endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene-2-carboxylic acid, a superior resolving agent for the high-performance liquid chromatographic separation of enantiomers of hydroxylated derivatives of two azaaromatic hydrocarbons

Resolution of chiral drugs by liquid chromatography based upon diastereomer formation with chiral derivatization reagents

Chiral derivatization reagents for resolution of biologically important compounds, such as chiral drugs by high-performance liquid chromatography (HPLC), based upon pre-column derivatization and diastereomer formation, are reviewed. The derivatization reagents for various functional groups, i.e., amine, carboxyl, carbonyl, hydroxyl and thiol, are evaluated in terms of reactivity, stability, wavelength, handling, versatility, sensitivity, and selectivity. The applicability of the reagents to the analyses of drugs and bioactive compounds are included in the text.

Diastereomeric selectivity of carbon-coated zirconia reversed-phase liquid chromatographic media

The determination of enantiomeric excess, that is, the relative amount of any pair of optical antipodes, constitutes a integral part of the work of analytical and synthetic chemists involved in natural products research or pharmaceutical development. Mosher's reagent [alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride] has evolved into a major tool for the determination of absolute configuration by NMR. We report here on the separation of diastereomers formed by derivatizing enantiomers with Mosher's reagent. We have shown that reversed-phase liquid-solid adsorption chromatography on carbon surfaces frequently gives considerably superior resolution of diastereomeric pairs than does RPLC on conventional bonded phases. The improved resolution results from the very high sensitivity of solid carbon surfaces to the geometric organization of the solute rather than from differences in column efficiency. We compare the separation of pharmaceutically and biologically important stereoisomeric mixtures, including (+/-)-warfarin and (+/-)-amino acid esters, on both conventional bonded phases and carbon surfaces prepared by chemical vapor deposition of organic compounds on porous zirconia microparticles.

Enantiomeric derivatization for biomedical chromatography

Derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers are reviewed, with emphasis on the literature published in the last 10 years. Three main aspects of chiral derivatization are discussed. (a) Enantiomers containing suitable functional groups (amino, carboxyl, hydroxyl, epoxy, etc.) are transformed into covalently bonded diastereomeric derivatives using homochiral derivatizing agents. The diastereomers formed (esters, amides, urethanes, urea and thiourea, etc., derivatives) can be separated on achiral stationary phases. The derivatization reactions often afford further advantages, such as the improvement of chromatographic properties and the detectability of the solutes using UV and fluorimetric detectors. (b) Covalent but achiral derivatization is often necessary even with the use of chiral stationary phases enabling in principle direct enantioseparations (Pirkle-type columns, cyclodextrin-bonded phases, glycoprotein column and functionalized cellulose columns). The main goals of these derivatization reactions (which are analogous to those discussed above), are to introduce functional groups into the molecule of the enantiomers that improve the possibilities for chiral interactions or block functional groups to avoid non-specific interactions. (c) In the broader sense, the dynamic formation of diastereomers using chiral mobile phase additives (cyclodextrins, various reagents to form diastereomeric ion pairs, adducts, mixed metal complexes) can also be considered to be chiral derivatization reactions and is therefore briefly discussed also.

Sensitive stereospecific assay of warfarin in plasma: reversed-phase high-performance liquid chromatographic separation using diastereoisomeric esters of (-)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]-hept-5- ene-2-carboxylic acid

A stereospecific reversed-phase high-performance liquid chromatographic (HPLC) assay for warfarin in plasma has been developed. The assay involves a rapid, simple clean-up procedure which separates warfarin from plasma constituents and warfarin metabolites. Warfarin enantiomers were assayed as their (-)-(1S,2R,4R)-endo-1,4,5,6,7,7-hexachlorobicyclo[2.2.1]hept-5-ene -2- carboxylic acid diastereoisomeric esters by reversed-phase HPLC. Excellent resolution of the diastereoisomers was achieved in less than 10 min. Sensitivity of the assay was approximately 5-10 ng/ml for each isomer.

High-performance liquid chromatographic separation of the enantiomers of hydroxychloroquine and its major metabolites in biological fluids using an alpha 1-acid glycoprotein stationary phase

An enantioselective two-stage off-line assay has been developed for the analysis of hydroxychloroquine and its three major metabolites in biological fluids. The first non-stereoselective stage of the assay (PRP-1 column) separates and quantitates parent drug and metabolites. Fractions containing hydroxychloroquine and each of the metabolites are collected manually, evaporated, reconstituted in mobile phase and re-injected onto an alpha 1-acid glycoprotein column to separate and determine proportions of individual enantiomers. Preliminary results from patients samples indicate that the disposition of hydroxychloroquine and its major metabolites is enantioselective. p6