Synthesis of Small Glycopeptides by Decarboxylative Condensation and Insight into the Reaction Mechanism
作者:Aditya K. Sanki、Rommel S. Talan、Steven J. Sucheck
DOI:10.1021/jo802278w
日期:2009.3.6
believed to result from an intramolecular cyclization of the O-tert-butyl ester on a nitrilium ion intermediate followed by aromatization. A decarboxylative condensation between O18-labeled phenyl pyruvic acid and N-hydroxyphenethylamine oxalate salt resulted in amide products lacking the O18-label, providing further support for the nitrilium ion in the reaction pathway.
均质糖蛋白和糖肽的化学合成促进了理解附着在蛋白质上的碳水化合物的功能作用的进展,并且在制备基于糖肽的治疗剂中很重要。一系列保护和未受保护的糖基的二肽,糖肽I,其含有在C末端的α酮酸部分,合成并用一系列连接ø -叔丁基-保护的Ñ -hydroxylamino酸,得到ö -叔丁基保护的糖基三肽,糖肽II。反应在无水和水性条件下在中性pH下进行,以产生糖肽产物,其产率范围为15%至86%,这取决于连接处存在的氨基酸。当α-酮酸和N-羟基氨基酸都包含中等大小的侧链时,可获得最佳产率。除了预期的三肽的产品,当2,5-取代的恶唑分离ö -叔-丁基保护的Ñ在反应中采用的-hydroxylamines甘氨酸。恶唑的形成被认为是由所述的分子内环化以得到ö -叔腈离子中间体上的叔丁酯,然后进行芳构化。之间○脱羧缩合18 -标记的苯丙酮酸和Ñ -hydroxyphenethylamine草酸盐导致缺乏将O酰胺产物18