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 β-<scp>d</scp>-Rhamnosides from <scp>d</scp>-Mannosyl Glycosyl Donors. Total Synthesis of α-<scp>d</scp>-Gal-(1→3)-α-<scp>d</scp>-Rha-(1→3)- β-<scp>d</scp>-Rha-(1→4)-β-<scp>d</scp>-Glu-OMe, the Repeating Unit of the Antigenic Lipopolysaccharide from <i>Escherichia</i> <i>h</i><i>ermannii</i> ATCC 33650 and 33652
作者:David Crich、Qingjia Yao
DOI:10.1021/ja048070j
日期:2004.7.1
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
描述了一种立体控制合成β-d-鼠李吡喃糖苷的方法,其中2,3-O-苄基或相关的4,6-O- [α-(2-(2-碘苯基)乙基硫代羰基)亚苄基]-甘露糖基硫糖苷是首先用于以高收率和立体选择性引入β-d-甘露吡喃糖苷键。糖基化之后,在回流下用三丁基氢化锡在甲苯中的氢化物处理可导致还原性自由基断裂,直接以高收率生成6-脱氧糖。这些在O3上带有羧基供体的供体的变异是高度α-选择性的甘露糖基,而在自由基断裂后为α-d-鼠李糖基供体。使用这种立体选择性糖基化/自由基片段化方法,