Separation of Optical Isomers as Diastereomeric Derivatives by High Performance Liquid Chromatography

New chiral high-performance liquid chromatographic methodology used for the pharmacokinetic evaluation of dexfenfluramine

A new chiral high-performance liquid chromatographic (HPLC) method utilizing ultraviolet (UV) detection has been developed for determining plasma and urinary concentrations of d-fenfluramine and its major metabolite d-norfenfluramine, while being able to determine the possible presence of l-fenfluramine after oral administration of enantiopure d-fenfluramine hydrochloride. Sensitivity, stability, and specificity were enhanced by derivatizing the extracted analytes with 3,5-dinitrophenylisocyanate while utilizing a Pirkle-type chiral recognition approach. In vitro and in vivo statistical data are analogous. Overall plasma inter-assay precision was less than 7% with a minimum quantitation limit of 10 ng/ml. Overall urine inter-assay precision was also less than 7% with a minimum quantitation limit of 25 ng/ml.

Stereoselective pharmacokinetics and inversion of suprofen enantiomers in humans

The stereoselective pharmacokinetics of suprofen enantiomers has been studied in humans by means of stable isotope-labeled pseudoracemate-diastereomer methodology. After a single oral dose of a near equimolar mixture of unlabeled-(R)-(-)- and [2H3]-(S)-(+)-suprofen [or unlabeled-(S)- and [2H3]-(R)-suprofen] to three healthy male subjects, the plasma concentrations of drug were determined by a stereospecific gas chromatography-mass spectrometry method. Racemic [2H7]suprofen was used as an internal standard. The method involved chiral derivatization with (S)-(-)-1-(naphthyl)ethylamine to form the diastereomeric amide. The plasma concentrations were consistently higher for the (R)-isomer than the (S)-isomer. No significant difference in the elimination half-life of the enantiomers was observed. An average of 6.8% of an administered dose of the (R)-isomer was stereospecifically inverted to the (S)-isomer. There was no measurable inversion of the (S)- to (R)-isomer. The present stable isotope-labeled pseudoracemate-diastereomer methodology has made it possible to evaluate the pharmacokinetics of each enantiomer, including the estimation of chiral inversion after administration of the racemic mixture.

Post-column reactors for sensitive and selective detection in high-performance liquid chromatography: categorization and applications

The increasing interest in the rapid trace analysis of large series of biomedical samples using column liquid chromatographic techniques requires the use of well balanced combinations of sample pretreatment, separation and detection techniques. In such work, selectivity, sensitivity and reproducibility are the key parameters. The application of automated or semi-automated on-line pre-column technology and/or post-column reaction detection are excellent ways to meet these requirements. A critical review is presented of the theoretical background of on-line post-column reactors with emphasis on their categorization, viz., open-tubular, packed-bed, segmented-stream and hollow-fibre membrane reactors. The evaluation of these reactor systems is performed by discussing selected applications of, for instance, systems based on electrochemical and redox, hydrolytic, photochemical, ion-pairing, true chemical derivatization, peroxyoxalate chemiluminescence and solid-phase reactions. As automation is becoming even more important, a number of labelling procedures, which can be performed in an on-line pre-column mode, are briefly discussed and a comparison is made between the potential of on-line pre- and post-column procedures.

Chromatographic separation of enantiomers

In this paper a review is presented on the chromatographic analysis of enantiomers with special attention to high pressure liquid chromatography. Also, some examples of resolution of racemates by thin layer chromatography and gas chromatography are given. The various procedures in the surveyed literature have been divided into three main classes: procedures with formation of diastereomeric compounds prior to the chromatographic separation, procedures in which a chiral mobile phase is used, and procedures with the use of a chiral stationary phase. These methods are subdivided and some examples of their application to drugs and related compounds are presented.

Profiling of amino acids in body fluids and tissues by means of liquid chromatography

The needs of urgent diagnoses and the needs emerging from acute forms of diseases have directed progress in amino acid profiling to modern, rapid, automated analyses that can be done at reasonable cost. The first step in this direction was the short programmes of classical ion-exchange chromatography. At the beginning of this review we attempted to survey methods of sample preparation and sample treatment, as these are frequently neglected stages where artefacts or erroneous results may arise. There are basically the following approaches in amino acid profiling by liquid chromatographic techniques. For preliminary screening of a large number of samples in clinical routine planar procedures are the methods of choice, as they allow large numbers of samples to be handled with minimum effort and at very reasonable cost. For more precise profiling, particularly where quantitative data are essential, one can choose between some of the modern procedures for separating underivatized amino acids using modern equipment for cation-exchange chromatography, by making use of a stepped series of lithium citrate buffers with ninhydrin, o-phthalaldehyde or 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole detection. Ninhydrin detection is preferred in those situations where the demands on sensitivity are not high. Where, however, only small amounts of samples are available or high sensitivity is required, one of the latter two methods is preferred. The o-phthalaldehyde procedure is not suitable for the detection of secondary amines and, if these are of interest, then diazole derivatization is to be preferred. At present, however, the ninhydrin and o-phthalaldehyde detection procedures are the most popular. The other choice is to use one of the sophisticated HPLC systems equipped with fluorescence detection and to separate amino acids as derivatives. Here o-phthalaldehyde and 4-fluoro-7-nitrobenzo-2,1,3-oxadiazole derivatives offer the most versatile possibilities. Automation and computerization have penetrated both categories of liquid column separation and are applied to automated sample delivery, automated and computerized gradient formation and quantitation of the data obtained. The tables of metabolic disorders of amino acids and the roles of different amino acids in these disorders should provide preliminary information for clinical chemists.

Activated alpha-alkyl-alpha-arylacetic acid enantiomers for stereoselective thin-layer chromatographic and high-performance liquid chromatographic determination of chiral amines

The separation of racemic benoxaprofen into the two benoxaprofen enantiomers by preparative high-performance liquid chromatography and the application of the activated enantiomers as derivatization reagents for the simultaneous stereoselective determination of chiral amines in biological material is described. Activated (+)- and (-)-benoxaprofen are both shown to be very sensitive and stable chiral fluorescence markers, applicable to thin-layer chromatography as well as to high-performance liquid chromatography.

Multiple inverse isotope dilution assay for the stereospecific determination of R(+)- and S(-)-oxprenolol in biological fluids

An isotope dilution assay has been developed for the determination of both oxprenolol enantiomers in biological samples after administration of the racemic 14C-labelled mixture. The enantiomers were reacted with optically pure S(-)-1-phenylethyl isocyanate and the diastereoisomeric urea derivatives formed were separated by normal-phase high-performance liquid chromatography. Quantitation was performed by on-line ultraviolet detection at 275 nm and off-line radiometry. Endogenous compounds and oxprenolol metabolites did not interfere with the assay. Analysis of water and blood, plasma and urine samples of rats and dogs spiked with [14C]oxprenolol hydrochloride showed mean recoveries for R(+)-oxprenolol hydrochloride of 99.2% (water), 99.3% (blood), 99.1% (plasma) and 97.9% (urine), and for S(-)-oxprenolol hydrochloride of 99.7% (water), 98.1% (blood), 98.6% (plasma) and 96.9% (urine). In a pilot study, the presented method was used to investigate the metabolic fate of the enantiomers in two dogs dosed orally with racemic [14C]oxprenolol hydrochloride (3 mg/kg). The results show that conjugation of R(+)-oxprenolol exceeded that of S(-)-oxprenolol.

Multiple inverse isotope dilution assay for the stereospecific quantitative determination of R(-) and S(+)-oxaprotiline in biological fluids

An isotope dilution assay for the determination of both oxaprotiline enantiomers in biological samples after administration of the racemic mixture has been developed. The enantiomers were reacted with synthetically prepared, optically pure N-trifluoroacetyl-S(-)-prolyl chloride, followed by high-performance liquid chromatographic separation of the diastereoisomers formed. Quantitation was performed by on-line UV detection at 260 nm and off-line radiometry by liquid scintillation counting. Endogenous compounds and metabolites do not interfere in the assay. Analysis of water and the blood and urine of rats spiked with [14C]oxaprotiline X HCl showed recoveries for S(+)-oxaprotiline X HCl (mean +/- coefficient of variation, n = 4-6) of 98.0 +/- 1.0% (water), 100.5 +/- 0.6% (blood) and 101.5 +/- 2.0% (urine), and for R(-)-oxaprotiline X HCl of 101.3 +/- 2.0% (water), 102.2 +/- 2.1% (blood) and 103.2 +/- 0.2% (urine). A pilot study to determine blood levels of the two enantiomers in two rats dosed with racemic [14C]oxaprotiline X HCl (10 mg/kg i.v.) was carried out to test the method. The results indicated stereoselective disposition of oxaprotiline enantiomers in the rat. The ratio of the areas under the blood concentration curves for R(-)-to S(+)-oxaprotiline X HCl was 1.14.

Simultaneous determination of d- and l-propranolol in human plasma by high-performance liquid chromatography

A method for the determination of d- and l-propranolol in human plasma is described. The method involves extraction of propranolol from plasma, and the formation of diastereomeric derivatives with the chiral reagent N-trifluoroacetyl-1-prolylchloride. Separation and quantitation of the diastereomeric propranolol derivatives are carried out by a reversed-phase high-performance liquid-chromatographic system with fluorimetric detection. The reproducibility in the determination of d- and l-propranolol in human plasma was 4.5% (relative standard deviation) at drug levels of 10 ng/ml. In two subjects who received a single 40-mg tablet of racemic propranolol the plasma levels of the d-isomer were lower than of the l-propranolol. The half-lives of d- and l-propranolol were similar.

Separation of enantiomeric iodinated thyronines by liquid chromatography of diastereomers

A method for the separation of D,L-triiodothyronine and D,L-tetraiodothyronine optical isomers is described. The iodinated thyronines are coupled with L-leucine and the resulting diastereomers are separated by reversed-phase liquid chromatography. The derivatives are detected in the UV region at 230 nm. The technique can be used for the determination of the optical purity of thyroid hormones. It is possible to determine 0.2% of the L-isomer in D-tetraiodothyronine with a relative standard deviation of 8%. One complete analysis takes about 2 h. The results are in good agreement with those of an enzymatic method.