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

Abstract

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.