O-Benzoyl side-chain conformations in 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1 - 4)-1,2,6-tri-O-benzoyl-beta-D-glucopyranose (ethyl acetate solvate) and 1,2,4,6-tetra-O-benzoyl-beta-D-glucopyranose (acetone solvate)

摘要

The crystal structures of 2,3,4,6-tetra-O-benzoyl-beta-D-galactopyranosyl-(1 - 4)-1,2,6-tri-O-benzoyl-beta-D-glucopyranose ethyl acetate hemisolvate, C61H50O18.0.5C(4)H(8)O(2), and 1,2,4,6-tetra-O-benzoyl-beta-D-glucopyranose acetone monosolvate, C34H28O10.C3H6O, were determined and compared to those of methyl beta-D-galactopyranosyl-(1 - 4)-beta-D-glucopyranoside (methyl beta-lactoside) and methyl ?-D-glucopyranoside hemihydrate, C7H14O6.0.5H(2)O, to evaluate the effects of O-benzoylation on bond lengths, bond angles and torsion angles. In general, O-benzoylation exerts little effect on exo- and endocyclic C-C and endocyclic C-O bond lengths, but exocyclic C-O bonds involved in O-benzoylation are lengthened by 0.02-0.04 angstrom depending on the site of substitution. The conformation of the O-benzoyl side-chains is highly conserved, with the carbonyl O atom either eclipsing the H atom attached to a 2 degrees-alcoholic C atom or bisecting the H-C-H bond angle of an 1 degrees-alcoholic C atom. Of the three bonds that determine the side-chain geometry, the C-O bond involving the alcoholic C atom exhibits greater rotational variability than the remaining C-O and C-C bonds involving the carbonyl C atom. These findings are in good agreement with recent solution NMR studies of the O-acetyl side-chain conformation in saccharides.