Two-Step Synthesis of Per-<i>O</i>-acetylfuranoses: Optimization and Rationalization

A simple two-step procedure yielding peracetylated furanoses directly from free aldoses was implemented. Key steps of the method are (i) highly selective formation of per-<i>O</i>-(<i>tert</i>-butyldimethylsilyl)­furanoses and (ii) their clean conversion into acetyl ones without isomerization. This approach was easily applied to galactose and structurally related carbohydrates such as arabinose, fucose, methyl galacturonate and <i>N</i>-acetylgalactosamine to give the corresponding peracetylated targets. The success of this procedure relied on the control of at least three parameters: (i) the tautomeric equilibrium of the starting unprotected oses, (ii) the steric hindrance of both targeted furanoses and silylating agent, and finally, (iii) the reactivity of each soft nucleophile during the protecting group interconversion

Oligo-β-(1 → 3)-glucans: Impact of Thio-Bridges on Immunostimulating Activities and the Development of Cancer Stem Cells

Recent developments of innovative anticancer therapies are based on compounds likely to stimulate the immune defense of the patients. β-(1 → 3)-Glucans are natural polysaccharides well-known for their immunostimulating properties. We report here on the synthesis of small oligo-β-(1 → 3)-glucans characterized by thioglycosidic linkages. The presence of sulfur atom(s) was not only crucial to prolong in vivo immunoactive activities in time, compared to native polysaccharides, but sulfur atoms also had a direct impact on the development of colorectal cancer stem cells. As a result, a short, pure, and structurally well-defined trisaccharidic thioglucan demonstrated similar activities compared to those of natural laminarin