title: Tunable stereoselectivity during sialylation using an N-acetyl-5-N,4-O-oxazolidinone-protected p-toluene 2-thio-sialoside donor with Tf(2)O/Ph(2)SO/TTBPy.
abstract: An N-acetyl-5-N,4-O-oxazolidinone-protected p-toluene 2-thio-sialoside donor, promoted by Ph(2)SO/Tf(2)O/TTBPy, was thoroughly investigated in the coupling to various acceptors. The stereoselectivity of the sialylation was found to be dependent on the various reaction conditions, such as pre-activation time, reaction time, the amount of Ph(2)SO, and TTBPy. A detailed Ph(2)SO/Tf(2)O-promoted glycosylation mechanism was proposed, which contained three crucial reactive species: an oxacarbenium ion, C2-sialyloxosulfonium salts, and oxosulfonium supramers. Our research results indicate that it is possible to tune the stereoselectivity of the sialylation by carefully changing the reaction conditions. For instance, Ph(2)SO (2.0-3.0 equiv)/TTBPy (0-1.0 equiv) promotion gives higher α-selective sialylation in dichloromethane, while Ph(2)SO (4-5 equiv)/TTBPy (0 equiv) or Ph(2)SO (2.0 equiv)/TTBPy (2.0 equiv) affords lower stereoselectivity.
authors.affiliation: Department of Chemistry, Beijing Normal University, Beijing 100875, China.
authors.forename: Ya-Juan
authors.initials: YJ
authors.lastname: Wang
authors.forename: Jia
authors.initials: J
authors.lastname: Jia
authors.forename: Zhen-Yuan
authors.initials: ZY
authors.lastname: Gu
authors.forename: Fen-Fen
authors.initials: FF
authors.lastname: Liang
authors.forename: Ri-Chen
authors.initials: RC
authors.lastname: Li
authors.forename: Ming-Hao
authors.initials: MH
authors.lastname: Huang
authors.forename: Cai-Shuang
authors.initials: CS
authors.lastname: Xu
authors.forename: Jia-Xin
authors.initials: JX
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Men
authors.forename: Guo-Wen
authors.initials: GW
authors.lastname: Xing
mesh_terms: D001555:Benzene Derivatives / Q000737:chemistry*; D006031:Glycosylation; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D019158:N-Acetylneuraminic Acid / Q000737:chemistry*
chemical_list: D001555:Benzene Derivatives; C048860:diphenyl sulfoxide; D019158:N-Acetylneuraminic Acid