Boat conformations part IV -: Synthesis, NMR spectroscopy, and molecular dynamics of methyl 4,6-O-benzylidene-3-deoxy-3-phthalimido-α-D-altropyranoside derivatives

Addition of the elements of phthalimide to methyl 2,3-anhydro-4,6-O-benzylidene-alpha -D-mannopyranoside (1) under fusion conditions has yielded methyl 4,6-O-benzylidene-3-deoxy-3-phthalimido-alpha -D-altropyranoside (2). The conformation of the pyranose ring of 2 has been shown to be non-chair by H-1 NMR spectroscopy, in contrast to the conformations of related derivatives having smaller substituents at C-3. Molecular dynamics simulations of 2 in explicit chloroform-d solvent have indicated four principal conformational possibilities. Of these, the C-7(5)/S-1(5) chair/skew boat form 2d has the lowest potential energy, and is largely consistent with the observed vicinal H-1-H-1 NMR coupling constants. (C) 2001 Elsevier Science Ltd. All rights reserved.