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Bio-Inspired Tools for Glycoscience

Periodic Reporting for period 4 - GLYCO-TOOLS (Bio-Inspired Tools for Glycoscience)

Reporting period: 2020-01-01 to 2020-12-31

Cell surface carbohydrates play key roles in cell recognition mechanisms. O-glycosylation is a ubiquitous post-translational modification that is highly dynamic and responsive to cellular stimuli through the action of cycling enzymes. Expression of specific O-glycans is linked to changes in gene expression in, for example, inflammatory bowel disease, cystic fibrosis and several types of cancer.
Protein-carbohydrate interactions typically exhibit high specificity and weak affinities toward their carbohydrate ligand. This low affinity is compensated in nature by the architecture of the protein, the host presenting the carbohydrate ligands in a multivalent manner or as clusters on the cell or mucosal surface. This effect is known as the multivalency or “cluster–glycoside effect” and has been well documented for lectin–carbohydrate interactions as increasing ligand affinity and selectivity. The fundamental understanding of these glycosylation patterns at molecular and functional levels will allow mechanisms associated with bacterial-host interactions, bowel disease and several cancers to be defined, which will facilitate the identification of effective treatments and diagnostics for these conditions in due course.
This is a multidisciplinary project involving synthetic organic and inorganic chemistry, enzymology and glycobiology. The proposal centres on the development of expedient synthetic and chemo-enzymatic methodologies for the preparation of novel multivalent O-glycan probes that will be used in the screening of O-glycosylation-linked interactions in health and in disease. These studies will help us understand the parameters controlling the combinatorial diversity of O-glycans and the implications of such diversity on receptor binding and subsequent intracellular signalling, which in turn will lead us to the development of new glycan-based diagnostic tools and therapeutics.

This research programme is comprised of three main objectives:

A. Development of expedient and catalytic methods for oligosaccharide assembly, which will pave the way to the automation of oligosaccharide synthesis.
B. Chemical and enzymatic synthesis of O-glycan targets. Harnessing of the glyco-synthetic machinery for the combinatorial synthesis of O-glycan probes.
C. Preparation of novel glyco-nanoparticles for the development of glycan-based targeted drug delivery systems (Smart Glyco-Nanomaterials).
WP1: We have developed atom economic stereoselective methods for the synthesis of glycosides of biological importance using organocatalysis and transition-metal catalysis particularly targeting deoxyglycosides which are important components of natural products and an area of carbohydrate chemistry which had been understudied until now when compared to the fully oxygenated counterparts (Org. Lett. 2020, 22, 1991; JOC 2020, 85, 5038; JOC 2019, 84, 2415; JACS 2017, 139, 14041; ACIE 2017, 56, 640; Org. Lett. 2017, 19, 2857; JOC 2017, 82, 407).

We also pioneered the use of ionic-liquid based tags for chromatography-free purification and MS reaction monitoring in chemical and enzymatic oligosaccharide synthesis (ICROS) and more recently demonstrated that ITag-glycans can also be used to label live cells in metabolic oligosaccharide engineering applications (Chem. Commun. 2016, 52, 4906; Bioorg. Med. Chem. Lett. 2015, 25, 4329). The ITag-glycans can also be used to harness glycan-modifying enzymes directly in natural systems such as human milk (“Hot paper” in OBC 2017, 15, 3575) and these ionic labels are now being used for the discovery of novel enzyme activity (OBC 2019, 17, 5920; OBC 2020, 18, 3142, ACS Catal. 2020, 10, 17, 9986 and J. Am. Soc. Mass Spectrom. 2021 In addition, we have developed chemoenzymatic routes to access a range of glycoside targets For example, the chemoenzymatic synthesis of 3-deoxy-3-fluoro L-fucosides (Chem. Commun., 2020, 56, 6408) and the biocatalytic synthesis of Pse5Ac7Ac containing glycosides (ACS Catal., 2020, 10, 17, 9986)

We have developed novel functional nanomaterials for selective cell targeting, bioimaging and intracellular delivery (Nanoscale, 2018, 10, 13908; Scientific Reports, 2018, 8,12234; ACS Omega 2018, 3, 9822; Nanoscale 2016, 8, 18630; J. Mat. Chem. A. 2014, 2, 6879 and ACIE. 2014, 53, 810 (Hot Paper)). We use the novel nanoprobes for the cell nuclear targeting and photothermal ablation of cervical (HeLa) cancer cells over human dermal fibroblasts (HDF) (Nanoscale Adv. 2019, 1, 2840). More recently, we demonstrated the in planta use of glucose-functionalized fluorescent carbon dots. Uptake of these nanoparticles directly from the soil improves photosynthesis and also increases crop production by 18% in Dwarf wheat (New Phytol. 2020 DOI:10.1111/nph.16886). Further work in this area has led to the development of a simple spray-on-gene editing transformation method in planta, where the non-toxic nanomaterials can act as a fast vehicle for carrying plasmids into mature plant cells, resulting in transient plant transformation in a number of important crop species (BioRxiv 2009, featured in Scientific American). The above work has been patented (PCT/EP2018/097143) and has led to Glaia Ltd. And CDotBio Ltd., University of Bristol spin-outs focused on the application of nanotechnologies in agriculture.
We also made important contributions towards the development of novel anticancer and antiparasitic drugs. We have developed synthetic and computational tools for the design and synthesis of small-molecules to selectively target G4 DNA over duplex DNA (Chem. Eur. J. 2017, 23, 6953; Chem. Eur. J. 2020, 26, 6224; Chem. Sci. 2021 ASAP) including photo-responsive ligands that can modulate (G4) DNA structure and activity as a therapeutic tool using light (Chem. Commun. 2020, 6224; ACIE. 2019, 131, 1).
Access to structurally defined oligosaccharide libraries is key for the advancement of glycobiology research and also for carbohydrate-based drug discovery. Therefore, the development of general and efficient methodologies for the synthesis of oligosaccharide tools which are not restricted to specialized labs, has the potential to transform the field.

Access to structurally defined oligosaccharide libraries is key for the advancement of glycobiology research and also for carbohydrate-based drug discovery. Therefore, the development of general and efficient methodologies for the synthesis of oligosaccharide tools which are not restricted to specialized labs, has the potential to transform the field.
Achievements made within this programme have addressed one of the major hurdles in oligosaccharide synthesis by developing tools that allows the ability to perform O-glycosylation reactions efficiently in a catalytic and stereoselective manner. In addition to developing the “know how”, using these new synthetic tools, we have provided access to a library of biologically important oligosaccharide targets and analogues which were not previously available.

Through another aspect of the programme we have developed a novel class of carbon-based functional and fluorescent nanomaterials to be used in a wide range of biomedical and agricultural applications which addresses key societal aspects. Our seminal contributions in these areas will have lasting impact in the areas of theranostics (e.g. materials that act as both diagnostic and therapeutics).