title: Direct experimental evidence for the high chemical reactivity of α- and β-xylopyranosides adopting a (2,5)B conformation in glycosyl transfer.
abstract: The effect of a (2,5)B boat conformation on xyloside reactivity has been investigated by studying the hydrolysis and glycosylation of a series of synthetic xyloside analogues based on a 2-oxabicyclo[2.2.2]octane framework, which forces the xylose analogue to adopt a (2,5)B conformation. The locked β-xylosides were found to hydrolyze 100-1200 times faster than methyl β-D-xylopyranoside, whereas the locked α-xylosides hydrolyzed up to 2×10(4) times faster than methyl α-D-xylopyranoside. A significant rate enhancement was also observed for the glycosylation reaction. The high reactivity of these conformers can be related to the imposition of a (2,5)B conformation, which approximates a transition state (TS) boat conformation. In this way, the energy penalty required to go from the chair to the TS conformation is already paid. These results parallel and support the observation that the GH-11 xylanase family force their substrate to adopt a (2,5)B conformation to achieve highly efficient enzymatic glycosidic bond hydrolysis.
authors.affiliation: UPMC Univ Paris 06, Institut Parisien de Chimie Moléculaire (UMR 7201), FR 2769, C181, 4 place Jussieu, 75005 Paris, France.
authors.forename: Luis
authors.initials: L
authors.lastname: Amorim
authors.forename: Filipa
authors.initials: F
authors.lastname: Marcelo
authors.forename: Cyril
authors.initials: C
authors.lastname: Rousseau
authors.forename: Lidia
authors.initials: L
authors.lastname: Nieto
authors.forename: Jesús
authors.initials: J
authors.lastname: Jiménez-Barbero
authors.forename: Jérôme
authors.initials: J
authors.lastname: Marrot
authors.forename: Amélia P
authors.initials: AP
authors.lastname: Rauter
authors.forename: Matthieu
authors.initials: M
authors.lastname: Sollogoub
authors.forename: Mikael
authors.initials: M
authors.lastname: Bols
authors.forename: Yves
authors.initials: Y
authors.lastname: Blériot
mesh_terms: D002236:Carbohydrate Conformation; D002384:Catalysis; D018360:Crystallography, X-Ray; D006027:Glycosides / Q000138:chemical synthesis / Q000737:chemistry*; D006031:Glycosylation; D006868:Hydrolysis; D015394:Molecular Structure; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D006027:Glycosides; C010807:xylosides