Detailed H-1 and C-13 NMR structural assignment and relative stereochemistry determination for three closely related sesquiterpene lactones

A complete analysis of H-1 and C-13 NMR spectra of the trypanocidal sesquiterpene lactone eremantholide C and two of its analogues is described. These structurally similar sesquiterpene lactones were submitted to H-1 NMR, C-13 (H-1) NMR, gCOSY, gHSQC, gHMBC, J-resolved and DPFGSE-NOE NMR techniques. The detailed analysis of those results, correlated to some computational calculations (molecular mechanics), led to the total and unequivocal assignment of all H-1 and C-13 NMR data. The determination of all H-1/H-1 coupling constants and all signal multiplicities, together with the elimination of previous ambiguities were also achieved. Copyright (C) 2008 John Wiley & Sons, Ltd.

Synthesis and total H-1- and C-13-NMR assignment of cephem derivatives for use in ADEPT approaches

We report the synthesis and total NMR characterization of 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[[[(4''-nitrophenoxy)carbonyl]oxy]-methyl]-8-oxo-7[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (5), a new cephalosporin derivative. This compound can be used as the carrier of a wide range of drugs containing an amino group. The preparation of the intermediate product, 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl-4-(6-methoxyquinolin-8-ylamino) pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]-diphenylmethyl ester-5-dioxide (6), as well as the synthesis of the antimalarial primaquine prodrug 5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid-3-[methyl-4-(6-methoxyquinolin-8-ylamino) pentylcarbamate]-8-oxo-7-[(2-thienyloxoacetyl)amino]-5-dioxide (7) are also described, together with their total H-1- and C-13-NMR assignments.

H-1 and C-13 NMR of some alpha-halo derivatives of o-xylene

C-13 and H-1 NMR data for a series of alpha-halo derivatives of o-xylene are presented. A dynamic H-1 NMR investigation of alpha,alpha,alpha',alpha'-tetrabromo-o-xylene (5) was performed and the spectrum of the most stable conformer at 213 K is presented. The free energy of activation for the rotation of the CHBr2 groups in 5 are determined for the first time. (C) 1997 Elsevier Science Ltd.

Detailed H-1 and C-13 NMR structural assignment and relative stereochemistry determination for three new and one known semi-synthetic sesquiterpene lactones

In this work is described a complete H-1 and C-13 NMR analysis for a group of four sesquiterpene lactones, three previously unknown. The unequivocal assignments were achieved by H-1 NMR, C-13{H-1} NMR, gCOSY. gHMQC, gHMBC and NOESY experiments and no ambiguities were left behind. All hydrogen coupling constants were measured, clarifying all hydrogen signals multiplicities. (C) 2011 Elsevier B.V. All rights reserved.

COMPLETE H-1 AND C-13 NMR STRUCTURAL ASSIGNMENTS FOR A GROUP OF FOUR GOYAZENSOLIDE-TYPE FURANOHELIANGOLIDES

Four goyazensolide-type sesquiterpene lactones - lychnofolide, centratherin, goyazensolide and goyazensolide acetate - were thoroughly studied by NMR experimental techniques. H-1 NMR, C-13 NMR {H-1}, COSY, HMQC, HMBC, J-res. and NOE experiments were performed to provide the needed structural information. Complete and unequivocal assignment, including the determination of all multiplicities, was obtained for each structure and the data collections are presented in tables.

C-13-NMR, H-1-NMR, and FT-Raman study of radiation-induced modifications in radiation dosimetry polymer gels

H-1- and C-13-NMR spectroscopy and FT-Raman spectroscopy are used to investigate the properties of a polymer gel dosimeter post-irradiation. The polymer gel (PACT) is composed of acrylamide, N,N'-methylene-bisacrylamide, gelatin, and water. The formation of a polyacrylamide network within the gelatin matrix follows a dose dependence nonlinearly correlated to the disappearance of the double bonds from the dissolved monomers within the absorbed dose range of 0-50 Gy. The signal from the gelatin remains constant with irradiation. We show that the NMR spin-spin relaxation times (T-2) of PAGs irradiated to up to 50 Gy measured in a NMR spectrometer and a clinical magnetic resonance imaging scanner can be modeled using the spectroscopic intensity of the growing polymer network. More specifically, we show that the nonlinear T-2 dependence against dose can be understood in terms of the fraction of protons in three different proton pools. (C) 2000 John Wiley & Sons, Inc.

Synthesis, spectral studies and X-ray crystal structure of N,N `-(+/-)-trans-1,2-cyclohexylenebis(3-ethoxysalicylideneamine) H-2(t-3-EtOsalchxn)

The synthesis, spectra and X-ray crystal structure of N,N`-(+/-)-trans-1,2-cyclohexylenebis(3-ethoxysalicylideneamine) H-2(t-3-EtOsalchxn), a salen-type ligand, are reported. The Schiff base was characterized by elemental analysis, m.p., IR, electronic spectra, H-1 and C-13 NMR spectra. The spectra are discussed and compared with those of N,N`-(+/-)-trans-1,2-cyclohexylenebis(salicylideneamine), H-2(t-salchxn). The electronic and IR spectra were also resolved by deconvolution. The influence of the ethoxy group on the IR, electronic spectrum, H-1 and C-13 NMR spectra is discussed. Strong intramolecular forces are present as supported by the IR and H-1 NMR spectra and the X-ray crystal structure. An intermolecular hydrogen bond is observed and appears twice in a pair of molecules in the unit cell. (c) 2007 Elsevier B.V. All rights reserved.

New insights on the Lewis acidity of diorganolead(IV) compounds: Diphenyllead(IV) complexes with N,O,S-chelating ligands

The reactions of PbPh2(OAC)(2) with alkylglyoxylate thiosemicarbazones (HRGTSC, R = Et, Bu) afforded complexes of the type [PbPh2(GTSC)] center dot H2O, [PbPh2(RGTSC)(2)] and [PbPh2Cl(BUGTSC)]. The structures of HRGTSC (R = Me, Et, Bu), [PbPh2(OAc)(RGTSC)](R = Me, Et, Bu), [PbPh2Cl(BuGTSC)] and [PbPh2(GTSC)] center dot H2O have been studied by X-ray diffraction. [PbPh2(OAc)(RGTSC)] and [PbPh2(GTSC)] center dot H2O have [PbC2NO3S] kernels and the coordination sphere of the metal is pentagonal bipyramidal. [PbPh2Cl(BuGTSC)] has a [PbC2NOSCI] kernel and the coordination geometry around lead is pentagonal bipyramidal with one vacant site. Analysis of the bond distances in [PbPh2(GTSC)] center dot H2O suggests a significant affinity between diphenyllead(IV) and carboxylate donor groups, supporting a borderline acidic character for this organometallic cation. H-1 and C-13 NMR spectra in DMSO-d(6) suggest the partial dissociation of the acetate in [PbPh2(OAc)(RGTSC)] solutions and indicate some differences in the coordination mode of the two RGTSC(-) ligands in [PbPh2(RGTSC)(2)] complexes. (C) 2007 Elsevier Ltd. All rights reserved.

Composition and quality of harvest residues and soil organic matter under windrow residue management in young hoop pine plantations as revealed by solid-state C-13 NMR spectroscopy

Solid-state C-13 nuclear magnetic resonance (NMR) with cross-polarisation (CP) and magic-angle-spinning (MAS) was used to: (a) examine the changes in carbon (C) composition of windrowed harvest residues during the first 3 years of hoop pine plantations in subtropical Australia; (b) assess the impacts of windrowed harvest residues on soil organic matter (SOM) composition and quality in the 0-10 cm soil layer. Harvest residues were collected from 0-, 1-, 2- and 3-year-old windrows of ca. 2.5 m width (15 m apart for 0-, 1- and 2-year-old sites and 10 m apart for 3-year-old site). Soils from the 0 to 10 cm soil layer were collected from the 1-, 2- and 3-year-old sites. The 13C NMR spectra of the harvest residues indicated the presence of lignin in the hoop pine wood, foliage and newly incorporated organic matter (NIOM). Condensed tannin structures were found in the decay-resistant bark, small wood and foliage, but were absent in other residue components and SOM. The NMR spectra of small wood samples contained condensed tannin structures because the outer layer of bark was not removed. NIOM showed a shift from foliage-like structures (celluloses) to lignin-type structures, indicating an incorporation of woody residues from the decomposing harvest residues. Suberins were also present in the small wood, foliage and bark. The 13C CP NMR spectra of SOM indicated that in areas where windrows were present, SOM did not show compositional changes. However, an increase in SOM quality under the windrows in the second year after their formation as characterised by the alkyl C/O-alkyl C (A/O-A) ratio was mainly due to inputs from the decomposition of the labile, readily available components of the windrowed harvest residues. (C) 2002 Published by Elsevier Science B.V.

Characterization of humic acids from a Brazilian Oxisol under different tillage systems by EPR, C-13 NMR, FTIR and fluorescence spectroscopy

The importance of soil organic matter functions is well known, but structural information, chemical composition and changes induced by anthropogenic factors such as tillage practices are still being researched. In the present paper were characterized Brazilian humic acids (HAs) from an Oxisol under different treatments: conventional tillage/maize-bare fallow (CT1); conventional tillage/maize rotation with soybean-bare fallow (CT2)-, no-till/maize-bare fallow (NT1); no-till/maize rotation with soybean-bare fallow (NT2); no-till/maize-cajanus (NT3) and no cultivated soil under natural vegetation (NC). Soil HA samples were analyzed by electron paramagnetic resonance (EPR), solid-state C-13 nuclear magnetic resonance (C-13 NMR), Fourier transform intra-red (FTIR) and UV-Vis fluorescence spectroscopies and elemental analysis (CHNS). The FTIR spectra of the HAs were similar for all treatments. The level of semiquinone-type free radical determined from the EPR spectra was lower for treatments no-till/maize-cajanus (NT3) and noncultivated soil (1.74 X 10(17) and 1.02 x 10(17) spins g(-1) HA, respectively), compared with 2.3 X 10(17) spins g(-1) HA for other soils under cultivation. The percentage of aromatic carbons determined by C-13 NMR also decreases for noncultivated soil to 24%, being around 30% for samples of the other treatments. The solid-state C-13 NMR and EPR spectroscopies showed small differences in chemical composition of the HA from soils where incorporation of vegetal residues was higher, showing that organic matter (OM) formed in this cases is less aromatic. The fluorescence intensities were in agreement with the percentage of aromatic carbons, determined by NMR (r = 0.97 P < 0.01) and with semiquinone content, determined by EPR (r = 0.97 P < 0.01). No important effect due to tillage system was observed in these areas after 5 years of cultivation. Probably, the studied Oxisol has a high clay content that offers protection to the clay-Fe-OM complex against strong structural alterations. (C) 2003 Elsevier B.V. All rights reserved.

Structural description of humic substances from subtropical coastal environments using elemental analysis, FT-IR and C-13-solid state NMR data

Elemental composition and spectroscopic properties (FT-IR and CP/MAS C-13-NMR) of sedimentary humic substances (HS) from aquatic subtropical environments (a lake, an estuary and two marine sites) are investigated. Humic acids (HA) are relatively richer in nitrogen and in aliphatic chains than fulvic acids (FA) from the same sediments. Conversely, FA are richer in carboxylic groups and in ring polysaccharides than HA. Nitrogen is mostly present as amide groups and for lake and marine HS the FT-IR peaks around 1640 cm(-1) and 1540 cm(-1) identify polypeptides. Estuarine HS exhibit mixed continental-marine influences, these being highly influenced by site location. Overall, the data suggest that aquatic and mixed HS are more aliphatic than has been proposed in current models and also that amide linkages form an important part of their structural configuration.

Iminopropadienones R-N=C=C=C=O and carbon suboxide, C3O2. Theoretical and experimental 13C NMR spectra

The C-13 NMR data of five iminopropadienones R-N=C=C=C=O as well as carbon suboxide, C3O2, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31 +G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5-10 ppm. The computationally faster GIAO/HF/6-31 + G**//B3LYP/6-31 G* level is also adequate. (C) 2004 Elsevier B.V. All rights reserved.

H-1 NMR spectroscopic studies of the stability of an oxazolidine condensation product

Condensation of (-)-norephedrine with excess formaldehyde under mild conditions leads to formation of the 2:1 condensation product N,N'-methylenebis(4-methyl-5-phenyl)oxazolidine compared with the reaction with 1 mol of formaldehyde, which leads to 4-methyl-5-phenyloxazolidine. H-1 and C-13 NMR spectroscopy was used to monitor the stability of this compound and its decomposition products. The 2:1 condensation product is found to be stable in CDC1(3) but breaks down rapidly in CD3OD to yield a 50:50 mixture of 4-methyl-5-phenyloxazolidine and 3-hydroxymethyl-4-methyl-5-phenyloxazolidine. Upon addition of D2O to this equimolar mixture, the latter compound decomposes to norephedrine and formaldehyde, whereas the former compound is stable. (C) 1997 by John Wiley & Sons, Ltd.

A comparative solid state C-13 NMR and thermal study of CO2 capture by amidines PMDBD and DBN

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)