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TDDFT-ECD and DFT-NMR studies of thaigranatins A–E and granatumin L isolated from Xylocarpus granatum
Authors:Attila Mndi  Jun Wu  Tibor Kurtn
Institution:Department of Organic Chemistry, University of Debrecen, P. O. Box 400, 4002 Debrecen Hungary, Fax: +36-52-512-744 ; School of Pharmaceutical Sciences, Southern Medical University, 1838 Guangzhou Avenue North, Guangzhou 510515 P. R. China,
Abstract:TDDFT-ECD calculations were utilized to explain the mirror image or different ECD spectra of previously reported homochiral natural products thaigranatins A–E and granatumin L, the simple comparison of which would result in a wrong stereochemical conclusion. The configurational assignment was confirmed independently and geometrical parameters of the chromophores governing the ECD spectra were identified in the structurally related natural products by analyzing the ECD spectra and geometries of the low-energy computed conformers obtained by different methods. Different conformations of the furan-2-yl-δ-lactone subunit were found responsible for the mirror image ECD spectra of the homochiral thaigranatins C–E. Two DFT 13C NMR chemical shift calculation methods and DP4+ analysis were performed on the C-6 epimers of thaigranatin D, which together with the ECD calculation, could determine the absolute configuration of C-6 as (R).

TDDFT-ECD calculations were utilized to explain the mirror image or different ECD spectra of thaigranatins A–E and granatumin L.
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