Recent developments in fast chromatographic enantioseparations now make high throughput analysis of enantiopurity on the order of a few seconds achievable. Nevertheless, routine chromatographic determinations of enantiopurity to support stereochemical investigations in pharmaceutical research and development, synthetic chemistry and bioanalysis are still typically performed on the 5-20 min timescale, with many practitioners believing that sub-minute enantioseparations are not representative of the molecules encountered in day to day research. In this study we develop ultrafast chromatographic enantioseparations for a variety of pharmaceutically-related drugs and intermediates, showing that sub-minute resolutions are now possible in the vast majority of cases by both supercritical fluid chromatography (SFC) and reversed phase liquid chromatography (RP-LC). Examples are provided illustrating how such methods can be routinely developed and used for ultrafast high throughput analysis to support enantioselective synthesis investigations.
In recent years, the use of halogen-containing molecules has proliferated in the pharmaceutical industry, where the incorporation of halogens, especially fluorine, has become vitally important for blocking metabolism and enhancing the biological activity of pharmaceuticals. The chromatographic separation of halogen-containing pharmaceuticals from associated isomers or dehalogenation impurities can sometimes be quite difficult. In an attempt to identify the best current tools available for addressing this important problem, a survey of the suitability of four chromatographic method development platforms (ultra high-performance liquid chromatography (UHPLC), core shell HPLC, achiral supercritical fluid chromatography (SFC) and chiral SFC) for separating closely related mixtures of halogen-containing pharmaceuticals and their dehalogenated isosteres is described. Of the 132 column and mobile phase combinations examined for each mixture, a small subset of conditions were found to afford the best overall performance, with a single UHPLC method (2.1 × 50 mm, 1.9 μm Hypersil Gold PFP, acetonitrile/methanol based aqueous eluents containing either phosphoric or perchloric acid with 150 mM sodium perchlorate) affording excellent separation for all samples. Similarly, a survey of several families of closely related halogen-containing small molecules representing the diversity of impurities that can sometimes be found in purchased starting materials for synthesis revealed chiral SFC (Chiralcel OJ-3 and Chiralpak IB, isopropanol or ethanol with 25 mM isobutylamine/carbon dioxide) as well as the UHPLC (2.1 × 50 mm, 1.8 μm ZORBAX RRHD Eclipse Plus C18 and the Gold PFP, acetonitrile/methanol based aqueous eluents containing phosphoric acid) as preferred methods.
The
use of NMR chiral solvating agents (CSAs) for the analysis
of enantiopurity has been known for decades, but has been supplanted
in recent years by chromatographic enantioseparation technology. While
chromatographic methods for the analysis of enantiopurity are now
commonplace and easy to implement, there are still individual compounds
and entire classes of analytes where enantioseparation can prove extremely
difficult, notably, compounds that are chiral by virtue of very subtle
differences such as isotopic substitution or small differences in
alkyl chain length. NMR analysis using CSAs can often be useful for
such problems, but the traditional approach to selection of an appropriate
CSA and the development of an NMR-based analysis method often involves
a trial-and-error approach that can be relatively slow and tedious.
In this study we describe a high-throughput experimentation approach
to the selection of NMR CSAs that employs automation-enabled screening
of prepared libraries of CSAs in a systematic fashion. This approach
affords excellent results for a standard set of enantioenriched compounds,
providing a valuable comparative data set for the effectiveness of
CSAs for different classes of compounds. In addition, the technique
has been successfully applied to challenging pharmaceutical development
problems that are not amenable to chromatographic solutions. Overall,
this methodology provides a rapid and powerful approach for investigating
enantiopurity that compliments and augments conventional chromatographic
approaches.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.