Metal Free Activation of Alkynyl Glycosyl Carbonate Donors

Abstract

Accessing homogenous glycoconjugates is of significance for assessing their biophysical activities and sometimes as vaccine candidate. Synthesis of glycoconjugates involves two species of which, glycosyl donor plays pivotal role in controlling the outcome of the glycosylation. Recently discovered alkynyl glycosyl carbonate donors possess self-stability, high reactivity, and fast reaction time (15–30 min) when activated with [Au]/[Ag]-catalysts. Herein, we report metal free conditions for the activation of the same alkynyl glycosyl carbonate donors using I2/TMSOTf in stoichiometric quantities. Extrusion product was characterized to be the vinylidene iodide by single crystal X-ray analysis. The reaction conditions were illustrated to be suitable for synthesis of various glycosides, purine/pyrimidine nucleosides and a pentasaccharide repeating unit of Klebsiella pneumoniae (O-3-antigen).