reaction offers a novel deprotection method for OtBu groups under neutral conditions, showing unique selectivities that have never been accomplished with conventional Brønsted or Lewis acidic promoters. Possible mechanisms for C,O cleavage are discussed on the basis of NMR spectroscopic analysis. [source]


Structural Studies of the O-Chain Polysaccharide from Plesiomonas shigelloides Strain 302,73 (Serotype O1)

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2008
Giuseppina Pieretti
Abstract Plesiomonas shigelloides is a Gram-negative bacterium belonging to the Enterobacteriaceae family. It has been found in an aquatic environment in the tropical and subtropical regions and is responsible for many gastrointestinal infections in humans, which take place from drinking untreated water or eating uncooked shellfish. Plesiomonas shigelloides has also been reported to provoke extraintestinal infections such as meningitis and bacteremia in immunocompromised adults and neonates. Despite the emerging importance of this pathogenic microorganism, only three different O-antigens have been characterised so far. The structure of the O-chain of the lipopolysaccharide (LPS) from Plesiomonasshigelloides strain 302,73 (serotype O1) was determined by chemical analysis, 1D and 2D NMR spectroscopy and MALDI-TOF mass spectrometry. The polysaccharide was constituted by a linear pentasaccharidic repeating unit as follows: ,3)-,- L -PneNAc4OAc(1,4)-,- L -FucNAc(1,4)-,- L -FucNAc(1,4)-,- L -FucNAc(1,3)-,- D -QuiNAc4NHb(1, (PneNAc = 2-acetamido-2,6-dideoxy-talose, Hb = (S)-3-hydroxybutanoyl) PneNAc O -acetylation was not stoichiometric and was found to be about 75,%. The position of the O -acetyl group and the amount of acetylation were deduced by NMR spectroscopic analysis. All the monosaccharides included in the repeating unit were deoxyamino sugars, which most probably, together with the presence of O -acetyl groups, were responsible for the recovery of the LPS in the phenol layer of the phenol/water extract of dried bacteria cells.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


Synthesis and Conformational Analysis of Tetrahydroisoquinoline-Fused 1,3,2-Oxazaphospholidines and 1,2,3-Oxathiazol­idines

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2008
Ildikó Schuster
Abstract The cyclizations of tetrahydroisoquinoline 1,2-amino alcohols with phenylphosphonic dichloride, bis(2-chloroethyl)phosphoramidic dichloride, thionyl chloride and sulfuryl chloride were utilized to synthesize 1,5,6,10b-tetrahydro-1,3,2-oxazaphospholo[4,3- a]isoquinolines (2, 3), 1,5,10,10a-tetrahydro-1,3,2-oxazaphospholo[3,4- b]isoquinolines (8, 9), 1,5,6,10b-tetrahydro-1,2,3-oxathiazolo[4,3- a]isoquinolines (4,6) anda 1,5,10,10a-tetrahydro-1,2,3-oxathiazolo[3,4- b]isoquinoline (11), which are the first representatives of these ring systems. NMR spectroscopic analysis revealed the existence of conformational equilibria that are fast on the NMR timescale. Theoretical DFT calculations pointed to the participation of generally two preferred conformers in the conformational equilibria; the positions of the equilibria were indicated by the experimental NMR spectroscopic parameters, and they are in good agreement with the theoretically calculated energy differences of the participating conformers. For two compounds, which could be not isolated (10, 12), both the preferred conformers and the stereochemistry could be concluded from the DFT calculation results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


Stereostructural Determination by a Synthetic and NMR-Based Approach of Three Oxazinins Isolated from Adriatic Mussels

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 32 2007
Patrizia Ciminiello
Abstract Two oxazinins, namely oxazinin-5 and -6, along with a related linear precursor (preoxazinin-7) were isolated from toxic mussels collected along the Northern Adriatic coasts in October 2005. Determination of the planar structure of these novel compounds was achieved through extensive NMR spectroscopic analysis, whereas a synthetic approach was crucial for their absolute stereochemical elucidation.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Synthesis, Characterization, and Reaction of Crystalline Fischer's Glucopyranosyl Isocyanate

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2004
Yoshiyasu Ichikawa
Abstract We have established a simple method for the preparation of crystalline Fischer's glucopyranosyl isocyanate 1. NMR spectroscopic analysis of 1 allowed the unambiguous determination of the stereochemistry at the anomeric position. Synthetic applications of glucopyranosyl isocyanate 1 were examined by its reactions with amines and alcohols to furnish a wide variety of neoglycoconjugates. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Preparative isolation and purification of six volatile compounds from essential oil of Curcuma wenyujin using high-performance centrifugal partition chromatography

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 11 2010
Yuan-Ye Dang
Abstract Six volatile compounds, curdione (1), curcumol (2), germacrone (3), curzerene (4), 1,8-cineole (5) and ,-elemene (6), were successfully isolated from the essential oil of Curcuma wenyujin by high-performance centrifugal partition chromatography using a nonaqueous two-phase solvent system consisting of petroleum ether-acetonitrile-acetone (4:3:1,v/v/v). A total of 8,mg of curdione (1), 4,mg of curcumol (2), 10,mg of germacrone (3), 18,mg of curzerene (4), 9,mg of 1,8-cineole (5) and 17,mg of ,-elemene (6) were isolated from the essential oil (300,mg) in 500,min. Their structures were determined by comparison of their retention times and MS data with those of the authentic samples as well as NMR spectroscopic analysis. [source]


Isolated Ethylene Units in Isotactic Polystyrene Chain: Stereocontrol of an Isospecific Post-Metallocene Titanium Catalyst

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3 2004
Carmine Capacchione
Abstract Summary: Copolymerization of styrene with small amounts of ethylene using the catalyst system dichloro{1,4-dithiabutanediyl-2,2,-bis(4,6-di- tert -butyl-phenoxy)}titanium/methylaluminoxane results in the unprecedented formation of isotactic polystyrene containing isolated ethylene units. 13C NMR spectroscopic analysis of the copolymer indicates that an "enantiomorphic site" control mechanism for isospecific propagation is operating. DSC measurements also indicate the presence of isolated ethylene units which modify the crystallization behavior of the isotactic polystyrene. Schematic representation of the copolymerization of styrene with small amounts of ethylene using dichloro{1,4-dithiabutanediyl-2,2,-bis(4,6-di-tert-butyl-phenoxy)}titanium/methylaluminoxane as catalyst system. [source]


NMR spectroscopic analysis of new spiro-piperidylrifamycins

MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2005
Eduardo Rubio
Abstract New spiro-piperidylrifamycin derivatives are presented. These compounds were synthesized from the reaction of 3-amino-4-iminorifamycin S and enantiomerically pure 4-piperidones, which generate diasteroisomeric rifabutin analogues with a new stereocentre at the spiranic carbon. The 1H and 13C NMR spectra of these new compounds, and also the configuration of the new stereogenic centres, were assigned using 2D NMR spectroscopic techniques. A preliminary study of the 1H and 13C NMR spectra of the starting compounds rifamycin S, 3-amino-4-iminorifamycin S and the related rifabutin was also carried out and as a result, their previously published 13C NMR data were corrected. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Reactive acrylic liquid rubber with terminal and pendant carboxyl groups as a modifier for epoxy resin

POLYMER ENGINEERING & SCIENCE, Issue 1 2007
D. Ratna
Reactive acrylate rubbers with the terminal and pendent carboxyl groups have been investigated as a modifier for a room temperature curing epoxy resin. The liquid rubbers with varying molecular weights and carboxyl-functionality were synthesized by bulk polymerization of 2-ethyl hexyl acrylate using acrylic acid as a comonomer. The liquid rubbers were characterized by FTIR, 13C NMR spectroscopic analysis, nonaqueous titration, vapor pressure osmometry, and solubility characteristics. The liquid rubbers were incorporated into the epoxy resin by the prereact method and the effect of functionality on impact properties of the modified networks were investigated. The results were explained in terms of dynamic mechanical properties and morphology analyzed by scanning electron microscope (SEM). Polym. Eng. Sci. 47:26,33, 2007. © 2006 Society of Plastics Engineers. [source]


Convenient Synthesis of Multifunctional EDTA-Based Chiral Metal Chelates Substituted with an S -Mesylcysteine

CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2005
Andrei Leonov Dr.
Abstract We describe the synthetic route to ethylenediaminetetraacetic acid (EDTA) derivatives that can be attached to surface-exposed thiol functional groups of cysteine residues in proteins, via a methylthiosulfonate moiety that is connected in a stereochemically unique way to the C-1 carbon atom of EDTA. Such compounds can be used to align proteins in solution without the need to add liquid crystalline media, and are, therefore, of great interest for the NMR spectroscopic analysis of biomolecules. The binding constant for the paramagnetic tag to lanthanide ions was determined by measuring luminescence. For the Tb+3,ligand complex, a Kb value of 6.5×1017,M,1 was obtained. This value is in excellent agreement with literature values for the related EDTA compound. In addition, it could be shown that there is no significant reduction in the luminescence intensity upon addition of a 104 excess of Ca2+ ions, indicating that this paramagnetic tag is compatible with buffers containing high concentrations of divalent alkaline earth ions. [source]


Structural Analysis of Chiral Complexes of Palladium(0) with 15-Membered Triolefinic Macrocyclic Ligands

CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2005
Anna Pla-Quintana
Abstract The complete structural analysis of the palladium complexes of the triolefinic macrocycles (E,E,E)-1,6,11-tris(arylsulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes, which featured from three identical to three different aryl groups, was achieved by performing X-ray diffraction studies, NMR spectroscopy, and other calculations. The stereochemical complexity is determined by the different isomers formed through complexation of the metal to one or other face of each of the three olefins involved. The palladacyclopropane formulation of the palladium,olefin interaction offers a clear picture of the stereogenicity of the olefin carbon atoms that are complexed to the metal. The energetically favorable isomers were identified in the solid-state and in solution by performing X-ray diffraction and NMR spectroscopic analysis, respectively. Els complexos de pal,ladi de macrocicles triolefínics de tipus (E,E,E)-1,6,11-tris(arilsulfonil)-1,6,11-triazaciclopentadeca-3,8,13-triè, contenint des de tres unitats aríliques iguals fins a tres de diferents han estat estudiats mitjançant difracció de Raigs-X, espectroscòpia de RMN i càlculs teòrics. La complexitat estereoquímica deriva dels diferents isomers que es poden formar degut a la complexació del metall amb cadascuna de les dues cares de les tres olefines. La representació dels enllaços metall-olefina com a pal,ladaciclopropans permet una visualització més senzilla de l,estereoquímica dels àtoms de carboni olefínics després de la complexació. Els isomers energèticament possibles han estat determinats en l,estat sòlid i en solució mitjançant difracció de Raigs-X i espectroscòpia de RMN respectivament. [source]


Oligomeric Alkoxysilanes with Cagelike Hybrids as Cores: Designed Precursors of Nanohybrid Materials

CHEMISTRY - AN ASIAN JOURNAL, Issue 3 2008
Hideki Kuge
Abstract Well-defined alkoxysilane oligomers containing a cagelike carbosiloxane core were synthesized and used as novel building blocks for the formation of siloxane-based hybrid networks. These oligomers were synthesized from the cagelike trimer derived from bis(triethoxysilyl)methane by silylation with mono-, di-, and triethoxychlorosilanes ((EtO)nMe3,nSiCl, n=1, 2, and 3). Hybrid xerogels were prepared by hydrolysis and polycondensation of these oligomers under acidic conditions. The structures of the products varied depending on the number of alkoxy groups (n). When n=2 and 3, microporous xerogels (BET surface areas of 820 and 510,m2,g,1, respectively) were obtained, whereas a nonporous xerogel was obtained when n=1. 29Si,NMR spectroscopic analysis suggested that partial rearrangement of the siloxane networks, which accompanied the cleavage of the Si,O,Si linkages, occurred during the polycondensation processes. By using an amphiphilic triblock copolymer surfactant as a structure-directing agent, hybrid thin films with a 2D hexagonal mesostructure were obtained when n=2 and 3. These results provide important insight into the rational synthesis of molecularly designed hybrid materials by sol,gel chemistry. [source]