NMR studies of the conformation of the natural sweetener rebaudioside A.

Rebaudioside A is a natural sweetener from Stevia rebaudiana in which four beta-D-glucopyranose units are attached to the aglycone steviol. Its (1)H and (13)C NMR spectra in pyridine-d(5) were assigned using 1D and 2D methods. Constrained molecular dynamics of solvated rebaudioside using NMR constraints derived from ROESY cross peaks yielded the orientation of the beta-D-glucopyranose units. Hydrogen bonding was examined using the temperature coefficients of the hydroxyl chemical shifts, ROESY and long-range COSY spectra, and proton-proton coupling constants.