摘要:

AbstractThe kinetics of base‐catalysedE/Zisomerization for a series of ethyl 2‐oxo‐3‐indolinylidenecyanoacetates in CDCl3solutions were studied by1H NMR spectroscopy. Both polarizable double bond considerations and steric requirements of the base must be considered in explaining the results. TheE/Zequilibrium of ethyl 1‐carbethoxy‐2‐oxo‐3‐indolinylidenecyanoacetate was reached faster than those of ethyl 2‐oxo‐3‐indolinylidenecyanoacetate and the 1‐methyl derivative by a factor ofca.10 in the presence of triethylamine, and the isomerizations were faster when quinuclidine was used. In pure DMSO‐d6solutions, the equilibria were established upon dissolution, but addition of small amounts of acid slowed the isomerizati

ISSN:0749-1581    

DOI:10.1002/mrc.1260301202

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe solution behaviour and redistribution reactions of tetraorganodistannoxane dimers were investigated by19F and119Sn NMR spectroscopy. The variable‐temperature NMR data suggest that both the ‘ladder’ and ‘staircase’ structures exist in solution. Redistribution between two different tetrabutylstannoxanes is rapid on the NMR time scale. The119Sn 2D EXSY NMR data for [Bu2Sn(F)OSnBu2(Cl)]2indicate that there is no exchange between exo‐ and endocyclic

ISSN:0749-1581    

DOI:10.1002/mrc.1260301203

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA pulse sequence is presented which allows one to perform an inversion–recovery experiment forT1determination on quadrupolar nuclei in the presence of acoustic ringing. The sequence is based on a modification of the reference baseline subtraction −90° pulse sequence. Some examples of17O and14N and relaxation are presented, including spectra with overlapping peaks from whichT1values cannot be simply extracted from line wi

ISSN:0749-1581    

DOI:10.1002/mrc.1260301204

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe allenic C37skeletal carotenoid all‐trans‐(3S, 5R, 6R, 3′S, 5′R, 6′S)‐peridinin, isolated fromAmphidinium carteraeby an improved isolation procedure, was subjected to a detailed1H and13C NMR spectroscopic analysis. Complete assignments of the 500.13 MHz1H and 125.76 MHz13C spectra, including determination of coupling constants and relative stereochemistry, were obtained by ID and 2D techniques. These included1H1H chemical shift correlated spectroscopy (2D COSY), phase‐sensitive double‐quantum COSY, difference 1D NOE experiments, 1D and 2D total correlation spectroscopy (HOHAHA, TOCSY) and 1D and 2D rotating frame nuclear Overhauser spectroscopy (ROESY, CAMELSPIN). The13C NMR assignments were obtained through editing sequences (DEPT) and heterocorrelated 2D experiments. In particular, the1H detected multiple bond1H13C correlated 2D experiment proved valuable for assignments of all 13 quatenary carbons together with 13 methine carbons in peridinin [C37H47O6(COCH3)]. Detailed analysis of the proton coupling constants supported the conformations and relative stereochemistry of the two end‐groups. Spectral simulation of protons in the conjugated chain was necessary in order to ascertain more accurate chemical shifts for some protons in the strongly overlapping olefinic region. Variation in thetransdouble bond3J(H, H) coupling was noted along

ISSN:0749-1581    

DOI:10.1002/mrc.1260301205

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract1‐Aryl‐3,3‐dialkyltriazenes have been synthesized by coupling the corresponding diazonium salts of substituted aniline derivatives with dialkylamines. The thermostability of these compounds was investigated by differential scanning calorimetry; activation energies of 240–280 kJ mol−1were determined for the thermal decomposition. The hindered rotation of the dialkylamino group was studied by1H NMR exchange measurements. Both experiments are interpreted in terms of an involvement of a 1,3‐dipolar structure of the NNN functional group. The influence of substituents, both on the aromatic ring and at the amino group, on the kinetic and activation parameters is investigated; results are analysed on the basis of mesomeric and steric effects on the dipolar charge distribut

ISSN:0749-1581    

DOI:10.1002/mrc.1260301206

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractPerindopril, thetert‐butylamine salt of 1‐{(2S)‐2‐[(1S)‐(1‐carbethoxybutyl)amino]‐1‐oxopropyl}‐(2S,3aS,7aS)‐perhydroindole‐2‐carboxylic acid, is an inhibitor of angiotensin‐converting enzyme (ACE) and a new drug for the treatment of hypertension. The interaction between the inhibitor and the enzyme was investigated by studying the active diacid metabolite of perindopril, its stereoisomers and a desmethyl analogue. The pharmacological study allowed the measurement of thein vitroactivities of the different compounds. The1H and13C NMR studies have shown that thecis‐transequilibrium about the amide bond is strongly dependent on the configuration of the chiral centres and on the pH of the solution. The pKaof the different acid‐base species were measured. The results show that perhydroindole derivatives are potent inhibitors of ACE as long as they fulfil the following basic requirements: (1) anSconfiguration of the carbon bearing the terminal carboxy group; (2) anSmethyl substituent in the alanine residue; however, the inhibitor potency is not modified on the replacement of the alanine residue of the perindopril by a glycine residue; and (3) less stringently, anSconfiguration of the C‐1 butyl carbon. Under these conditions the Zn binding ligand (chain carboxylate group) is devoid of steric hindrance in thetransconformers. No direct relationship appeared between the relative amount of thetransform and the activity. The cyclic skeleton of the perhydroindole derivatives provided a strong hydrophobic interaction with the active enzymatic site, whatever the configurations at C‐3a and C‐7a. Lipophilic interactions involving the different parts of the inhibito

ISSN:0749-1581    

DOI:10.1002/mrc.1260301207

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe carbon and proton NMR spectra ofsyn‐ andanti‐tricyclo[5.1.0.03,5]octanes and their dichlorocarbene CH bond insertion products were determined by conventional 1D and 2D methods. Partially relaxed proton spectroscopy was carried out in some instances to aid in the separation of badly overlapped multiplets. A detailed analysis of the spectra was carried out with the aid of a new equation relating both the torsion angles and the CCH angles to the vicinal proton coupling constants. These values were combined with molecular modeling to draw conclusions regarding the conformational preferences for these

ISSN:0749-1581    

DOI:10.1002/mrc.1260301208

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA novel topological method was developed for the analysis of13C chemical shifts in polyoxygenated benzenes, C6H6‐n(OY)n, where Y = H, Me and Ph. Carbon chemical shifts were described with individual and collective increments for oxygen itself and for oxygen substituents. The oxygens themselves have only one two‐particle increment (1,4‐dioxy interaction) in addition to the individual positional increments (ipso,ortho,meta,para). The 1,2‐dioxy interaction exerts no influence on any ring carbon chemical shifts, and thus the 1,2‐di‐ortho‐subgraphs were connected with the steric properties of the oxygen substituents. The results are in agreement with molecular mechanics calculations and NMR data in the solid state. Hydrogen bonding with specific solvents deshielded theipsoandorthocarbons by about 1.5 ppm. This predictive set completely described the13C NMR spectra of all the polyoxygenated benzenes studied within the experimental accuracy (RRMS = 0.6 ppm). The incremental scheme will be predictive and useful for P

ISSN:0749-1581    

DOI:10.1002/mrc.1260301209

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe conformational behaviour of 7‐[(3‐chloro‐6,11‐dihydro‐6‐methyldibenzo[c, f][1,2]thiazepin‐11‐yl)amino] heptanoic acid 5,5 dioxide (tianeptine), a new antidepressant drug, was studied by means of1H and13C NMR. The ring skeleton exhibits two distinct conformations at low temperature. The conformational exchange is still restricted at room temperature, particularly in the solvents D2O and CDCl3, where significant aggregation of the molecules occurs. The side‐chain seems to adopt a preferential conformation where it is bent over the unsubstituted aromatic ring. This conformational preference in the biologically active structure might be related to the observed loss of activity when substituents are introduced on t

ISSN:0749-1581    

DOI:10.1002/mrc.1260301210

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractSolid‐state CP/MAS31P NMR spectra were measured for the following unsaturated phosphorus–nitrogen–sulfur ring systems: 1,5‐R4P2N4S2(R = Me, Et, Ph), 1,5‐Ph4P2N4S2Ph2, Ph2PN4S3NPPh3and Ph2PN3S2. The isotropic solid‐state shifts correlate well with the corresponding shifts in solution, the largest difference being 9.0 ppm, indicating that there are no phase‐dependent structural features. Analysis of the principal elements of the shielding tensor by the spinning side band method showed that one of these elements is primarily responsible for the anomalously low‐field isotropic chemical shifts of 1,5‐R4P2N4S2, but no correlation was found between this individual tensor component and any of the structural parameters of these folded eight‐membered rings. Two isotropic shifts were observed for the crystallographically inequivalent phosphorus atoms of 1,5‐Et4P2N4S2, but the individual31P isotropic shifts of 1,5‐Me4

ISSN:0749-1581    

DOI:10.1002/mrc.1260301211

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY