Ben F. H. Drenth

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.

High-performance liquid chromatography in the elucidation of the metabolic fate of butoprozine : Screening for unknown metabolites in the rat

A systematic approach to the investigation of metabolic degradation of drugs is presented. Extraction of the biological sample is avoided by direct injection of bile or urine in a reversed-phase high-performance liquid chromatography system. Good separation of the various metabolites is obtained by changing the composition of the mobile phase so that all components become separated from the solvent front and are eluted from the column. The metabolites can be detected by measuring the amount of radioactivity in the column effluent, which also serves as a check on the overall recovery. Simultaneous registration of the UV absorbance permits certain conclusions to be drawn with regard to the nature of the metabolites. This approach is illustrated in the screening for metabolites of Butoprozine, a new anti-anginal drug, in rat bile. Essentially, all metabolites could be followed by suitable adaptations of the mobile phase, thus providing a metabolid profile with a recovery of 95% of the radioactivity.

Unequal Disposition of Enantiomers of the Organic Cation Oxyphenonium in the Rat Isolated Perfused Liver

Abstract— This paper describes the results of pharmacokinetic experiments in the rat isolated perfused liver with enantiomers of oxyphenonium. The study was performed with the [14C]methyl labelled compounds. In this preparation both metabolism and biliary excretion were significantly different for the (+)‐ and the (‐)‐isomer. Hepatic uptake rate was similar, but total biliary excretion (including metabolites) of the (‐)‐isomer was only 55% compared with the excretion of the (+)‐isomer. In line with these data, after 2 h only 30% of the dose of the (+)‐isomer and over 50% of the dose of the (‐)‐isomer was still found in the liver, predominantly in the form of metabolites. The metabolic profile was investigated using ion pair TLC. At least two metabolites were detected in bile for both enantiomers. However, unchanged (‐)‐oxyphenonium persisted for longer in bile, indicating either a more rapid canalicular transport of the (+)‐isomer and/or a more rapid metabolism of (+)‐oxyphenonium to cholephilic metabolites.

Percutaneous absorption, disposition, metabolism, and excretion of 14C-labelled Cyoctol in humans after a single dermal application

Abstract 14C-labelled cyoctol was applied in an ethanolic solution to the forearm of four young healthy volunteers for 8 h under non-occluding conditions, to investigate its absorption, disposition, and excretion after a single dermal application. Urine and feces were collected to determine the absorbed amounts of radioactivity, while ipsi- and contralateral blood samples were taken in order to obtain an insight into the kinetics of the penetration and elimination processes. The application area was stripped with cellophane adhesive tape at three different time points to study the retention of cyoctol in the stratum comeum. Cyoctol was found to be absorbed by human skin at levels of approx. 10% of the applied dose and appeared to penetrate at a relatively fast rate. Radioactivity accumulated neither in the skin nor in any other site in the body as total recovery values were close to 100% at 120 h after removal of the dose. Radioactivity was eliminated primarily through the kidneys ( ⪢ 99%) in the form of polar metabolites. Another interesting phenomenon was that cyoctol was completely metabolized when passing through the skin as no unchanged Cyoctol could be detected in ipsilateral plasma samples. This may eliminate the occurrence of adverse systemic effects after dermal application.

A Note on Separation of Enantiomers of Oxyphenonium Bromide by High-Performance Liquid Chromatography

Oxyphenonium bromide (Fig. 1) is a quaternary ammonium compound with strong anticholinergic properties. As with many other anticholinergics, the enantiomers of this drug exhibit large differences in therapeutic effects as well as in biliary and urinary excretion[1]. For a detailed study of the fate of oxyphenonium bromide enantiomers in the body, an assay is required that allows the simultaneous determination of the two enantiomers in the same sample. High performance liquid chromatographic (HPLC)-techniques are preferred, as quaternary ammonium compounds are very sensitive to decom-positon upon injection in GC.

Chiral Differences in the Disposition of the Quaternary Anticholinergic Drug Oxyphenonium Bromide

As for many other anticholinergic drugs, the enantiomers of oxyphenonium bromide exhibit large differences in affinity to muscarinic receptors as well as in therapeutic effect [1]. For detailed study of the fate of the enantiomers in the body an assay is required that determines both enantiomers simultaneously in the biological sample. Although various chiral Chromatographic systems have been developed over the years [2], we were unable to separate the enantiomers of oxyphenonium bromide [3]. Recently we succeeded in resolving racemic oxyphenonium bromide on an α1-acid glycoprotein (EnantioPac®) column; but this system had insufficient efficiency and stability for bioanalytical applications. In order to study differences between oxyphenonium bromide enantiomers in absorption, distribution, metabolism and excretion, another approach was adopted, in which the enantiomers were synthesized separately (Fig. 1).

Attempts to Obtain Separations of Chiral Anticholinergic Drugs

Where a drug has enantiomeric forms, each should be measurable in the same sample, as now investigated with oxyphenonium and some quaternary atropine analogues. Resolution was attempted with a chiral-HPLC system, containing d-camphorsulphonic acid as a mobile phase component or (cf. W.U. Pirkle’s work) with chiral stationary phases. Neither approach was successful, due to the relatively long distance between the chiral centre and the quaternized nitrogen.