Traceless Staudinger Ligation of Glycosyl Azides with Triaryl Phosphines: Stereoselective Synthesis of Glycosyl Amides
作者:Aldo Bianchi、Anna Bernardi
DOI:10.1021/jo060409s
日期:2006.6.1
α-Glycosyl amides can be synthesized from the corresponding O-benzyl-α-glycosyl azides using a traceless Staudinger ligation with diphenylphosphanyl-phenyl esters 4. All the phosphines employed and their phenol precursors are stable to air at 4 °C for months. Fast intramolecular trapping of the reduction intermediates results in the direct formation of the amide link, which, in turn, prevents epimerisation
α-糖基酰胺可通过无痕施陶丁格与二苯基膦酰基-苯基酯的连接由相应的O-苄基-α-糖基叠氮化物合成4。所用的所有膦及其苯酚前体在4°C的空气中均可保持稳定数月。还原中间体的快速分子内捕集导致酰胺键的直接形成,继而防止了差向异构化并允许在异头碳上保留构型。当反应在极性非质子溶剂中进行时,产率和α-选择性高。苄基醚保护基的去除是通过催化氢化来实现的。α-糖基酰胺代表了一类实际上未开发的不可水解的单糖衍生物,可以作为糖模拟物找到有用的应用。NMR光谱的构象研究证实,葡萄糖,半乳糖和fuco系列中的脱保护α-糖基酰胺保留了单糖的正常吡喃糖构象。膦的反应4用四ø -乙酰基葡糖基叠氮化物是nonstereoconservative,并在良好的产率,并与来自两个α和β叠氮化物开始完整的立体选择性获得β糖基酰胺。