title: Synthesis of a selectively protected trisaccharide building block of the capsular polysaccharide of Streptococcus pneumoniae types 6A and 6B.
abstract: 4-Methoxybenzyl 2,4-di-O-benzyl-3-O-[2,4,6-tri-O-benzyl-3-O-(3,4,6-tri-O-benzyl-alpha-D- galactopyranosyl)-alpha-D-glucopyranosyl]-alpha-L-rhamnopyranoside (22), a building block for the alpha-D-Galp-(1----3)-alpha-D-Glcp-(1----3)-alpha-L-Rhap fragment of the capsular polysaccharides of Streptococcus pneumoniae types 6A and 6B [----2)-alpha-D-Galp-(1----3)-alpha-D-Glcp-(1----3)-alpha-L-Rhap-( 1----X)-D- RibOH-(5-P----]n (6A, X = 3; 6B, X = 4) has been synthesised. Ethyl 3-O-allyl-2,4,6-tri-O-benzyl-1-thio-beta-D-glucopyranoside was coupled with 4-methoxybenzyl 2,4-di-O-benzyl-alpha-L-rhamnopyranoside in ether, using methyl triflate as promoter. The resulting alpha-D-Glcp-(1----3)-alpha-L-Rhap derivative was deallylated with KOBut in N,N-dimethylformamide followed by 0.1M HCl in 9:1 acetone-water. The product was coupled with 3,4,6-tri-O-acetyl-2-O-allyl-alpha,beta-D-galactopyranosyl trichloroacetimidate in ether, using trimethylsilyl triflate, to yield 19. Deacetylation, benzylation, and deallylation then gave 22.
authors.affiliation: Department of Bio-Organic Chemistry, Utrecht University, The Netherlands.
authors.forename: T M
authors.initials: TM
authors.lastname: Slaghek
authors.forename: M J
authors.initials: MJ
authors.lastname: van Vliet
authors.forename: A A
authors.initials: AA
authors.lastname: Maas
authors.forename: J P
authors.initials: JP
authors.lastname: Kamerling
authors.forename: J F
authors.initials: JF
authors.lastname: Vliegenthart
mesh_terms: D002240:Carbohydrate Sequence; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000138:chemical synthesis*; D013296:Streptococcus pneumoniae / Q000145:classification; D014312:Trisaccharides / Q000138:chemical synthesis*
chemical_list: D011135:Polysaccharides, Bacterial; D014312:Trisaccharides; C063862:4-methoxybenzyl 2,4-di-O-benzyl-3-O-(2,4,6-tri-O-benzyl-3-O-(3,4,6-tri-O-benzyl-alpha-galactopyranosyl)-alpha-glucopyranosyl)-alpha-rhamnopyranoside