NMR study of methyl 3,4,6-tri-O-acetyl-2-deoxy-2-(alkylureido)-β-D-glucopyranosides

Five derivatives of methyl 3,4,6-triacetyl-2-deoxy-(3'-dialkylureido)-beta-D-glucopyranoside were studied by H-1 and C-13, NMR Spectroscopy in CDCl3 solutions and by C-13 NMR spectroscopy in the solid state. Sterically crowded substituents such as n-hexyl and cylcohexyl change the chemical shifts of H-1, H-2 and H-3 and also the chemical shifts of C-2 and C-3 of the glucopyranose ring. The low-temperature 1H and C-13 spectra showed separate signals of the two alkyl groups, located E and Z with respect to C-2'=O. The barrier to rotation of the N-3'-R-2 fragment (Delta G(not equal)) is 40.4 kJ mol(-1) for the diethyl and 39.2 kJ mol(-1) for the di-n-hexyl substituent. The solid-state C-13 NMR spectra indicated that both of the above compounds are polymorphic, exhibiting two to four different forms. Copyright (C) 1999 John Wiley & Sons. Ltd.