Chiral ion-pair chromatographic separation of two dihydropyridines with camphorsulfonic acids on porous graphitic carbon

Abstract

The direct enantiomeric separation of the two racemic dihydropyridines amlodipine (AML) and UK52.829 (UK) with (1 S)-(+)-10-camphorsulfonic acid [(+)-CSA] as a chiral counter-ion, on porous graphitic carbon Hypercarb-S, is described. The enantiomers of AML and UK were separated in a mobile phase system consisting of 5 m M (+)-CSA in dichloromethane—methanol (25:75, v/v). When the enantiomeric separation of AML and UK was studied in a mobile phase system consisting of 5 m M (1 S)-(+)-3-bromo-10-camphorsulfonic acid [Br-(+)-CSA] in dichloromethane—methanol (25:75, v/v) the capacity factor, k′, was markedly increased while the separation factor, α, was slightly decreased compared to the mobile phase with (+)-CSA as chiral counter-ion. No enantiomeric separation of AML or UK was seen in a chromatographic system with acetonitrile substituted for methanol as mobile phase solvent, neither with (+)-CSA nor Br-(+)-CSA as chiral counter-ion.