Allosteric Recognition of Homomeric and Heteromeric Pairs of Monosaccharides by a Foldamer Capsule

The recognition of either homomeric or heteromeric pairs of pentoses in an aromatic oligoamide double helical foldamer capsule was evidenced by circular dichroism (CD), NMR spectroscopy, and X‐ray crystallography. The cavity of the host was predicted to be large enough to accommodate simultaneously two xylose molecules and to form a 1:2 complex (one container, two saccharides). Solution and solid‐state data revealed the selective recognition of the α‐4C1‐d‐xylopyranose tautomer, which is bound at two identical sites in the foldamer cavity. A step further was achieved by sequestering a heteromeric pair of pentoses, that is, one molecule of α‐4C1‐d‐xylopyranose and one molecule of β‐1C4‐d‐arabinopyranose despite the symmetrical nature of the host and despite the similarity of the guests. Subtle induced‐fit and allosteric effects are responsible for the outstanding selectivities observed. Two monosacharides fit in an aromatic double helical foldamer container. Binding is shown to be selective in terms of the sugar anomer, pyranose/furanose tautomer, and helix handedness, and leads to well defined homomeric or heteromeric complexes. One heteromeric complex selectively forms out of 42 different possibilities.