Synthesis of lupane saponins from acetylated glycosyl donors by acetonitrile directed glycosylation

Acetylated Schmidt donors are cheap and versatile starting materials for the synthesis of the glycosidic bond. Acetyl migration from donor to acceptor molecules is, however, usually observed during their reaction with lupane-type triterpenes. As a result, acetylated triterpenes are isolated as main, and sometimes only products instead of the expected glycosides. In this paper we propose the use of acetonitrile as a solvent in the glycosylation step. In the presence of acetonitrile, reaction of acetylated Schmidt donors with lupanes affords the required saponins in high yield. This methodology opens a fast, cheap and efficient way for the preparation of lupane saponins. (C) 2015 Elsevier Ltd. All rights reserved.