title: Efficient synthesis of methyl lycotetraoside, the tetrasaccharide constituent of the tomato defence glycoalkaloid alpha-tomatine.
abstract: Branched oligosaccharide lycotetraose, beta-D-glucopyranosyl-(1-->2)-[beta-D-xylopyranosyl-(1-->3)]-beta-D-glucopyranosyl-(1-->4)-beta-D-galactopyranose, is a key constituent of many steroidal saponins, including glycoalkaloid alpha-tomatine, which is involved in protection of plants from invading pathogens. A new synthesis of the methyl beta-lycotetraoside () is described. Key steps of the synthesis include two successive glycosylation reactions of disaccharide acceptor methyl (4,6-O-benzylidene-3-O-p-methoxybenzyl-beta-D-glucopyranosyl)-(1-->4)-2,3,6-tri-O-benzyl-beta-D-galactopyranoside with readily available benzoylated trichloroacetimidates of alpha-D-glucopyranose and alpha,beta-D-xylopyranose. This scheme allows sequential glycosylation in one-pot on account of the convenient in situ removal of a p-methoxybenzyl protecting group under the acid conditions of the first glycosylation step. Following deprotection, tetrasaccharide was obtained in 19% yield over eight steps.
authors.affiliation: Centre for Carbohydrate Chemistry, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, UK.
authors.forename: Nigel A
authors.initials: NA
authors.lastname: Jones
authors.forename: Sergey A
authors.initials: SA
authors.lastname: Nepogodiev
authors.forename: Robert A
authors.initials: RA
authors.lastname: Field
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D006031:Glycosylation; D018551:Solanum lycopersicum / Q000737:chemistry*; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000138:chemical synthesis*; D014053:Tomatine / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D009844:Oligosaccharides; C506707:methyl lycotetraoside; D014053:Tomatine