Enantioselective HPLC separation of bioactive C5-chiral 2-pyrazolines on lux amylose-2 and lux cellulose-2: Comparative and mechanistic approaches

Stereoselective analytical HPLC separations have been developed for a series of biologically active chiral 2-pyrazolines (1-22) to be used in monitoring their resolution reactions or to custom semipreparative HPLC separations prior to biological assessment of both enantiomers. Polysaccharide-based chiral stationary phases (CSPs), namely, Lux amylose-2 and cellulose-2, have been used. Both normal (n-hexane/ethanol) and polar organic (ethanol, methanol, acetonitrile, or mixtures thereof) elution modes were very beneficial for the achievement of baseline separations. The impact of various chemical moieties embedded in the structures of 2-pyrazolines 1-22 and the adopted stationary phases on chiral recognition has been investigated. A case of reversed order of elution following alterations in either stationary phase or elution mode has been observed. Our findings recommend that normal elution mode can be used for optimizing semipreparative HPLC methods whereas polar organic mobile phases (such as acetonitrile and ethanol) are more suited to stereoselective reactions monitoring, routine quality control work, or for pharmacological and toxicological assays. These results settle the implementation of polysaccharide-based CSPs using different elution modes and declare the practicality of such CSPs in stereoselective HPLC.