Unusual enantiomeric separation due to residual amines in chiral crown ether stationary phase linked by long alkyl...

A new chiral stationary phase (CSP) in which (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid was linked to a silica gel surface through a long alkyl chain and which did not contain additional aminoundecyl groups was prepared. Generally, when enantiomers containing a primary amine group are optically resolved using a crown-ether-type CSP, a higher resolution is achieved if the surface of the CSP does not contain any residual amine. In this study, the chiral separation factor and resolution factor of a CSP with a long alkyl chain such as the aminoundecyl group were unusually low in the absence of the residual aminoundecyl groups. In this study, a chiral column was prepared by introducing a chiral selector having a long alkyl chain on the surface of silica gel to separate enantiomers of α-amino acids. Furthermore, it was confirmed that the residual-amine-containing CSP, which was easier to synthesize, facilitated more effective enantiomeric separation than the CSP without residual amines.