Highly Effective Hydrogen‐Bonding Receptors for Guanine Derivatives

In the complexation of neutral organic molecules, preorganization of the receptors can play a crucial role, as studies on a new series of hydrogen-bonding receptors demonstrate. The receptor shown in the complex on the right binds guanine derivatives in [D6]DMSO/CDCl3 (1/4) with a stability constant (Ka) greater than 1.9 × 105 M−1. In comparison, a complex with a more flexible host and the same number of primary hydrogen-bonding sites is at least 4.1 kcalmol−1 less stable.