Christopher Jones

Pneumococcal Capsules and Their Types: Past, Present, and Future

SUMMARY Streptococcus pneumoniae (the pneumococcus) is an important human pathogen. Its virulence is largely due to its polysaccharide capsule, which shields it from the host immune system, and because of this, the capsule has been extensively studied. Studies of the capsule led to the identification of DNA as the genetic material, identification of many different capsular serotypes, and identification of the serotype-specific nature of protection by adaptive immunity. Recent studies have led to the determination of capsular polysaccharide structures for many serotypes using advanced analytical technologies, complete elucidation of genetic basis for the capsular types, and the development of highly effective pneumococcal conjugate vaccines. Conjugate vaccine use has altered the serotype distribution by either serotype replacement or switching, and this has increased the need to serotype pneumococci. Due to great advances in molecular technologies and our understanding of the pneumococcal genome, molecular approaches have become powerful tools to predict pneumococcal serotypes. In addition, more-precise and -efficient serotyping methods that directly detect polysaccharide structures are emerging. These improvements in our capabilities will greatly enhance future investigations of pneumococcal epidemiology and diseases and the biology of colonization and innate immunity to pneumococcal capsules.

Similarity of monosaccharide, oligosaccharide and polysaccharide structures in gum exudate of Anacardium occidentale

The gum exudate from the Brazilian cashew-nut tree (Anacardium occidentale) contained traces of the reducing sugars, rhamnose (0.005%), arabinose (0.03%), mannose (0.007%), galactose (0.03%), glucose (0.02%), beta-D-Galp-(1-->6)-alpha beta-D-Gal (0.05%), alpha-L-Rhap-(1-->4)-alpha beta-D-GlcA (0.008%) and alpha-L-Rhap-(1-->4)-beta-D-GlcpA-(1-->6)-beta-D-Galp-(1-->6 )-alpha beta-D-Gal (0.008%). Rhamnose, arabinose, glucose and the three oligosaccharides are components of the side-chains of the gum polysaccharide, which has a main chain of (1-->3)-linked beta-D-Galp units. The structure of this polysaccharide was determined and found to differ from that previously reported for the gum of a tree growing in India, lacking units of 4-O-methylglucuronic acid. Other new side-chain structures were characterized, particularly -alpha-D-Galp-(1-->6)-D-Galp- and alpha-L-Araf-(1-->6)-D-Galp-).

Structural elucidation of the repeat unit in highly branched acidic exopolysaccharides produced by nitrogen fixing Burkholderia

Burkholderia kururiensis, strain M130, an endophytic diazotrophic bacterium isolated from rice roots, produces acetylated acidic exopolysaccharides which can be separated by anion exchange chromatography. These were characterized by nuclear magnetic resonance spectroscopy, methylation analysis and Smith degradation. The exopolysaccharides eluted with 0.5 M NaCl were produced when the bacterium was grown in a medium containing mannitol as the sole carbon source, and showed to be a mixture of two different polymers, composed of hepta or octasaccharide repeat units, consistent with following structure: [structure: see text]. The ability of diazotrophic Burkholderia to produce two exopolysaccharides that differ by the presence of a terminal glucosyl residue provides insight into polysaccharide function with potentially significant biological consequences in the endophytic-host plant interaction.

Facile aerial oxidation of a porphyrin. Part 3. Some metal complexes of meso-tetrakis-(3,5-di-t-butyl-4-hydroxyphenyl)porphyrin

Metal complexes of the title porphyrin were prepared and their behaviour in basified dichloromethane solution examined using u.v.–visible and e.s.r. spectroscopy. The free base, ZnII, FeIII, and CoII complexes undergo drastic colour changes with rapid and irreversible aerial oxidation. Acidification does not regenerate the porphyrin spectrum, but shaking with aqueous metabisulphite or dithionite does. The VIVO, MnIII, CuII, SnIV, PdII, and PtII complexes also change colour but their metalloporphyrin u.v.–visible spectra largely return on acidification. Some deterioration over time in the returned B band intensity is noted, which is greatest for the NiII complex and is most likely due to autoxidation. E.s.r. spectra, arising from oxidation or autoxidation of the complexes to radical species, were observed for the MnIII, NiII, ZnII, and SnIV complexes, the latter in neutral dichloromethane. This gave a triplet e.s.r. spectrum that decayed with second-order kinetics. Addition of base to the SnIV complex quenched the e.s.r. spectrum. An explanation is offered in which the metal modulates electron transfer onto the macrocycle, from the phenoxy meso-substituents, via back-bonding and changes in porphyrin conformation.

Synthesis of phosphorylated fragments of Streptococcus pneumoniae type 19F capsular polysaccharide

Serotype 19F is one of the most virulent of the Streptococcus pneumoniae serotypes, causing meningitis, otitis media, septicemia and pneumonia. Effective protection against infection is mediated by antibodies directed against its capsular polysaccharide (CPS), composed of the trisaccharide repeating units (→4-β-D-ManpNAc-(1→4)-α-D-Glcp-(1→2)-α-L-Rhap-1→) bridged by phosphate diesters. Unfortunately, CPSs are typical T-independent type 2 immunogens. Therefore, the conjugation of putative saccharide haptens to a protein carrier, which invokes T-cell involvement, has proved to be extremely effective in enhancing the immune response. In a project aimed at ascertaining the role played by the different structural factors in the immunogenicity of new vaccines against Streptococcus pneumoniae type 19F, we planned the synthesis of a family of trisaccharide repeating unit derivatives where the phosphate group is a) absent; b) linked only to the rhamnose unit; or c) linked only to the N-acetylmannosamine unit. Compound of type a) and c) also bear an appropriate spacer for conjugation to the protein carrier. Moreover, the synthesis of a dimer of the CPS repeating unit, in which a phosphate diester bridges two repeating units, was carried out.

Facile aerial oxidation of a porphyrin. Part 4. Unsymmetrical meso-tetra aryl porphyrins with 3,5-di-t-butyl-4-hydroxyphenyl and 4-hydroxyphenyl substituents

A series of porphyrins (2a)–(5a), unsymmetrically substituted in their meso-positions with 3,5-di-tbutyl-4-hydroxyphenyl(DtB4HP) and 4-hydroxyphenyl (4HP) groups, has been synthesised and characterised. The two di-DtB4HP di-4HP isomeric porphyrins, (3a) and (4a)(called ‘cis’ and ‘trans’, respectively), in particular are distinguishable by 1H n.m.r. spectroscopy. In basified dichloromethane (DCM) solutions, the porphyrins undergo drastic colour and u.v.–visible changes which, in 1 mol dm–3 methanolic potassium hydroxide, is indicative of irreversible aerial oxidation that is slower and less extensive than for the symmetrically tetrakis-DtB4H P substituted porphyrin (1). Cyclic voltammetry supports this, indicating that in basified DCM solutions, one-electron oxidation of porphyrins (2a)–(5a) becomes increasingly more difficult than for (1), as the DtB4HP groups are replaced by 4HP. An explanation of the relative redox activity of these porphyrins compared with (1), is offered in terms of the different electron-releasing properties of the two types of phenolic substituent.

Residual paramagnetism in silver(III) metalloporphyrin complexes

Silver(III) metalloporphyrin complexes, AgIIIP [where P = octaethylporphyrin (1), meso-tetraphenylporphyrin (2), meso-tetra(2,4,6-trimethoxyphenyl)porphyrin (3)] were unexpectedly found to contain residual paramagnetism owing to the presence of AgIIP in small amounts; the possibility of generating molecular conductors and semiconductors, based on silver metalloporphyrin complexes, is examined.