Effective Recognition of Caffeine by Diaminocarbazolic Receptors

Caffeine is a competitive inhibitor of adenosine receptors and possesses wide pharmacological activity. Artificial receptors recognizing caffeine potentially have a wide range of biomedical and industrial applications. Herein, we describe two structurally related and readily available artificial receptors: 1) a macrocyclic receptor, which binds caffeine with the unprecedented affinity of 9.3 microM, though with poor selectivity; and 2) a tweezers-like structure, showing an affinity of 26 microM and a 4.5-fold and 6-fold selectivity toward theophylline and theobromine, respectively. Binding affinities were measured by 1H NMR titrations and were confirmed by isothermal titration calorimetry. The X-ray structure of the complex between caffeine and the acyclic receptor revealed the origin of the recognition, explained the selectivity, and shed light on the role of hydrogen bonding and CH-pi/pi-pi interactions.