Search results for "MR"
showing 10 items of 3001 documents
Assigning the C-15 configuration of 15-hydroxy-, 15-methoxy-, 15-ethoxy-hexahydrofurofuran neoclerodane diterpenoids
2004
Abstract Examination of 1 H and 13 C NMR spectra allows the establishment of rules for assigning the correct configuration at C-15 of 15-hydroxy-, 15-methoxy-, 15-ethoxy-hexahydrofurofuran neoclerodane diterpenoids. The structure of several diterpenoids has been assigned or ammended.
Experimental and theoretical investigations of structural isomers of dichalcogenoimidodiphosphinate dimers: dichalcogenides or spirocyclic contact io…
2007
A synthetic protocol for the tert-butyl-substituted dichalcogenoimidodiphosphinates [Na(tmeda){(EPtBu(2))(2)N}] (3 a, E=S; 3 b, E=Se; 3 c, E=Te) has been developed. The one-electron oxidation of the sodium complexes [Na(tmeda){(EPR(2))(2)N}] with iodine produces a series of neutral dimers (EPR(2)NPR(2)E--)(2) (4 b, E=Se, R=iPr; 4 c, E=Te, R=iPr; 5 a, E=S, R=tBu; 5 b, E=Se, R=tBu; 5 c, E=Te, R=tBu). Attempts to prepare 4 a (E=S, R=iPr) in a similar manner produced a mixture including HN(SPiPr(2)). Compounds 4 b, 4 c and 5 a-c were characterised by multinuclear NMR spectra and by X-ray crystallography, which revealed two alternative structures for these dimeric molecules. The derivatives 4 b,…
Metal ion complexation by tetraester derivatives of bridged calix [4] arenes
1992
A series of bridged calix [4] arenes (5–10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 105 for Na +) for the shorter methylene chains. 1H NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraest…
Structural study of ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates: conformation and transmission of substituent effects acro…
2001
Nine new ethyl 3-arylcarbamoyl-2,3-diazabicyclo[2.2.1]hept-5-ene-2-carboxylates were prepared by a [4 + 2] cycloaddition and their FTIR, 1H, 13C and 15N NMR spectra were measured and assigned. Single crystals were grown for five compounds and their X-ray data were obtained. The electronic structure and the conformations were calculated by the semi-empirical AM1 method. Using correlations between the spectral, empirical and theoretical structural data, the transmission of substituent effects and the preferential conformation connected with the consecutive double nitrogen inversion and regarding the mutual orientation of NH and CO bonds were investigated. The results are compared with those f…
Crystal structure, dielectric properties and molecular motions in ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9
2000
Abstract The crystal structure of ( i -C 4 H 9 NH 3 ) 3 Bi 2 Br 9 at room temperature has been determined and refined to R =0.036. The crystal is orthorhombic, space group Ama 2. The structure is built up of the i -butylammonium cations and isolated Bi 2 Br 9 3− anions. The complex dielectric permittivity along the a -axis has been measured between 500 Hz and 1000 MHz in the vicinity of two phase transitions at 252 and 263 K. The dielectric response close to 252 K is well described by the Debye equation. The activation energy of the reorientation of the i -butylammonium cations is found to be 0.68 eV. The temperature dependencies of the proton relaxation time T 1 and of the second moment of…
Spiroterpenoids from Hypericum reflexum
1993
Abstract Two new spiroterpenoids, hyperireflexolide A and B, were isolated from Hypericum reflexum . Their structures and stereochemistry were established by spectroscopic methods, including 13 C NMR, DEPT and HMQC, and X-ray data.
The fungal lactone oxacyclododecindione is a potential new therapeutic substance in the treatment of lupus-associated kidney disease.
2013
Recently oxacyclododecindione (Oxa), a macrocyclic lactone isolated from the imperfect fungus Exserohilum rostratum, has been described as a potent transcription inhibitor of inducible proinflammatory and profibrotic genes in cell culture models. As kidney disease in systemic lupus erythematosus is characterized by aberrant expression of inflammatory mediators and infiltration of immune cells, we investigated the effect of Oxa in MRL-Fas(lpr) mice, a model of systemic lupus erythematosus. These mice develop a spontaneous T-cell and macrophage-dependent autoimmune disease including severe glomerulonephritis that shares features with human lupus. Comparable to the results of in vitro models, …
Bimodal tracers synthesis for medical imaging PET/MRI
2015
Today physicians can use a wide variety of medical imaging techniques to establish early and accurate diagnosis. Nevertheless, each modality has its own advantages and drawbacks. This is why bi- or multimodality approach seems interesting. Among them, PET/MRI combination seems very promising because it can bring complementary informations. It is therefore necessary to inject to patients tracers specific to each imaging modality. This work described the synthesis of molecular platforms for MRI and PET imaging, according to 2 different strategies. The first one consisted in the synthesis of a DO3A macrocycle allowing the chelation of both gadolinium for MRI and gallium 68 for PET. The aim her…
Hydrogen bond-stabilised N-alkylammonium resorcinarene halide cavitands
2010
A family of hydrogen bond-stabilised N-alkylammonium resorcinarene chloride and bromide cavitands were synthesised and characterised with 1H NMR and ESI mass spectrometry. The seven compounds exhibit interestingly either self-inclusion or guest complexation in the solid state evidenced by single crystal X-ray diffraction. The four dimers show self-inclusion of the upper rim propyl chains and consist of two hydrogen-bonded resorcinarene tetracations and six halide anions, while the remaining two halide anions are located in between the dimers linking them via hydrogen bonding. Small solvent molecules such as dichloromethane, methanol, n-butanol or chloroform are complexed into the resorcinar…
(1Z,3Z)-3-[Quinolin-2(1H)-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol: An unexpected most stable tautomer of 1,3-bis(quinolin-2-yl)acetone
2009
Abstract 1 H, 13 C and 15 N NMR spectra reveal that CDCl 3 solution of 1,3-bis(quinolin-2-yl)acetone contains only ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol. The proton transfer takes place between two basic centers of the molecule, which means that the process is an identity reaction by character. The situation is completely different from that detected in chloroform solution of 1,3-bis(pyridin-2-yl)acetone where three different tautomers are in equilibrium with each other. Although the proton transfers in both ( 1Z , 3Z )-3-[quinolin-2(1 H )-ylidene]-1-(quinolin-2-yl)prop-1-en-2-ol and ( 1Z , 3Z )-3-hydroxy-1-[quinolin-2(1 H )-ylidene-4-quinolin-2-yl]but-3-e…