On Orthogonal and Selective Activation of Glycosyl Thioimidates and Thioglycosides: Application to Oligosaccharide Assembly
摘要:
Discrimination among S-thiazolinyl (STaz), S-benzoxazolyl (SBox), and S-ethyl anomeric leaving groups was achieved by fine-tuning activation conditions. Preferential glycosidation of a certain leaving group is determined neither by the strength of the activating reagent nor by the stability of the leaving group itself; instead, the type of activation plays the key role. The activation conditions established herein were applied to a sequential five-step synthesis of a hexasaccharide using six monosaccharide building blocks equipped with six different leaving groups.
<i>S</i>-Benzoxazolyl as a Stable Protecting Moiety and a Potent Anomeric Leaving Group in Oligosaccharide Synthesis
作者:Medha N. Kamat、Cristina De Meo、Alexei V. Demchenko
DOI:10.1021/jo071191s
日期:2007.8.31
As a part of a program for developing new versatile building blocks for stereoselective glycosylation and convergent oligosaccharide synthesis, we demonstrated that S-benzoxazolyl (SBox) glycosides are stable toward major protecting group manipulations employed in carbohydrate chemistry. On the other hand, they can be glycosidated under relatively mild reaction conditions to afford either 1,2-trans
Revisiting the Armed−Disarmed Concept Rationale: <i>S</i>-Benzoxazolyl Glycosides in Chemoselective Oligosaccharide Synthesis
作者:Medha N. Kamat、Alexei V. Demchenko
DOI:10.1021/ol050969y
日期:2005.7.1
2-O-benzyl-3,4,6-tri-O-acyl SBox glycosides are significantly less reactive than even "disarmed" peracylated derivatives. This finding has been applied to the synthesis of various oligosaccharides, the monomeric units of which are connected via cis-cis, trans-cis, and cis-trans sequential glycosidic linkages. Two-stage activation of the armed (benzylated) donor over moderately (dis)armed (acylated) and, subsequently