Multicentered hydrogen bonding in 1-[(1-deoxy-b- D-fructopyranos-1-yl)azaniumyl]cyclopentanecarboxylate (D-fructose-cycloleucine)

Abstract

The title compound, C12H21NO7, (I), is conformationally unstable; the predominant form present in its solution is the-pyranose form (74.3%), followed by the- and-furanoses (12.1 and 10.2%, respectively),-pyranose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the 2C5-pyranose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclopentane ring assuming the E9 envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of antiparallel infinite chains of fused R3 3(6) and R3 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-H/H-O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other d-fructose-amino acids. The 1H 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.