Assessment of Configurational and Conformational Properties of Naringenin by Vibrational Circular Dichroism

The electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectra of both enantiomers of naringenin (4',5,7-trihydroxyflavanone) in acetonitrile solution have been measured. The enantiomers were obtained by chiral HPLC separation of the racemic sample. DFT calculations have been performed for relevant conformers and subsequent evaluations of VCD spectra are compared with VCD experiments: safe assignment of the absolute configuration is provided, based in particular on the VCD data. The relevance of the rotational conformers of the hydroxyl groups and of the mobility of phenol moiety is studied: based on this, we provide a first interpretation of the observed intense and broad couplet at 1325/1350 cm(-1). Four conformers contribute to this pattern with different sign and amplitude as shown by DFT calculations. Time dependent DFT calculations have been performed and compared with ECD experimental data, under the same assumption of conformational properties and mobilities investigated by VCD. Chirality 21:436-441, 2009. (C) 2008 Wiley-Liss, Inc.