Conformational analysis of the anomeric forms of sophorose, laminarabiose, and cellobiose using MM3

Relaxed-residue energy maps based on the MM3 force-field were computed for relative orientations of the pyranosyl rings of sophorose, laminarabiose, and cellobiose, respectively the (1----2)-beta-; (1----3)-beta-; and (1----4)-beta-linked D-glucosyl disaccharides. Sixteen starting conformations of the rotatable exocyclic side-groups were considered for each molecule. All of the energy surfaces have two intersecting low-energy troughs and illustrate the importance of exo-anomeric effects in determining disaccharide conformation. Local minima were found by relaxed minimization without restriction. The energy surfaces of these disaccharides are very similar to the energy surfaces of their corresponding 6-methyltetrahydropyran analogues. There is good agreement between disaccharide structures having minimal MM3 energy and those found by crystallography.