Programmable intermediate-controlled sialylation reactions

S9.3 Stereoselectivity in glycosylation reactions
Location (hall): 
Start/end time: 
Thursday, July 4, 2019 - 15:30 to 15:45
Kesatebrhan Haile

Kesatebrhan Haile Asressu1,2,3, Chun-Wei Chang1,4,5, Sarah Lam6, Cheng-Chung Wang1,2,4

1Institute of Chemistry, Academia Sinica, Taipei , Taiwan, 2Taiwan International Graduate Program (TIGP), Sustainable Chemical Science and Technology (SCST), Academia Sinica, Taipei, Taiwan, 3Applied Chemistry Department, National Chiao Tung University , Hsinchu , Taiwan, 4Chemical Biology and Molecular Biophysics Program, Taiwan International Graduate Program (TIGP), Academia Sinica, Taipei, Taiwan, 5Department of Chemistry, National Taiwan University, Taipei , Taiwan, 6Institute of Condensed Matter and Nanosciences, Université Catholique de Louvain, Louvain-la-Neuve, Belgium

Although tremendous efforts have been made for the efficient preparation of natural sialosides, controlling the stereochemical outcome of sialylation is still the most challenging task. Herein, we developed a new strategy performing high stereoselectivity and yield of O-sialylation on several p-tolyl thiosialosides in NIS/TfOH system by using their corresponding RRV as an indicator. In the reaction mechanism, we further confirmed that unexpected glycosyl halide intermediates were generated with the participation of halogens by using low temperature NMR technique, which greatly enhanced the α-selectivity. Eventually, a precise mechanism was proposed with numerous crucial factors including donor functionalities, acceptors, promoters (NXS, X = Cl, Br, I), temperature, and activation time.