Influencing the regioselectivity of lipase-catalyzed hydrolysis with [bmim]PF6
摘要:
An easy preparation of mono-deprotected thioglucopyramosides via a selective Candica cylindracea lipase-catalyzed hydrolysis of a commercially available peracetylated precursor is described. Especially, ethyl 2,3,4-tri-O-acetyl-1-thio-beta-D-glucopyranoside and ethyl 2,3,6-tri-O-acetyl-1-thio-beta-D-glucopyranoside were obtained in 100% and 54% isolated yields, respectively. The influence of the ratio of [bmim]PF6/buffer towards the regioselectivity of the deacetylation step and the acyl migration is discussed. (c) 2009 Elsevier Ltd. All rights reserved.
How the Arming Participating Moieties can Broaden the Scope of Chemoselective Oligosaccharide Synthesis by Allowing the Inverse Armed−Disarmed Approach
作者:James T. Smoot、Alexei V. Demchenko
DOI:10.1021/jo801551r
日期:2008.11.21
A new method for stereocontrolled glycosylation and chemoselective oligosaccharide synthesis has been developed. It has been determined that complete 1,2-trans selectivity can be achieved with the use of a 2-O-picolyl moiety, a novel neighboring group that is capable of efficient participation via a six-membered intermediate. The application of the picolyl concept to glycosidations of thioimidoyl, thioglycosyl, and trichloroacetimidoyl glycosyl donors is demonstrated. The picolyl moiety also retains the glycosyl donor in the armed state, as opposed to conventional acyl participating moieties. We name this new approach the "inverse armed-disarmed" strategy, because it allows for the chemoselective introduction of a 1,2-trans glycosidic linkage prior to other linkages. In the context of the oligosaccharide synthesis, the strategy provides trans-trans and trans-cis patterned oligosaccharides as opposed to classic Fraser-Reid's armed-disarmed approach leading to cis-trans and cis-cis linkages.