Enantioselective analyses of antihistaminic drugs by high performance liquid chromatography

High-performance liquid chromatographic methods have been developed for stereoselective separations of terfenadine and its active metabolite fexofenadine.Satisfactory enantioseparations of racemic terfenadine were achieved on a Chiralcel column by normal phase elution. Analysis of racemic fexofenadine, as such, took a very long time and achieved poor enantioselectivity on this column; nevertheless, the analyte when derivatised with diazomethane was well resolved.Racemic fexofenadine was also derivatised using a chiral agent: R-(+)-1-phenylethylisocyanate and subjected to achiral LC on a reversed-phase analytical column. Complete enantioseparations were achieved in short analysis times; excess reagent eluted before the diastereoisomeric pair and did not interfere.