Driving Force of the Pyranoside-into-Furanoside Rearrangement.

Ab initio calculations of fully O-sulfated model monosaccharides, including common hexoses (glucose, galactose, fucose, and mannose) and pentoses (arabinose and xylose), were performed to study the energetic properties of the recently discovered pyranoside-into-furanoside (PIF) rearrangement. It was shown that the per-O-sulfated derivatives of furanoside isomers generally had lower energies than the corresponding per-O-sulfated pyranosides, while nonsulfated furanosides were always less favored than nonsulfated pyranosides. Mannose, which is known to be unreactive in PIF rearrangement, was the only exception. The results of the theoretical calculations were confirmed by experimental studies of monosaccharide models and explained the driving force of such unusual ring contraction process as PIF rearrangement. The conclusions of performed investigation can be used for prediction of new substrates applicability for PIF rearrangement.