Regioselective strategies mediated by lanthanide triflates for efficient assembly of Oligomannans
Regioselective strategies mediated by lanthanide triflates for efficient assembly of Oligomannans
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DOI：
10.1021/jo070018t
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发表时间：
2007-07-20
影响因子：
3.6
通讯作者：
Fraser-Reid, Bert
中科院分区：
文献类型：
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作者：
Jayaprakash, K. N.;Chaudhuri, Siddhartha Ray;Fraser-Reid, Bert
易于制备的甘露糖基正戊烯基原酯 (NPOE) 本身可作为供体，并可作为其他糖基供体的方便中间体，例如正戊烯基糖苷 (NPG)、硫代糖苷和三氯乙酰亚胺酯。这些不同的供体由不同的试剂激活，因此适合多种、有区别的使用。三氟甲磺酸钪和镱对这些供体的反应非常不同，因此可以实现 NPOE、NPG、三氯乙酰亚胺酯以及乙基和苯基硫代糖苷之间的化学选择性区分。适当的NPOE还能够通过重排或糖苷形成提供2,6和3,6二醇受体，并且这些可用于基于正交供体的一锅连续糖苷化和原位双微分糖苷化。因此，由碘鎓离子（特别是由三氟甲磺酸镱/N-碘代琥珀酰亚胺产生）激活的NPOE可用于快速将二醇单糖苷化，具有精细的区域选择性，有时还具有化学选择性。残留的 NPOE 转化为解除武装的 NPG，它对反应条件是难熔的，因此不会对单糖苷化产物的游离 OH 构成威胁。然后可以通过直接添加三氯乙酰亚胺酯或乙基硫代糖苷来实现后者的进一步糖苷化。该基本策略已用于制备支链十五甘露聚糖。这一成功是区域选择性糖基化供体/受体 MATCH 概念高效的一个例子。
Readily prepared mannosyl n-pentenylorthoesters (NPOEs) serve as donors in themselves and as convenient intermediates for other glycosyl donors, such as n-pentenyl glycosides (NPGs), thioglycosides, and trichloroacetimidates. These various donors are activated by different reagents, and are therefore amenable to versatile, discriminate use. Scandium and ytterbium triflates respond very differently to these donors, with the result that chemoselective discrimination between NPOEs, NPGs, trichloroacetimidates as well as ethyl and phenyl thioglycosides can be achieved. Appropriate NPOEs are also able to provide 2,6 and 3,6 diol acceptors via rearrangement or glycoside formation, and these can be used for one-pot, sequential glycosidations based on orthogonal donors, and in situ double differential glycosidations. Thus NPOEs activated by iodonium ion, specifically generated from ytterbium triflate/N-iodosuccinimide, can be used to monoglycosidate the diols rapidly, with exquisite regio, and sometimes chemo, selectivity. The residual NPOE is converted into disarmed NPG, which is refractory to the reaction conditions, and so poses no threat to the free-OH of the monoglycosidation product. Further glycosidation of the latter can then achieved by direct addition of a trichloroacetimidate or ethyl thioglycoside. This basic strategy has been used to prepare a branched chain pentadecamannan. The success is an example of the efficiency of donor/acceptor MATCH concept for regioselective glycosylation.