Several different derivatized /8-cyclodextrlns were synthesized and used as chiral stationary phases In normal-phase liquid chromatography. The multiply substituted derivatives were made with acetic anhydride, (/?)-and (S )-1-( 1-naphthyl)ethyl Isocyanate, 2,6-dlmethylphenyl Isocyanate, and p-toluoyl chloride. The first successful cyclodextrln-based, normalphase separation of enantiomers was accomplished on these derivative phases. In contrast to chiral separations on the native /9-cyclodextrln stationary phase, the enantiomeric separation mechanism on these new phases Is not thought to be dependent on Inclusion complexation. The similarities and differences between the derivatized cyclodextrin stationary phases and the cellulosic stationary phases are discussed.
Enantiomeric resolution of more than fifty racemic primary amines can be achieved on a column that utilizes a crown ether as a chiral selector. The racemic solute is solubilized in an acidic solvent, forming an ammonium ion from the primary amine functional group. An interaction between the lone pair electrons on the oxygens of the crown ether and the positive charge of the ammonium group leads to the formation of an inclusion complex. Due to the chirality of the crown ether there is stereoselective interaction resulting in enantiomeric separation. Excellent resolution is possible for amino acids, amino alcohols, amino esters and amines. Compounds are separated that were poorly resolved by conventional ligand exchange columns and by other means.
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