X-ray structural and n.m.r.-spectral studies of methyl α- l-evalopyranoside: Reassignment of anomeric configuration for the methanolysis product of methyl 6-deoxy-3- C-methyl-α- l-mannofuranoside

The methanolysis product of methyl 6-deoxy-3- C-methyl-α- l-mannofuranoside has been reassigned as methyl 6-deoxy-3- C-methyl-α- l-mannopyranoside by X-ray crystallographic and n.m.r.-spectral analyses. The crystals of methyl α- l-evalopyranoside are monoclinic, space group C2, with cell dimensions: a = 12.913(2), b = 8.052(1), c = 9.766(2) Å, B = 105.13(2)°. The pyranoside ring exists in the 1 C 4 conformation, with the methoxyl and 3- C-methyl groups axial. Nuclear Overhauser effects were measured for selected proton resonances in the 1H-n.m.r. spectrum. Irradiation of the 3- C-methyl and 5- C-methyl group proton signals resulted in enhancements for H-2, H-4, H-5, and the methoxyl group hydrogen atoms, but not for H-1.