Enantiomeric Water‐Soluble Octopus[3]arenes for Highly Enantioselective Recognition of Chiral Ammonium Salts in Water

Abstract

Study of enantioselective recognition in water by synthetic chiral macrocyclic receptors is undoubtedly of theoretical and practical significance, but it is a big challenge to achieve the enantioselective recognition with both high enantioselectivity and high affinity in water probably due to the deficiency of such water‐soluble macrocyclic receptors with stable chiral cavities. Herein, we report a new class of chiral macrocyclic arenes named octopus[3]arenes. The enantiomeric macrocycles are composed of three homochiral ethenoanthracene subunits, and they can be synthesized by two pathways and then easily converted into water‐soluble octopus[3]arenes P‐1 and M‐1. Notably, P‐1 and M‐1 with the rigid hexagonal structures and stable chiral hydrophobic cavities exhibit highly enantioselective recognition towards three pairs of chiral ammonium salts in water with the association constant up to 106 M−1 and the S/R selectivity up to 12.89.

Enantioselective Molecular Recognition in a Flexible Self-Folding Cavitand

“…Remarkably, cavitand 3 is able to exert enantioselective molecular recognition for most of the guests tested and provides a notable K R / K S ratio of 1:18.7 for ( R )- G3 (Table , entry 3). This is the highest ratio so far reported for enantioselective molecular recognition of quaternary ammonium salts, to the best of our knowledge . Remarkably, cavitand 3 provides similar association constants with guests of differing sizes, an intriguing observation that is likely the consequence of the receptor’s adaptable nature.…”

“…Taking inspiration from the molecular recognition phenomena occurring in Nature, a myriad of synthetic host–guest systems have been developed throughout the years, targeting applications such as catalysis, , sensing, or transport . For all of these applications, the emergence of enantioselective molecular recognition has been a long sought objective. − A universal design principle of synthetic hosts is that a receptor must be preorganized to develop significant and efficient molecular recognition behavior, although this typically comes at the expense of reducing the flexibility and adaptability of a host. In practice, the majority of synthetic host–guests systems falls short of reproducing the rich induced-fit behavior and conformational heterogeneity of proteinogenic receptors that are key to their exceptional properties. , …”

“…This is facilitated by the flexible nature of the host, leading to superior induced-fit and conformational selection phenomena in comparison with previously reported receptors. The new design allows efficient relay of chiral information from the stereogenic elements to the cavity by means of noncovalent interactions and is a step forward from chiral hosts which are highly symmetrical − , and/or do not allow efficient transfer of chirality to the molecular recognition units. , By screening a relatively reduced set of chiral quaternary ammonium ions, we have readily identified structures that provide good diastereomeric ratios. The corresponding ΔΔ G values would yield useful enantioselectivity levels if they corresponded to hypothetical diastereomeric transition states, giving good prospects for the use of 3 or variants thereof in supramolecular enantioselective catalysis .…”

Methylene-bridged naphthotubes: new macrocyclic arenes with great potential for supramolecular chemistry

“…61 To construct macrocyclic arenes with more well-defined cavities and less structural flexibility, the participation of methylene groups should be reduced. 62,63 In this respect, it is an effective approach to utilize rigid and curved aromatic structures instead of planar aromatic rings as building blocks. 64 In this highlight, we introduce the new breakthrough in the macrocyclic field by Quan, Jiang and co-workers, who have adopted a novel class of macrocyclic arenes with well-defined cavities for molecular recognition and chiral sensing.…”

Pagoda[n]arenes (n = 4, 5): Extremely Strong Binders for the Tropylium Cation

“…Macrocyclic arenes, a crucial component of supramolecular chemistry, have demonstrated intriguing recognition properties and functional applications. Calixarenes, resorcinarene, cyclotriveratrylene, pillar­[ n ]­arenes, helicarenes, biphenarenes, octopusarenes, prismarenes, and others have been extensively employed to create appealing and useful compounds and molecular assemblies. In the past few decades, the emergence of a large number of synthetic macrocyclic arenes has greatly enriched the field of supramolecular chemistry and seeded many potential applications in biology, materials, and environmental science …”