In oligosaccharides containing pyranosyl residues, most, if not all, of the constituent rings are rigid, existing in one of two possible chair conformations. Thus, the major degrees of freedom available to an oligopyranoside are rotation about glycosidic bonds, which can be described by two torsion angles and rotation about the exocyclic C—C bond (torsion angle w), as indicated in Figure 19 . Three possible staggered conformations of w are possible (gg, gt, and tg, Fig. 20) and usually a mixture is present in solution . NMR studies focused on elucidating oligosaccharide structure have relied heavily on the measurement, of 3Jh,h to determine ring conformations and rotamer populations of exocyclic hydroxymethyl groups of the
Was this article helpful?