Direct resolution of (+/-)-ephedrine and atropine into their enantiomers by impregnated TLC

Enantioseparations by thin-layer chromatography

An up-to-date overview of thin-layer chromatography (TLC) techniques for chiral separations of various significant and/or recent examples of enantioresolutions is reported. Furthermore, examples for chiral separations obtained on achiral commercially available C18 TLC plates are described in detail. These include the enantioseparation of methylthiohydantoin-phenylalanine and methylthiohydantoin-tyrosine using hydroxyethyl-β-cyclodextrin as mobile phase additive and the separation of the enantiomers of warfarin and p-chlorowarfarin using bovine serum albumin as mobile phase additive.

Amino acids as chiral selectors in enantioresolution by liquid chromatography

Amino acids are unique in terms of their structural features and multidimensional uses. With their simple structures and the ready availability of both enantiomers, amino acids not only serve as a chiral pool for synthesis but also provide an inexpensive pool for resolution studies. There has been no attempt to review the application of amino acids as chiral selectors for chromatographic enantioresolution of pharmaceuticals and other compounds. The present paper deals with application of l-amino acids and complexes of l-amino acids with a metal ion, particularly Cu(II), as an impregnating reagent in thin-layer chromatography or as a chiral ligand exchange reagent or a chiral mobile phase additive in both thin-layer chromatography and high-performance liquid chromatography. Enantiomeric resolution of β-blockers, nonsteroidal anti-inflammatories, amino acids (and their derivatives) and certain other compounds is discussed.

Chiral separation of atropine by high-performance liquid chromatography

The separation and quantitation of the enantiomers and also the determination of the enantiomeric purity are now current and indispensable tasks for the pharmaceutical analysis. Among the various techniques, liquid chromatography remains the best modality owing to several advantages. High speed, sensitivity, and reproducible results make LC the method of choice in almost all laboratories. Phases that contain alpha1-acid glycoprotein as chiral selector are suitable for separation of charged and uncharged enantiomers with widely different structure. Atropine is widely used as parasympatolytic, anticholinergic and antiemetic drugs. It is one of the preferred antidote for immediate management of toxicity associated with nerve agents. Stereoselective separation was achieved with a prepacked alpha1-acid glycoprotein column without any derivatization procedure. The liquid chromatography system is coupled to mass spectrometry with an atmospheric pressure chemical ionization interface in the positive-ion mode. The chromatographed analytes are detected in selective ion monitoring after optimisation using factorial experimental design. Small amount of enantiomeric composition can be evaluated either by MS or by UV spectrometry (less than 5%).

Resolution of (�)-ibuprofen using (?)-brucine as a chiral selector by thin layer chromatography

The enantiomeric resolution of (+/-)-ibuprofen into its enantiomers was achieved by TLC on silica gel plate using optically pure (-)-brucine as a chiral selector and acetonitrile-methanol (5:1, v/v) as the solvent system. Spots were located in an iodine chamber. The detection limit was 4.9 microg. The effect of concentration of the chiral selector, temperature and pH on resolution has been studied.

Enantiomeric resolution of some 2-arylpropionic acids using L-(-)-serine-impregnated silica as stationary phase by thin layer chromatography

The enantiomeric resolution of certain 2-arylpropionic acids was achieved on thin silica gel plates impregnated with optically pure L-(-)-serine as chiral selector. The mobile phase enabling successful resolution of (+/-)-ibuproxam and (+/-)-ketoprofen was acetonitrile-methanol-water (16:4:0.5, v/v/v) and (16:3:0.5, v/v/v) for (+/-)-tiaprofenic acid. The spots were detected with iodine vapors and the detection limits were found to be different for each of the 2-arylpropionic acid, ranging between 0.25 and 0.50 microg/ml. The effect of concentration of the impregnating chiral selector, temperature and pH on resolution has been studied. The procedure was applied successfully to resolve commercial ampoules of ketoprofen dosage formulation.

Thin layer chromatographic resolution of some 2-arylpropionic acid enantiomers using L-(-)-serine, L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine-impregnated silica gel as stationary phases

Impregnated silica TLC plates with L-(-)-serine and L-(-)-threonine and a mixture of L-(-)-serine and L-(-)-threonine (1:1) as chiral selectors were prepared to use as chiral stationary phases (CSPs) in thin layer chromatography. The resolution of the enantiomers of 2-arylpropionic drugs, including ibuprofen, ibuproxam, ketoprofen, pranoprofen, benoxaprofen, flurbiprofen and tiaprofenic acid was investigated on these CSPs. A mobile phase system of acetonitrile-methanol-water (16:4:0.5, v/v/v) was used. The spots were detected with iodine vapours and the detection limits were found to range between 0.25 and 0.5 micro g/mL for all racemic compounds investigated. The effect of temperature, pH and concentration of the impregnating chiral selectors on resolution has been studied.

Beta-phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids and compounds derived from them, including further products of oxidation, condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2001 to June 2002 is reviewed, with 581 references cited.