Preparation of a new chiral acridino-18-crown-6 ether-based stationary phase for enantioseparation of racemic protonated primary aralkyl amines

Abstract

Starting from commercially available and relatively cheap chemicals first enantiopure dimethyl-substituted monoaza-18-crown-6 ether ( R, R)- 21 containing a diphenylamine unit was prepared, which was then transformed to dimethyl-substituted acridino-18-crown-6 ligand ( R, R)- 19 having an N-allyl-carbamoyl linker by several steps. The terminal double bond of the latter made possible to attach ( R, R)- 19 to γ-mercaptopropyl-functionalized spherical HPLC quality silica gel obtaining a new chiral stationary phase ( R, R)-CSP- 37. Based on electronic circular dichroism (ECD) studies the N-allyl-carbamoyl group attached to the acridine ring of the chiral host ( R, R)- 19 does weaken exciton interaction between the host and guest molecules, but does not destroy the discriminating power of the chiral host. An HPLC column filled with ( R, R)-CSP- 37 was tested for the enantioseparation of racemic 1-(1-naphthyl)- and 1-(2-naphthyl)ethylamine hydrogenperchlorates using isocratic conditions.