Several transition states from C1 to skew conformations of β-d-glucopyranose

The interconversion pathways in the ring distortion of β-d-glucopyranose were investigated using density functional calculations. We examined the energies of several conformers of β-d-glucopyranose and tried to obtain the transition-state conformation and determine the pathway between a ⁴C₁ chair and some distorted ring conformers. The results showed that two E₃/²H₃ conformations and one E₃/⁴H₃ conformation were transition states in such ring puckering. The transition state with the lowest energy conformation is the E₃/²H₃ ring conformation with the side-chain conformation of r-ggG⁺. Intrinsic reaction coordinate calculations indicated that the E₃/²H₃ conformation with the lowest conformational energy is a transition state of the ring interconversion path between the conformations of ⁴C₁ and ²S_O/B_3,O. The energy barrier of this interconversion was 6.13 kcal/mol. As far as we know, this is the first example of finding pathways for an interconversion of glucopyranose ring puckering at the level of a quantum chemical calculation.