Stereoselective N-glycosylation with N4-acyl cytosines and efficient synthesis of gemcitabine
2019
Liu, Tongchao | Tang, Jiadeng | Liang, Jianpeng | Chen, Yabin | Wang, Xiaowen | Shen, Jingkang | Zhao, Dongmei | Xiong, Bin | Cen, Jun-Da | Chen, Yue-Lei
Through systematical comparison of various N4-protected cytosine derivatives in the glycosylation step of gemcitabine synthesis, highly beta-stereoselective and high yielding TBAI catalyzed N-glycosylation was achieved with N4-Bz cytosine and anomeric mixture of 2,2‘-difluororibose mesylate donor. The subsequent global deprotection gave gemcitabine efficiently. Meanwhile, the anomeric chloride intermediate and fluoride-displaced side products of this N-glycosylation were identified, too. This new glycosylation method reveals the importance of N4-protection in the stereoselective preparation of pyrimidine nucleoside, also provides a potential alternative to current industrial process to gemcitabine.
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