1H and13C NMR assignments and conformational analysis of some tetracyclic compounds with a bicyclo[4.2.0]octane ring system

Arnó, Manuel; Marín, Marta; Zaragozá, Ramón J.

doi:10.1002/(sici)1097-458x(199808)36:8<579::aid-omr344>3.0.co;2-f

Cited by 5 publications

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References 2 publications

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“…Table lists the total energy, the conformer population, and the geometry of the more relevant minimum energy conformers of lippifoliane derivatives 1 − 3 . The percentage distribution for the conformers was estimated by taking into consideration the Boltzmann populations in relation to their DFT energy values as detailed in the Experimental Section, , while a quantitative description of the six-membered rings geometry of 1 − 3 was achieved by using the polar set of parameters proposed by Cremer and Pople . These parameters were calculated with the RICON program, using the DFT coordinates.…”

Section: Resultsmentioning

confidence: 99%

“…4), 379 (33), 377 (66), 375 (34), 335 (10), 299 (9), 298 (49), 297 (79), 296 (57), 295 (73), 294 (10), 218 (16), 227 (100), 216 (71), 215 (77), 203 (81), 201 (83), 173 (99).…”

Section: Methodsunclassified

“…A cyclic equilibrium at 298 K among all the calculated conformers for compounds 1 − 3 was modeled. For example, the case of an equilibrium among three conformers was treated by considering k 1,2 = n 2 / n 1 , k 2,3 = n 3 / n 2 , k 3,1 = n 1 / n 3 , and n 1 + n 2 + n 3 = 1. , Taking into account the Boltzmann equation n i = e -Δ E ( i )/ kT /∑ j e -Δ E ( j )/ kT where Δ E is the DFT energy difference between pairs of conformers, equations n 1 = n 2 e -( E 2 - E 1 / kT ) , n 3 = n 2 e -( E 2 - E 3 / kT ) , and n 2 = 1 − n 1 − n 3 were employed to calculate the conformational populations.…”

Section: Methodsmentioning

confidence: 99%

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Absolute Configuration of Lippifoliane and Africanane Derivatives

et al. 2005

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The absolute configuration of naturally occurring lippifoliane derivatives isolated from the widely used plant Lippia integrifolia was assigned by analysis of the circular dichroism data in combination with density functional theory minimum energy molecular models of (1S,4R,6S,9S,10R)-lippifolian-1-ol-5-one (1), (4R,9S,10R)-lippifoli-1(6)-en-5-one (2), and (4S,9S,10R)-lippifoli-1(6)-en-4-ol-5-one (3) and application of the octant rule for saturated ketone 1 and the helicity rules for alpha,beta-unsaturated ketones 2 and 3. The results were reinforced by the anomalous dispersion effect observed in the X-ray diffraction analysis of (4S,9S,10R)-4,10,11-tribromo-10,11-seco-lippifoli-1(6)-en-5-one (4) prepared from 2. The biogenetic relationships between lippifolianes 1-3 and africanane derivatives 7-9 and 13 isolated from the same species, together with chiroptical data for africananes isolated from the Hepaticae family, complete a stereochemical scenario in relation to the absolute configuration of africananes from L. integrifolia.

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Section: Resultsmentioning

confidence: 99%

“…4), 379 (33), 377 (66), 375 (34), 335 (10), 299 (9), 298 (49), 297 (79), 296 (57), 295 (73), 294 (10), 218 (16), 227 (100), 216 (71), 215 (77), 203 (81), 201 (83), 173 (99).…”

Section: Methodsunclassified

Section: Methodsmentioning

confidence: 99%

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Absolute Configuration of Lippifoliane and Africanane Derivatives

et al. 2005

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“…The molecular mechanics global minima of 5 − 9 and 11 and the three more stable rotameric species of 10 and 12 were submitted to density functional theory calculations (DFT/B3LYP/6-31G*). , Conversions from dihedral angles to vicinal coupling constants ( 3 J HH ) for each conformer were done using the Altona equation. , The population-weighted average coupling constant for each H−C−C−H dihedral fragment was calculated using the equation 3 J calcd = n 1 J 1 + n 2 J 2 + ∑ n i J i . For compounds 10 and 12 a cyclic equilibrium at 298 K between the three selected conformers included in Table was assumed, which afforded k 1,2 = n 2 / n 1 , k 2,3 = n 3 / n 2 , k 3,1 = n 1 / n 3 , and n 1 + n 2 + n 3 = 1. , Taking into account the Boltzmann equation n i = e -Δ E i / kT /∑ j e -Δ E j / kT , where Δ E is the DFT energy difference between pairs of conformers, equations n 1 = n 2 e -( E 2- E 1/ kT ) and n 3 = n 2 e -( E 2- E 3/ kT ) were then solved to calculate the molar fraction of each conformer.…”

Section: Methodsmentioning

confidence: 99%

Conformational Analysis of Sulfur-Containing 6-Deoxy-l-hexose Derivatives by Molecular Modeling and NMR Spectroscopy. A Theoretical Study and Experimental Evidence of Intramolecular Nonbonded Interactions between Sulfur and Oxygen

et al. 2003

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6-Deoxy-l-mannose diphenyldithioacetal (1) unexpectedly gave the rearranged products phenyl 3,4-di-O-acetyl-2-S-phenyl-1,2-dithio-6-deoxy-beta-l-glucopyranoside (9) and 3,4-di-O-acetyl-2,5-anhydro-6-deoxy-l-glucose diphenyldithioacetal (10) upon treatment with acetyl chloride, while 6-deoxy-l-mannose ethylenedithioacetal (3) yielded (4aR,6S,7S,8R,8aS)-7,8-diacetyloxy-6-methylhexahydro-4aH-[1,4]dithiino[2,3b]pyran (11), whose structure was further confirmed by X-ray diffraction, and 3,4-di-O-acetyl-2,5-anhydro-l-rhamnose ethylenedithioacetal (12). The geometry of the four rearranged products as well as that of 1-thio-6-deoxy-l-mannopyranosides 5 and 7 and their acetyl derivatives 6 and 8 was studied by density functional theory (B3LYP/6-31G) molecular models, in combination with a Karplus-type analysis of the NMR vicinal coupling constants, revealing that the six-membered ring of pyranosides 5-9 and 11 exists in a slightly distorted chair conformation (6-13% distortion) and that the conformational behavior of the 2,5-anhydro-6-deoxy-l-glucose dithioacetals 10 and 12 is strongly influenced by the presence of stabilizing intramolecular nonbonded sulfur-oxygen 1,4- and 1,5-interactions. Compounds 9-12 were formed by a molecular rearrangement via sulfonium ion intermediates followed by stereoselective intramolecular cyclizations as formulated by the quantum chemical calculations performed in the present study.

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DFT and NMR parameterized conformation of valeranone

Torres-Valencia

Meléndez-Rodrı́guez

Álvarez-García

et al. 2004

Magnetic Reson in Chemistry

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A Monte Carlo random search using molecular mechanics, followed by geometry optimization of each minimum energy structure employing density functional theory (DFT) calculations at the B3LYP/6-31G* level and a Boltzmann analysis of the total energies, generated accurate molecular models which describe the conformational behavior of the antispasmodic bicyclic sesquiterpene valeranone (1). The theoretical H-C-C-H dihedral angles gave the corresponding 1H, 1H vicinal coupling constants using a generalized Karplus-type equation. In turn, the 3J(H,H) values were used as initial input data for the spectral simulation of 1, which after iteration provided an excellent correlation with the experimental 1H NMR spectrum. The calculated 3J(H,H) values closely predicted the experimental values, excepting the coupling constant between the axial hydrogen alpha to the carbonyl group and the equatorial hydrogen beta to the carbonyl group (J(2beta, 3beta)). The difference is explained in terms of the electron density distribution found in the highest occupied molecular orbital (HOMO) of 1. The simulated spectrum, together with 2D NMR experiments, allowed the total assignment of the 1H and 13C NMR spectra of 1.

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1H and13C NMR assignments and conformational analysis of some tetracyclic compounds with a bicyclo[4.2.0]octane ring system

Cited by 5 publications

References 2 publications

Absolute Configuration of Lippifoliane and Africanane Derivatives

Absolute Configuration of Lippifoliane and Africanane Derivatives

Conformational Analysis of Sulfur-Containing 6-Deoxy-l-hexose Derivatives by Molecular Modeling and NMR Spectroscopy. A Theoretical Study and Experimental Evidence of Intramolecular Nonbonded Interactions between Sulfur and Oxygen

DFT and NMR parameterized conformation of valeranone

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