Syntheses of fluorinated ligands to probe binding of antigenic determinants of Vibrio cholerae O:1, serotypes Inaba and Ogawa, to antibodies

Electron ionization mass spectrometric study of monomeric models of O-polysaccharides of Vibrio cholerae O:1, serotypes Ogawa and Inaba

Fragmentation mechanisms of electron ionization (EI) mass spectrometry of the title compounds have been elucidated by high-resolution (HR) mass spectrometric measurements of the elemental composition and measurements of the metastable transitions (B(2)/E, CID). The experimental results were interpreted with the help of Mass Frontier 3.0 software, which aided the elucidation of fragmentation mechanisms and helped to deduce structures of the ions formed. Characteristic under the conditions of EI-MS measurement was the production of protonated adducts. Three distinct pathways observed include the formation of oxonium type ions, the conjugated transfer of electrons in the pyranose ring, and cleavage of the acylamide side chains. By applying the results obtained, the molecular mass, as well as the structures of both the saccharide and acylamide side chain involved in related substances, can be determined.

The binding of synthetic analogs of the upstream, terminal residue of the O-polysaccharides (O-PS) of Vibrio cholerae O:1 serotypes Ogawa and Inaba to two murine monoclonal antibodies (MAbs) specific for the Ogawa lipopolysaccharide (LPS)

The binding of nineteen analogues of the upstream, terminal, monosaccharide residue of each of the O-polysaccharide (O-PS) of Vibrio cholerae O:1, serotype Ogawa and Inaba, with two murine monoclonal IgG antibodies both specific for the Ogawa LPS were measured using fluorescence spectroscopy. The use of the deoxy and the deoxyfluoro analogs allowed further refinement of the hydrogen-bonding pattern involved in the binding. Based on the binding characteristics observed for some of the ligands in the Inaba series, the binding of the monosaccharide that represents the upstream, terminal unit of the O-PS of V. cholerae O:1 serotype Inaba was redefined. We show for the first time that the upstream, terminal monosaccharide of the Inaba O-PS shows weak binding with these two anti-Ogawa antibodies. The results obtained allow further rationalization of the structural basis for the binding of V. cholerae O:1 antigens to their homologous antibodies.

Synthetic explorations towards 3-deoxy-3-fluoro derivatives of D-perosamine

Based on a literature precedent, preparation of methyl 4-azido-3,4,6-trideoxy-3-fluoro-alpha-D-mannopyranoside (18) was attempted via fluorination of methyl 4-azido-2-O-benzyl-4,6-dideoxy-alpha-D-altropyranoside with diethylaminosulfur trifluoride (DAST). Contrary to expectations, the reaction took place with retention of configuration at the site of the fluorination yielding methyl 4-azido-2-O-benzyl-3,4,6-trideoxy-3-fluoro-alpha-D-altropyranoside. Treatment with DAST of methyl 4-azido-2-O-benzyl-4,6-dideoxy-alpha-D-allopyranoside (8), or its 2-(p-methoxybenzyl) analog 9 resulted in fluorination with inversion of configuration at position 3, to give the corresponding 3-deoxy-3-fluoro glucopyranosides 10 and 11, respectively. Accordingly, compound 18 was prepared from 11, by de-p-methoxybenzylation at O-2, followed by inversion of configuration at C-2 in the resulting methyl 4-azido-3,4,6-trideoxy-3-fluoro-alpha-D-glucopyranoside. The 2-O-methyl analog of 18 (19) was prepared by methylation of 18. Compounds 18 and 19 were converted, conventionally, into the 3-fluoro analogs of the terminal determinants of the O-PS of Vibrio cholerae O:1, serotype Inaba and Ogawa, respectively.