High Performance Liquid Chromatographic Enantioseparation of Chiral Bridged Polycyclic Compounds on Chiralcel OD-H and Chiralpak OT(+)

The HPLC enantiomeric separation of 29 racemic bridged polycyclic compounds was examined on commercially available Chiralcel OD-H and Chiralpak OT( 1) columns. The separations were evaluated under normal-phase mode (hexane containing mobile phase) for Chiralcel OD-H and under normal-phase as well as under reversed-phase mode (pure MeOH, temperature 58C) for Chiralpak OT(1). Almost all compounds were resolved either on Chiralcel OD-H or on Chiralpak OT( 1), in some cases on both. The use of trifluoroacetic acid (TFA), as modifier of the hexanic mobile phase, had a beneficial effect on the enantioseparation of some polar and acidic com-pounds on Chiralcel OD-H. The influence of small chemical structural modifications of the analytes on the enantioseparation behavior is discussed. A structure–retention rela-tionship has been observed on both stationary phases. This chromatographic evaluation may provide some information about the chiral recognition mechanism: in the case of Chiralcel OD-H, hydrogen bonding, p -p and distereoselective repulsive are supposed to be the major analyte-CSP interactions. In the case of Chiralpak OT( 1), a reversed-phase enantioseparation could take place through hydrophobic interactions between the aro-matic moiety of the analytes and the chiral propeller structure of the CSP. The synthesis of some unknown racemic bromobenzobicyclo[2.2.1] analytes is also described