Configuration controlled crystal and/or gel formation of protected D-Glucosamines supported by promiscuous interaction surfaces and a conformationally heterogeneous solution state.

The configuration dependent self-association mode of the two anomers of O-Ac,N -Fmoc-D-Glucosamine, a foldamer building block, leading to gel and/or single crystal formation is described. The beta-anomer of the sugar amino acid ( 2 ) forms a gel from various solvents (confirmed by SEM, rheology measurements, NMR and ECD spectroscopy), while the alpha-anomer ( 1 ) forms none of those tested. Transition from solution state to gel is coupled to a concurrent shift of the Fmoc-groups: from a freely rotating (almost symmetrical) to a specific, asymmetric orientation. While the crystal structure of the alpha-anomer is built as an evenly packed 3D-system, the beta-anomer forms a looser superstructure of well-packed 2D-layers. Modeling indicates that in the lowest energy, but scarcely sampled conformer of the beta-anomer, the Fmoc-group bends above the sugar moiety, stabilized by intramolecular CH pi interaction between the aromatic rings. We conclude that possessing an extended and promiscuous interaction surface and a conformationally heterogeneous solution state are among the basic requirements of gel formation for a candidate molecule.