Structures of three minor alkaloids of Fumariaofficinalis L.

1969 ◽  
Vol 47 (19) ◽  
pp. 3593-3599 ◽  
Author(s):  
D. B. MacLean ◽  
R. A. Bell ◽  
J. K. Saunders ◽  
C.-Y. Chen ◽  
R. H. F. Manske
Keyword(s):  
Ring System ◽  
Model Systems ◽  
Spectroscopic Methods ◽  
Structural Problem ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects

The structures of fumaricine, fumaritine, and fumariline, minor alkaloids of F. officinalis, have been deduced by spectroscopic methods and by comparison with model systems. Nuclear Overhauser effects observed in these systems aided in the solution of the structural problem. The three alkaloids have a common ring system and are structurally related to ochotensimine.

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.

Analysis of short interproton distances in proline peptides as a guide in the interpretation of nuclear Overhauser effects

1988 ◽  
Vol 53 (11) ◽  
pp. 2801-2809 ◽  
Author(s):  
Chandrashekharan Ramakrishnan ◽  
Ramanathan Sowdhamini ◽  
Padmanabhan Balaram
Keyword(s):  
Nuclear Overhauser Effect ◽  
Model Systems ◽  
Pyrrolidine Ring ◽  
Ramachandran Map ◽  
Overhauser Effect ◽  
Ring Puckering ◽  
Nuclear Overhauser ◽  
Nuclear Overhauser Effects ◽  
Interproton Distances ◽  
Helical Region

The conformational dependence of interproton distances in model proline peptides has been investigated in order to facilitate interpretation of the results of Nuclear Overhauser Effect (NOE) studies on such peptides. For this purpose two model systems, namely, Ac-Pro-NHMe and Ac-Pro-X-NHMe have been chosen and used. In the former, short interproton distances detectable in NOE experiments permit a clear distinction between conformations with Pro ψ = -300 (helical region) and those in which ψ is around 1200 (polyproline region). For the latter, the variation of distances between the protons of methyl amide and the Pro ring have been studied by superimposing on the Ramachandran map in the (φ3, ψ3) plane. The results show that β-turns and non-β-turn conformations can be readily distinguished from NOE data and such long range NOEs should be detectable for specific non-β-turn conformations. NOEs involving Cβ and Cγ protons are particularly sensitive to the state of pyrrolidine ring puckering.

Pyrido [2,3-d] thieno [3,2-b] [6H]thiopyran - ein neues heterocyclisches Ringsystem [1] / Pyrido [2,3-d]thieno[3,2-b] [6 H]thiopyran - a New Heterocyclic Ring System [1]

1979 ◽  
Vol 34 (11) ◽  
pp. 1573-1575 ◽  
Author(s):  
Klaus Beelitz ◽  
Klaus Praefcke ◽  
Salo Gronowitz
Keyword(s):  
Uv Irradiation ◽  
Benzene Solution ◽  
Heterocyclic Ring ◽  
Ring System ◽  
Spectroscopic Methods ◽  
System 1

Abstract UV irradiation of S-(3′-thienyl)2-chloro-thionicotinate (1) in benzene solution leads via dehydrohalogenation and cy clization in competition to α-cleavage to formation of thio-lactone 2 besides aldehyde 3 and disulphide 4. 2 contains a new heterocyclic ring system which has been confirmed by spectroscopic methods.

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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