RELAXED-RESIDUE CONFORMATIONAL MAPPING OF THE 3 LINKAGE BONDS OF ISOMALTOSE AND GENTIOBIOSE WITH MM3(92)

Isoenergy surfaces were calculated for the alpha- and beta-anomers of isomaltose and gentiobiose, based on 46,656 conformers for each disacc haride. Low-energy regions exist for each of the three staggered posit ions about the C-5'-C-6' bonds, and known crystal structures lie in tw o of these regions. As expected, the molecular partition function show ed greater flexibility for these three-bond-linked disaccharides than for comparable two-bond-linked structures. A model miniature crystal o f gentiobiose accounts for most of the remaining structural difference s between the modeled isolated molecule and the crystal structure. Bas ed on models of isolated molecules of isomaltose and gentiobiose, the predicted Boltzmann-weighted nmr coupling constants were satisfactory, as were predicted optical rotations for gentiobiose. (C) 1994 John Wi ley and Sons, Inc.