13C CP MAS and high-resolution 1H, 15N NMR study of ureido sugars

Ureido sugars with eight various alkyl groups at N-3 were studied by means of 1H, 13C, and 15N NMR spectroscopy in CDCl3 solution and a 13C CP MAS technique in the solid state. The analysis of chemical shifts and coupling constants suggests the Z,Z-anti conformation of the ureido part of molecule. Differences of δ between the liquid and solid state are observed for the C-2, C-6, and OMe carbon atoms of the d-glucopyranose moiety, as well as the splitting of the anomeric carbon C-1 and OMe signals. The possibility of various conformations in the solid state are discussed. IR spectra of solid ureido sugars indicate that both NH groups are involved in hydrogen bonding. On the other hand, dilution with CDCl3 followed by 1H NMR showed that N-1-H forms a stronger bond than N-3-H.