Synthesis and nuclear magnetic resonance studies of some N-acylated methyl 4-amino-4,6-dideoxy-α-D-mannopyranosides

The methyl α-glycosides of 4-amino-4,6-dideoxy-D-mannopyranose (perosamine), N-acylated with either formic, acetic, or (S)-2,4-dihydroxybutanoic acid, have been synthesized. The 1H and 13C n.m.r. spectra of these substances and the parent, non-N-acylated glycoside, demonstrated how the chemical shifts are influenced by the N-acylation. The N-formyl derivative occurred in two conformations, s-cis and s-trans, and the free-energy barrier between these, 86.9 kJ mol–1, was defined by dynamic n.m.r. spectroscopy.