Acetone-sensitized photodimenzation of 3-carene-2,5-dione

1970 ◽  
Vol 48 (10) ◽  
pp. 1526-1532 ◽  
Author(s):  
Ian W. J. Still ◽  
C. J. Macdonald ◽  
(Mrs.) Y.-N. Oh
Keyword(s):  
Spectroscopic Study ◽  
Ultraviolet Irradiation ◽  
Head Orientation ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

Ultraviolet irradiation of 3-carene-2,5-dione 1 in acetone has been found to yield three cyclobutanetype photodimers. A detailed spectroscopic study of these compounds has shown that the two most abundant dimers possess the head-to-head orientation. The head-to-head dimers have been shown to possess the anti-anti-anti and syn-anti-syn structures 10 and 8 respectively, while the minor, head-to-tail product has one of the corresponding structures 9 or 11. In all three cases, the cyclobutane and cyclohexane rings are cis-fused. Nuclear Overhauser effects enable structures 8 and 10 to be specifically assigned to dimer B and dimer A, respectively.

Regiospecificity and Stereoselectivity in the Photodimerization of 2,3-Dihydro-2,6-dimethyl-4-pyrone

1973 ◽  
Vol 51 (8) ◽  
pp. 1267-1277 ◽  
Author(s):  
Peter Yates ◽  
Donald J. MacGregor
Keyword(s):  
Aqueous Solution ◽  
Ultraviolet Irradiation ◽  
Spectroscopic Methods ◽  
Magnetic Spectrum ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dimerization Reaction

Ultraviolet irradiation of 2,3-dihydro-2,6-dimethyl-4-pyrone in aqueous solution leads to the regiospecific and stereoselective formation of three cis–anti–cis photodimers of the cyclobutane type, i.e0., octahydro-2,7-8a,8b-tetramethylcyclobuta[1,2-b:4,3-b′]dipyran-4,5-diones, whose structures have been established by chemical and spectroscopic methods, including studies of nuclear Overhauser effects in the proton magnetic spectrum of one of them. The dimers undergo photointerconversion, and it is proposed that this process involves photoreversion to monomer and that the reversibility of the dimerization reaction may be a factor in determining the regiochemistry and stereochemistry of the photodimers. A bisdehydro product prepared from the dimers of the dihydropyrone has been shown to undergo photocleavage to 2,6-dimethyl-4-pyrone, and it is proposed that reversibility may also be a factor affecting the course of the photodimerization of this pyrone.

scholarly journals NMR solution conformation of heparin-derived tetrasaccharide

1996 ◽  
Vol 318 (1) ◽  
pp. 93-102 ◽  
Author(s):  
Dmitri MIKHAILOV ◽  
Kevin H. MAYO ◽  
Ioncho R. VLAHOV ◽  
Toshihiko TOIDA ◽  
Azra PERVIN ◽  
...  
Keyword(s):  
Chair Conformation ◽  
Coupling Constants ◽  
Solution Conformation ◽  
1H And 13C Nmr ◽  
Small Deviations ◽  
J Coupling Constants ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Dynamics Simulations ◽  
Ring Conformations

The solution conformation of the homogeneous, heparin-derived tetrasaccharide ΔUA2S(1 → 4)-α-d-GlcNpS6S(1 → 4)-α-l-IdoAp2S(1 → 4)-α-d-GlcNpS6S (residues A, B, C and D respectively, where IdoA is iduronic acid) has been investigated by using 1H- and 13C-NMR. Ring conformations have been defined by J-coupling constants and inter-proton nuclear Overhauser effects (NOEs), and the orientation of one ring with respect to the other has been defined by inter-ring NOEs. NOE-based conformational modelling has been done by using the iterative relaxation matrix approach (IRMA), restrained molecular dynamics simulations and energy minimization to refine structures and to distinguish between minor structural differences and equilibria between various ring forms. Both glucosamine residues B and D are in the 4C1 chair conformation. The 6-O-sulphate group is oriented in the gauche–trans configuration in the D ring, whereas in the B ring the gauche–gauche rotomer predominates. Uronate (A) and iduronate (C) residues are mostly represented by 1H2 and 2S0 twisted boat forms, respectively, with small deviations in expected coupling constants and NOEs suggesting minor contributions from other A and C ring conformations.

Structure assignment of some 3,4′-diquinolinyl sulfides studied by Nuclear Overhauser Effects, X-ray analysis and reactions with sodium methoxide

2010 ◽  
Vol 109 (10) ◽  
pp. 509-514 ◽  
Author(s):  
Stanislaw Boryczka ◽  
Andrzej Maślankiewicz ◽  
Miroslaw Wyszomirski ◽  
Teresa Borowiak ◽  
Maciej Kubicki
Keyword(s):  
Sodium Methoxide ◽  
X Ray ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Structure Assignment

scholarly journals Comparison of Methods for Bulk Automated Simulation of Glycosidic Bond Conformations

2020 ◽  
Vol 21 (20) ◽  
pp. 7626
Author(s):  
Victor Stroylov ◽  
Maria Panova ◽  
Philip Toukach
Keyword(s):  
Density Functional ◽  
Structural Features ◽  
Functional Theory ◽  
Conformational Ensembles ◽  
Explicit Solvent ◽  
Empirical Force Field ◽  
Automated Simulation ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Accuracy Speed

Six empirical force fields were tested for applicability to calculations for automated carbohydrate database filling. They were probed on eleven disaccharide molecules containing representative structural features from widespread classes of carbohydrates. The accuracy of each method was queried by predictions of nuclear Overhauser effects (NOEs) from conformational ensembles obtained from 50 to 100 ns molecular dynamics (MD) trajectories and their comparison to the published experimental data. Using various ranking schemes, it was concluded that explicit solvent MM3 MD yielded non-inferior NOE accuracy with newer GLYCAM-06, and ultimately PBE0-D3/def2-TZVP (Triple-Zeta Valence Polarized) Density Functional Theory (DFT) simulations. For seven of eleven molecules, at least one empirical force field with explicit solvent outperformed DFT in NOE prediction. The aggregate of characteristics (accuracy, speed, and compatibility) made MM3 dynamics with explicit solvent at 300 K the most favorable method for bulk generation of disaccharide conformation maps for massive database filling.

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