Conformation of 5-Amino-5-deoxypentonolactams

1997 ◽  
Vol 62 (12) ◽  
pp. 1919-1930 ◽  
Author(s):  
Karel Kefurt ◽  
Jaroslav Havlíček ◽  
Michaela Hamerníková ◽  
Zdeňka Kefurtová ◽  
Hana Votavová
Keyword(s):  
Carbonyl Group ◽  
Chemical Shifts ◽  
Cd Spectroscopy ◽  
Coupling Constants ◽  
Cd Spectra ◽  
Vicinal Coupling Constants ◽  
Predominant Conformation ◽  
Karplus Relationship

Four configuration isomers of 5-amino-5-deoxy-D-pentonolactam 1a-4a and their tri-O-acetyl derivatives 1b-4b were studied using NMR and CD spectroscopy. For all compounds chemical shifts of the 1H and 13C nuclei as well as of vicinal coupling constants were obtained. Comparison of the observed 3J(H,H) with those calculated for various conformations by a modified Karplus relationship led to the assignment of predominant conformation 3H4(D) or 4H3(D) to the lactams 1a-4a and 1b-4b in solution. The most important factor for determining the conformation seems to be the pseudoequatorial position of the substituent on the carbon next to the carbonyl group. The results of the CD spectra of the lactams 1a-4a in water, interpreted according to the currently used rules, agreed with the NMR results.

Conformation of 6-amino-6-deoxyhexonolactams

1989 ◽  
Vol 54 (8) ◽  
pp. 2156-2170 ◽  
Author(s):  
Karel Kefurt ◽  
Zdeňka Kefurtová ◽  
Petr Trška ◽  
Karel Bláha ◽  
Ivo Frič ◽  
...  
Keyword(s):  
Carbonyl Group ◽  
Chemical Shifts ◽  
Cd Spectroscopy ◽  
Coupling Constants ◽  
Equatorial Position ◽  
Cd Spectra ◽  
Vicinal Coupling Constants ◽  
Predominant Conformation ◽  
Karplus Relationship

Eight configurational isomers of 6-amino-6-deoxyhexonolactam Ia-VIIIa and their tetra-O-acetyl derivatives Ib-VIIIb were studied using NMR and CD spectroscopy. For all the compounds most values of chemical shifts of the 1H and 13C nuclei as well as of vicinal coupling constants were obtained. Comparison of the observed values with 3J(H,H) values, calculated for various conformations of the studied compounds by a modified Karplus relationship, led to assignment of predominant conformation 1,NC4(D) or 4C1,N(D) to the lactams Ia-VIIIa and Ib-VIIIb in solution. For the measured set of compounds, the decisive conformation-determining requirement seems to be the equatorial position of substituent on the carbon next to the carbonyl group. The CD spectra of the lactams Ia-VIIIa in water, interpreted according to the currently used rules, in six cases agreed and in two cases disagreed, with the NMR results. The reasons of this discrepancy are discussed.

Neue Untersuchung über Inhaltsstoffe aus Aloe-und Rhamnus-Arten, XV [1] Homonataloin A und B aus Aloe lateritia: Reindarstellung, Konstitutions-und Konfigurationsaufklärung der Diastereomeren / A New Investigation on Constituents of Aloe and Rhamnus Species, XV [1] Hom onataloins A and B from Aloe lateritia: Isolation, Structure and Configurational Determ ination of the Diastereomers

1991 ◽  
Vol 46 (3-4) ◽  
pp. 177-182 ◽  
Author(s):  
Hans-W. Rauwald ◽  
Deo-D. Niyonzima
Keyword(s):  
Chemical Shifts ◽  
Optical Rotation ◽  
Coupling Constants ◽  
Cd Spectra ◽  
Large Coupling ◽  
H Nmr ◽  
Leaf Exudate ◽  
Hydroxyl Protons ◽  
Nmr Signals ◽  
C Nmr

From the leaf exudate of Aloe lateritia ENGLER the C-glucosyl com pounds homonataloin, aloeresin A and aloesin (synon. aloeresin B) were isolated together with the anthraquinone nataloeem odin-8-methylether and spectroscopically identified. Hom onataloin, widely distributed in Aloe species, was separated into homonataloin A and B by combined TLC and DCCC. In their 1 D and 2D 1H NMR spectra only the shifts of the 2′-hydroxyl protons of both glucosyl residues differ significantly, indicative of 10 S (A) resp. 10 S (B) configurations. In both com pounds the anthrone is in β-position of the D-glucopyranosyl, as determined by the large coupling constants of the anomeric protons. The 13C NMR signals are unambiguously assigned by the use of DEPT, APT and gated-decoupling methods. Only the chemical shifts of C -11 and C -14 show significant differences between both diastereomers due to the adjacent 2′-sugar hydroxyls. The two homonataloins differ mostly in optical rotation and circulardichroism due to different configurations at C - 10 of the anthrone part. The absolute configurations of the diastereomers are determined by correlation of their CD spectra with the CD spectra of the structural analogues 7-hydroxyaloins A and B, which shows that hom onataloin A is the 10 S, 1′S-compound and that homonataloin B has 10 R, 1′S-configuration.

The 1H NMR spectra and the conformation of 1,6-anhydro-β-D-hexopyranoses and their triacetates

1979 ◽  
Vol 44 (6) ◽  
pp. 1949-1964 ◽  
Author(s):  
Miloš Buděšínský ◽  
Tomáš Trnka ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Shift Reagent ◽  
Point Of View ◽  
Coupling Constants ◽  
Lanthanide Shift Reagent ◽  
Pyranose Ring ◽  
H Nmr ◽  
Vicinal Coupling Constants

The 1H NMR spectra of 1,6-anhydro-β-D-hexopyranoses and their triacetates, measured in hexadeuteriodimethyl sulfoxide or deuteriochloroform, confirmed the existence of these compounds in 1C4(D) conformations, with the pyranose ring partly planarized in dependence on the configuration of the substituents in positions C(2), C(3) and C(4). The effects of the substituents on the chemical shifts and the adjusted relationship for the dependence of vicinal coupling constants on the torsion angle are discussed in detail from the point of view of the determination of the configuration and the conformation of 1,6-anhydro-β-D-hexopyranoses and their derivatives. The 1H NMR spectra of triacetates were also measured in the presence of the lanthanide shift reagent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione) europium (III) [Eu.(FOD)3].

An 1H NMR conformational analysis of 3-phenylpentane in solution

1993 ◽  
Vol 71 (4) ◽  
pp. 520-525 ◽  
Author(s):  
Ted Schaefer ◽  
Lina B.-L. Lee
Keyword(s):  
Alkyl Chain ◽  
Chemical Shifts ◽  
Close Approach ◽  
Solvent Mixture ◽  
Coupling Constants ◽  
Coupling Constant ◽  
Proton Proton ◽  
Vicinal Coupling Constants ◽  
Proton Coupling ◽  
Proton Chemical Shifts

Some 30 proton chemical shifts and proton–proton coupling constants are reported for a 4.7 mol% solution of 3-phenylpentane in a CS2/C6D12/TMS solvent mixture at 300 K. The long-range coupling constant over six formal bonds between the methine and para protons is used to deduce an apparent twofold barrier of 15.0 ± 0.3 kJ/mol to rotation about the Csp2—Csp3 bond, at least twice as large as that for isopropylbenzene in solution. AM1 computations agree with experiment in finding the conformation of lowest energy as that in which the methine C—H bond is situated in the phenyl plane, but predict a barrier height of only 13.9 kJ/mol. The vicinal coupling constants are consistent with a fractional population, 0.38(2), of the TT conformer, that in which all the carbon atoms of the alkyl chain lie in a plane. A doubly degenerate conformer, TG+(G−T), in which one methyl group is twisted away from the phenyl substituent, then has a fractional population of 0.62(2). The assumption that only these three conformers are present is tested with the signs and magnitudes of the four different coupling constants over four bonds. These coupling constants are consistent with the absence of significant proportions of the other six all-staggered conformers. These six are characterized by a close approach of the methyl groups (1,5 interactions) or by proximity of the methyl and phenyl moieties.

Nuclear magnetic resonance spectra of pyrrolizidine alkaloids. II. The pyrrolizidine nucleus in ester and non-ester alkaloids and their derivatives

1965 ◽  
Vol 18 (10) ◽  
pp. 1625 ◽  
Author(s):  
CCJ Culvenor ◽  
WG Woods
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Pyrrolizidine Alkaloids ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Vicinal Coupling Constants ◽  
Nuclear Magnetic Resonance Spectra ◽  
Saturated Ring ◽  
Magnetic Resonance Spectra

Chemical shifts and coupling constants are tabulated for the protons of the pyrrolizidine nucleus in 40 pyrrolizidine alkaloids and derivatives. The effect of acylation of hydroxyl substituents on C7 and C9 and the very large difference in chemical shift of the H9 protons in the macrocyclic diester alkaloids is discussed. The direction of buckling of the saturated ring can be ascertained from the H5,H6 vicinal coupling constants or from the width of the H7 multiplet if H7 bears an oxygen substituent. In general, retronecine derivatives are exo-buckled whereas heliotridine derivatives consist of interconverting exo- and endo-buckled forms.

Flavan derivatives. XXI. Nuclear magnetic resonance spectra, configuration, and conformation of flavan derivatives

1968 ◽  
Vol 21 (8) ◽  
pp. 2059 ◽  
Author(s):  
JW Clark-Lewis
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Heterocyclic Ring ◽  
Coupling Constants ◽  
Vicinal Coupling Constants ◽  
Nuclear Magnetic Resonance Spectra ◽  
Configuration And Conformation ◽  
Magnetic Resonance Spectra ◽  
Nuclear Magnetic

Nuclear magnetic resonance spectra of 80 compounds belonging to several classes of flavan derivative have been analysed, and chemical shifts and coupling constants of heterocyclic ring protons and aromatic protons are tabulated and discussed. Compounds examined include flav-2-enes, flav-3-enes, 3-substituted flavanones and flavans, 2- and 4-substituted isoflavans, 3,4-disubstituted flavans, and flavan-4-ols. The geometrical configurations of substituents in the heterocyclic ring follow unequivocally from the magnitudes of the vicinal coupling constants.

THE CONFORMATIONS IN SOLUTION OF trans-CYCLOHEXENE DIHALIDES AND cis- AND trans-1,2-CYCLOHEXANEDIOLS AND DERIVATIVES

1964 ◽  
Vol 42 (4) ◽  
pp. 893-910 ◽  
Author(s):  
R. U. Lemieux ◽  
J. W. Lown
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spectral Parameters ◽  
Conformational Equilibria ◽  
Karplus Relationship ◽  
In Trans ◽  
Cis And Trans ◽  
Isopropylidene Derivatives ◽  
Derivatives Of

trans-1,4,4-Trideuteriocyclohexene dichloride, dibromide, and diiodide and the 1,4,4-trideuterio-cis- and trans-1,2-cyclohexanediols together with their O-acetyl, O-tosyl, and O-isopropylidene derivatives were synthesized. Their nuclear magnetic resonance (NMR) spectral parameters were obtained with a spectrometer operating at 100 Mc.p.s. and employing double irradiation to establish the chemical shifts and the signs of the coupling constants. The interpretation of the data according to expectations based on the Karplus relationship, for dihedral angles and coupling constants, support the conformational equilibria assigned to the trans-dichloride and trans-dibromide of cyclohexene on the basis of dipole moment measurements (previously published results). The results indicate that trans-cyclohexene diiodide exists to about 84% in the diaxial conformation. In the case of the 1,2-cis-disubstituted cyclohexanes, the occurrence of the signal for the 3-hydrogen in trans relation to the 2-hydrogen at lower field than its geminal 3-hydrogen is assigned to the deshielding influence on the 3-hydrogen when in axial orientation by an opposing axial oxygen at the 1-position. Support for this contention was obtained by determination of the chemical shifts of the geminal hydrogens at the 3- and 5-positions of the cis- and trans-4-t-butyl-2,2,6,6-tetradeuterio-1-methylcyclohexanols. The conformational equilibria indicated for the 1,2-diol, 1,2-diacetoxy, and 1,2-ditosyloxy trans derivatives of 1,4,4-trideuteriocyclohexane by NMR parameters obtained from the spectrum of the O-isopropylidene derivatives of the trans-diol allowed conclusions regarding the non-bonded interaction energies involved. The Karplus relation had to be adjusted to the form, [Formula: see text] and [Formula: see text] to accommodate the results. Solvent effects on conformation are noted. Also, the investigation provided further evidence for the opposite signs of the coupling constants for geminal and vicinal hydrogens. A consideration of the chemical shifts observed for a variety of derivatives of cyclohexanol appears to indicate that intramolecular shielding effects are better accounted for on the basis of neighboring atomic groupings than on the basis of individual chemical bonds.

Discussion on 13C nuclear magnetic resonance spectra of structurally rigid cyclonucleosides. Violation of Karplus relationship between 3JC,H and dihedral angles

1984 ◽  
Vol 62 (8) ◽  
pp. 1555-1557 ◽  
Author(s):  
Jun Uzawa ◽  
Kentaro Anzai
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Coupling Constants ◽  
Dihedral Angles ◽  
Vicinal Coupling Constants ◽  
Nuclear Magnetic Resonance Spectra ◽  
13C Nuclear Magnetic Resonance ◽  
Karplus Relationship ◽  
Derivatives Of ◽  
C Nmr

Using structurally rigid cyclonucleoside derivatives of adenosine, the effect of the oxygen functional groups on the vicinal coupling constants between carbon and hydrogen in, 13C nmr was investigated.

Long-range formyl proton coupling constants of 4-X-phenyl formats (X = H, F, CH3, NO2) and 2,6-dichlorophenyl formate. Conformations in solution

1988 ◽  
Vol 66 (8) ◽  
pp. 1787-1793 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Glenn H. Penner
Keyword(s):  
Carbonyl Group ◽  
Long Range ◽  
Chemical Shifts ◽  
Aldehyde Group ◽  
Coupling Constants ◽  
Polar Solvents ◽  
Proton Coupling ◽  
Nitro Derivatives ◽  
Proton Chemical Shifts

The signs and magnitudes of the long-range coupling constants between the formyl and ring protons over five, six, seven, and eight bonds in phenyl formate and its 4-fluoro, 4-methyl, and 4-nitro derivatives are reported. These numbers are combined with CNDO/2 and INDO MO FPT computations of their conformational dependence and with STO-3G MO populational distributions to provide a description of the conformational behaviour of these molecules. The Z conformers, predominantly nonplanar and having the carbonyl group pointing towards the ring, appear to account for more than 95% of the molecules in CS2 solution at 300 K. In polar solvents, significant populations of the E conformers are indicated by the long-range coupling constants. The long-range coupling constants for the formyl proton in 2,6-dichlorophenyl formate are consistent with geometry-optimized STO-3G MO computations, which imply that the Z conformation, with the aldehyde group lying near the plane perpendicular to the benzene plane, is again at least 95% abundant at 300 K. The proton chemical shifts are also consistent with these conclusions.

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