An adamantane-based disubstituted binding motif with picomolar dissociation constants for cucurbit[n]urils in water and related quaternary assemblies

Abstract

A non-axial centerpiece based on 1,3-disubstituted adamantane was designed, and three new guests were prepared. In the structure of the heterotritopic guests, the central adamantane site was combined with two terminal butyl or 1-adamantyl sites. The new central binding motif displayed an extraordinarily high affinity towards CB8 (K_a = (5.3 ± 0.3) × 10¹² M⁻¹ in water) to allow formation of quaternary assemblies with geometries which are dependent on the nature of macrocycles. Based on the individual binding strengths, the replacement of CB7 by CB8 led to inverse arrangements of the quaternary assemblies; i.e., β-CD is capped at the central site by two CB7 units, while the CB8 prefers the central site to be capped with two β-CD units.