Conformation and stereodynamics of N,N-dialkylbenzamides; a 1H and 13C nuclear magnetic resonance investigation of para-substituted 4-benzoyl-cis-2,6-dimethylmorpholines

Jennings, W. Brian; Saket, B. M.

doi:10.1039/p29850001005

Cited by 5 publications

(2 citation statements)

References 2 publications

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“…The barriers observed here for compounds of type 2 are, as an average, 4.2 kcal mol -1 larger than those of the corresponding acyl mesityl ketones, 1 . This seems too large an enhancement to be solely explained by the electron-withdrawing properties of the second RCO moiety in position 4 . An additional contribution to this enhancement should be also attributable to the reciprocal buttressing effect of the aryl-bonded methyl groups in derivatives 2 .…”

Section: Resultsmentioning

confidence: 92%

Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Casarini

Lunazzi

1996

J. Org. Chem.

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The orthogonal syn and anti isomers, originated by the restricted rotation about the Ar-C(O)Bu(t) single bonds in 1,4-bis(2,2-dimethylpropanoyl)durene (2e), have been separated by preparative thin layer chromatography. In solution they reach an equilibrium where the syn-anti ratio depends upon the polarity of the solvent. This allowed us to assign the anti structure, which has a null dipole moment, to the least retained isomer. The free energy of activation (DeltaG) for the interconversion was found to be 22.5 kcal mol(-)(1), a value high enough for identifying these species as configurational isomers. When less hindered derivatives, also having two RCO (R = Pr(i), Et, Me) substituents in the positions 1,4 of the durene moiety, were examined, the syn and anti forms could be detected only at low temperature by means of NMR spectroscopy. The corresponding interconversion barriers (DeltaG = 13.4, 11.7, 10.9 kcal mol(-)(1), respectively) are, in fact, much lower than for R = Bu(t), indicating that in these cases we are dealing with conformational rather than with configurational isomers.

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Section: Resultsmentioning

confidence: 92%

Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Casarini

Lunazzi

1996

J. Org. Chem.

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“…20 Light absorption by the trans peptide bond causes photoisomerization into an excess population of cis conformer 30 that provides the tool for measuring isomerization kinetics. Given the rate effects found for N-substituted amides, [31][32][33][34] extrapolation from the isomerization rates of k cis f trans ) 2.3 ( 0.3 s -1 (N-methylacetamide) and k cis f trans ) 14 ( 2 s -1 (Gly-Gly) would lead to faster isomerization rates for any peptide bond but Xaa-Gly linkages.…”

Section: Introductionmentioning

confidence: 99%

Barriers to Rotation of Secondary Amide Peptide Bonds

et al. 1998

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We present results on the identification and molecular characterization of conformers with secondary cis amide peptide bonds for a number of oligopeptides containing tyrosine and phenylalanine in aqueous solution. Employing 1 H NMR techniques, peptide bonds adjacent to the aromatic amino acid were found to generate a cis isomer population ranging from 0.1% to 1% in dependence on the chain length and the ionization state of the peptide. The rate constant of the trans f cis interconversion for zwitterionic Ala-Tyr was 2.4 × 10 -3 s -1 at 298 K and thus in a range typical of imidic prolyl peptide bonds. However, the rate constant k cis f trans ) 0.6 s -1 of the reverse isomerization revealed a much faster process in Ala-Tyr. Extending the peptide chain in both directions of the Ala-Tyr moiety led to a decrease of both the cis content and the barrier to rotation in the cis f trans direction. The linear Arrhenius plots gave E a values of 76.7 ( 1.5 and 64.6 ( 1.5 kJ mol -1 for the dipeptide Ala-Tyr and the corresponding bond in the pentapeptide Ala-Ala-Tyr-Ala-Ala, respectively. Isomerization rates were affected by both the position and the nature of amino acids flanking the isomerizing bond as could be proved by comparison of peptides containing Gly, Tyr, and Phe residues. These studies provide data that permit the extraction of kinetic events originating from the isomerization of "normal" peptide bonds in protein backbone structuring.

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Folded conformations ofN-(aminoalkyl)-9-phenanthrenecarboxamides in the crystal and solution

Lewis

Burch

Stern

1997

J. Phys. Org. Chem.

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The molecular structures of three tertiary N‐(aminoalkyl)‐9‐phenanthrenecarboxamides were investigated in solution and the solid state by means of 1H NMR spectroscopy and x‐ray crystallography. The tertiary amides exist as a mixture of E and Z isomers in solution and the aminoalkyl groups exist as a mixture extended and folded conformers. A crystalline N‐(aminoethyl)amide was obtained as the pure Z isomer in which the phenanthrene and amide planes are nearly perpendicular and the aminoethyl group is folded over the less hindered face of the amide group. Rotation about the Ar–C(O) bond is slow in resolution rendering these molecules chiral on the NMR time‐scale. As a consequence, the α‐methylene protons display large diasterotopic splittings when the aminoalkyl group is syn to the amide carbonyl. Folded conformations place the Z and E aminoalkyl groups in the deshielding and shielding regions, respectively, of the phenanthrene rings, resulting in large differences in chemical shifts. © 1997 John Wiley & Sons, Ltd.

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Conformation and stereodynamics of N,N-dialkylbenzamides; a 1H and 13C nuclear magnetic resonance investigation of para-substituted 4-benzoyl-cis-2,6-dimethylmorpholines

Cited by 5 publications

References 2 publications

Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Barriers to Rotation of Secondary Amide Peptide Bonds

Folded conformations ofN-(aminoalkyl)-9-phenanthrenecarboxamides in the crystal and solution

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Conformation and stereodynamics of N,N-dialkylbenzamides; a 1H and 13C nuclear magnetic resonance investigation of para-substituted 4-benzoyl-cis-2,6-dimethylmorpholines

Cited by 5 publications

References 2 publications

Conformational Studies by Dynamic NMR. 57.1 Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Conformational Studies by Dynamic NMR. 57.1 Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Barriers to Rotation of Secondary Amide Peptide Bonds

Folded conformations ofN-(aminoalkyl)-9-phenanthrenecarboxamides in the crystal and solution

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Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes

Conformational Studies by Dynamic NMR. 57.¹ Stereodynamics of Syn−Anti Interconversion of Disubstituted Acyl Durenes