Submitted to: Journal of Natural Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2009
Publication Date: 2/15/2010
Citation: Ding, Y., Li, X., Ferreira, D. 2010. 4-Arylflavan-3-ols as Proanthocyanidin Models: Absolute Configuration via Density Functional Calculation of Electronic Circular Dichroism. Journal of Natural Products. 73:435-440. Interpretive Summary: This manuscript describes a study that employed the density functional theory/B3LYP method to assess the conformations and configurations of selected 4-arylflavan-3-ols. The results provide an understanding of the theoretical basis of the empirical aromatic quadrant rule applied to the assignment of the absolute configuration of this class of compounds.
Technical Abstract: 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 4R-and 4-aryl substituents, respectively.