Enantiomeric separation of racemic 4-aryl-1,4-dihydropyridines and 4-aryl-1,2,3,4-tetrahydropyrimidines on a chiral tetraproline stationary phase.

The chromatographic chiral resolution of 4-aryl-1,4-dihydropyridines (1-32), 4-aryl-2-thioxo-1,2,3,4-tetrahydropyrimidines (33-38), and 4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidines (39-41) was studied on a tetraproline-immobilized chiral column synthesized in our lab. This tetraproline chiral stationary phase can resolve most of these compounds. The 4-aryl-2-thioxo-1,2,3,4-tetrahydropyrimidines (33-38) and 4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidines (39-41) were more efficiently resolved than the racemic 4-aryl-1,4-dihydropyridines on the tetraproline chiralstationary phase. Analytes with 5,5-dimethyl groups (39-41) were less efficiently resolved than analytes without 5,5-dimethyl substituents (1-16). The 4-aryl-2-oxo-1,2,3,4-tetrahydropyrimidines (39-41) without a sulfur atom were much more efficiently resolved than 4-aryl-2-thioxo-1,2,3,4-tetrahydropyrimidines (33-38). No obvious electronic effects on the resolution of any of these analytes (1-41) were observed on the tetraproline chiral stationary phase. The tetraproline chiral stationary phase separated enantiomers mainly via hydrogen bonding interactions.