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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.

International audience; A synthetic helical aromatic oligoamide foldamer receptor with high affinity and selectivity for tartaric acid was subjected to a structure-based evolution of its sequence via mutations, additions and deletions of monomers to produce a new receptor having high affinity and selectivity for malic acid, a guest that differs from tartaric acid by a single oxygen atom. Seven iteratively modified sequences were synthesized. Detailed structural investigations of host-guest complexes were carried out systematically to guide the design of the next generation. A first outcome was a reversal of selectivity of the receptors, with a starting preference for tartaric acid over malic acid of over 10 2 and an ending sequence showing a preference for malic acid over tartaric acid of over 10 2. Another outcome was a very strong enhancement of the affinity for malic acid, despite the fact it has fewer recognition features for binding through polar interactions such as hydrogen bonds. Such level of discrimination between very much resembling guests exemplifies the amenability of foldamers to outstanding achievements in molecular recognition. Altogether, our results demonstrate the viability of a rational receptor design approach that exploits the modularity of foldamer sequences and, in the case of aromatic amide foldamers, their amenability to structural elucidation, their relative ease of synthesis and the predictability of their structure.