Magnetic Resonance in Chemistry

doi: 10.1002/mrc.1260301201pmid: N/A

Morales‐Rios, Martha S.; Mora‐Pérez, Yolanda; Joseph‐Nathan, Pedro

doi: 10.1002/mrc.1260301202pmid: N/A

The kinetics of base‐catalysed E/Z isomerization for a series of ethyl 2‐oxo‐3‐indolinylidenecyanoacetates in CDCl3 solutions were studied by 1H NMR spectroscopy. Both polarizable double bond considerations and steric requirements of the base must be considered in explaining the results. The E/Z equilibrium 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 of ca. 10 in the presence of triethylamine, and the isomerizations were faster when quinuclidine was used. In pure DMSO‐d6 solutions, the equilibria were established upon dissolution, but addition of small amounts of acid slowed the isomerization process in these systems.

Jain, Vimal K.; Mokal, V. B.; Sandor, P.

doi: 10.1002/mrc.1260301203pmid: N/A

The solution behaviour and redistribution reactions of tetraorganodistannoxane dimers were investigated by 19F and 119Sn 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. The 119Sn 2D EXSY NMR data for [Bu2Sn(F)OSnBu2(Cl)]2 indicate that there is no exchange between exo‐ and endocyclic tin centres.

Bagno, Alessandro

doi: 10.1002/mrc.1260301204pmid: N/A

A pulse sequence is presented which allows one to perform an inversion–recovery experiment for T1 determination 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 of 17O and 14N and relaxation are presented, including spectra with overlapping peaks from which T1 values cannot be simply extracted from line widths.

Krane, Jostein; Aakermann, Torunn; Liaaen‐Jensen, Synnøve

doi: 10.1002/mrc.1260301205pmid: N/A

The allenic C37 skeletal carotenoid all‐trans‐(3S, 5R, 6R, 3′S, 5′R, 6′S)‐peridinin, isolated from Amphidinium carterae by an improved isolation procedure, was subjected to a detailed 1H and 13C NMR spectroscopic analysis. Complete assignments of the 500.13 MHz 1H and 125.76 MHz 13C spectra, including determination of coupling constants and relative stereochemistry, were obtained by ID and 2D techniques. These included 1H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). The 13C NMR assignments were obtained through editing sequences (DEPT) and heterocorrelated 2D experiments. In particular, the 1H detected multiple bond 1H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 the trans double bond 3J(H, H) coupling was noted along the conjugated chain.

Lippert, Th.; Wokaun, A.; Dauth, J.; Nuyken, O.

doi: 10.1002/mrc.1260301206pmid: N/A

1‐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−1 were determined for the thermal decomposition. The hindered rotation of the dialkylamino group was studied by 1H 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 distribution in the molecule.

Bouchet, J. P.; Volland, J. P.; Laubie, M.; Vincent, M.; Marchand, B.; Platzer, N.

doi: 10.1002/mrc.1260301207pmid: N/A

Perindopril, the tert‐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 the in vitro activities of the different compounds. The 1H and 13C NMR studies have shown that the cis‐trans equilibrium about the amide bond is strongly dependent on the configuration of the chiral centres and on the pH of the solution. The pKa of 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) an S configuration of the carbon bearing the terminal carboxy group; (2) an S methyl 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, an S configuration of the C‐1 butyl carbon. Under these conditions the Zn binding ligand (chain carboxylate group) is devoid of steric hindrance in the trans conformers. No direct relationship appeared between the relative amount of the trans form 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 inhibitor are not independent of each other.

Xu, Linxiao; Brinker, Udo H.; Smith, William B.

doi: 10.1002/mrc.1260301208pmid: N/A

The carbon and proton NMR spectra of syn‐ and anti‐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 molecules.

Dostovalova, Valentina I.; Fedorov, Lev A.

doi: 10.1002/mrc.1260301209pmid: N/A

A novel topological method was developed for the analysis of 13C 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 the ipso and ortho carbons by about 1.5 ppm. This predictive set completely described the 13C 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 PC programming.

Platzer, N.; Bouchet, J. P.; Malen, C.; Labrid, C.; Mocaer, E.

doi: 10.1002/mrc.1260301210pmid: N/A

The 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 of 1H and 13C 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 the aromatic rings.