Synthesis of bionic glycoproteins for the treatment of uropathogenic E. coli

This thesis first describes methods for the synthesis of bionic glycoproteins with potential activity against Uropathogenic Escherichia coli. Work to achieve this goal initially focused on the synthesis of constructs capable of binding to the FimH receptor; a trisaccharide (α-D-mannopyranoside-(1->3) -α-D-mannopyranoside- (1->4) 3-azidopropyl-β-D-glucopyranoside) and two small mannose-based molecules. While the monosaccharide building blocks required for the trisaccharide synthesis were successfully synthesised, the small FimH-binding mannose-based species proved more suitable for the generation of bionic glycoproteins. One of the small mannose-based molecules was used in conjunction with on-resin copper-catalysed click ligation to synthesize three mannose-based probes capable of bio-conjugation to either colicin Ia or E9 proteins via organocatalyst-mediated protein aldol ligation (OPAL). Subsequently, in the first ever example of OPAL being used to conjugate glycans to proteins, these probes were used to synthesize a library of FimH-binding mannose-presenting colicin conjugates.
A selection of auto-aggregation and microscopy assays were conducted to determine whether the FimH-binding mannose-presenting colicin conjugates could induce aggregation of samples non-pathogenic E. coli strains. Unfortunately, the results of these experiments were inconclusive and further work is required to fully establish the biological activity of the mannose-based colicin conjugates.
This thesis also describes efforts towards the synthesis of trisaccharide (α-D-mannopyranoside-(1 ->3) -α-D-mannopyranoside- (1 ->4) 3-Azidopropyl-β-D-glucopyranoside) Although completion of this synthesis was not achieved due to the timescale of this project, significant progress was made. Reported herein is the work performed thus far including a reliable method for the formation of β-mannosidic bonds (a notoriously difficult feat). In addition to investigating chemical methods for β-mannoside formation, enzymatic synthetic methods using the phosphorylase BT-1033 were also developed. To the best of our knowledge we present the first investigation into the substrate promiscuity of BT-1033 towards unnatural glucosamine analogues and mannose-1-phosphates.