Multicentered hydrogen bonding in 1-[(1-deoxy-β-D-fructopyranos-1-yl)azaniumyl]cyclopentane-carboxylate ('D-fructose-cycloleucine')

The title compound, C12H21NO7, (I), is conformationally unstable; the predominant form present in its solution is the beta-pyranose form (74.3%), followed by the beta- and alpha-furanoses (12.1 and 10.2%, respectively), alpha-pyranose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the C-2(5) beta-pyranose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclopentane ring assuming the E-9 envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of antiparallel infinite chains of fused R-3(3)(6) and R-3(3)(8) rings. The molecule features extensive intramolecular hydrogen bonding, which is uniquely multicentered and involves the carboxylate, ammonium and carbohydrate hydroxy groups. In contrast, the contribution of intermolecular O center dot center dot center dot H/H center dot center dot center dot O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other D-fructose-amino acids. The H-1 NMR data suggest a slow rotation around the C1 - C2 bond in (I), indicating that the intramolecular heteroatom contacts survive in aqueous solution of the molecule as well.