Does Neighboring Group Participation by Non-Vicinal Esters Play a Role in Glycosylation Reactions? Effective Probes for the Detection of Bridging Intermediates
作者:David Crich、Tianshun Hu、Feng Cai
DOI:10.1021/jo801630m
日期:2008.11.21
tert-butyl cation, providing convincing evidence of participation by esters at that position. However, no evidence was found for such a fragmentation of carbonate esters at the 3-O-equatorial, 4-O-axial and -equatorial, and 6-O positions, indicating that neighboring group participation from those sites does not occur under typical glycosylation conditions. Further probes employing a 4-O-(2-carboxy)benzoate
通过使用叔丁氧羰基酯,探查了在糖吡喃糖基化反应中的相邻基团在各种供体的3-O-轴向和-赤道,4-O-轴向和-赤道以及6-O-位的酯。预期的中间体环状二氧杂环戊烷基阳离子被轴向3-O衍生物打断,导致形成1,3-O-环状碳酸酯,而叔丁基阳离子丢失,这提供了令人信服的证据表明酯参与了那个位置。但是,没有证据表明在3-O-赤道,4-O-轴和-赤道以及6-O位置发生碳酸酯的这种断裂,表明在典型的糖基化作用下不会发生这些基团的邻近基团的参与。条件。使用4-O-(2-羧基)苯甲酸酯和4-O-(4-甲氧基苯甲酸酯)的其他探针,