Arihara Ryoichi, Kakita Kosuke, Suzuki Noritoshi, Nakamura Seiichi, Hashimoto Shunichi
Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
J Org Chem. 2015 May 1;80(9):4259-77. doi: 10.1021/acs.joc.5b00138. Epub 2015 Apr 15.
A direct construction of 1,2-trans-β-linked 2-acetamido-2-deoxyglycosides was investigated. The 3,4,6-tri-O-benzyl- and 3,4,6-tri-O-acetyl-protected glycosyl diethyl phosphites and 4,6-O-benzylidene-protected galactosyl diethyl phosphite each reacted with a variety of acceptor alcohols in the presence of a stoichiometric amount of Tf2NH in CH2Cl2 at -78 °C to afford the corresponding β-glycosides in good to high yields with complete stereoselectivity. Some experiments provided strong evidence that the corresponding oxazolinium ions are not responsible for the reaction. We demonstrated that glycosylations with the corresponding glycosyl imidate and thioglycoside also proceeded at a low temperature, indicating the possibility of these donors being attractive alternatives to the phosphite. A plausible reaction mechanism, which features glycosyl triflimide and contact ion pair as reactive intermediates, is proposed on the basis of the results obtained with 2-acetamido-2-deoxymannosyl donors.
研究了1,2-反式-β-连接的2-乙酰氨基-2-脱氧糖苷的直接构建方法。3,4,6-三-O-苄基和3,4,6-三-O-乙酰基保护的糖基二乙基亚磷酸酯以及4,6-O-亚苄基保护的半乳糖基二乙基亚磷酸酯，在二氯甲烷中于-78℃、化学计量的Tf₂NH存在下，分别与多种受体醇反应，以良好至高产率、完全立体选择性地得到相应的β-糖苷。一些实验提供了有力证据，表明相应的恶唑啉离子与该反应无关。我们证明，相应的糖基亚氨酸酯和硫代糖苷的糖基化反应也在低温下进行，这表明这些供体有可能成为亚磷酸酯的有吸引力的替代物。基于用2-乙酰氨基-2-脱氧甘露糖基供体获得的结果，提出了一种合理的反应机理，其特征是以糖基三氟甲磺酰亚胺和接触离子对作为反应中间体。
