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4-arylflavan-3-ols as proanthocyanidin models: absolute configuration via density functional calculation of electronic circular dichroism.
Ding, Yuanqing; Li, Xing-Cong; Ferreira, Daneel.
Afiliação
  • Ding Y; National Center for Natural Products Research, Research Institute of Pharmaceutical Sciences, and Department of Pharmacognosy, School of Pharmacy, The University of Mississippi, University, Mississippi 38677, USA.
J Nat Prod ; 73(3): 435-40, 2010 Mar 26.
Article em En | MEDLINE | ID: mdl-19947587
Density functional theory/B3LYP has been employed to optimize the conformations of selected 4-arylflavan-3-ols and their phenolic methyl ether 3-O-acetates. The electronic circular dichroism spectra of the major conformers have been calculated using time-dependent density functional theory to validate the empirical aromatic quadrant rule applied to the assignment of the absolute configuration of this class of compounds. The modest 6-31G* basis set was sufficient to produce reasonable spectra. The calculated Cotton effects at 220-240 nm, crucial for the assignment of the C-4 absolute configuration, result from electronic transitions of the molecular orbitals involving the pi-electrons of the spatially close aromatic A-ring and 4-aryl moieties. The sign of this Cotton effect is determined by the orientation of the 4-aryl substituent: the negative and positive Cotton effects are associated with 4alpha- and 4beta-aryl substituents, respectively.
Assuntos

Texto completo: 1 Base de dados: MEDLINE Assunto principal: Flavonoides / Modelos Moleculares / Proantocianidinas Idioma: En Ano de publicação: 2010 Tipo de documento: Article

Texto completo: 1 Base de dados: MEDLINE Assunto principal: Flavonoides / Modelos Moleculares / Proantocianidinas Idioma: En Ano de publicação: 2010 Tipo de documento: Article