Conformational analysis of 8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives by NMR and theoretical calculations

Alcântara, Antônio F. C.; Piló‐Veloso, Dorila; Almeida, Wagner B. De; Maltha, Célia R. A.; Barbosa, Luiz C. A.

doi:10.1016/j.molstruc.2006.01.016

Cited by 15 publications

(18 citation statements)

References 33 publications

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“…Thus, the best correlations are verified between the experimental 13 C NMR data of 2 and HF/6-31G* calculated carbon chemical shifts of 2, which agree with the structure proposed in the literature. As a consequence, this procedure may also be considered valid to determine the configuration of the labdane diterpenoid isolated from P. ornatus.…”

Section: Resultssupporting

confidence: 87%

“…(3). Correlations between 13 C NMR data of 2 and HF/6-31G* calculated carbon chemical shifts of 2 (structure in the gaseous phase).…”

Section: Resultsmentioning

confidence: 99%

“…For example, the activation of adenyl cyclase can stimulate gastric secretions and the presence of 2 in P. barbatus may explain its use in the popular treatment of digestive disorders. Although the 1D ( 1 H and 13 C) and 2D ( 1 H-1 H COSY, 1 H-13 C HSQC, and 1 H- 13 C HMBC) NMR analyses of the labdane diterpenoid isolated from P. ornatus are in agreement for 1, the configurations of C-8 and C-13 have not been confirmed. The stereochemistry of the forskolin derivatives is normally deduced by NOESY experiment [6][7][8][9] and the exciton chirality circular dichroism method [6].…”

Section: Introductionmentioning

confidence: 88%

“…Therefore, the present work describes the configurational and conformational analyses of the labdane diterpenoid isolated from P. ornatus based on correlations between 13 C NMR data and calculated carbon chemical shift values. Geometry optimizations and carbon chemical shift calculations were performed using HF [10] and DFT [11] methods.…”

Section: Introductionmentioning

confidence: 99%

“…Geometry optimizations and carbon chemical shift calculations were performed using HF [10] and DFT [11] methods. This procedure has been efficiently employed in the structural determination of diterpenoids [12] and other organic compounds [13,14]. Correlations between calculated and experimental chemical shifts from 13 C NMR data of 2 were considered a validation criterion of this procedure in the con-figurational determination of the labdane diterpenoid isolated from P. ornatus.…”

Section: Introductionmentioning

confidence: 99%

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A New Configurational Analysis of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one Isolated from Plectranthus ornatus Based on NMR and Theoretical Calculations

Oliveira¹,

Pacheco²,

Pacheco³

et al. 2009

TONPJ

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This work describes the configurational and conformational analyses of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one, a labdane diterpenoid isolated from Plectranthus ornatus. Its relative stereochemistry was previously proposed by comparison with 1 H and 13 C NMR data of forskolin (2); however, the configurations of C-8 and C-13 have not been confirmed. Correlations between 13 C NMR experimental data and HF/6-31G* calculated values of carbon chemical shifts were performed for configurational and conformational analyses. This procedure was formerly applied to the configurational analysis of 2. Among the seven different forskolin-type structures investigated, the 13 C NMR data of 2 correlated best with those with the same stereochemistry of 2 described in the literature. Thus, the same procedure was considered valid for configurational analysis of the labdane diterpenoid isolated from P. ornatus. The relative stereochemistry of this compound based on theoretical calculations was similar to the structure previously proposed, but the best results were obtained considering configurational inversion at C-13.

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Section: Resultssupporting

confidence: 87%

“…(3). Correlations between 13 C NMR data of 2 and HF/6-31G* calculated carbon chemical shifts of 2 (structure in the gaseous phase).…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A New Configurational Analysis of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one Isolated from Plectranthus ornatus Based on NMR and Theoretical Calculations

Oliveira¹,

Pacheco²,

Pacheco³

et al. 2009

TONPJ

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13C longitudinal relaxation time measurements and DFT-GIAO NMR computations for two ammonium ions of a tetraazamacrocyclic scorpiand system

Nazarski

2013

J Incl Phenom Macrocycl Chem

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Spin–lattice relaxation times, T1s, for 13C nuclei in two cations Hn1n+ (n = 1, 5) of N-(2-aminoethyl)-cyclam (1, scorpiand) were determined by means of 13C{1H} NMR experiments in aqueous solution at pH 11.5 and 0.2. The theoretical study [modeling with OPLS-AA, B3LYP/6-31G(d) geometry optimizations, dispersion-corrected energies (DFT-D3), and DFT-GIAO predictions of the NMR chemical shifts (including an IEF-PCM simulation of hydration)] was also done for several conformers of the tautomer iso-H414+ not investigated before. The binding directions in protonated polyamino receptors necessary for efficient complexation of the nitrate anion(s) were briefly outlined, as well. All these results were discussed in terms of ‘abnormal’ 13C chemical shift changes found previously for the side-chain carbons of amine 1 in strongly acidic solution (HNO3). In conclusion, an earlier proposal of its association with NO3− at pH <1 was rejected. Instead, the participation of small amounts of a micro-species iso-H414+Dhydr under such conditions can be proposed.Graphical AbstractA small contribution of iso-H414+Dhydr (see figure) to an ionic mixture of pentamine 1 was proposed to explain the ‘abnormal’ 13C NMR shifts observed for atoms C11 and C12 in its side-chain arm, at pH <1.Electronic supplementary materialThe online version of this article (doi:10.1007/s10847-013-0298-x) contains supplementary material, which is available to authorized users.

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Conformational study of 3β,16β-dihydroxyfriedelane by NMR and ab initio calculations

et al. 2009

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The complete chemical shift assignments of 3b,16b-dihydroxyfriedelane, a natural compound isolated from the hexane extract of Maytenus acanthophylla leaves was achieved through 1D/2D NMR spectral data. Combining ab initio Hartree-Fock [HF/6-31G(d)] and Density Functional Theory [DFT/B3LYP/6-31G(d,p)] calculations with NMR spectral data, it was possible to establish the predominance of the chair-chair-chair-boat-boat conformation for the five six-membered ring systems in this pentacyclic triterpene.

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Conformational analysis of 8-oxabicyclo[3.2.1]oct-6-en-3-one derivatives by NMR and theoretical calculations

Cited by 15 publications

References 33 publications

A New Configurational Analysis of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one Isolated from Plectranthus ornatus Based on NMR and Theoretical Calculations

A New Configurational Analysis of 1,6,7-triacetoxy-8,13-epoxy-14-labden-11-one Isolated from Plectranthus ornatus Based on NMR and Theoretical Calculations

13C longitudinal relaxation time measurements and DFT-GIAO NMR computations for two ammonium ions of a tetraazamacrocyclic scorpiand system

Conformational study of 3β,16β-dihydroxyfriedelane by NMR and ab initio calculations

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