Enantioselective amino acid recognition using acyclic thiourea receptors

A series of acyclic thiourea derivatives, designed to create a cleft with four hydrogen bond donors suitable for carboxylate recognition, have been prepared, and their ability to bind to N-protected amino acid carboxylate salts has been investigated. The crystal structure of one of the thioureas has been determined showing that it forms a hydrogen bonded centrosymmetric dimer in the solid-state, in a conformation appropriate for the desired binding of carboxylates. The thioureas show good discrimination between different amino acids and those thioureas incorporating chiral moieties show moderate enantioselectivity for a range of amino acid derivatives.