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“Solid phase synthesis, biophysical study and biological evaluation of cyclic glycopeptides for inhibition of protein protein interactions”

Final Report Summary - GLYCOPEPTIDES ('Solid phase synthesis, biophysical study and biological evaluation of cyclic glycopeptides for inhibition of protein protein interactions')

Project context and objectives

Protein-protein interactions are important processes as they explain how the peptide hormones bind to their receptors and proteins recruit other proteins to effect signal transduction. Molecular modelling studies suggested that macrocyclic scaffolds comprised of saccharide structure will provide a basis for targeting protein-protein interactions. The evaluation of new macrocyclic compounds to inhibit the BAK-Bcl interaction using biophysical techniques will be new tool for cell biological studies or cancer therapy development. To find a protein-protein interaction inhibitor, it is important to screen a number of derivatives. It is well known that to synthesise a number of derivatives in solution is a lengthy and time-consuming process, which can reduce the progress of the project if the goal is to optimise bioactivity.

Work performed

The initial project objective was to address the solution and solid phase synthesis of macrocyclic glycopeptides and their biophysical and biological evaluation of such structures. New monomers were to be synthesised in solution. During the project, four different glucopyranoside monomeric building blocks with pharmacophoric groups attached were synthesised. These monomers were then to be incorporated on the solid phase and four neoglycopeptides synthesised. Each of these goals was achieved. However, further work is still required before publication of this work, especially the final products from the solid-phase synthesis.

The nuclear magnetic resonance (NMR) spectra from the final structures were very broad and although MS indicated that the correct product had been obtained, there is still uncertainty as to the purity of the compound. The researcher, Dr Dilip Jarikote, completed the proposed project up to the penultimate step but was unable to solve the final problem before he finished the fellowship. However he worked on other related projects, which did lead to published work. All these projects together allowed him to develop some new skills and knowledge in the fields of carbohydrates and also in the area of biological evaluation, an experience that will be useful in his career.

The first area investigated was synthesis of cyclic glycopeptides in solution. This made use of reactions like click chemistry, ring-closing metathesis and ring-closing reductive amination. Monomers for solid phase synthesis were prepared and then cyclic compounds were generated from it. Monomers were efficiently prepared by ultrasonic methods and a paper was published on this. This work will also be published in a book entitled 'Carbohydrate Proven Methods'.

The solid-phase synthesis was successful to a degree with a number of steps successfully carried out. However, the final step and purification of the final compound was difficult and, as mentioned above, the final NMR spectra were broad and interpretation was not possible. The solid-phase synthesis work is not yet therefore publishable. However Dr Jarikote carried out synthetic work in solution on related compounds that will be published in due course. In this case, the PI's group were able to figure out how to purify the compounds and give NMR spectra that were interpretable. Dr Jarikote's contribution to this area will be acknowledged in publications in due course.

Dr Jarikote also worked on other types of carbohydrate-based peptidomimetics during his time in the PI group. He worked on the biophysical studies and synthesis of Echinomycin mimetics, which was completed and a paper has been published on this research area. Here novel macrocyclic sugar-based scaffolds presented quinoxaline residues and these are echinomycin analogues. Synthesis of such compounds was carried out by using a modification of a previously reported procedure from our group. The compounds were studied using ultra violet/Vis absorbance and steady-state fluorescence before and after the addition of calf thymus deoxyribonucleic acid (DNA) duplex varying concentration. The circular dichroism was carried out to find out the possible modes of interaction of the labelled oligomeric scaffold to the DNA. Dr Jarikote also worked on the synthesis of a new bivalent glycoclusters presenting lactose. A paper has been published on this work, which shows a compound that has a very high selectivity for galectin-3, the chimera type galectin with important roles in a variety of diseases.

Major results

This is a highlight from the Marie Curie Fellowship. This fellowship was very important for Dr Jarikote. Overall, the fellow got good experience of synthesis and carbohydrate chemistry in general, areas that he was not very knowledgeable on previously. He is a co-author of three publications to date and at least one more is expected on the alpha-helical peptidomimetics. Dr Jarikote also gained experience in writing a review, which was also published. The work is relevant to the development of new cancer therapeutics and further work is currently being continued in the project’s host group.

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