Exploring the Chiral Recognition of Carboxylates by C2-Symmetric Receptors Bearing Glucosamine Pendant Arms.

Two urea-based receptors containing a glucosamine derivative were synthesized and investigated in terms of their ability to recognize chiral and achiral anions. Both receptors demonstrated a high affinity toward carboxylates in very competitive DMSO/water mixtures. The chiral recognition properties of these compounds were studied using structurally differentiated guests derived from mandelic acid and α-amino acids. We found that receptor 1 exhibits significantly higher enantioselectivities than compound 2 for all anions investigated, with a KS/KR ratio of up to 2. This low enantiodiscrimination in the case of receptor 2 is attributed to a lack of interactions between its sugar moieties and the side chain of chiral anions, due to their inadequate spatial arrangement.