Investigations into the role of oxacarbenium ions in glycosylation reactions by ab initio molecular dynamics.
We present a constrained ab initio molecular dynamics method that allows the modeling of the conformational interconversions of glycopyranosyl oxacarbenium ions. The model was successfully tested by estimating the barriers to ring inversion for two 4-substituted tetrahydropyranosyl oxacarbenium ions. The model was further extended to predict the pathways that connect the (4)H(3) half-chair conformation of 2,3,4,6-tetra-O-methyl-d-glucopyranosyl cation to its inverted (5)S(1) conformation and the (4)H(3) half-chair conformation of 2,3,4,6-tetra-O-methyl-d-mannopyranosyl cation to its inverted (3)E conformation. The modeled interconversion pathways reconcile a large body of experimental work on the acid-catalyzed hydrolysis of glycosides and the mechanisms of a number of glucosidases and mannosidases.
Ionescu
Andrei R
AR
Steacie Institute for Molecular Sciences, NRC Canada, 100 Sussex Drive, Ottawa, Ont., Canada.
Whitfield
Dennis M
DM
Zgierski
Marek Z
MZ
Nukada
Tomoo
T
D002236:Carbohydrate Conformation; D002412:Cations / Q000737:chemistry*; D006031:Glycosylation; D008958:Models, Molecular; D011714:Pyrans / Q000737:chemistry
D002412:Cations; D011714:Pyrans