Modeling of aldopyranosyl ring puckering with MM3(92)
1994
Dowd, M.K. | French, A.D. | Reilly, P.J.
The molecular mechanics algorithm MM3 was used to compute energy surfaces for aldopyranosyl rings having a full range of shapes. Energies were plotted against the phi-H puckering coordinates of Cremer and Pople. The 4C1 conformations of the model pyranosyl rings are dominant for both anomers of D-allose, D-galactose, D-glucose, D-mannose, and D-talose, as are the 4C1 conformations of beta-D-altropyranose, beta-D-gulopyranose, and beta-D-idopyranose. alpha-D-Altropyranose is predicted to exist as an equilibrium of 1C4 and 4C1, alpha-D-idopyranose as an equilibrium among 0S2, 1C4, and 4C1, and alpha-D-gulopyranose is predominately 4C1 but has some contribution from 1C4 (18%) and 0S2 (9%). The calculated and measured hydrogen-hydrogen coupling constants agree well, although the energies for the beta anomers in water are systematically low by an average of 0.4 kcal/mol. Because the errors in the predicted anomeric ratios are small and are similar for the eight hexoses, and because the only concession to the solvent was a dielectric constant of 3.0, specific solvent effects are apparently small.
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