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Abstract
Two chiral stationary phases (CSP) containing a free primary amino group were prepared by bonding (S)-phenylglycine and (R)-4-methoxyphenylglycine to silica gel and applied in resolving various N-(3,5-dinitrobenzoyl)-α-amino acids. Among various mobile phases, methylene chloride containing 0.2% acetic acid and 0.1% triethylamine was found most useful as a mobile phase. Between the two CSPs, the one based on (R)-4-methoxyphenylglycine was more effective than the other based on (S)-phenylglycine in the resolution of N-(3,5-dinitrobenzoyl)-α-amino acids, indicating the importance of the π-basicity of the aromatic group of the CSP in the chiral recognition. The π-acidity of the N-(3,5-dinitrobenzoyl) group of analytes was also found important for the effective chiral recognition.
From these results, the π–π interaction between the CSP and the analytes was concluded to be the important factor for the chiral recognition. On the contrary, N-(3,5-dinitrobenzoyl)leucine methyl ester was not resolved at all on the CSPs. Consequently, the free carboxylic acid group was expected to be absolutely necessary for the chiral recognition, indicating the importance of the ion-pairing or the electrostatic interaction in the chiral recognition. These two factors necessary for the chiral recognition were exactly consistent with the chiral recognition mechanism proposed previously, based on the relaxed scan calculation combined with a Monte Carlo conformation search in solution-phase.
ACKNOWLEDGMENT
This work has been supported by KISTEP (NRL Program : M1-0104-00-0005).