Synthesis, conformational studies and binding properties of acyclic receptors for N-protected amino acids and dipeptides

Solid-phase syntheses of novel receptors featuring a 2,6-diamidopyridine "head" group and bearing sulfonamidopeptide sidearms are described, NMR conformational studies show that the 'two-armed" receptors collapse into an intramolecularly folded structure through formation of a hydrogen-bonding network. In order to accommodate the guests, receptors have to unfold, breaking the intramolecular hydrogen bonds. The absolute binding constants of receptors with N-protected amino acids and dipeptides are therefore relatively weak. However, one receptor shows a high selectivity for N-CbZ-D-Ala-D-AlaOH over its enantiomer N-Cbz-L-Ala-L-AlaOH