2,3-Anhydrosugars in glycoside bond synthesis. Application to the preparation of C-2 functionalized α- d-arabinofuranosides

Abstract

A novel two-step route has been developed for the synthesis of a panel of oligosaccharides ( 9– 17 ) containing C-2 functionalized α- d-arabinofuranosyl residues. The first step in this route consists of a highly stereocontrolled glycosylation reaction using a 2,3-anhydrosugar thioglycoside ( 6 ). In the second step, the epoxide ring in the 2,3-anhydrosugar glycoside is regioselectively opened at C-2 with sodium methoxide and sodium azide thus providing products with the α- d-arabinofuranosyl stereochemistry. This approach to these targets circumvents the potential stereocontrol problems inherent in glycosylations with arabinofuranosyl donors possessing non-participating groups at C-2. The route is also highly convergent, allowing the preparation of a range of C-2′ and C-2″ modified oligosaccharides upon reaction of epoxy glycosides 27– 29 with nucleophiles.