Conformational analysis of sulfated alpha-(1 -> 3)-linked D-galactobioses using the MM3 force-field

The conformational maps of eight derivatives of the disaccharide alpha-D-Ga lp-(1-->3)-beta-D-Galp sulfated in different positions were obtained using the MM3 force-field specially parameterized for sulfate ester groups. As oc curred with MM2, the conformational flexibility of the glycosidic linkage i s only slightly hindered by sulfation. A substantial effect of sulfation of the beta-D-galactose unit on position 4 shifts the global minimum to posit ive psi(H) (C1'-O3-C3-H3) angles, while sulfation at position 2 of the same unit deepens the well at negative psi(H) angles. On the other hand, sulfat ion on the alpha-D-galactose unit has a lesser effect, which in any case te nds to stabilize the minimum at negative psi(H) angles.