Six pairs of phenylpropanoid enantiomers from Cinnamomum mollifolium.

Six pairs of undescribed phenylglycerol benzoate enantiomers, (±)-mollifolines A-F, which can also be categorized into three two-pairs of epimers, were isolated from Cinnamomum mollifolium H. W. Li (Lauraceae). The relative configurations (threo or erythro) of the epimers were determined by conformational searching of the lowest energy conformers and analyses of the relationship between the dihedral angle of H-7'─C-7'─C-8'─H-8' and the ³ J _{H-7', H-8'} coupling constant according to the Karplus equation. Furthermore, intramolecular hydrogen bonds were proved to play an important role in stabilizing the lowest conformations by using reduced density gradient (RDG) method for noncovalent interactions. Chiral resolutions of these enantiomer pairs were accomplished by immobilized polysaccharide derivative-based chiral HPLC columns. Absolute configurations of the 12 optically pure isomers were finally determined by quantum chemical time-dependent density functional theory (TDDFT) calculations of their electronic circular dichroism (ECD) spectra.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Li-She Gan reports financial support was provided by National Natural Science Foundation of China. Li-She Gan reports financial support was provided by Department of Education of Guangdong Province. Li-She Gan reports financial support was provided by Jiangmen Program for Innovative Research Team. Chuan-Rui Zhang reports financial support was provided by China Pharmaceutical University State Key Laboratory Of Natural Medicines.
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