Convergent synthesis of the hexasaccharide repeating unit of the capsular polysaccharide of Klebsiella serotype K-34. (17th December 2022)

• Record Type: Journal Article
• Authors: Shit, Pradip; Sahaji, Samim; Misra, Anup Kumar
• Is Part Of: Tetrahedron. Volume 129(2022)
• Publication Date: 2022-12-17
• Subjects: Hexasaccharide -- Polysaccharide -- Klebsiella -- Glycosylation -- Oxidation -- HClO4–SiO2; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2022.133159
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: A convergent [4 + 2] block synthetic strategy has been developed for the synthesis of the hexasaccharide repeating unit of the capsular polysaccharide of Klebsiella serotype K-34 in very good yield. A tetrasaccharide acceptor was synthesized by sequential stereoselective glycosylations of four suitably protected d -glucose and l -rhamnose units and a disaccharide thioglycoside was prepared by orthogonal glycosylation of d -galactosyl thioglycoside acceptor and l -rhamnosyl trichloroacetimidate donor. A combination of N -iodosuccinimide (NIS) and perchloric acid supported over silica (HClO4 –SiO2 ) has been used as thiophilic glycosylation activator in the stereoselective glycosylations. A late stage oxidation of primary hydroxyl group to a carboxylic group in the hexasaccharide was achieved in excellent yield using a combination of TEMPO and bis(acetoxy)iodobenzene (BAIB). All glycosylation reactions were highly stereoselective. Graphical abstract: Image 1 Highlights: Hexasaccharide of the capsular polysaccharide of Klebsiella serotype K-34 was synthesized. A combination of NIS and HClO4 -SiO2 as thiophilic glycosylation activator. A convergent stereoselective [4+2] glycosylation furnished hexasaccharide derivative. "Orthogonal" glycosylation was applied in the synthetic strategy. TEMPO and BAIB mediated selective oxidation of 1° hydroxyl group to carboxylic acid.