Unravelling the structure of glycosyl cations via cold-ion infrared spectroscopy
News from Oct 10, 2018
In the 1890s, Emil Fischer introduced the glycosylation reaction that became crucial in the chemical assembly of carbohydrates. The reaction is believed to proceed under most reaction conditions via a key ionic species, the glycosyl oxocarbenium ion. However, the transient nature of this short-lived reaction intermediate impeded its isolation and detailed structural characterization. Here, we report an in-depth structural analysis of glycosyl cations using a combination of cold-ion infrared spectroscopy and first-principles theory. Participating C2 protective groups form indeed a covalent bond with the anomeric carbon that leads to C1-bridged acetoxonium-type structures. The resulting bicyclic structure strongly distorts the ring, which leads to a unique conformation for each individual monosaccharide. This gain in mechanistic understanding fundamentally impacts glycosynthesis and will allow to tailor building blocks and reaction conditions in the future.
Go to article: https://www.nature.com/articles/s41467-018-06764-3