Liquid chromatographic methods for separation, determination, and bioassay of enantiomers of etodolac: A review.

The control of enantiomeric purity and determination of individual enantiomeric drug molecules remains the subject of importance for clinical, analytical, and regulatory purposes and to facilitate an accurate evaluation of the risks posed by them to human health. A large number of pharmaceuticals are marketed and administered as racemates. Etodolac is among such nonsteroidal anti-inflammatory drugs. Overall literature reports on its enantioseparation are scanty. Liquid chromatography (LC) methods of enantioseparation of (±)-etodolac, including certain unconventional ones, are well covered and discussed in this paper. Methods of direct approach without using chiral columns or chiral thin-layer chromatography plate and of indirect approach using certain chiral derivatizing agents such as (S)-naproxen and (S)-levofloxacin are described. Most interesting aspects include establishment of structure and molecular asymmetry of chemically different types of diastereomeric derivatives using liquid chromatography with mass spectrometry (LC-MS), 1 H NMR spectroscopy and by drawing conformations in three dimensional views by using certain software. The methods provide chirality recognition even in the absence of pure enantiomers. Besides, recovery of pure enantiomers by detagging or via solubility difference of chiral inducing reagent and the analyte, without racemization at any stage, has been achieved. The limits of detection and quantification are much lower than the industry benchmarks.

Singh M ，Sethi S ，Bhushan R 《-》

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

(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.

Singh M 《-》

Preparative resolution of etodolac enantiomers by preferential crystallization method.

Dung PT ，Trung TQ ，Kim KH 《-》

Enantioselective HPLC-DAD method for the determination of etodolac enantiomers in tablets, human plasma and application to comparative pharmacokinetic study of both enantiomers after a single oral dose to twelve healthy volunteers.

An enantioselective high performance liquid chromatographic method with diode array detection (HPLC-DAD) was developed and validated for the determination of etodolac enantiomers in tablets and human plasma. Enantiomeric separation was achieved on a Kromasil Cellucoat chiral column (250 mm × 4.6mm i.d., 5 µm particle size) using a mobile phase consisting of hexane: isopropanol: triflouroacetic acid (90:10:0.1 v/v/v) at a flow rate of 1.0 mL min(-1). The chromatographic system enables the separation of the two enantiomers and the internal standard within a cycle time of 8 min. The resolution between the two enantiomers was 4.25 and the resolution between each enantiomer and the internal standard was more than 2.0. Detection was carried out at 274 nm, and the purity assessment was performed using a photodiode array detector. Solid phase extraction technique using C-18 cartridge was applied to extract the analytes from the plasma samples, and the percentage recovery was more than 95% for the lower quantification limit. The method has been validated with respect to selectivity, linearity, accuracy and precision, robustness, limit of detection and limit of quantification. The validation acceptance criteria were met in all cases. The linearity range for the determination of each enantiomer in human plasma was 0.4-30.0 µg mL(-1) and the limits of quantification of R-etodolac and S-etodolac were 0.20 and 0.19 µg mL(-1), respectively. The validated method was successfully applied to the determination of etodolac enantiomers in tablets and to a comparative pharmacokinetic study of the two enantiomers after the administration of 300 mg single oral dose etodolac racemate tablets to twelve healthy volunteers.

Hewala II ，Moneeb MS ，Elmongy HA ，Wahbi AA ... -  《-》

A novel approach for enantioseparation as applied to (RS)-etodolac from pharmaceutical formulations: LC MS and density functional theory support for confirmation of diastereomers so separated.

In the present studies formation of diastereomers of (RS)-etodolac was confirmed using LC-MS when [M + H](+) or [M](+) were recorded for the diastereomers. The lowest energy optimized structures of two diastereomers were drawn, which confirmed the three-dimensional geometry of the diastereomers. This supports the optimized analytical separation conditions. In addition, separation of diastereomers was successful using a 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. The separation method was validated as per International Conference on Harmonization guidelines. (RS)-Etodolac was isolated from commercial tablets and purified and characterized to be used as racemic standard. Three pairs of diastereomers were synthesized using enantiomerically pure amines, namely, (R)-(+)-α-methyl benzyl amine, (S)-(-)-α,4-dimethylbenzylamine and (R)-(-)-1-cyclohexylethylamine. Derivatization reactions were carried out under conditions of stirring at room temperature (30 °C for 2 h) as well as under microwave irradiation (MWI), and the two types of diastereomers were compared. Reaction conditions for derivatization were optimized with respect to mole ratio of chiral derivatizing agent and (RS)-etodolac and MWI time. No racemization was observed throughout the study.

Singh M ，Bhushan R 《-》