A Karplus equation for (3)J(HCCN) in amino sugar derivatives |
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Authors: | Coxon Bruce |
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Institution: | National Institute of Child Health and Human Development, 31 Center Drive, MSC 2423, National Institutes of Health, Bethesda, MD 20892, USA. coxonb@mail.nih.gov |
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Abstract: | The (1)H-(15)N coupling constants of a suite of organic-soluble amino sugar derivatives have been measured by one-dimensional and two-dimensional (1)H/(15)N heteronuclear single quantum, multiple bond correlation (HSQMBC), and the values so obtained are compared with those measured by analysis of (1)H spectra of (15)N-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 (1)H-(15)N coupling constants (3)J(HCCN) have been correlated with (1)H/(15)N dihedral angles phi computed for the favored conformations by molecular dynamics with molecular mechanics energy minimization. Non-linear regression of the coupling constants on the dihedral angles has yielded a Karplus equation: (3)J(HCCN)=3.1 cos(2) 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 cos(2)phi term found to be numerically smallest for (3)J(HCCN). |
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Keywords: | Amino sugars 13C NMR chemical shifts COSY Cryoprobe 1H NMR chemical shifts HMBC HSQC HSQMBC Karplus equation Molecular dynamics 15N NMR coupling constants |
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