A Karplus equation for ~3J_(HCCN) in amino sugar derivatives

摘要

The 1H-15N coupling constants of a suite of organic-soluble amino sugar derivatives have been measured by one-dimensional and two-dimensional 1H/15N heteronuclear single quantum,multiple bond correlation (HSQMBC),and the values so obtained are compared with those measured by analysis of 1H spectra of 15N-labeled amino sugar derivatives.A number of bicyclic amino sugar models have been studied,including methyl 2- (and 3-)amino-4,6-O-benzylidene-2- (and 3-)deoxy-alpha-D-hexopyranosides in chair or skew conformations,and methyl 2,6-anhydro-3-deoxy-3-phthalimido-alpha-D-mannopyranoside in a locked,almost classical boat conformation.The magnitudes of the vicinal 1H-15N coupling constants ~3J_(HCCN) have been correlated with 1H/15N dihedral angles phi computed for the favored conformations by molecular dynamics with molecular mechanics energy minimization.Nonlinear regression of the coupling constants on the dihedral angles has yielded a Karplus equation: ~3J_(HCCN) = 3.1 cos2 phi - 0.6 cos phi + 0.4.The coefficients of the terms in this equation have been compared with those reported for 15 other pairs of nuclei,and the coefficient of the important cos2 phi term found to be numerically smallest for ~3J_(HCCN).