Study of stereoselective interactions of carbamoylated quinine and quinidine with 3,5-dinitrobenzoyl α-amino acids using VCD spectroscopy in the region of C−H stretching vibrations.

The stereoselective complexation of tert-butylcarbamoyl quinine and tert-butylcarbamoyl quinidine selectors (SOs) with 3,5-dinitrobenzoyl (DNB) derivatives of D- and L-alpha amino acids (DNB-Ala, DNB-Val, DNB-Leu, and DNB-Ile) as well as achiral DNB-Gly has been studied by vibrational circular dichroism (VCD) spectroscopy in the spectral region of C−H stretching vibrations. All the complexes of SOs and sterically compatible enantiomers of derivatized amino acid selectands (SAs) showed induced circular dichroism (ICD) bands in the region of aromatic C−H stretching vibrations, indicating the occurrence of a π-π interaction between the aromatic moieties of SA and SO. To our knowledge, this is the first report in which a π-π interaction was observed by VCD spectroscopy in this spectral region. No ICD bands were disclosed in the spectra of the sterically incompatible SA and SO complexes. The spectral pattern in the region of aliphatic C−H stretching vibrations showed interaction-induced conformational adaptations in sterically favorable SA and SO complexes. No such spectral changes were observed for any of the sterically incompatible complexes. The DNB-Gly complexes exhibited spectral patterns similar to those observed for sterically favorable pairs of SOs and chiral SAs.