4-arylflavan-3-ols as proanthocyanidin models: absolute configuration via density functional calculation of electronic circular dichroism.
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.
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1
Base de dados:
MEDLINE
Assunto principal:
Flavonoides
/
Modelos Moleculares
/
Proantocianidinas
Idioma:
En
Ano de publicação:
2010
Tipo de documento:
Article