The solution conformation of cyclic β-casomorphin-5 analogues

Kleinpeter, Erich; Ströhl, Dieter; Peinze, Skadi; Brandt, Wolfgang; Schmidt, Ralf; Neubert, Klaus

doi:10.1007/bf02278739

Cited by 7 publications

(11 citation statements)

References 25 publications

(28 reference statements)

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“…Steric hindrance in the urea compounds is also revealed by their non-planarity, leading to almost C 2 , instead of C 2v symmetry (excluding the proton). This non-planarity is consistent with previous studies on unsubstituted urea and thiourea (with NH 2 , instead of NMe 2 groups), 43 as well as for cyclic analogues 44 where the C-N rotational barriers are lower than in the amide analogues.…”

Section: The Free Ligands and Their Protonation Energiessupporting

confidence: 91%

Interaction of M3+ lanthanide cations with amide, urea, thioamide and thiourea ligands: a quantum mechanical study †

Berny

Wipff

2001

J. Chem. Soc., Perkin Trans. 2

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Section: The Free Ligands and Their Protonation Energiessupporting

confidence: 91%

Interaction of M3+ lanthanide cations with amide, urea, thioamide and thiourea ligands: a quantum mechanical study †

Berny

Wipff

2001

J. Chem. Soc., Perkin Trans. 2

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“…Our results prove previous suggestions [1] that differences in the rotational barriers of the partial C,N double bond, with respect to the size of the NR2 substituents, depend on different conjugation due to different ground-state destabilization via steric hindrance.…”

Section: Discussionsupporting

confidence: 91%

“…Due to mesomerism within NR2-aryl/heteroaryl systems the N-aryl bond has some double-bond character which can be experimentally proved on the NMR time scale [1] and theoretically studied by quantum chemical calculations [2].…”

Section: Introductionmentioning

confidence: 99%

Restricted rotation about partial C,N double bonds

Koch

Kleinpeter

1997

Struct Chem

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The restricted rotation about the partial C,N double bond in 2-chloro-6-NR2-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations. Ab initio calculations at the HF/6-31G* level were carded out using a continuum model to take solvent effects into account. The delocalization of r-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR 2 substituents (pyrrolidino > dimethylamino > morpholidino > piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR2 substituents in the GS for the restricted rotation.

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“…In addition, the high energy barrier of the s- cis –s- trans isomerization (84–89 kJ/mol) stabilizes the amide conformers kinetically ( Scheme 1 ) [ 3 ]. By comparison of the amide rotational rates of peptidyl-Pro with the ones of the closest Pro structural analogues, azetidine-2-carboxylic acid (norproline) and pipecolic acid (homoproline) [ 4 ], it appears that the high isomerization barrier is a feature associated with the 5-membered pyrrolidine ring of Pro [ 5 ].…”

Section: Introductionmentioning

confidence: 99%

cis–trans-Amide isomerism of the 3,4-dehydroproline residue, the ‘unpuckered’ proline

Kubyshkin¹,

Budiša²

2016

Beilstein J. Org. Chem.

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SummaryProline (Pro) is an outstanding amino acid in various biochemical and physicochemical perspectives, especially when considering the cis–trans isomerism of the peptidyl-Pro amide bond. Elucidation of the roles of Pro in chemical or biological systems and engineering of its features can be addressed with various Pro analogues. Here we report an experimental work investigating the basic physicochemical properties of two Pro analogues which possess a 3,4-double bond: 3,4-dehydroproline and 4-trifluoromethyl-3,4-dehydroproline. Both indicate a flat pyrroline ring in their crystal structures, in agreement with previous theoretical calculations. In solution, the peptide mimics exhibit an almost unchanged equilibrium of the trans/cis ratios compared to that of Pro and 4-trifluoromethylproline derivatives. Finally we demonstrate that the 3,4-double bond in the investigated structures leads to an increase of the amide rotational barriers, presumably due to an interplay with the transition state.

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The solution conformation of cyclic β-casomorphin-5 analogues

Cited by 7 publications

References 25 publications

Interaction of M3+ lanthanide cations with amide, urea, thioamide and thiourea ligands: a quantum mechanical study †

Interaction of M3+ lanthanide cations with amide, urea, thioamide and thiourea ligands: a quantum mechanical study †

Restricted rotation about partial C,N double bonds

cis–trans-Amide isomerism of the 3,4-dehydroproline residue, the ‘unpuckered’ proline

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