Synthesis of kojitetraose and kojipentaose

Reagent controlled stereoselective synthesis of teichoic acid α-(1,2)-glucans

The stereoselective construction of 1,2-cis-glycosidic linkages is key in the assembly of biologically relevant glycans, but remains a synthetic challenge. Reagent-controlled glycosylation methodologies, in which external nucleophiles are employed to modulate the reactivity of the glycosylation system, have become powerful means for the construction of 1,2-cis-glycosidic linkages. Here we establish that nucleophilic additives can support the construction of α-1,2-glucans, and apply our findings in the construction of a d-alanine kojibiose functionalized glycerol phosphate teichoic acid fragment. This latter molecule can be found in the cell wall of the opportunistic Gram-positive bacterium, Enterococcus faecalis and represents a structural element that can possibly be used in the development of therapeutic vaccines and diagnostic tools.

Synthesis of a pentasaccharide fragment of Polysaccharide II of Mycobacterium tuberculosis

Stereocontrolled, stepwise synthesis of decyl glycosides of alpha-(1-->2)-linked di- to pentaglucosides (1-5) is described; these constitute fragments of Polysaccharide II of Mycobacterium tuberculosis. Phenyl 3,4,6-tri-O-acetyl-2-O-benzyl-1-thio-alpha-D- glucopyranoside (7) was used as the single key intermediate, obtained from 1,3,4,6-tetra-O-acetyl-2-O-benzyl-beta-D-glucopyranose (6) and PhSSiMe3. Halogenolysis of 7 afforded the isolated beta bromide (10) and beta chloride (13). Solvolysis of 10 with decanol without heavy metal salts gave decyl 3,4,6-tri-O-acetyl-2-O-benzyl-alpha-D-glucopyranoside (14) in a highly stereoselective reaction, in high yield. Subsequent, iterative hydrogenolytic removal of the O-benzyl group and glycosylation with the beta-chloride 13 under catalysis by silver salts afforded the protected di- to penta-saccharide glycosides 16, 19, 21, and 23, which were conventionally deblocked.

The synthesis and characterisation of 2-O-(6-O-L-glycero-alpha,beta-D-manno-heptopyranosyl-alpha-D-glucopyran osyl)-alpha,beta-D-glucopyranose

The title compounds were synthesised, and appropriate derivatives were characterised by GLC, GLC-MS, and NMR spectroscopy. The GLC and GLC-MS data proved 2-O-(6-O-L-glycero-alpha-D-manno-heptopyranosyl-alpha-D-glucopyranosyl)- D- glucopyranose to be a constituent of the outer-core region of the lipopolysaccharide from Escherichia coli K-12, indicating the heptosyl residue to be linked to the terminal glucopyranose residue.