PENTENYL GLYCOSIDES IN TRANSFORMATIONS AT ANOMERIC CTR

在糖的异头中心处的反应在糖的合成中是极其重要的。 几乎所有的化学领域-有机，生物理论，物理， 和药用。 例如，越来越明显的是， 糖蛋白"糖"可能比"蛋白质"更重要， "糖"充满了异头中心。 现在已知寡聚体是 重要的免疫决定因素。 糖酵解酶作用于异头中心。 因此，毫不奇怪，化学家们投入了巨大的努力， 异头中心的合成、理论和物理研究，以及 它的重要性已被载入异头效应等概念中， 和立体电子控制。 然而，这种现象越多， 研究，更多的差距和缺点被发现。 我们最近发现了一种反应， 对异头中心进行广泛的调查。 的 当N-戊烯基糖苷被 用卤离子处理。 发生的反应有（1） 在中性条件下水解糖苷，（2）特异性 在其它保护剂存在下端基异构中心的脱保护 基团，特异性活化（3）糖苷交换或（4） 寡糖偶联，和（5）将糖苷基团武装或解除武装 通过将C2取代基从酯变为醚。 前四个属性中的每一个都有先例。 然而，正戊烯基 糖甙是唯一一种结合了所有四种糖的糖衍生物。 甚至 更重要的是独特的、压倒一切的和前所未有的属性（5）。 特别的吸引力来自于技术的简单性。 本集团 通过使用市售试剂易于安装，并利用 经典方法 作为一种O-烷基糖苷，它坚固、稳定， 继承了处理这类问题的大量"专业知识"， 化合物. 寡糖合成的优势是显而易见的， 因为氧化过程是中性的， 来处理敏感分子。 从机制的观点来看，假定的中间体具有一个 氧鎓离子在异头中心类似的假设， 质子化糖苷 因此，氧化去糖苷化可用作 研究酶促糖酵解裂解的模型，中性氧化 条件比酸催化模型更有吸引力 传统就业。 立体电子控制的概念也可以 在中性条件下测试。

Reactions at the anomeric center of sugars are of immense importance in virtually all areas of chemistry-organic, biological theoretical, physical, and medicinal. For example, it is increasingly apparent that an glycoproteins the "glyco" may be more important that the "protein" and the "glyco" is full of anomeric centers. Oligosaccharides are now known to be important immunodeterminants. Glycolytic enzymes work on anomeric centers. Therefore, not surprisingly, chemists have invested enormous effort in synthetic, theoretical, and physical studies of the anomeric center, and its importance has been enshrined in concepts such as the anomeric effect and stereoelectronic control. Nevertheless, the more the phenomenon is studied, the more gaps and shortcomings are revealed. We have recently discovered a reaction which promises to accommodate a broad spectrum of investigations dealing with the anomeric center. The process in question occurs chemospecifically when n-pentenyl glycosides are treated with halonium ions. Among the reactions occurring are (1) hydrolysis of the glycoside under neutral conditions, (2) specific deprotection of the anomeric center in the presence of other protecting groups, specific activation for (3) glycoside exchange or (4) oligosaccharide couplings, and (5) arming or disarming the glycosidic group by changing the C2 substituent from an ester to an ether. Each of the first four attributes has precedent. However, the n-pentenyl glycoside is the only sugar derivative that incorporates all four. Even more important is the unique, overriding, and unprecedented attribute (5). Particular appeal arises from the simplicity of the technique. The group is easy to install by using a commercially available reagent, and utilizes classical methods. Being an O-alkyl glycoside, it is sturdy, stable, and inherits the enormous body of "know-how" on handling this class of compounds. The advantages for oligosaccharide synthesis are obvious, and because the oxidative process is neutral, it is particularly advantageous for dealing with sensitive molecules. From the standpoint of mechanism, the postulated intermediate carries an oxonium ion at the anomeric center similar to that postulated for protonated glycosides. Therefore, oxidative deglycosidation can be used as a model for studying enzymatic glycolytic cleavage, the neutral oxidative conditions being more appealing than the acid catalyzed models traditionally employed. Concepts of stereoelectronic control can also be tested under neutral conditions.