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Differentiation of enantiomeric anions by NMR spectroscopy with chiral bisurea receptors

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Abstract

Chiral anionic species are ubiquitous and play important roles in biological systems. Despite the recent advancements in synthetic anion receptors bearing urea functionalities, urea-based chiral solvating agents (CSAs) that can separate the NMR signals of racemic anions remain limited. Herein, three dibenzofuran-based C2-symmetric chiral bisureas were synthesized from the reaction of (R,R)-4,6-bis(1-aminopropyl)dibenzo[b,d]furan with phenyl isocyanate, phenyl thioisocyanate, or tosyl isocyanate. The chiral anion recognition properties of these bisureas were examined by 1H NMR spectroscopy using DL-tetrabutylammonium mandelate (TBAM) as a model substrate. A clear baseline separation of the enantiomeric signals of the benzylic proton of TBAM was achieved upon mixing with 0.5 equivalents of bis(phenylurea). In contrast to previous urea-based chiral anion receptors that differentiate the enantiomers of chiral anions by forming 1 : 1 host–guest complexes, a high chiral recognition ability of chiral bis(phenylurea) was achieved owing to the generation of an equilibrium between free guests, 1 : 1 host–guest complexes, and 1 : 2 host–guest complexes. Chiral bis(phenylurea) was also successfully employed in the separation of the enantiomeric 1H NMR signals of various racemic anions.

Graphical abstract: Differentiation of enantiomeric anions by NMR spectroscopy with chiral bisurea receptors

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Publication details

The article was received on 16 Sep 2017, accepted on 04 Nov 2017 and first published on 06 Nov 2017


Article type: Paper
DOI: 10.1039/C7OB02318A
Citation: Org. Biomol. Chem., 2018, Advance Article
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    Differentiation of enantiomeric anions by NMR spectroscopy with chiral bisurea receptors

    S. Ito, M. Okuno and M. Asami, Org. Biomol. Chem., 2018, Advance Article , DOI: 10.1039/C7OB02318A

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