title: Synthesis of a 2,3,4-triglycosylated rhamnoside fragment of rhamnogalacturonan-II side chain A using a late stage oxidation approach.
abstract: Pectic polysaccharide RG-II, a key component of plant primary cell walls, is known to exist as a dimer formed by means of borate diester cross-links between apiosyl residues of one of its constituent side-chain oligosaccharides. Described herein is the strategy for the synthesis of the branched tetrasaccharide alpha-d-GalA-(1-->2)-[beta-D-GalA-(1-->3)]-[alpha-L-Fuc-(1-->4)]-alpha-L-Rha-OMe, an RG-II fragment that is linked to the apiosyl residue that is thought to be responsible for the borate complexation in RG-II dimer. Iterative glycosylation of the rhamnoside acceptors derived from the key 2,3-orthoacetate of methyl 4-O-methoxybenzyl-alpha-d-rhamnopyranoside afforded the protected tetrasaccharide. The target dicarboxylic acid saccharide was subsequently prepared by removal of protecting groups followed by TEMPO-mediated oxidation of galactopyranosyl residues to galactopyranosyluronic acids.
authors.affiliation: Centre for Carbohydrate Chemistry, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Chauvin
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Nepogodiev
authors.forename: Robert A
authors.initials: RA
authors.lastname: Field