Warfarin chiral resolution

In 1973, Stewart and Doherty [9] resolved enantiomers of tryptophan on a column packed with BSA-succinoylaminoethyl-agarose in a discontinuous elution procedure. The mobile phase used was 0.1 M borate buffer (pH 9.2). The chromatograms of this classical research are shown in Figure 2. Several years later, this technique was applied for the chiral resolution of warfarin enantiomers [10]. In 1981, the enantiomers of tryptophan and warfarin racemates were resolved on various serum albumin CSPs [11,21,22]. The same method was used for the resolution of other drugs [12-14]. Allenmark et al. [23] studied the resolution of a series of active racemic sulfoxides on a BSA column using 0.08 M phosphate buffer (pH 5.8) as the eluting solvent. 

The protein phases were the first to be developed and are still in use for the chiral resolution of different racemates. Because both BSA and HSA are similar in structure, they have similar enantiorecognition capabilities. Warfarin and... 

In addition to high-performance liquid chromatography (HPLC), the chiral resolution using CMPAs was also carried out by supercritical fluid chromatography (SFC) [91] and capillary electrochromatography (CEC) [92-98]. Salvador et al. [91] used dimethylated /1-cyclodextrin as the mobile phase additive on porous graphite carbon as the solid phase for the chiral resolution of tofizopam, warfarin, a benzoxazine derivative, lorazepam, flurbiprofen, temazepam, chlorthalidone, and methyl phehydantoin by SFC. The authors also studied the effect of the concentration of dimethylated /1-cyclodextrin, the concentration of the mobile phase, the nature of polar modifiers, outlet pressure, and the column temperature on the chiral resolution. 

CEC has also been used for the chiral analysis of pollutants, using a variety of chiral mobile phase additives. Cyclodextrin chiral selectors have been used for the chiral resolution of ibuprofen [49], 2-phenylpropionic acid and warfarin [50]. Other chiral selectors that have been resolved include warfarin on human semm albumin [51], ibuprofen on avidin [52], dichloroprop, ibuprofen, warfarin and thalidomide on vancomycin [53], ibuprofen and warfarin on teicoplanin [54], thalidomide and warfarin on... 

FIGURE 2 Chiral resolution of warfarin using a Cogent EE column. 

In reference 22, only qualitative responses were examined in the 12-experiment PB design, i.e., the selectivity factor and the resolution of the propranolol, praziquantel, and warfarin enantiomers. In Table 8, the resolution results of the three chiral substances are given. 

This reaction was amrmg the earliest used for the GLC resolution of enantiomeric alcohols Studies 20 years ago showed that the reaction of (—)-menthyI chloroformate, [17], with chiral alcohols produced dia-stereomeric carbonates that could be resolved on packed columns (71,162). Despite its commercial availability, this CDA has been little used for the resolution of alcohols, Prelusky et al. (163) used [17] in a study of enantio-selecrive metabolic ketone reductions. The metabolite alcohols were deri-vatized with [17] and the derivatives were separated by capillary GLC. Good resolution was obtained under the chromatographic conditions used (163). The derivatization of warfarin with [17] and LC of the derivatives was described, but the peaks were not fully separated, even with retention times of 80-100 min (164). Brash et al. used CDA [17] to determine the enantiomeric composition of several enantiomeric pairs of hydroperoxy-eicosatetraenoic acids using silica LC, but some of the derivatives could not be resolved (165). It appears that [17] may be useful in the resolution of hydroxyl compounds and the evaluation of capillary GLC in the separations deserves attention. 

The type 11 CSPs have been used to resolve a wide variety of pharmacologically active compounds, both with and without derivatization (9-11). Some of the compounds that have been resolved without derivatization are hexobarbital (OA-CSP) (51), glutethimide (OB, OC, OK) (51), warfarin (OB, OC) (51), compounds containing a chiral sulfur atom (OB, OC) (52), verapamil (AD) (53), propranolol (OD) (54), and flurbiprofen (AD) (55), The resolution of the latter two compounds, propranolol, an ot, p-amino-alcohd, and flurbiprofen, a carboxylic acid, is representative of new applications for the cellulosic CSPs that are primarily used with hexane alcohol mobile phases. In the case of propranolol, the mobile phase was modified with N,N-dimethyIoctyl amine, and when flurbiprofen was chromatographed, trifluoroacetic acid was used as the modifier. 

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