The Chemistry of n-Pentenyl Acetals

本研究项目由有机合成项目资助。弗雷泽-里德博士将探索一种控制碳水化合物中异构中心化学反应的新方法的合成潜力。这将为碳水化合物的研究提供一个重要的新工具。这将为自然界在细胞表面用作识别元素的复杂碳水化合物提供新的途径。在早期的工作中，在合成Streptovaricin a的ansa链时，一个偶然的观察结果导致了对n-戊烯基糖苷（npg）的化学研究。结果表明，卤鎓离子诱导的npg反应提供了特定的活化中心，使糖苷在中性条件下水解。与糖醇偶联可以产生更高的糖，而C-2酯“解除武装”，而C-2醚“解除武装”，为控制低聚糖的合成提供了一个现成的方案。然而，也发现，依赖于卤素离子的无机来源，可以使解除武装的酯容易反应。因此，npg提供了启动子特异性和/或底物特异性反应的潜力，从而在复杂低聚糖的组装中具有很大的灵活性。将进行旨在制订这种方法的研究。根据上述，还发现顺式二醇作为环缩醛的保护使NPG的反应比作为苯醚的保护更慢。这也将作为另一种武装/解除武装战略加以审查。将进行一项研究，使这些不同的反应合理化，并利用MM2和从头计算的结果。npg反应产生的(R)-1-卤代甲基呋喃对映体过量约80%。我们将研究如何优化这一值并制备复杂的呋喃烷类化合物，如昆虫信息素。

This research program is being funded by the Organic Synthesis Program. Dr. Fraser-Reid will explore the synthetic potential of a new method for controlling the chemistry of the anomeric center in carbohydrates. It will provide an important new tool for carbohydrate research. This will lead to new routes to the complex carbohydrates that nature uses at cell surfaces as recognition elements. During the earlier work, a serendipitous observation was made, while synthesizing the ansa chain of Streptovaricin A, which led to a study of the chemistry of n-pentenyl glycosides (NPGs). It was shown that halonium ion-induced reaction of NPGs provides for specific activation of the anomeric center enabling the hydrolysis of glycosides under neutral conditions. Coupling to sugar alcohols afforded higher saccharides, and the fact that a C-2 ester "disarms", while a C-2 ether "arms" the NPG, provided a ready protocol for controlled synthesis of oligosaccharides. However, it was also found that, depending on the inorganic source of halonium ion, the disarmed ester can be made to react readily. Thus, NPGs offer the potential for promoter-specific and/or substrate-specific reactions, thereby allowing great flexibility in the assembly of complex oligosaccharides. Studies aimed at developing this methodology will be undertaken. Pursuant to the above, it was also found that protection of a cis-diol as a cyclic acetal causes an NPG to react more slowly than protection as benzyl ethers. This will also be examined as an alternative armed/disarmed strategy. A study to rationalize these various reactivities will be undertaken and will take advantage of results of MM2 and ab initio calculations. The reactions of NPGs have been found to eject a (R)-1-halomethylfuran with about 80% enantiomeric excess. Ways to optimize this value and to prepare complex furanoids, such as insect pheromones, will be investigated.