Cationic acyclic cucurbit[n]uril-type containers: synthesis and molecular recognition toward nucleotides

Abstract

We report the synthesis of M2NH3 which is a tetracationic analogue of our prototypical acyclic CB[n]-type molecular container M2. Both M1NH3 and M2NH3 possess excellent solubility in D₂O and do not undergo intermolecular self-association processes that would impinge on their molecular recognition properties. Compounds M1NH3 and M2NH3 do, however, undergo an intramolecular self-complexation process driven by ion–dipole interactions between the ureidyl C=O portals and the OCH₂CH₂NH₃ arms along with inclusion of one aromatic wall in its own hydrophobic cavity. The K_a values for M1NH3 and M2NH3 towards seven nucleotides were determined by ¹H NMR titration and found to be quite modest (K_a in the 10²–10³ M⁻¹ range) although M2NH3 is slightly more potent. The more highly charged guests (e.g. ATP) form stronger complexes with M1NH3 and M2NH3 than the less highly charged guest (e.g. ADP, AMP). The work highlights the dominant influence of the ureidyl C=O portals on the molecular recognition behaviour of acyclic CB[n]-type receptors and suggests routes (e.g. more highly charged arms) to enhance their recognition behaviour towards anions.

Keywords:

• Cucurbituril
• molecular container
• anion recognition
• glycoluril
• nucleotides

Funding

This work was financially supported by the National Cancer Institute of the National Institutes of Health [CA168365 to L. I.].

Supplemental material

Supplemental data for this article can be accessed online here: http://dx.doi.org/10.1080/10610278.2016.1167893