Structural features affecting chiral discrimination of terpene derivatives on a carbamated amylose stationary phase.
The chiral discrimination of enantiomeric derivatives of alpha-pinene was studied using amylose tris(3,5-dimethylphenylcarbamate) as a chromatographic stationary phase. The effect of structural features of these enantiomeric pairs on their chromatographic resolution was systematically studied to understand further the correlation between these features and chiral discrimination by the carbamated amylose. Structural analysis by molecular mechanics indicated that the conformation of the alpha-pinene skeleton was preserved with substitution in all its derivatives. However, in spite of the rigidity of the molecular backbone of these molecules, their resolution capabilities were different. Apparently, the site of the hydrogen-bonding substituents affected chiral discrimination by the stationary phase rather than conformational changes. Separation was achieved in spite of the fact that none of the members in the series had an aromatic moiety, and therefore pi-pi interactions with the stationary phase were insignificant. Hence it was concluded that the most important interaction of the terpene derivatives with the carbamated amylose was hydrogen bonding.