Enantioselective binding of dipeptides using acyclic receptors

Novel receptors featuring a 2,6-diamidopyridine ‘head’ group and bearing sulfonamidopeptide sidearms have been prepared on the solid-phase; one receptor showed high selectivity for N-Cbz-D-Ala-D-AlaOH over its enantiomer N-Cbz-L-Ala-L-AlaOH, but absolute binding constants were relatively weak, which can be understood in terms of receptors which have to unfold, breaking intramolecular hydrogen bonds, in order to accommodate the guests.