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Large Water‐Soluble Cyclophanes with Convergent Intracavity Functionality
Author(s) -
Diederich François,
Carcanague Daniel R.
Publication year - 1994
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19940770320
Subject(s) - chemistry , cyclophane , steric effects , diphenylmethane , stereochemistry , crystallography , amine gas treating , ether , supramolecular chemistry , molecule , crystal structure , organic chemistry , catalysis
New tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H 2 O‐soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H 2 O‐solubility with amine or crown‐ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X‐ray crystal‐structure analysis of the tritopic receptor 18 with one potential neutral‐molecule and two cation‐binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O‐atoms of two convergent CO groups. Despite the binding‐site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring‐guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔ G °> 2 kcal mol −1 ) of the complexes formed by three structurally closely related hybrid receptors with convergent CO, OH or CH 2 groups and 6‐hydroxynaphthalene‐2‐carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation.