Department of Molecular Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195, Berlin, Germany.
Institute of Chemistry and Biochemistry, Freie Universität Berlin, Takustraße 3, 14195, Berlin, Germany.
Nat Commun. 2018 Oct 9;9(1):4174. doi: 10.1038/s41467-018-06764-3.
Glycosyl cations are the key intermediates during the glycosylation reaction that covalently links building blocks during the synthetic assembly of carbohydrates. The exact structure of these ions remained elusive due to their transient and short-lived nature. Structural insights into the intermediate would improve our understanding of the reaction mechanism of glycosidic bond formation. 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.
糖基阳离子是糖基化反应过程中的关键中间体，该反应通过共价键连接合成碳水化合物过程中的构建块。由于这些离子具有瞬态和短暂的特性，因此其确切结构仍然难以捉摸。对中间体的结构洞察将提高我们对糖苷键形成反应机制的理解。在这里，我们使用冷离子红外光谱和第一性原理理论的组合报告了对糖基阳离子的深入结构分析。参与的 C2 保护基确实与导致 C1 桥接乙酰氧鎓型结构的端基碳原子形成共价键。由此产生的双环结构强烈扭曲了环，从而导致每个单糖具有独特的构象。这种对机制理解的提高从根本上影响了糖合成，并将允许在未来定制构建块和反应条件。
