An Enantioselective Benzofuran‐Based Receptor for Dinitrobenzoyl‐Substituted Amino Acids

Abstract

AbstractThe easily accessible benzofuran skeleton has been used as a platform for building two synthetic receptors able to associate with carboxylic acids and dinitrobenzoyl‐substituted (DNB) amino acids. The synthesis of the benzofuran framework allows for functionalization with hydrogen bond binding sites such as amide and sulfonamide units, in a straightforward way. Substrates containing carboxylic acids are bound in the receptor cleft by multiple H‐bonding interactions. The resulting associations can be further stabilized when new interactions such as aromatic π–π stacking are established. These binding interactions become important in the recognition of the dinitrobenzoyl‐substituted amino acids, as charge transfer interactions between the electron‐deficient dinitrobenzoyl group and the rich aromatic rings in the receptors are established. Reasonable enantioselectivities have been achieved for some of the tested dinitrobenzoyl‐substituted amino acids, allowing the resolution of the racemic receptor by preparative TLC. Experimental data (NMR titrations and ROESY experiments) and molecular modelling have been used to propose reasonable structures for the diastereomeric complexes.