Conformational analysis of seven-membered 1-N-iminosugars by NMR and molecular modelling

2012 ◽  
Vol 36 (4) ◽  
pp. 1008 ◽  
Author(s):  
Javier Pérez-Castells ◽  
Marco Fontanella ◽  
Ana Ardá ◽  
F. Javier Canãda ◽  
Matthieu Sollogoub ◽  
...  
Keyword(s):  
Conformational Analysis ◽  
Molecular Modelling

Conformational analysis of glutamic acid analogues as probes of glutamate receptors using molecular modelling and NMR methods. Comparison with specific agonists

1997 ◽  
Vol 5 (2) ◽  
pp. 335-352 ◽  
Author(s):  
Nathalie Todeschi ◽  
Josyane Gharbi-Benarous ◽  
Francine Acher ◽  
Valery Laure ◽  
Jean-Philippe Pin ◽  
...  
Keyword(s):  
Conformational Analysis ◽  
Glutamic Acid ◽  
Glutamate Receptors ◽  
Molecular Modelling ◽  
Methods Comparison ◽  
Nmr Methods

Synthesis, high-field NMR, X-ray structure, and conformational analysis of a 10-membered diamide disulfide ring

1997 ◽  
Vol 75 (2) ◽  
pp. 140-161 ◽  
Author(s):  
Rabindranath B. Maharajh ◽  
James P. Snyder ◽  
James F. Britten ◽  
Russell A. Bell
Keyword(s):  
Conformational Analysis ◽  
Molecular Modelling ◽  
Density Functional ◽  
Nuclear Overhauser Effect ◽  
Chemical Shifts ◽  
Lone Pair ◽  
Oxidative Cyclization ◽  
Conformational Space ◽  
Aromatic Solvent ◽  
X Ray

N,N′-[Dimethyl-(2,2′-dithiobisacetyl)]ethylenediamine (1) has been synthesized in 30% overall yield from N,N′-dimethylethylenediamine and thioacetic acid by an improved procedure involving simultaneous deprotection and oxidative cyclization with iodine. This cyclic diamide disulfide exists in solution as a mixture of two Z,Z and one Z,E disulfide, and amide ring conformers and has been characterized by nuclear Overhauser effect (NOE), 1H–1H, 1H–13C shift-correlated 2D-NMR and molecular modelling studies. Among the Z,Z ring conformers Z,Z1 and Z,Z2, the former predominates and interconverts with the latter isomer by rotation about the S—S bond with an activation energy of 14.5 ± 1.3 kcal/mol. Coalescence of N-CH3 signals occurred at ca. 127 °C (500 MHz), which corresponded to an approximate barrier to amide rotation of 19.3 kcal/mol. Aromatic solvent-induced shifts in C6D6 corroborated molecular mechanics and NOE predictions of amide stereochemistry. The structure of the Z,E stereoisomer of 1 has been determined by single-crystal X-ray diffraction at 296 K. A large geminal N-CH2 inequivalence (>2 ppm in CDCl3) was observed for the Z,Z conformers. Proton chemical shifts have been calculated for the conformers of 1 and related molecular fragments with DFT/GIAO theory. Absolute chemical shifts are modelled within 0.2 ppm of experiment. The unusual nonequivalence of geminal N-CH2 and S-CH2 protons can be understood as a combination of shielding mechanisms derived from short N-methyl contacts, amide group orientation, and sulfur lone-pair disposition. An implication of these results is the possibility of using α-CH (and eventually α-CH) shifts to probe the local conformational space in cyclic peptides and other conformationally constrained rings. Keywords: amide/disulfide rotamers, conformational analysis, density functional theory, DFT/GIAO NMR shift calculations, methylene nonequivalence, molecular modelling.

Conformational analysis of azithromycin by nuclear magnetic resonance spectroscopy and molecular modelling

Tetrahedron ◽  
1993 ◽  
Vol 49 (3) ◽  
pp. 721-730 ◽  
Author(s):  
Gorjana Lazarevski ◽  
Mladen Vinković ◽  
Gabrijela Kobrehel ◽  
Slobodan Đokić ◽  
Biserka Metelko ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Conformational Analysis ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Molecular Modelling ◽  
Resonance Spectroscopy ◽  
Nuclear Magnetic
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