Boat conformations: synthesis, NMR spectroscopy, and molecular modeling of methyl 2,6-anhydro-3-deoxy-3-phthalimido-α-d-mannopyranoside and its 15N-labeled analog

Methyl 2,6-anhydro-3-deoxy-3-phthalimido-α-d-mannopyranoside and its 15N-labeled analog have been synthesized by reaction of methyl 2,6:3,4-dianhydro-α-d-altropyranoside with a mixture of phthalimide and potassium phthalimide or their 15N-labeled analogs. The geometry of the skew conformation of the mannopyranoside derivative has been characterized by molecular dynamics with simulated annealing and correlated with vicinal and long-range 1H1H and vicinal 1H15N coupling constants measured by 1H NMR spectroscopy. Dihedral angle comparisons have been made with derivatives of the parent 2,2,2-bicyclo-octane structure. The 1H15N coupling constant data provide further values for definition of a Karplus equation for analysis of the stereochemistry of aminoglycosides.