Solvation effects on conformational equilibria. Studies related to the conformational properties of 2-methoxytetrahydropyran and related methyl glycopyranosides

1969 ◽  
Vol 47 (23) ◽  
pp. 4427-4439 ◽  
Author(s):  
R. U. Lemieux ◽  
A. A. Pavia ◽  
J. C. Martin ◽  
K. A. Watanabe
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Methoxy Group ◽  
Resonance Spectrum ◽  
Optical Rotation ◽  
The Other ◽  
Anomeric Effect ◽  
Methyl Group ◽  
Profound Influence ◽  
Conformational Equilibria ◽  
Conformational Properties

Further evidence is presented (8) that changes in optical rotation at the D-line of sodium which occur with changes in solvent largely reflect changes in conformational equilibria.Changes in the nuclear magnetic resonance spectrum of 4,4,5,5-tetradeuterio-2-methoxytetra-hydropyran and in the rotation of s(+)-2-methoxytetrahydropyran with changes in solvent are interpreted to show that solvents capable of donating a hydrogen to a hydrogen bond have an effect on the magnitude of the anomeric effect which is greater than that resulting from the change in the dielectric constant of the solvent. In the case of methyl 2-deoxypyranosides with the methoxy group in axial orientation, water appears to have an especially profound influence in stabilizing that orientation of the methyl group which brings it into gauche relationship with both the C2-grouping and the anomeric hydrogen; that is, counter to the anomeric effect.The methyl 2-deoxy-β-L-erythro-pentopyranoside was synthesized from di-O-acetyl-L-arabinal by way of an iodomethoxylation. Deuterolysis of the resulting 1,2-trans-acetylated methyl 2-deoxy-2-iodopentosides is shown to proceed in one case with extensive inversion of configuration and with extensive retention in the other case and offers a route to the preparation of 2-deoxy-2-deuterio-erythro-pentose with a high proportion (>75%) of the diastereoisomer with the arabino-configuration.

scholarly journals Isolation, determination of structure and synthesis of the acid-labile conjugate of aldosterone

1976 ◽  
Vol 157 (1) ◽  
pp. 1-14 ◽  
Author(s):  
P C Carpenter ◽  
V R Mattox
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Methyl Ester ◽  
Resonance Spectrum ◽  
Optical Rotation ◽  
The Other ◽  
Acetate Methyl ◽  
Human Volunteers ◽  
Homogeneous Acid ◽  
Acid Labile

1. After administration of 600mg of 3H-labelled aldosterone to human volunteers, 57 mg of homogeneous acid-labile conjugate was isolated from the urine and identified as aldosterone 18 beta-D-glucosiduronic acid. 2. Esterification and acetylation of the conjugate gave a tetra-acetate methyl ester, which, by measurement of the optical rotation and nuclear-magnetic-resonance spectrum, was shown to be a beta-glucosiduronate. This tetra-acetate methyl ester was synthesized in approx. 10% yield by the Koenigs-Knorr procedure. 3. Removal of the acetyl and methyl ester groups from the tetra-acetate methyl ester with alkali was accompanied by almost complete isomerization at C-17 to give 17-isoaldosterone 18 beta-D-glucosiduronic acid. 4. To prevent inversion at C-17 during removal of the acetate and ester groups of beta-glucosiduronate (a) the 3,20-disemicarbazone was prepared, (b) the acetate and ester groups were removed from the disemicarbazone by treatment with alkali, and (c) the semicarbazone groups were removed from the product at pH 2.0, and aldosterone 18 beta-D-glucosiduronic acid was obtained in 47% overall yield. 5. In the presence of components used to synthesize beta-glucosiduronate by the Koenigs-Knorr reaction this substance is converted slowly into the alpha-glucosiduronate; this conversion is responsible, in part, for the low yield of beta-glucosiduronate. 6. Two additional conjugates were obtained in the Koenigs-Knorr reaction; a provisional structure was assigned to one substrate. The other substance is a C-18 alpha-glucosiduronate. Removal of the acetyl and ester groups from C-18 alpha-glucosiduronate gave the alpha-glucosiduronic acid in 84% yield and the 17-isoaldosterone alpha-glucosiduronic acid in 12% yield. 7. The rate at which several types of beta-glucuronidase hydrolyse the foregoing steroidal alpha- and beta-glucosiduronic acids is given.

Conformational analysis of 2-substituted methylenecyclohexanes and 3-substituted cyclohexenes and the anomeric effect

1977 ◽  
Vol 55 (6) ◽  
pp. 1015-1023 ◽  
Author(s):  
Jean Lessard ◽  
Phan Viet Minh Tan ◽  
Robert Martino ◽  
John K. Saunders
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Double Bond ◽  
Magnetic Resonance ◽  
Conformational Analysis ◽  
Methoxy Group ◽  
Anomeric Effect ◽  
Magnetic Resonance Data ◽  
Electronegative Substituent ◽  
Axial Conformer ◽  
Resonance Data

The analysis of the 13C and 1H nuclear magnetic resonance data of 2-substituted methylenecyclohexanes and 3-substituted cyclohexenes demonstrates that a double bond stabilizes the axial conformer for an electronegative substituent. Introduction of a methoxy group on the double bond further increases the relative stability of the axial conformer. These results are interpreted in terms of the 'double bond – no bond' resonance.

Correlation of specific rotation with conformation. A new approach to the study of conformational equilibria

1968 ◽  
Vol 46 (8) ◽  
pp. 1453-1455 ◽  
Author(s):  
R. U. Lemieux ◽  
A. A. Pavia
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Optical Rotation ◽  
Specific Rotation ◽  
New Approach ◽  
Conformational Equilibria ◽  
Nuclear Magnetic

The marked changes in optical rotation which occur on dissolving the methyl 2-deoxy-α-L-and 3-deoxy-β-L-erythro-pentopyranosides in a variety of solvents including chloroform, acetone, acetonitrile, pyridine, dimethylsulfoxide, and water were found by nuclear magnetic resonance to result almost exclusively from changes in conformational equilibria. The changes in rotation are in agreement with those expected from Brewster's rules.

Long-range 13C,1H and 13C,19F coupling constants as indicators of the conformational properties of 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole

1984 ◽  
Vol 62 (8) ◽  
pp. 1592-1597 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen ◽  
Timothy A. Wildman ◽  
James Peeling ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Long Range ◽  
Methoxy Group ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Dynamic Nmr ◽  
Methyl Group ◽  
Conformational Properties ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Rotor Model

Long-range spin–spin coupling constants over six bonds between 13C nuclei in the methyl group and ring protons or 19F nuclei in the para position are reported for 4-fluoroanisole, 2,3,5,6-tetrafluoroanisole, and pentafluoroanisole in solution. The couplings are σ–π electron mediated, as indicated by INDO MO FPT computations and by measurements on anisole, 2,6-dibromoanisole, 2,6-dichloroanisole, 2,6-dibromo-4-fluoroanisole, and 2,6-dibromo-4-methylanisole. On the basis of the measured coupling magnitudes and a hindered rotor model, it is concluded that the barrier to internal rotation about the [Formula: see text] bond in 4-fluoroanisole lies near 6 kcal/mol, is nearly zero in the tetrafluoroanisole, and is somewhat less than 1 kcal/mol in the pentafluoroanisole. In the latter, the preferred conformation is that in which the methoxy group lies in a plane perpendicular to the pentafluorophenyl plane. Some inconclusive dynamic nmr experiments on anisole, including T1ρ measurements, are briefly discussed.

THE STRUCTURE OF STRYCHNOSPERMINE EVIDENCE FROM DOUBLE IRRADIATION AND VARIABLE TEMPERATURE N.M.R.

1963 ◽  
Vol 41 (4) ◽  
pp. 883-888 ◽  
Author(s):  
F. A. L. Anet
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrum ◽  
Room Temperature ◽  
Resonance Spectrum ◽  
Variable Temperature ◽  
Aromatic Proton ◽  
Methyl Group ◽  
Restricted Rotation ◽  
Acetyl Group

The nuclear magnetic resonance spectrum of strychnospermine has been measured at −20°, room temperature, and at +80°. The changes observed are attributed to restricted rotation in the N-acetyl group. At room temperature the rate of rotation is such that the band of one aromatic proton is extremely broad and therefore almost invisible. Double irradiation has been used to determine the environment of the C-methyl group of the alkaloid. The n.m.r. results confirm the structure previously postulated.

Structural properties of modified deoxyadenosine structures in solution. Impact of the gauche and anomeric effects on the furanose conformation

1987 ◽  
Vol 65 (9) ◽  
pp. 2089-2094 ◽  
Author(s):  
Leo H. Koole ◽  
Henk M. Buck ◽  
Agnes Nyilas ◽  
Jyoti Chattopadhyaya
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Variable Temperature ◽  
Nuclear Magnetic Resonance Study ◽  
Modified Nucleosides ◽  
Anomeric Effect ◽  
Magnetic Resonance Study ◽  
Temperature Changes ◽  
Gauche Effect ◽  
Conformational Properties ◽  
Anomeric Effects

A variable temperature high resolution 1H nuclear magnetic resonance study (at 300 or 500 MHz) of the two modified nucleosides 9-(2′-deoxy-β-D-threo-ribofuranosyl)-adenine (1) and 9-(3′-deoxy-β-D-threo-ribofuranosyl)-adenine (2) has been performed. It was found that the furanose conformation in 1 and 2 can be best described as a rapid North (N) [Formula: see text] South (S) equilibrium that is biased toward the N-form. For 1, a marked temperature dependence of the [Formula: see text] equilibrium was found, whereas the furanose conformation in 2 is virtually insensitive to temperature changes. Comparison of these results with the well-known conformational properties of the natural nucleosides 2′-deoxyadenosine (2′-dA) and 3′-deoxyadenosine (3′-dA) revealed that the net result of the gauche effect and the anomeric effect is of major importance in determining the furanose conformation. A brief discussion in terms of the thermodynamic parameters that govern the [Formula: see text] equilibria in the investigated nucleosides is given.

scholarly journals Bioactive Polyketides From the Potato Endophytic Fungus Aspergillus carneus

2020 ◽  
Vol 15 (12) ◽  
pp. 1934578X2098522
Author(s):  
Xian Zhang ◽  
Fa-Lei Zhang ◽  
Xing Wu ◽  
Ke Ye ◽  
Xiao Lv ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Nuclear Magnetic Resonance ◽  
Antioxidant Activity ◽  
Endophytic Fungus ◽  
Spectroscopic Data ◽  
Plant Pathogens ◽  
Inhibitory Concentration ◽  
Optical Rotation ◽  
Nitric Oxide Production ◽  
Effective Antioxidant

A previously undescribed polyketide (1) and 3 known analogs (2-4) were obtained from cultures of the potato endophytic fungus Aspergillus carneus. The structures were elucidated on the basis of extensive nuclear magnetic resonance spectroscopic data. The absolute configuration of 1 was further determined by electronic circular dichroism and optical rotation calculations. Compounds 1-4 showed moderate antifungal activity against plant pathogens. Compounds 1, 2, and 4 inhibited nitric oxide production in lipopolysaccharide-stimulated RAW264.7 cells, with half-maximal inhibitory concentration values of 13.36, 30.16, and 51.47 µM, respectively. Compound 4 showed effective antioxidant activity.

Sign in / Sign up

Export Citation Format

Share Document