The Chemistry of n-Pentenyl Acetals

该研究项目由有机合成资助。 程序. 弗雷泽-里德博士将探索 控制异头异构体化学性质的新方法 以碳水化合物为中心。 它将提供一个重要的新工具 用于碳水化合物研究。 这将导致新的路线， 自然界在细胞表面使用的复杂碳水化合物， 识别元素。 在早期的工作中，有一个偶然的观察， 同时合成了静脉曲张链菌素A的柄链， 导致了对戊烯基糖苷的化学研究 （NPG）。 结果表明，卤离子诱导的 NPG提供异头中心的特异性活化 使得糖苷能够在中性条件下水解。 与糖醇偶联得到高级糖，并且 事实上，C-2酯“解除武装”，而C-2醚“武装” NPG，提供了一个现成的协议，控制合成的 低聚糖。 然而，还发现，根据 在卤离子的无机源上，解除武装的酯可以 使其易于反应。 因此，NPG提供了 启动子特异性和/或底物特异性反应，从而 允许在组装复杂的 低聚糖。 旨在发展这一方法的研究 将进行。 根据上述规定，还发现保护一个 作为环状缩醛的顺式二醇使NPG反应更慢 而不是苄基醚。 这一点也将受到审查 这是一种替代的武装/解除武装策略。 一项研究以 将进行合理化这些各种反应， 将利用MM 2和从头算的结果 计算。 已经发现NPG的反应喷射出 （R）-1-卤甲基呋喃，对映体过量约80%。 方式 为了优化该值并制备复杂的类呋喃， 作为昆虫信息素，将被研究。

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.