Crich David, Jayalath Prasanna
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607-7061, USA.
J Org Chem. 2005 Sep 2;70(18):7252-9. doi: 10.1021/jo0508999.
[reaction: see text] Phenyl 4,6-di-O-benzyl-2,3-O-carbonyl-beta-D-glucothiopyranoside and the regiosiomeric phenyl 2,6-di-O-benzyl-3,4-O-carbonyl-beta-D-glucothiopyranoside were prepared and studied as glucosyl donors at -60 degrees C in dichloromethane with preactivation by 1-benzenesulfinyl piperidine before addition of the acceptor alcohol. The 2,3-O-carbonate protected donor showed moderate to excellent beta-selectivity under these conditions depending on the acceptor employed, thereby providing a means for 1,2-trans-equatorial glycosidic bonds without recourse to neighboring group participation and its associated problem of ortho ester formation. In contrast, the 3,4-O-carbonate protected donor showed moderate to no beta-selectivity under the conditions employed. The results obtained in this study with carbonate protected glucopyranosyl donors are contrasted with those obtained previously in the manno- and rhamnopyranosyl series when the 2,3-O-carbonate protected is alpha-selective and the 3,4-O-carbonate is beta-selective.
[反应：见正文] 制备了苯基4,6-二-O-苄基-2,3-O-羰基-β-D-硫代吡喃葡萄糖苷和区域异构体苯基2,6-二-O-苄基-3,4-O-羰基-β-D-硫代吡喃葡萄糖苷，并在-60℃的二氯甲烷中，在加入受体醇之前用1-苯基亚磺酰基哌啶进行预活化，将其作为糖基供体进行研究。取决于所使用的受体，在这些条件下，2,3-O-碳酸酯保护的供体表现出中等至优异的β-选择性，从而提供了一种形成1,2-反式赤道糖苷键的方法，而无需借助邻基参与及其相关的原酸酯形成问题。相比之下，在所用条件下，3,4-O-碳酸酯保护的供体表现出中等至无β-选择性。本研究中使用碳酸酯保护的吡喃葡萄糖基供体所获得的结果，与之前在甘露糖基和鼠李糖基系列中所获得的结果形成对比，当时2,3-O-碳酸酯保护的是α-选择性，而3,4-O-碳酸酯是β-选择性。
