Analysis of the linkage positions in D-fructofuranosyl residues by the reductive-cleavage method

The suitability of the reductive-cleavage method for analysis of the linkage positions in D-fructofuranosyl residues of D-fructans was examined by using sucrose, chicory-root inulin, and Aerobacter levanicum levan as models. Permethylation, and reductive cleavage with triethylsilane in the presence of either boron trifluoride etherate or trimethylsilyl trifluoromethanesulfonate, gave the expected methylated derivatives of 2,5-anhydro-D-mannitol and 2,5-anhydro-D-glucitol. With either catalyst, nonreducing (terminal) D-fructofuranosyl groups and D-fructofuranosyl residues linked at O-1 gave derivatives having the manno configuration as the major product, whereas D-fructofuranosyl residues linked at O-6, and at both O-1 and O-6, gave derivatives having the gluco configuration as the major product. The independent synthesis, and n.m.r.- and mass-spectral characterization, of the methylated 2,5-anhydro-D-mannitol and 2,5-anhydro-D-glucitol derivatives formed from these residues by reductive cleavage are reported.