Proton and carbon chemical-shift assignments for 6-kestose and neokestose from two-dimensional n.m.r. measurements.

The proton and carbon chemical shift assignments of the simplest levan, 6-kestose, [O-beta-D-fructofuranosyl-(2----6)-beta-D-fructofuranosyl-(2 in equilibrium with 1)-alpha-D-glucopyranoside], along with another trisaccharide, neokestose, [O-beta-D-fructofuranosyl-(2----6)-alpha-D-glucopyranosyl-(1 in equilibrium with 2)-beta-D-fructofuranoside], were determined using two-dimensional (2D) homonuclear and heteronuclear n.m.r. methods. The 1H peak of H-1 of the glucose residue was determined by its chemical shift. Using H-H coupling information to this proton, the chemical shifts of most of the proton signals of the glucose moiety were determined. Though the signals from the two fructose residues were very close, a NOESY experiment and long-range C-H correlation experiments allowed their complete carbon and proton assignment. This work completes and corrects literature assignments.