Potential energy surfaces of α-(1→3)-linked disaccharides calculated with the MM3 force-field

The adiabatic conformational surfaces of sixteen 4',6',6-trideoxy-alpha-D(1-->3)-linked disaccharides were obtained using the MM3 force-field at two different dielectric constants. Calculations were carried out on disaccharides with different configurations at C2, C4 and C2', which are neighbors to the glycosidic linkage, as well as that of the linked carbon (C3). The resulting maps were similar, indicating that the substituents do not play a major role in the conformational features of these disaccharides. However, the preferred minimum conformation and the flexibility were found to be slightly dependant on the configurations of the carbons. Although equatorial bonds and vicinal axial substituents tend to increase the overall flexibility, it was found that these factors can have a cross over effect; i.e., an axial hydroxyl group on C2 may decrease the flexibility if the glycosyl group on C3 is also axial. The relative stabilities of the minimal energy conformations of the 16 compounds also show deviations of the predicted increased stabilities of equatorially substituted compounds over axially substituted ones: these deviations occur mainly for the C2 substituent.