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Absolute configuration of naturally occurring glabridin

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journal contribution
posted on 26.04.2016 by Charlotte Simmler, Frank R Fronczek, Guido F Pauli, Bernard D Santarsiero
The title compound {systematic name: 4-[(3R)-8,8-dimethyl-3,4-di­hydro-2H-pyrano[2,3-f]chromen-3-yl]benzene-1,3-diol, commonly named glabridin}, C20H20O4, is a species-specific biomarker from the roots Glycyrrhiza glabra L. (European licorice, Fabaceae). In the present study, this prenylated isoflavan has been purified from an enriched CHCl3 fraction of the extract of the root, using three steps of medium-pressure liquid chromatography (MPLC) by employing HW-40F, Sephadex LH-20 and LiChroCN as adsorbents. Pure glabridin was crystallized from an MeOH-H2O mixture (95:5 v/v) to yield colorless crystals containing one mol­ecule per asymmetric unit (Z' = 1) in the space group P212121. Although the crystal structure has been reported before, the determination of the absolute configuration remained uncertain. Stereochemical analysis, including circular dichroism, NMR data and an X-ray diffraction data set with Bijvoet differences, confirms that glabridin, purified from its natural source, is found only in a C3 R configuration. These results can therefore be used as a reference for the assignment of the configuration and enantio­purity of any isolated or synthetic glabridin sample.


This research was supported by NCCAM and ODS through grant No. P50 AT000155. The authors acknowledge use of the Life Sciences Collaborative Access Team (LS-CAT) beamline 21-ID-D for the initial data collection; use of the Advanced Photon Source at Argonne National Laboratory was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Upgrade of the diffractometer was made possible by grant No. LEQSF(2011-12)-ENH-TR-01, administered by the Louisiana Board of Regents. Finally, we thank Dr José Napolitano, UIC Chicago (Illinois), and Matthias Niemitz, Perch Solutions Ltd, Kuopio (Finland), for helpful NMR discussions and PERCH support.



International Union of Crystallography





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