Isolation and stereospecific determination of the enantiomers of oxindazac by direct liquid chromatographic resolution on triacetylcellulose.
The preparation of the optically pure enantiomers of the antiphlogistic trial drug oxindazac via liquid chromatographic resolution of the corresponding tert.-butyl or benzyl ester on triacetylcellulose is described. Cleavage of the optically pure enantiomeric esters to the acids proceeds without significant racemization. The methyl ester of oxindazac is also completely resolved on the same chiral phase. Whereas oxindazac racemizes easily upon derivatization to diastereomers, no racemization is observed upon methylation to the corresponding methyl ester with diazomethane. An inverse isotope dilution method has been developed to determine both enantiomers of the drug in biological fluids after administration of 14C-labelled oxindazac. The enantiomers are converted into their methyl esters and separated on triacetylcellulose. Quantitation is performed by on-line UV detection at 290 nm and off-line radiometry. In the analysis of plasma samples, endogenous compounds do not interfere. The recoveries of [14C]oxindazac from water, rat and human plasma were 99.6 +/- 1.8% for the (+/- and 96.0 +/- 1.4% for the (-)-enantiomer. The plasma concentrations and urinary excretion of the two enantiomers were determined in a human volunteer who had received 200 mg of racemic 14C-labelled oxindazac.