13C CP MAS and high-resolution 1H, 13C, 15N NMR study of new ureido sugars, derivatives of 2-amino-2-deoxy-β-d-glucopyranose and l-amino acid

Ureido sugars with seven various l-amino acid ester residues were studied by means of 1H, 13C, and 15N NMR in solution and 13C CP MAS in the solid state. The chemical shifts and coupling constants in the 1H, 13C, and 15N NMR spectra indicated that the replacement of one amino acid residue by another has no significant effect on the conformation of glucopyranose moiety. The shielding of nitrogen linked to glucose does not change, whereas the shielding of nitrogen of amino acid residues increases in the order Ala < Leu < Phe < Val < Gly and can be explained by the β-effect of the alkyl substituent at Cα. 13C CP MAS spectra of 1–5 were recorded and assigned. The C-3 and C-6 carbons of sugar, the carbonyl carbons of the ureido bridge, and the carbons of the amino acid ester residues are deshielded in the solid state compared to the respective values for CDCl3 solution owing to the loss of conformational flexibility and different intermolecular interactions.