NMR Spectroscopic Methods (nmr + spectroscopic_methods)

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Selected Abstracts

Preparation of Diamidochloro(cyclopentadienyl)titanium Derivatives as Pre-Catalysts for Olefin Polymerization , X-ray Molecular Structure of [Ti(,5 -C5H5){1,2-C6H4(NCH2CH2CH3)2}Cl] and [Ti{,5 -C5H4(SiMe3)}{1,2-C6H4(NCH2CH2CH3)2}Cl]

Vanessa Tabernero
Abstract The synthesis of N,N,-alkyl 1,2-phenylenediamines 1,2-C6H4(NHR)2 [R = CH2CH2CH3 (nPr), CH2tBu (Np)] was carried out in three steps by lithiation of the primary 1,2-phenylenediamine, reaction with the appropriate acyl chloride and reduction with LiAlH4. The addition of nBuLi to a stirred solution of N,N,-alkyl diamines in cold hexane resulted in the immediate deposition of the corresponding lithium salts, which react with [MCpR,Cl3] to give the diamidochloro(,5 -cyclopentadienyl)titanium and -zirconium complexes [MCpR,{1,2-C6H4(NR)2}Cl] (4,10) [M = Ti, Zr; CpR, = ,5 -C5H5, ,5 -C5(CH3)5, ,5 -C5H4(SiMe3); R = nPr, Np]. The compound [Ti(,5 -C5H5){1,2-C6H4(NnPr)2}Cl] (3) was obtained by treatment of [Ti(,5 -C5H5)Cl3] with 1,2-C6H4(NHnPr)2 in the presence of NEt3 in toluene. All the reported compounds were characterized by the usual analytical and NMR spectroscopic methods. The molecular structures of 3 and 7 were determined by single-crystal X-ray crystallography. The compounds described here were further investigated as potential olefin polymerization catalysts. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Uncommon Sesquiterpenoids and New Triterpenoids from Jatropha neopauciflora (Euphorbiaceae)

Abraham García
Abstract Eight new terpenoids (1,8) were isolated from the bark of Jatropha neopauciflora, together with eight known compounds. The new isolates include the sesquiterpenoids (1R,2R)-diacetoxycycloax-4(15)-ene (1); (1R,2R)-dihydroxycycloax-4(15)-ene (2), (2R)- , -cadin-4-ene-2,10-diol (3), (2R)- , -cadina-4,9-dien-2-ol (4), (1R,2R)-dihydroxyisodauc-4-en-14-ol (5) and its acetonide 6 (artifact), as well as the two triterpenoids (3,,16,)-16-hydroxylup-20(29)-en-3-yl (E)-3-(4-hydroxyphenyl)prop-2-enoate (7) and (3,,16,)-16-hydroxyolean-18-en-3-yl (E)-3-(4-hydroxyphenyl)prop-2-enoate (8). The structures of these compounds were established by extensive 1D- and 2D-NMR spectroscopic methods, and their absolute configurations were determined by circular-dichroism (CD) experiments, and by X-ray crystallographic analysis (compound 7; Fig.,3). A plausible biosynthesis of the sesquiterpenoids 1,5 is proposed (Scheme), starting from (,)-germacrene D as the common biogenetic precursor. [source]

Structure elucidation and 3D solution conformation of the antibiotic enduracidin determined by NMR spectroscopy and molecular dynamics

F. Castiglione
Abstract Enduracidin and ramoplanin belong to the large family of cyclodepsipeptide antibiotics, highly effective against Gram-positive bacteria. The primary and 3D solution structure of ramoplanin is already well known, and the primary structure of enduracidin has been determined by a combination of chemical and NMR spectroscopic methods. Both antibiotics share a similar peptide core of 17 amino acids and differ mainly in the length of the acyl chain and the presence of two D -mannose moieties in ramoplanin. Based on the high sequence homology with ramoplanin, the structure in solution of enduracidin is modeled as a cyclic peptide. The tertiary structure thus obtained was refined through molecular dynamics (MD) simulation, in which the interatomic NOE-derived distance restraints were imposed. MD simulations yielded a family of representative 3D structures (RMSD = 0.89), which highlighted a backbone geometry similar to that of ramoplanin in its ,-hairpin arrangement. In contrast, enduracidin displays a different arrangement of the side-chain and of the residues forming the hydrophobic core. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Preparation and use of polymer-supported chiral ruthenium complex catalyst

Jing-Xing Gao
Abstract The chiral diiminodiphosphine ligand, [(R,R)-P2N2],­has been prepared by the condensation of o -(diphenylphosphino)benzaldehyde and 1,2-diaminocyclohexane. [(R,R)-P2N2] was reduced with excess NaBH4 in refluxing ethanol to afford the corresponding diaminodiphosphine ligand [(R,R)-P2(NH)2]. The interaction of [(R,R)-P2(NH)2] with trans -RuCl2(DMSO)4 gave the chiral ruthenium complex [(R,R)-RuP2(NH)2] in 84% yield. The reaction of [(R,R)-RuP2(NH)2] with poly-(acrylic acid) using dicyclohexylcarbodiimine as the coupling agent, gave water soluble poly(acrylic acid salt)-supported chiral ruthenium complex [PAA-(R,R)-RuP2(NH)2]. These chiral ligands and ruthenium complexes have been fully characterized by microanalysis and IR, NMR spectroscopic methods. The polymer-bound ruthenium complex [PAA-(R,R)-RuP2(NH)2] as catalyst was used in asymmetric transfer hydrogenation of acetophenone in 2-propanol, producing the 1-phenylethanol in 95% yield and 96% ee. The catalyst was reused twice with some loss of activity and enantioselectivity. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Enzyme-Catalysed Synthesis and Absolute Configuration Assignments of cis -Dihydrodiol Metabolites from 1,4-Disubstituted Benzenes

Abstract A series of ten cis -dihydrodiol metabolites has been obtained by bacterial biotransformation of the corresponding 1,4-disubstituted benzene substrates using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). Their enantiomeric excess (ee) values have been established using chiral stationary phase HPLC and 1H,NMR spectroscopy. Absolute configurations of the majority of cis -dihydrodiols have been established using stereochemical correlation and X-ray crystallography and the remainder have been tentatively assigned using NMR spectroscopic methods but finally confirmed by circular dichroism (CD) spectroscopy. These configurational assignments support and extend the validity of an empirical model, previously used to predict the preferred stereochemistry of TDO-catalysed cis -dihydroxylation of ten 1,4-disubstituted benzene substrates, to more than twenty-five examples. [source]

1H, 13C, and 15N NMR stereochemical study of cis -fused 7a(8a)-methyl and 6-phenyl octa(hexa)hydrocyclopenta[d][1,3]oxazines and [3,1]benzoxazines

CHIRALITY, Issue 2-3 2002
Petri Tähtinen
Abstract Four 7a-methyl octa(or hexa)hydrocyclopenta[d][1,3]oxazines, five 8a-methyl octa(or hexa)hydro[3,1]benzoxazines, two 6-phenyl hexahydro[3,1]benzoxazinones, and 8a-methyl hexahydro[1,3]benzoxazinone, all cis -fused, were prepared and their stereostructures studied by various one- and two-dimensional 1H, 13C, and 15N NMR spectroscopic methods. In solution, the cyclopentane-fused 2-oxo derivatives and the 1,3-benzoxazinone were found to attain exclusively the N-in/O-in conformation, whereas the 6-phenyl 2-oxo/thioxo derivatives were found to be present predominantly in the N-out conformation. The C-2 unsubstituted and the 2-oxo/thioxo 7a/8a-methyl derivatives were all present in solution as a rapidly interconverting equilibrium of the N-in and N-out conformations. The C-2 methyl derivatives were each found to be interconvertable mixtures of epimers (at C-2) with the N-in conformer predominating for one epimer and the N-out conformer predominating for the other, with both predominating conformers having the C-2 methyl group equatorially orientated. The substituent on the nitrogen (H or Me) was found to be always predominantly equatorial with respect to the heteroring, except for the epimeric 2-methyl derivatives with N-out conformations where steric constraints and the generalized anomeric effect resulted in the axial orientation of the C-2 methyl being favored. Chirality 14:187,198, 2002. © 2002 Wiley-Liss, Inc. [source]

Synthesis of oxazolo[3,2- b]hetero[1,2,4]thiadiazine S,S-dioxides ,

Salvador Vega
Six bromomethyl derivatives of the new 2,3-dihydrooxazolo[3,2- b]thieno[3,4- e][1,2,4]thiadiazine 5,5-dioxides, 2,3-dihydrooxazolo[3,2- b]thieno[2,3- e][1,2,4]thiadiazine 5,5-dioxides and 6,7-dihydrooxazolo-[3,2- b]pyrazolo[4,3- e][1,2,4]thiadiazine 9,9-dioxides heterocyclic ring systems were synthesized. These compounds are good intermediates for the preparation and development of promising antiviral and psy-chotropic drugs. The structures of the products are supported by different nmr spectroscopic methods and mass spectrometry. [source]