Molecular modelling, NOED and spin—lattice relaxation study of the stereochemistry of some terpenoids

Qing, Ning; Colebrook, Lawrence D.; Commodari, Fernando

doi:10.1002/mrc.1260290509

Cited by 5 publications

(8 citation statements)

References 11 publications

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“…The anti arrangement of 6‐H and 7‐H, observed in 1A , 1B , 1E , and 1F , is thus favored for 81.4 % of cases and the cisoid arrangement of the α,β‐unsaturated ketone, observed in 1A , 1C , 1E , and 1G , accounts for 77.2 %. Our calculations thus confirm the preference of the side chain for a pseudoaxial orientation, also deduced from the CD spectrum of compound 1 ,18b as well as the anti arrangement of 6‐H and 7‐H, supported by the value of the corresponding observed 1 H NMR coupling constant 18c. Both the cisoid and transoid arrangements of the α,β‐unsaturated ketone are predicted to be populated by our calculations (77 % and 23 %, respectively), in agreement with the enhancement of both the 7‐H and 8‐H NMR signals upon irradiation of the acetyl methyl group of 1 18c and with a NOESY experiment (see Supporting Information) performed by us on a commercial sample of 1 .…”

Section: Resultssupporting

confidence: 83%

“…The relationship between molecular structure and odor characteristics in this group has not yet been examined systematically, although scattered studies on the preferred conformations of α‐ionone ( 1 ),18a,18c and cis ‐ ( 4 ) and trans ‐α‐irone18a,18b ( 5 ) have appeared in the literature. Recently, the dramatic dependence of olfactory properties of ionones and irones on their chiralities has been clearly demonstrated 8.…”

Section: Introductionmentioning

confidence: 99%

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A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

et al. 2008

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A modeling study at the B3LYP/6-31G(d) level was performed on a group of natural odorants. These included α-, β-, and γ-ionones, β-irone, cis-and trans-α-and -γ-irones, and three synthetic α-ionone analogues, all containing an identical E-enone moiety and differing in the endo or exo positions of another double bond and an additional alkyl group at C(2) or at C(13). Data showed a shift of the conformational preference of the butenone chain from an axial or pseudoaxial orientation, as favored in α-ionone and in trans-α-and -γ-irones, to an equatorial or pseudoequatorial orientation, as favored in γ-ionone and in cis-α-and -γ-irones. These changes have been correlated with the enhanced olfactory

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Section: Resultssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

et al. 2008

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“…The second calculation process (sim-Ðt) used a T 1 modiÐed version of the non-linear simplex algorithm23 in which the intensities of the peaks of interest were Ðtted independently against the relaxation delay by Eqn (2). All of the results for both the pix-Ðt and the sim-Ðt techniques are presented here with 95% conÐdence interval values.…”

Section: Acquisition and Pulse Sequencementioning

confidence: 99%

“…16 kHz experimental frequency range. A computer-simulated excitation proÐle for an average 180¡ pulse of 15 ls showed at 12% deviation from maximum excitation at the extremes of this range ; the approximate o †set (o) values which compensate for incomplete inversion were, therefore, substituted when the data were Ðtted to Eqn (2).…”

Section: Acquisition and Pulse Sequencementioning

confidence: 99%

Estimation of the spin-lattice relaxation time constants of low molecular weight solutes in dilute complex aqueous solutions: application to urinary metabolites

et al. 1998

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“…Methyl group rotational barriers may be calculated using the "dihedral driver" option of the MM2 and MMP2 algorithms (7), following optimization of the molecular structure (8). In this procedure, the energy of the structure is minimized for each chosen dihedral angle of the group being rotated, so that the energy calculated for the transition state for rotation allows for conformational changes in the rest of the molecule to accommodate rotation.…”

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confidence: 99%

A study of computed rotational barriers of methyl groups and ¹H and ¹³C spin-lattice relaxation rates in some steroids

Colebrook¹,

Qing²

1992

Can. J. Chem.

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LAWRENCE D. COLEBROOK and NING QING. Can. J. Chem. 70, 2 154 (1992).'H and I3C spin-lattice relaxation rates of the methyl groups of 15 steroids have been measured, and rotational barriers of the methyl groups have been calculated, using force field methods. Correlations between relaxation rates and computed rotational barriers have been investigated. 'H and "C relaxation rates are consistent, and correlate with rotational barriers in simpler steroids. Steroids that are highly substituted with polar groups, and that must be investigated in polar solvents, tend to show poor correlations, an observation that is attributed to limitations in the computational model employed, which does not account for the effects of specific solvation or molecular association. In dilute solution ( 5 0 . 1 M in a deuteriated solvent) the spin-lattice relaxation of most 'H and I3c nuclei is dominated by the intramolecular dipole-dipole mechanism. For a molecule tumbling isotropically, the dipole-dipole contribution, R,(dd), to the overall relaxation rate is given by eq.[ l ] in terms of the relaxation contribution between two nonequivalent nuclei, i, j:where y, and yj are the magnetogyric ratios of the i and j nuclei, rij is their internuclear separation, and s,.(i, j) is the motional correlation time of the vector between them. The net R, value for a nucleus is dependent on the overall tumbling rate of the molecule as a unit, plus the contribution from any additional motion of a substituent group that carries that particular nucleus. Because of the l/r6 term in eq.[ l ] , the influence of a relaxation pathway is attenuated very rapidly with increasing distance between nuclei, so that it is the near neighbours of a nucleus which dominate its relaxation. A methyl proton relaxes largely to its neighbouring protons on the same carbon atom. The carbon atom of a methyl group is relaxed almost exclusively by the protons it carries. Differences between the I H relaxation rates of methyl groups in the same molecule arise, therefore, largely from differences in the correlation times for local rotational motion of the methyl groups, while differences between the I3c relaxation rates of methyl groups in the same molecule arise almost exclusively from this origin (1). An increase in the rate of methyl group rotation reduces the efficiency of the dipole-dipole relaxation mechanism.Relaxation in small molecules, which experience fast tumbling and fast methyl group rotation, may be compli-'~u t h o r to whom correspondence may be addressed. '~evision received January 14, 1992. cated by contributions from the spin-rotation mechanism (2), which has an inverse dependence on the rotational rate of the methyl group (3). The effect of the spin-rotation contribution is to reduce the sensitivity of the overall relaxation rate, which is usually dominated by the dipole-dipole mechanism (I), to steric factors that influence the methyl group rotational rate.The sensitivity of methyl group relaxation in steroids to steric factors was first systematically investi...

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Molecular modelling, NOED and spin—lattice relaxation study of the stereochemistry of some terpenoids

Cited by 5 publications

References 11 publications

A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

Estimation of the spin-lattice relaxation time constants of low molecular weight solutes in dilute complex aqueous solutions: application to urinary metabolites

A study of computed rotational barriers of methyl groups and ¹H and ¹³C spin-lattice relaxation rates in some steroids

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Molecular modelling, NOED and spin—lattice relaxation study of the stereochemistry of some terpenoids

Cited by 5 publications

References 11 publications

A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

A Full Conformational Characterization of Natural Ionones and Irones, as well as 13‐Alkyl‐Substituted α‐Ionones

Estimation of the spin-lattice relaxation time constants of low molecular weight solutes in dilute complex aqueous solutions: application to urinary metabolites

A study of computed rotational barriers of methyl groups and 1H and 13C spin-lattice relaxation rates in some steroids

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A study of computed rotational barriers of methyl groups and ¹H and ¹³C spin-lattice relaxation rates in some steroids