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 alpha-C-4(1)-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 alpha-C-4(1)-d-xylopyranose and one molecule of beta-C-1(4)-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.