Multicentered hydrogen bonding in 1-[(1-de-oxy-β-d-fructo-pyranos-1-yl)aza-nium-yl]cyclo-pentane-carboxyl-ate ('d-fructose-cyclo-leucine').

The title compound, C(12)H(21)NO(7), (I), is conformationally unstable; the predominant form present in its solution is the β-pyran-ose form (74.3%), followed by the β- and α-furan-oses (12.1 and 10.2%, respectively), α-pyran-ose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the (2) C (5) β-pyran-ose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclo-pentane ring assuming the E (9) envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of anti-parallel infinite chains of fused R (3) (3)(6) and R (3) (3)(8) rings. The mol-ecule features extensive intra-molecular hydrogen bonding, which is uniquely multicentered and involves the carboxyl-ate, ammonium and carbohydrate hy-droxy groups. In contrast, the contribution of inter-molecular O⋯H/H⋯O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other d-fructose-amino acids. The (1)H NMR data suggest a slow rotation around the C1-C2 bond in (I), indicating that the intra-molecular heteroatom contacts survive in aqueous solution of the mol-ecule as well.