Benzylidene acetal fragmentation route to 6-deoxy sugars: direct reductive cleavage in the presence of ether protecting groups, permitting the efficient, highly stereocontrolled synthesis of beta-D-rhamnosides from D-mannosyl glycosyl donors. Total synthesis of alpha-D-Gal-(1-->3)-alpha-D-Rha-(1-->3
Benzylidene acetal fragmentation route to 6-deoxy sugars: direct reductive cleavage in the presence of ether protecting groups, permitting the efficient, highly stereocontrolled synthesis of beta-D-rhamnosides from D-mannosyl glycosyl donors. Total synthesis of alpha-D-Gal-(1-->3)-alpha-D-Rha-(1-->3
复制标题
DOI：
--
复制
发表时间：
2004
影响因子：
15
通讯作者：
D. Crich;Q. Yao
中科院分区：
文献类型：
--
作者：
D. Crich;Q. Yao
描述了一种立体控制合成β-d-吡喃鼠李糖苷的方法，其中首先使用2，3-O-苄基或相关的4，6-O-[α-（2-（2-碘苯基）乙硫基羰基）亚苄基]-甘露糖基硫代糖苷以高产率和立体选择性引入β-d-吡喃甘露糖苷键。糖基化后，在甲苯中回流用氢化三丁基锡处理，以高产率直接还原自由基断裂成6-脱氧糖。在O3上带有羧基化供体的这些供体的变体是高度α-选择性的甘露糖基，并且在自由基片段化后是α-d-鼠李糖基供体。使用这种立体选择性的糖基化/自由基断裂的方法，一个简洁的标题四糖的合成实现，其中的β-D-和α-D-吡喃鼠李糖单元在一个单一的步骤中获得的双自由基断裂的改性的亚苄基缩醛。
An approach to the stereocontrolled synthesis of beta-d-rhamnopyranosides is described in which 2,3-O-benzyl or related 4,6-O-[alpha-(2-(2-iodophenyl)ethylthiocarbonyl)benzylidene]-mannosyl thioglycosides are first used to introduce the beta-d-mannopyranoside linkage in high yield and stereoselectivity. Following glycosylation, treatment with tributyltin hydride in toluene at reflux brings about reductive radical fragmentation directly to the 6-deoxy sugar in high yield. A variation of these donors bearing a carboxylated donor on O3 is a highly alpha-selective mannosyl and, after radical fragmentation, alpha-d-rhamnosyl donor. Using this stereoselective glycosylation/radical-fragmentation approach, a concise synthesis of the title tetrasaccharide is realized in which both the beta-d- and alpha-d-rhamnopyranosyl units are obtained in a single step by a double radical fragmentation of the modified benzylidene acetals.