Protecting-group-free O-glysosidation using p-toluenesulfonohydrazide and glycosyl chloride donors
摘要:
A range of N '-glycosylsulfonohydrazides (GSHs) display good reactivity but poor stereoselectivity in protecting- group-free O-glycosidations when a moderate excess of the model acceptor n-decanol is employed. This stable, readily-accessed class of donor may be more tractable for the glycosylation of non-volatile acceptors than Fischer's glycosidation conditions. It is possible to generate unprotected glycosyl chlorides from GSHs in situ. In an effort to find conditions to improve glycosidation stereoselectivity, methanolysis of unprotected glucosyl chloride under halide-ion exchange conditions was examined. Relative to its tetra-O-benzyl analogue, this donor displays moderate, inverted stereoselectivity and a significantly faster reaction rate. (C) 2013 Elsevier Ltd. All rights reserved.
Protecting-Group-Free Synthesis of Glycosyl 1–Phosphates
摘要:
Glycosyl 1-phosphates enriched in the alpha-anomer are obtained without the use of protecting groups in two steps starting from the free hemiacetal. Condensation of free hemiacetals with toluenesulfonylhydrazide yields a range of glycosylsulfonohydrazide donors which can be oxidized using cupric chloride in the presence of phosphoric acid and the coordinating additive 2-methyl-2-oxazoline to give useful yields of the fully deprotected glycosyl 1-phosphates.
Stability studies of hydrazide and hydroxylamine-based glycoconjugates in aqueous solution
作者:Anna V. Gudmundsdottir、Caroline E. Paul、Mark Nitz
DOI:10.1016/j.carres.2008.11.007
日期:2009.2
Glycoconjugates can be readily formed by the condensation of a free-reducing terminus and a strong alpha-effect nucleophile, such as a hydrazide or a hydroxylamine. Further characterization of a series of glycoconjugates formed from xylose, glucose and N-acetylglucosamine, and either p-toluenesulfonyl hydrazide or an N-methylhydroxylamine, was carried out to gain insight into the optimal conditions for the formation of these useful conjugates, and their stability. Their apparent association constants (974 M-1) at pH 4.5; as well, as rate constants for hydrolysis, at pH 4.0, 5.0 and 6.0 (37 degrees C), were determined. The half-lives of the conjugates varied between 3 h and 300 days, All the compounds were increasingly stable as the pH approached neutrality. Conjugate hydrolysis rates mirrored those found for O-glycoside hydrolysis where conjugates formed from electron-rich monosaccharides hydrolyzed more rapidly. (C) 2008 Elsevier Ltd. All rights reserved
Protecting-Group-Free Synthesis of Glycosyl 1–Phosphates
作者:Landon John G. Edgar、Somnath Dasgupta、Mark Nitz
DOI:10.1021/ol3019083
日期:2012.8.17
Glycosyl 1-phosphates enriched in the alpha-anomer are obtained without the use of protecting groups in two steps starting from the free hemiacetal. Condensation of free hemiacetals with toluenesulfonylhydrazide yields a range of glycosylsulfonohydrazide donors which can be oxidized using cupric chloride in the presence of phosphoric acid and the coordinating additive 2-methyl-2-oxazoline to give useful yields of the fully deprotected glycosyl 1-phosphates.
Protecting-group-free O-glysosidation using p-toluenesulfonohydrazide and glycosyl chloride donors
作者:Rohan J. Williams、Caroline E. Paul、Mark Nitz
DOI:10.1016/j.carres.2013.08.019
日期:2014.3
A range of N '-glycosylsulfonohydrazides (GSHs) display good reactivity but poor stereoselectivity in protecting- group-free O-glycosidations when a moderate excess of the model acceptor n-decanol is employed. This stable, readily-accessed class of donor may be more tractable for the glycosylation of non-volatile acceptors than Fischer's glycosidation conditions. It is possible to generate unprotected glycosyl chlorides from GSHs in situ. In an effort to find conditions to improve glycosidation stereoselectivity, methanolysis of unprotected glucosyl chloride under halide-ion exchange conditions was examined. Relative to its tetra-O-benzyl analogue, this donor displays moderate, inverted stereoselectivity and a significantly faster reaction rate. (C) 2013 Elsevier Ltd. All rights reserved.