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Investigations of molecular recognition aspects related to the enantiomer separation of 2‐methoxy‐2‐(1‐naphthyl)propionic acid using quinine carbamate as chiral selector: An NMR and FT‐IR spectroscopic as well as X‐ray crystallographic study †
Author(s) -
Akasaka Kazuaki,
GyimesiForrás Krisztina,
Lämmerhofer Michael,
Fujita Takuma,
Watanabe Masataka,
Harada Nobuyuki,
Lindner Wolfgang
Publication year - 2005
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.20203
Subject(s) - chemistry , enantiomer , carbamate , chiral derivatizing agent , chirality (physics) , stereochemistry , proton nmr , organic chemistry , chiral column chromatography , chiral symmetry , nambu–jona lasinio model , physics , quantum mechanics , quark
The chiral recognition mechanism of a cinchona alkaloid‐based chiral stationary phase (CSP) showing high enantiomer discrimination potential for 2‐methoxy‐2‐(1‐naphthyl)propionic acid (MαNP acid) was investigated. Conformational and structural analyses of the 1:1 complexes of 9‐ O ‐( tert ‐butylcarbamoyl) quinine selector (SO) and MαNP acid (selectand, SA) were carried out employing NMR spectroscopy in solution, Fourier‐transform infrared (FT‐IR) spectroscopy, and solid‐state X‐ray diffraction analysis. Intramolecular NOEs of a soluble analogue of the CSP afforded the conformational states of the free and complexed form of the selector. The 1 H‐NMR spectra revealed that the free form of the SO constitutes anti‐open as well as anti‐closed and/or syn‐closed conformers. Upon complexation with the ( S )‐MαNP acid enantiomer to form the more stable diastereomeric associate, a conformational transition of the selector takes place, resulting in the synthesis of the anti‐open conformer nearly exclusively. FT‐IR spectra reveal that, besides the primary ion‐pairing interaction, stereoselective hydrogen bonding stabilizes the more stable complex via the amide hydrogen of the SO. X‐ray diffraction analysis of 9‐ O ‐( tert ‐butylcarbamoyl)quinine and ( S )‐MαNP acid complex further revealed the occurrence of a bidentate H‐bond‐mediated ionic interaction between SO and SA as well as the lack of π–π interaction in the 1:1 complex, and corroborated the conclusions derived from spectroscopic and chromatographic studies. © 2005 Wiley‐Liss, Inc. Chirality 17:544–555, 2005.