Tunable stereoselectivity during sialylation using anN-acetyl-5-N,4-O-oxazolidinone-protectedp-toluene 2-thio-sialoside donor with Tf2O/Ph2SO/TTBPy

Ya-Juan Wang, Jia Jia, Zhen-Yuan Gu, Fen-Fen Liang, Ri-Chen Li, Ming-Hao Huang, Cai-Shuang Xu, Jia-Xin Zhang, Yi Men, Guo-Wen Xing, Ya-Juan Wang, Jia Jia, Zhen-Yuan Gu, Fen-Fen Liang, Ri-Chen Li, Ming-Hao Huang, Cai-Shuang Xu, Jia-Xin Zhang, Yi Men, Guo-Wen Xing

Index: Carbohydr. Res. 346(11) , 1271-6, (2011)

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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.Copyright © 2011 Elsevier Ltd. All rights reserved.