Liquid chromatographic enantioseparation of (RS)-etodolac using (S)-levofloxacin and determination of absolute configuration of the diastereomeric derivatives.

Abstract

(RS)-Etodolac was isolated from commercial tablets and was purified and characterized to be used as racemic standard. A pair of diastereomeric derivatives was synthesized using (S)-levofloxacin as a chiral derivatizing reagent. The derivatization reaction was carried out under conditions of stirring at room temperature (30°C for 1.5 h) as well as under microwave irradiation; the derivatives obtained by the two methods were compared. Reaction conditions for derivatization were optimized with respect to mole ratio of chiral derivatizing reagent and (RS)-etodolac. No racemization was observed throughout the study. Separation of diastereomeric derivatives was successful using C18 column and a binary mixture of methanol and triethyl ammonium phosphate buffer of pH 4.5 (80:20, v/v) as mobile phase at a flow rate of 1 mL min-1 and UV detection at 223 nm. An efficient approach for recognizing chirality and determining the absolute configuration of the diastereomeric derivatives of (RS)-etodolac is described, which in turn is a measure of the enantiomeric purity of (RS)-etodolac since the diastereomeric derivatives were separated and isolated using preparative thin-layer chromatography.