Saccharide sensing with molecular receptors based on boronic acid

The lock-and-key principle of natural systems is based on complex interactions like hydrogen bonding. Many synthetic systems that attempt to mimic natural systems have also used hydrogen bonding as the main binding force and have met with great success in non-hydrogen-bonding solvents that do not compete with the guest for the binding pocket. In contrast, natural systems function in water, a very competitive solvent. Synthetic hydrogen-bonding systems may yet evolve to be successful in water. If this transition can not be made, synthetic answers can nevertheless take inspiration from nature without slavishly following the blue print. This is not an attempt to re-invent the "lock": a new locking mechanism merely replaces the existing one. The inspiration might be the view of the hydrogen bond as an easily reversible "covalent" bond. Screening the literature we rediscovered boronic acids, which have been known for over 100 years. Conveniently, boronic acids rapidly and reversibly form cyclic esters with diols in basic aqueous media. Saccharides and other related "keys" contain a contiguous array of cyclic alcohols. In this work we hope to demonstrate that saccharide "keys" and boronic acid "locks" can open the door to a new and exciting field of research. © VCH Verlagsgesellschaft mbH. D-69451 Weinheim, 1996.