4-arylflavan-3-ols as proanthocyanidin models: absolute configuration via density functional calculation of electronic circular dichroism.
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.
Ding
Yuanqing
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.
Li
Xing-Cong
XC
Ferreira
Daneel
D
D000465:Algorithms; D002942:Circular Dichroism; D005419:Flavonoids / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D044945:Proanthocyanidins / Q000737:chemistry*; D013816:Thermodynamics
D005419:Flavonoids; D044945:Proanthocyanidins; C013221:proanthocyanidin; C404987:flavan-3-ol