Rapid assembly of the doubly-branched pentasaccharide domain of the immunoadjuvant jujuboside A via convergent B(C6F5)3-catalyzed glycosylation of sterically-hindered precursors. Issue 43 (12th May 2017)

• Record Type: Journal Article
• Authors: Karimov, Rashad R.; Tan, Derek S.; Gin, David Y.
• Is Part Of: Chemical communications. Volume 53:Issue 43(2017)
• Page Start: 5838
• Page End: 5841
• Publication Date: 2017-05-12
• Subjects: Chemistry -- Periodicals; 540
• DOI: 10.1039/c7cc01783a
• Languages: English
• ISSNs: 1359-7345

Abstract

Abstract : An efficient, convergent synthesis is achieved using optimized reaction conditions to overcome inherent complete α-selectivity in this challenging glycosylation reaction. Abstract : A convergent synthesis of the complex, doubly-branched pentasaccharide domain of the natural-product immunoadjuvant jujuboside A is described. The key step is a sterically-hindered glycosylation reaction between a branched trisaccharide trichloroacetimidate glycosyl donor and a disaccharide glycosyl acceptor. Conventional Lewis acids (TMSOTf, BF3 ·Et2 O) were ineffective in this glycosylation, but B(C6 F5 )3 catalyzed the reaction successfully. Inherent complete diastereoselectivity for the undesired α-anomer was overcome by rational optimization with a nitrile solvent system (1 : 5 t -BuCN/CF3 Ph) to provide flexible, effective access to the β-linked pentasaccharide.