摘要:
Methyl beta-allolactoside [methyl beta-d-galactopyranosyl-(1 -> 6)-beta-D-glucopyranoside], (II), was crystallized from water as a monohydrate, C(13)H(24)O(11 center dot)H(2)O. The beta Galp and beta Glcp residues in (II) assume distorted (4)C(1) chair conformations, with the former more distorted than the latter. Linkage conformation is characterized by phi ' (C2(Gal)-C1(Gal)-O1(Gal)-C6(Glc)), psi ' (C1(Gal)-O1(Gal)-C6(Glc)-C5(Glc)) and omega (C4(Glc)-C5(Glc)-C6(Glc)-O1(Gal)) torsion angles of 172.9 (2), -117.9 (3) and -176.2 (2)degrees, respectively. The psi ' and omega values differ significantly from those found in the crystal structure of beta-gentiobiose, (III) [Rohrer et al. (1980). Acta Cryst. B36, 650-654]. Structural comparisons of (II) with related disaccharides bound to a mutant beta-galactosidase reveal significant differences in hydroxymethyl conformation and in the degree of ring distortion of the beta Glcp residue. Structural comparisons of (II) with a DFT-optimized structure, (II(C)), suggest a link between hydrogen bonding, pyranosyl ring deformation and linkage conformation.