Chemical Synthesis of Staphylococcal Oligosaccharides

The Gram positive, cluster forming bacteria Staphylococcus aureus belongs to the family of opportunistic pathogens that may cause blood stream infections when the integrity of skin is broken and the immune system can no longer fight the infection. S. aureus has become one of the most frequent causes of infections in newborns, surgical patients, trauma and burn patients, patients receiving an implant, and dialysis patients with high mortality rates. As a matter of fact, S. aureus has become one of the largest public health and economic impacts amongst all bacterial infectious diseases worldwide. This situation is further complicated by the rapid increase in anti-microbial drug resistance. Since the S. aureus bacterial cell is surrounded by a polysaccharide capsule, preventive vaccination based on polysaccharide or saccharide-protein conjugates is a suitable tool against the bacterial invasion. Serotyping has revealed that the majority of S. aureus strains express either capsular polysaccharides type 5 (CP5) or type 8 (CP8). Previous studies at Pfizer Inc. involved the preparation of conjugates of the purified native CPs derived from fermentation with protein carriers. Characterization of the activated products derived from purified native CPs by spectroscopic methods proved to be difficult owing to their large size. It was also noted that over activation and side reactions taking place during the conjugation process could lead to a loss of the epitopes required to achieve high immunogenicity of CP conjugate vaccines. This, in turn, can lead to the failure of the vaccine candidates in clinical trials. This thesis details the total syntheses of oligosaccharides structurally related to the repeating units of capsular polysaccharides S. aureus type 5 and 8. Our targets including two disaccharides, two trisaccharides and a hexasaccharide that will be studied by our collaborators at Pfizer Inc. to understand chemical activation for conjugation to the experimental carrier proteins. The improved understanding of the conjugation process will, in turn, lead to a more controlled, predictable, and reproducible outcome of polysaccharide conjugations. The additional potential outcome of this synthetic study is the development of alternative treatments to fight S. aureus infections

Optimization of Magnetic and Paper-Based Molecularly Imprinted Polymers for Selective Extraction of Charantin in <i>Momordica charantia</i>

Charantin is a mixture of β-sitosterol and stigmastadienol glucosides, which effectively lowers high blood glucose. Novel molecularly imprinted polymers coated magnetic nanoparticles (Fe3O4@MIPs) and filter paper (paper@MIPs) were synthesized by sol-gel polymerization to selectively extract charantin. β-sitosterol glucoside was selected as a template for imprinting a specific recognition owing to its larger molecular surface area than that of 5,25-stigmastadienol glucoside. Factorial designs were used to examine the effects of the types of porogenic solvents and cross-linkers on the extraction efficiency and imprinting factor before investigating other factors (for example, amounts of template and coated MIPs, and types of substrates for MIP immobilization). Compared to traditional liquid–liquid extraction, the optimal Fe3O4@MIP-based dispersive micro-solid phase extraction and paper@MIP extraction provided excellent extraction efficiency (87.5 ± 2.1% and 85.0 ± 2.9%, respectively) and selectivity. Charantin was well separated, and a new unidentified sterol glucoside was observed using the developed high-performance liquid chromatography with diode-array detection (Rs ≥ 2.0, n > 16,400). The developed methods were successfully utilized to extract and quantify charantin from M. charantia fruit powder and herbal products. Moreover, these methods are rapid (<10 min), inexpensive, simple, reproducible, and environmentally friendly

A Concise Synthesis of the Repeating Unit of Capsular Polysaccharide <i>Staphylococcus aureus</i> Type 8

The first synthesis of the repeating unit of <i>S. aureus</i> capsular polysaccharide type 8 is described. The repeating unit is an unusual trisaccharide sequence of three uncommon sugars, all connected via 1,2-<i>cis</i> linkages. The synthetic trisaccharide was equipped with capping methyl groups at the points of propagation of the polysaccharide sequence