RESUMO
A new practical, catalytic, and highly stereoselective method for directly accessing 1,1-α,α'-linked 2-deoxy trehalose analogues via AuCl3-catalyzed dehydrative glycosylation using hemiacetal glycosyl donors and acceptors is described. The method relies on the chemoselective Brønsted acid-type activation of tribenzylated 2-deoxy hemiacetals in the presence of other less reactive hemiacetals.
Assuntos
Trealose , Catálise , Glicosilação , EstereoisomerismoRESUMO
The stereoselective synthesis of oligosaccharides remains one of the biggest challenges in carbohydrate chemistry. Many factors, including reaction conditions and the type of glycosyl donor and acceptor used, can affect the outcome of glycosylation reactions. In this Perspective, we discuss methods aimed to control the reactivity and stereoselectivity of glycosylation reactions using conformationally constrained glycosyl donors, with a focus on more recently developed chemistry.
Assuntos
Oligossacarídeos , Glicosilação , EstereoisomerismoRESUMO
We demonstrate that tuning the reactivity of Cu by the choice of oxidation state and counterion leads to the activation of both "armed" and "disarmed" type glycals toward direct glycosylation leading to the α-stereoselective synthesis of deoxyglycosides in good to excellent yields. Mechanistic studies show that CuI is essential for effective catalysis and stereocontrol and that the reaction proceeds through dual activation of both the enol ether as well as the OH nucleophile.
Assuntos
Cobre/química , Glicosídeos/síntese química , Catálise , Glicosídeos/química , Glicosilação , Estrutura Molecular , OxirreduçãoRESUMO
Heparan sulfate (HS) and dermatan sulfate (DS) are l-iduronic acid containing glycosaminoglycans (GAGs) which are implicated in a number of biological processes and conditions including cancer and viral infection. Chemical synthesis of HS and DS is required to generate structurally defined oligosaccharides for a biological study. Herein, we present a new synthetic approach to HS and DS oligosaccharides using chemoselective glycosylation which relies on a disarmed [2.2.2] l-ido lactone motif. The strategy provides a general approach for iterative-reducing end chain extension, using only shelf-stable thioglycoside building blocks, exploiting a conformational switch to control reactivity, and thus requires no anomeric manipulation steps between glycosylations.