Complete asymmetric induction of supramolecular chirality in a hydrogen-bonded assembly

Chirality at the supramolecular level involves the non-symmetric arrangement of molecular components in a non-covalent assembly(1,2). Supramolecular chirality is abundant in biology, for example in the DNA double helix(3), the triple helix of collagen(4) and the lu-helical coiled coil of myosin(5). These structures are stabilized by inter-strand hydrogen bonds, and their handedness is determined by the configuration of chiral centres in the nucleotide or peptide backbone. Synthetic hydrogen-bonded assemblies have been reported that display supramolecular chirality in solution(6-8) or in the solid state(9-12). Complete asymmetric induction of supramolecular chirality-the formation of assemblies of a single handedness-has been widely studied in polymeric superstructures(13,14). It has so far been achieved in inorganic metal-coordinated systems(15-17), but not in organic hydrogen-bonded assemblie(18-20). Here we describe the diastereoselective assembly of enantio-pure calix[4]arene dimelamines and 5,5-diethylbarbituric acid (DEB) into chiral hydrogen-bonded structures of one handedness. The system displays complete enantioselective self-resolution: the mixing of homomeric assemblies (composed of homochiral units) with opposite handedness does not lead to the formation of heteromeric assemblies. The noncovalent character of the chiral assemblies, the structural simplicity of the constituent building blocks and the ability to control the assembly process by means of peripheral chiral centres makes this system promising for the development of a wide range of homochiral supramolecular materials or enantioselective catalysts.