Conformational analysis of inulobiose by molecular mechanics

Abstract

Conformational energies for inulobiose [β- d-fructofuranosyl-(2→1)-β- d-fructofuranoside], a model for inulin, were computed with the molecular mechanics program MMP2(85). The torsion angles of the three linkage bonds were driven in 20° increments, and the steric energy of all other parameters was minimized. The linkage torsion angles defined by C1′-C-2′OC-1 (ϕ) and O-C1C-2O-2 (ω) have minima at +60° and −60°, respectively, regardless of side group orientation; accessible minima exist at other staggered conformations. The torsion angle at the central bond C-2′O-1C-1C-2 (ψ) was approximately 180° in all the low-energy conformers. This appears to be generally true for rings linked by three bonds. The fructofuranose rings initially had low-energy 4 3 T conformations (angle of pseudorotation, ϕ 2 = 265°) that were retained except when the linkage conformations created severe inter-residue conflicts. In those cases, almost all puckerings of the furanose rings were found.