Convergent synthesis of a pentasaccharide corresponding to the cell wall O-polysaccharide of enteropathogenic Escherichia coli O115. Issue 8 (21st February 2020)

• Record Type: Journal Article
• Authors: Kundu, Monalisa; Gucchait, Arin; Misra, Anup Kumar
• Is Part Of: Tetrahedron. Volume 76:Issue 8(2020)
• Publication Date: 2020-02-21
• Subjects: Pentasaccharide -- Glycosylation -- β-l-rhamnoside -- TEMPO oxidation -- E. coli O115; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2020.130952
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: A pentasaccharide corresponding to the cell wall O -polysaccharide of the enteropathogenic Escherichia coli O115 has been synthesized using a convergent block glycosylation strategy in satisfactory yield. The synthetic strategy involves several stereoselective glycosylation steps, in which a remote picolinoyl group at C-3 mediated hydrogen bond acceptor aglycon delivery approach for the beta-linked L-rhamnosylation is worth mentioning. An orthogonal glycosylation approach has also been adopted for the preparation of a thioglycoside disaccharide derivative, which was used in the block synthesis. Perchloric acid supported over silica (HClO4 –SiO2 ) has been used as a solid acid catalyst for the activation of glycosyl trichloroacetimidate derivative as well as in the thioglycoside activations. The d -galacturonic acid moiety in the molecules was incorporated by linking a d -galactose unit in appropriate glycosyl linkage followed by a late stage TEMPO mediated regioselective oxidation of the primary hydroxyl group using diacetoxyiodo benzene (DAIB). All intermediate glycosylations were high yielding with satisfactory stereo outcome. Graphical abstract: Image 1 Highlights: Pentasaccharide of the O-antigen of Escherichia coli O115 was synthesized. A combination of NIS and HClO4 -SiO2 as glycosylation activator. p -Methoxybenzyl (PMB) was used as in situ removable protecting groups. Beta-L-rhamnosylation was achieved by remote picolinoyl group mediated hydrogen bond acceptor aglycon delivery. Diacetoxyiodo benzene (DAIB) mediated late stage TEMPO mediated oxidation.