Ring expansion of oxyglycals. Synthesis and conformational analysis of septanoside-containing trisaccharides.

Oxyglycals, derived from lactose and maltose, were expanded to trisaccharides through a ring expansion method. Trisaccharides with 6-7-5 and 6-7-6 ring sizes were prepared through the ring expansion method, with high diastereoselectivities, in each step of their synthesis. The NOE and ROESY NMR spectroscopies were used to assess the dipolar couplings within the trisaccharide. A computational study was undertaken, from which low energy conformations, as well as, dihedral angles that define the glycosidic linkages were identified.