PENTENYL GLYCOSIDES IN TRANSFORMATIONS AT ANOMERIC CTR

糖的异构体中心的反应在 几乎化学的所有领域--有机、生物理论、物理、 而且是药用的。例如，越来越明显的是，一个 糖蛋白“糖蛋白”可能比“蛋白质”和 “Glyco”充满了不正常的中心。低聚糖现在已知是 重要的免疫决定因素。糖酵解酶作用于异构体中心。 因此，毫不奇怪，化学家们投入了巨大的努力 对异常中心的综合、理论和物理研究，以及 它的重要性已经体现在一些概念中，比如反常效应 和立体电子控制。然而，这种现象越多， 研究越多，就越暴露出差距和不足。 我们最近发现了一种反应，有望适应 涉及异常中心的广泛调查。这个 当正戊烯基苷是 用卤离子处理。发生的反应有：(1) 糖苷在中性条件下的水解，(2)特异性 在存在其他保护的情况下解除对异常中心的保护 (3)糖苷交换或(4)特异性激活基团 低聚糖偶联，和(5)解除或解除糖苷基团的武装 通过将C2取代基从酯改变为乙醚。 前四个属性中的每一个都有先例。然而，正戊烯基 糖苷是唯一一种结合了这四种成分的糖衍生物。连 更重要的是独一无二的、压倒一切的、前所未有的属性(5)。 特别吸引人的是这项技术的简单性。这群人 通过使用市场上可获得的试剂易于安装，并利用 经典的方法。作为一种O-烷基糖苷，它坚固、稳定和 继承了大量的处理这类 化合物。低聚糖合成的优势是明显的， 因为氧化过程是中性的，所以它特别有利 用来处理敏感分子。 从机理的观点来看，假定的中间产物带有一个 反常中心的氧离子类似于假设的 质子化糖苷。因此，氧化脱糖苷可作为 一种研究酶促糖酵解裂解的模型--中性氧化 比酸催化模型更吸引人的条件 传统上受雇的。立体电子控制的概念也可以是 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.