Solid-phase synthesis of N-trichloroacetyl mannosamine 1-phosphate repeating units mimicking capsular polysaccharide derived from Neisseria meningitidis serotype A.

N-Trichloroacetyl analogs of N-acetylmannosamine 1-phosphate repeating units, which are found in capsular polysaccharides of Neisseria meningitidis serotype A, were successfully obtained via solid-phase synthesis using an oxazaphospholidine monomer. The introduction of the trichloroacetyl group into the amino group of mannosamine resulted in the stabilization of the reaction intermediates. Monosaccharide, disaccharide, and tetrasaccharide derivatives were obtained and isolated. This is the first example to demonstrate the synthesis of the N-acylated mannosamine 1-phosphate structure having no less than four phosphate linkages.

Synthesis of Modular Building Blocks using Glycosyl Phosphate Donors for the Construction of Asymmetric N-Glycans.

Glycosyl phosphates are known as versatile donors for the synthesis of complex oligosaccharides both chemically and enzymatically. Herein, we report the stereoselective construction of modular building blocks for the synthesis of N-glycan using glycosyl phosphates as donors. We have synthesized four trisaccharide building blocks with orthogonal protecting groups, namely, Manß2GlcNAc(OAc)3ß6GlcNAc (9), Manß2GlcNAc-ß6GlcNAc(OAc)3 (15), Manß2GlcNAc(OAc)3ß4GlcNAc (18) and Manß2GlcNAcß4GlcNAc(OAc) (22) for further selective elongation using glycosyltransferases. The glycosylation reaction using glycosyl phosphate was found to be high yielding with shorter reaction time. Initially, The phthalimide protected glucosamine donor was exploited to ensure the formation of ß-glycosidic linkage and later converted to the N-acetyl group before the enzymatic synthesis. The selective deprotection of O-benzyl group was performed prior to enzymatic synthesis to avoid its negative interference.

Structure of the ß-l-fucopyranosyl phosphate-containing O-specific polysaccharide of Escherichia coli O84.

Fine structure of the O-polysaccharide chain of the lipopolysaccharide (O-antigen) defines the serospecificity of bacterial cells, which is the basis for O-serotyping of medically and agriculturally important gram-negative bacteria including Escherichia coli. In order to obtain the O-polysaccharide for structural analysis, the lipopolysaccharide was isolated from cells of E. coli O84a by phenol/water extraction and degraded with mild acid. However, the O-polysaccharide was cleaved at a highly acid-labile ß-l-fucopyranosyl phosphate (ß-l-Fucp-1-P) linkage to give mainly a pentasaccharide that corresponded to the O-polysaccharide repeat. Therefore, the lipopolysaccharide and the pentasaccharide as well as their O-deacylated derivatives were studied using sugar analysis, NMR spectroscopy, and (for oligosaccharides) ESI HR MS, and the O84-polysaccharide structure was established. The O-polysaccharide is distinguished by the presence of ß-l-Fucp-1-P and randomly di-O-acetylated 6-deoxy-d-talose, which are found for the first time in natural carbohydrates. The gene cluster for the O84-antigen biosynthesis was analysed and its content was found to be consistent with the O-polysaccharide structure.

Expanding the Pyrimidine Diphosphosugar Repertoire: The Chemoenzymatic Synthesis of Amino- and Acetamidoglucopyranosyl Derivatives.

The exploitation of a unique thymidylyltransferase (Ep ) allows the rapid syntheses of thymidine and uridine 5'-(aminodeoxy-α-D-hexopyranosyl diphosphates), 5'-(acetamidodeoxy-α-D-hexopyranosyl diphosphates), and even 5'-(aminodideoxy-α-D-hexopyranosyl diphosphates), which are amino analogues of the products from the native reaction of Ep .