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
Versatile Synthesis and Mechanism of Activation of <i>S</i>-Benzoxazolyl Glycosides
作者:Medha N. Kamat、Nigam P. Rath、Alexei V. Demchenko
DOI:10.1021/jo0711844
日期:2007.8.31
As a part of a program for developing new efficient procedures for stereoselectiveglycosylation, a range of S-benzoxazolyl (SBox) glycosides have been synthesized. The mechanistic aspects of the SBox moiety activation for glycosylationvia a variety of conceptually different pathways in the presence of thiophilic, electrophilic, or metal-based promoters have been investigated.
Application of Glycosyl Thioimidates in Solid-Phase Oligosaccharide Synthesis
作者:M. Cristina Parlato、Medha N. Kamat、Haisheng Wang、Keith J. Stine、Alexei V. Demchenko
DOI:10.1021/jo701902f
日期:2008.3.1
S-benzoxazolyl (SBox) and S-thiazolinyl (STaz) glycosides, were investigated as glycosyl donors for solid-phaseoligosaccharidesynthesis. It was demonstrated that these derivatives are suitable for both glycosyl acceptor-bound and glycosyl donor-bound strategies, commonly employed in resin-supported oligosaccharidesynthesis.
Silver(I) tetrafluoroborate as a potent promoter for chemical glycosylation
作者:Sophon Kaeothip、Papapida Pornsuriyasak、Alexei V. Demchenko
DOI:10.1016/j.tetlet.2007.12.105
日期:2008.2
promoter for the activation of various glycosyldonors including glycosyl halides, trichloroacetimidates, thioimidates, etc. Easy handling and no requirement for azeotropic dehydration prior to application makes AgBF(4) especially beneficial in comparison to the commonly used AgOTf. Selective activation of glycosyl halides or thioimidates over thioglycosides or n-pentenyl glycosides, including simple
On the stereoselectivity of glycosidation of thiocyanates, thioimidates, and thioglycosides
作者:Sophon Kaeothip、Steven J. Akins、Alexei V. Demchenko
DOI:10.1016/j.carres.2010.08.003
日期:2010.10
Comparative side-by-side glycosylation studies demonstrated that glycosyl thiocyanates, thioimidates, and thioglycosides provide comparative stereoselectivities in glycosylations. Very high alpha-stereoselectivity that was previously recorded for glycosyl thiocyanates can be achieved, but only if glycosyl acceptors are equipped with electron-withdrawing acyl substituents. Partially benzylated glycosyl acceptors provided relatively modest stereoselectivity, which was on a par with other common glycosyl donors. Accordingly, thioimidates and thioglycosides showed high stereoselectivity similarly to that of thiocyanates with different classes of acylated primary and secondary glycosyl acceptors. (C) 2010 Elsevier Ltd. All rights reserved.