Chirality and its importance in drug development: a synthetic chemist's perspective

19 F-Labeled Probes for Recognition-Enabled Chromatographic 19 F NMR

The NMR technique is among the most powerful analytical methods for molecular structural elucidation, process monitoring, and mechanistic investigations; however, the direct analysis of complex real-world samples is often hampered by crowded NMR spectra that are difficult to interpret. The combination of fluorine chemistry and supramolecular interactions leads to a unique detection method named recognition-enabled chromatographic (REC) 19 F NMR, where interactions between analytes and 19 F-labeled probes are transduced into chromatogram-like 19 F NMR signals of discrete chemical shifts. In this account, we summarize our endeavor to develop novel 19 F-labeled probes tailored for separation-free multicomponent analysis. The strategies to achieve chiral discrimination, sensitivity enhancement, and automated analyte identification will be covered. The account will also provide a detailed discussion of the underlying principles for the design of molecular probes for REC 19 F NMR where appropriate.

Tailoring the Recognition Property of a 19F-Labeled Gallium-Based NMR Probe: The Influence of the Metal Center

Chirality is a fundamental property of nature and an essential element of the life process. As the biological activities, metabolic pathways, and toxicity of individual enantiomers are often varied, methods to rapidly and accurately discriminate chiral analytes are in great demand. Here, we report a ¹⁹F-labeled gallium-based probe for the enantiodifferentiation of chiral monoamines, diamines, amino alcohols, amino acids, and N-heterocycles. A comparison between the new gallium-based probe and the previously developed aluminum aminotrisphenolate complex was performed. It was revealed that the gallium metal center displays a much stronger affinity toward the amino group compared to the hydroxy group, thereby producing simplified ¹⁹F NMR signals for analytes with multiple Lewis basic sites. For sterically bulky analyte, the replacement of the aluminum with gallium is envisioned to expand the binding pocket of the probe to allow different binding models to interconvert rapidly. This feature is important to the creation of easily interpretable ¹⁹F signals corresponding to each enantiomer. It is further demonstrated that the gallium-based probe is suitable for the assessment of the enantiomeric excess values of the crude products obtained in asymmetric reactions without the need for purification.

Chiral separation of lobeline analogs using high performance capillary electrophoresis and derivatized cyclodextrins as chiral additives

High performance capillary electrophoresis (HPCE) methods are described that will separate the enantiomers of various lobeline analogs synthesized in these laboratories. "Cyclodextrin array analysis" was used for preliminary screening and electrophoresis conditions were optimized for each investigated analog. The lobeline analogs under consideration were investigated as potential nicotinic agonists for the treatment of neurodegenerative disorders, such as Alzheimer's disease. Native alpha (alpha)-, beta (beta)-, and gamma (gamma)-cyclodextrins, methyl-beta-cyclodextrin (M-beta-CD), heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD), and heptakis-(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM-beta-CD), hydroxypropyl-alpha-cyclodextrin (HP-alpha-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and hydroxypropl-gamma-cyclodextrin (HP-gamma-CD) were used as run buffer additives and their effect on the enantiomeric resolution of the lobeline analogs was investigated. The effect of pH, buffer concentration, voltage, temperature and organic modifier concentration on the enantiomeric resolution of the lobeline analogs was investigated. The most suitable conditions for each compound were chosen and, with detection at a wavelength of 200 nm, optimized.

Enzymes in the synthesis of chiral drugs

The majority of synthetic chiral drugs are now marketed as racemates. This situation is rapidly changing due to the recent advances in asymmetric chemical synthesis and biocatalytic methods. This article reviews the use of enzymes in the synthesis and modification of optically pure drugs. Special attention is focused on the synthesis of new pharmaceuticals which may require efficient procedures for large-scale synthesis in the future.