Differentiation of enantiomeric anions by NMR spectroscopy with chiral bisurea receptors. Issue 2 (14th November 2017)

• Record Type: Journal Article
• Authors: Ito, Suguru; Okuno, Manami; Asami, Masatoshi
• Is Part Of: Organic & biomolecular chemistry. Volume 16:Issue 2(2017)
• Page Start: 213
• Page End: 222
• Publication Date: 2017-11-14
• Subjects: Chemistry, Organic -- Periodicals; Bioorganic chemistry -- Periodicals; Chemistry, Physical organic -- Periodicals; 547
• DOI: 10.1039/c7ob02318a
• Languages: English
• ISSNs: 1477-0520

Abstract

Abstract : Enantiomeric 1 H NMR signals of chiral anions are separated by forming 1 : 1 and 1 : 2 host–guest complexes with chiral bisurea. 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 C 2 -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 1 H NMR spectroscopy usingdl -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 1 H NMR signals of various racemic anions.