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

Chirality at the supramolecular level involves the non-symmetric arrangemen t of molecular components in a non-covalent assembly(1,2). Supramolecular c hirality is abundant in biology, for example in the DNA double helix(3), th e 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 h andedness is determined by the configuration of chiral centres in the nucle otide or peptide backbone. Synthetic hydrogen-bonded assemblies have been r eported that display supramolecular chirality in solution(6-8) or in the so lid 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 inorgan ic metal-coordinated systems(15-17), but not in organic hydrogen-bonded ass emblie(18-20). Here we describe the diastereoselective assembly of enantio- pure calix[4]arene dimelamines and 5,5-diethylbarbituric acid (DEB) into ch iral hydrogen-bonded structures of one handedness. The system displays comp lete 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 chir al assemblies, the structural simplicity of the constituent building blocks and the ability to control the assembly process by means of peripheral chi ral centres makes this system promising for the development of a wide range of homochiral supramolecular materials or enantioselective catalysts.