Issue 19, 2021

Imino-thiolate-templated synthesis of a chloride-selective neutral macrocyclic host with a specific “turn-off–on” fluorescence response for hypochlorite (ClO)

Abstract

A precise replacement of one oxygen atom with sulfur in the intra-annular amide-1-methylene-pyrene substituent allowed us to efficiently synthesize a novel macrocyclic host 2 for selective recognition of chloride ions. The high yield of the macrocyclization process (64%) between sterically demanding substrates was attributed to a combination of external and internal templating effects of chloride and – previously unrecognized in the literature – thioimidate anions –C([double bond, length as m-dash]N–)S (generated in situ by deprotonation of thioamide by sodium methoxide), respectively. Both templating agents help to adopt a favorable folded conformation of the open-chain intermediate leading to a sterically crowded structure of 2. The host was characterized by single crystal X-ray analysis and its anion recognition properties were determined by 1H-NMR titration experiments in a demanding (DMSO-d6 + 0.5% H2O) solvent mixture. The host exhibits one of the highest reported selectivities toward chloride among systems binding anions by hydrogen bonding interactions (Ka,Cl = 1130 M−1, Ka,Cl/Ka,anion up to 35.3). Host 2 is essentially nonfluorescent due to the quenching effect of a thioamide group, however, the selective oxidation of the C[double bond, length as m-dash]S moiety by the hypochlorite (ClO) anion was found to fully restore the fluorescence (λem = 377 nm). This demonstrates the first example of metal-free macrocyclic sensors for the selective detection of this biologically important analyte.

Graphical abstract: Imino-thiolate-templated synthesis of a chloride-selective neutral macrocyclic host with a specific “turn-off–on” fluorescence response for hypochlorite (ClO−)

Supplementary files

Article information

Article type
Research Article
Submitted
31 Mrz 2021
Accepted
14 Jul 2021
First published
14 Jul 2021

Org. Chem. Front., 2021,8, 5258-5264

Imino-thiolate-templated synthesis of a chloride-selective neutral macrocyclic host with a specific “turn-off–on” fluorescence response for hypochlorite (ClO)

K. Dąbrowa, M. Lindner, A. Tyszka-Gumkowska and J. Jurczak, Org. Chem. Front., 2021, 8, 5258 DOI: 10.1039/D1QO00504A

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