Synthesis of 2-(p-Trifluoroacetamidophenyl)ethylO-β-D-Mannopyranosyl-(l→2)-O-α-D-Mannopyranosyl-(l→2)-O-[α-D-Glucopyranosyl-(1→3)]-O-α-D-Mannopyranosyl-(1→2)-O-β-D-Manpopyranosyl-(1→3)-2-Acetamido-2-Deoxy-β-D-Gluco-Pyranoside, Corresponding to the Repeating Unit of theSalmonella Thompson, Serogroup C1O-Antigen Lipopolysaccharide, and of a Pentasaccharide Fragment Thereof

A synthetic strategy to xylose-containing thioglycoside tri- and tetrasaccharide building blocks corresponding to Cryptococcus neoformans capsular polysaccharide structures

C. neoformansthiosaccharide building blocks were prepared and their conversion to glycosyl acceptors as well as use as glycosyl donors investigated.

Total synthesis of quercetin 3-sophorotrioside

5,7-dihydroxy-3-[beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl]-2-(3,4-dihydroxyphenyl)-4H-1-benzopyran-4-one (quercetin 3-sophorotrioside), a flavonol triglycoside, isolated from Pisum sativum shoots and showing protective effects on liver injury induced by chemicals, was synthesized for the first time. The target compound was successfully synthesized in eight linear steps and in 39% overall yield through a combination of phase-transfer-catalyzed (PTC) quercetin C-3 glycosylation and silver triflate (AgOTf) promoted carbohydrate chain elongation using both sugar bromide and trichloroacetimidate donors.

Synthesis of a pentasaccharide corresponding to the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar D

The assembly of the pentasaccharide repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar D (i.e. 1) is described. The glucuronic acid residue in 1 is introduced as a glucopyranoside and oxidized in a later stage of the synthesis. Thus, iodonium ion-assisted glycosylation of the partially protected methyl mannopyranoside 11 with ethylthio donor 14 gave, after selective deprotection, disaccharide 18. Elongation of the latter with D-glucopyranoside 35 gave trisaccharide 36. Subsequent protective group manipulations yielded the acceptor 37. Condensation of disaccharide donor 31 with trisaccharide acceptor 37 yielded pentasaccharide 38. Protective group manipulations of 38 afforded 42, the glucoside of which was oxidized to yield the corresponding glucuronide 44. Hydrogenolysis of 44 gave the target pentasaccharide 1.

Synthesis of Oligosaccharide Structures from the Lipopolysaccharide of Moraxella catarrhalis

The synthesis of the octasaccharide [p-(trifluoroacetamido)phenyl]ethyl 4-O-[2-O-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)-beta-D-glucopyranosyl]-6-O-[2-O-[4-O-(4-O-alpha-D-galactopyranosyl-beta-D-galactopyranosyl)-alpha-D-glucopyranosyl]-beta-D-glucopyranosyl]-3-O-beta-D-glucopyranosyl-alpha-D-glucopyranoside, representing the outer part of the lipooligosaccharide from Moraxella catarrhalis serotype A, is described, together with a hepta-, a hexa-, and a pentasaccaride, composing parts thereof with shorter oligosaccharide chains substituted in the 6-position of the central 3,4,6-branched glucose moiety. The versatility of the use of thioglycosides in oligosaccharide synthesis is shown, since throughout the synthesis thioglycosides are used as glycosyl donor precursors, either directly in dimethyl(methylthio)sulfonium triflate (DMTST)-promoted coupling reactions or after conversion to the corresponding glycosyl bromide in silver triflate-promoted couplings. The effects of different protecting groups, anomeric leaving groups, and solvents used in the various coupling reactions are often substantial, which necessitates the use of easily convertible intermediates.

Chemistry of 1-Alkoxy-1-glycosyl Radicals: The Manno- and Rhamnopyranosyl Series. Inversion of alpha- to beta-Pyranosides and the Fragmentation of Anomeric Radicals

The formation and stereoselective quenching of 1-mannopyranosyl radicals by a tributyltin hydride-mediated intramolecular 1,5-hydrogen abstraction sequence is described. A competing process is 1,4-hydrogen atom abstraction leading principally to glucopyran-2-ulosides. Fragmentation of the anomeric radical resulting in the formation of ring opened products is a problem in certain series. The chemistry is dictated to a considerable extent by the nature of the protecting groups employed with the 4,6-benzylidene series and, for rhamnose, the Ley 3,4-dispiroketal, being particularly susceptible to the 1,4-hydrogen atom abstraction but less to the fragmentation. Photochemical conditions are described, in which these side reactions are practically eliminated, and applied to the inversion of an alpha- to a beta-mannoside in a disaccharide.

Synthesis of the methyl glycosides of a tri- and a tetra-saccharide related to heparin and heparan sulphate

The methyl glycoside of a tetrasaccharide isolated from heparin, methyl O-(alpha-L-idopyranosyluronic acid)-(1-->4)-O-(2-acetamido-2-deoxy-alpha-D- glucopyranosyl)-(1-->4)-O-(beta-D-glucopyranosyluronic acid)-(1-->3)-O-beta-D-galactopyranoside disodium salt and a trisaccharide derivative thereof, methyl O-(alpha-L-idopyranosyluronic acid)-(1-->4)-O-(2-acetamido-2- deoxy-alpha-D-glucopyranosyl)-(1-->4)-O-beta-D-glucopyranosyluronic acid disodium salt, were synthesized using a block-type strategy. A suitable protected disaccharide block of iduronic acid and glucosamine (IdoA-GlcN) was used as a key intermediate for the syntheses and was glycosidated with a protected galactose derivative and a disaccharide block of glucuronic acid and galactose (GlcA-Gal) to give tri- and tetra-saccharide derivatives, respectively. Deprotection gave the target compounds.