Chiral columns development screening

Reversed phase chiral separations are desired simply for efficiency in generating results from laboratories whose instrumentation is routinely configured to run in reversed and not normal phase modes.Normal phase conditions are less attractive to the analytical chemist for this reason and deter laboratory efficiency. Typical commercial chiral LC columns found on pharmaceutical reversed phase LC chiral method development screens are listed in Table 8. Table 11 shows suggested chromatographic conditions employed in reversed phase chiral screening. 

Each glycopeptide CSP has unique selectivity as well as complementary characteristics, and a considerable number of racemates have been resolved on all three of them. Interestingly, most of the resolved enantiomers have the same retention order on these macrocyclic CSPs. When they are mixed or coupled with each other, the selectivity on one CSP will not be canceled by another. Even if some compounds may not have the same retention order, the complementary effects will result in an identifiable selectivity. Therefore, the coupled chiral columns can be used as a screening tool and save chromatographers substantial time in method development. 

Finally, it may be noted that some chiral column vendors provide free screening or method development support. 

TABLE I Polysaccharide-Based Chiral Columns Commonly Used in Pharmaceutical HPLC Method Development Screening Systems... 

TABLE 8 Chiral Columns Screening Systems Commonly Used in Pharmaceutical Method Development... 

A knowledge-based chiral method development strategy can be very effective on chiral column selection. For example, a chiral screening method was used to monitor the enantiomeric purity of an atropisomeric dmg candidate. It returned the Chiralcel OD-RH column in reversed phase with a baseline enantioseparation of both atropi-somers (Fig. 12a). There was a need to redevelop the chiral method as the compound moved into development stages. Based on possible interaction sites around the chiral asymmetric axis of the compound (a primary amine for ionic and H-bonding interactions and an aromatic ring for k-k interaction), Chirobiotic V2 was tested since... 

Method development remains the most challenging aspect of chiral chromatographic analysis, and the need for rapid method development is particularly acute in the pharmaceutical industry. To complicate matters, even structurally similar compounds may not be resolved under the same chromatographic conditions, or even on the same CSP. Rapid column equilibration in SFC speeds the column screening process, and automated systems accommodating multiple CSPs and modifiers now permit unattended method optimization in SFC [36]. Because more compounds are likely to be resolved with a single set of parameters in SFC than in LC, the analyst stands a greater chance of success on the first try in SFC [37]. The increased resolution obtained in SFC may also reduce the number of columns that must be evaluated to achieve the desired separation. 

The approach to method development is similar to the one described for HPLC and can be characterized as a rapid stationary phase screen using column and solvent switching with gradient elution followed by development of an isocratic preparative method. SFC has been successfully applied to the analytical and preparative separation of achiral and chiral compounds. 

Although classical column chromatography over chiral stationary phases has been used for several years, HPLC has until recently been regarded mainly as an analytical tool. However, methods have now been developed and many papers have been published on the various applications of particular stationary phases in preparative HPLC, which may be the method of choice when the preparation of small amounts of material are required for screening purposes, for use in biological assays, or as standards in purity assays. The use of chromatographic techniques may be quicker and less risky than custom synthesis and resolution and can guarantee material to a defined specification. 

---