Late-Stage Functionalisation of Peptides via Photocatalytic Modification of Tryptophan

Lead Research Organisation: University of Nottingham
Department Name: Sch of Chemistry


Peptides can be modified to show more favourable characteristics compared to their original analogue, allowing them to be used for numerous applications in the pharmaceutical industry including the production of novel drugs, aiding drug delivery, and providing techniques to gain insight into biological systems. However, to functionalise a peptide or protein, often modification of a single amino acid is required which is difficult, due to the complexity of native biomolecules. Frequently used is cysteine (Cys) modification, due to its low abundance (~ 2% relative abundance across the proteome), however Cys residues are often vital for protein folding, and/or are involved in the active site of enzymes, therefore functionalisation could hinder the protein's activity. A new strategy which targets residues with a low abundance and a less crucial role within the protein, such as Trp with ~ 1.4% relative abundance, is in high demand.

Recent advances in the field of photoredox chemistry have unlocked novel methods for the selective functionalisation of amino acids under mild and more sustainable conditions; however, application of this chemistry to biomolecules is still relatively underdeveloped. The conditions associated with this chemistry often abide by multiple green principles; for instance, catalysis, the use of energy efficient single wavelength LEDs and safer solvents. However, despite the advances in this field, some procedures have drawbacks due to the use of additives and/ or certain components in excess creating waste. Also, these methods often employ precious metal catalysts which is unsustainable in the longer term. The development of a mild photochemical method for Trp functionalisation would be of broad value and would be likely to have applications in a range of fields.

Proposed solution and methodology

This project will develop a mild and efficient photocatalytic strategy for selectively modifying Trp within peptides and proteins, expanding upon the limited number of methods currently available for achieving this transformation. A key goal is to ensure the chemistry aligns with green principles to further enhance the impact of the research. Ultimately the products (small molecule-peptide conjugates) will find applications in drug delivery and in vivo imaging.

The project will build upon existing methods for modifying an indole moiety using visible-light The initial aim will be to identify sustainable and biocompatible conditions enabling the conjugation of a small molecule to Trp. The reaction must be selective for Trp within peptides despite the presence of interfering/ competing amino acids. The reaction will be applied to a variety of more complex Trp-containing peptides (greater than or equal to 5 amino acids) to gain an understanding of the chemoselectivty. To expand the number of conjugates we make and enable further applications of the products, the small molecule will also be varied to create a library of modified peptides each with distinct properties. A range of small molecules can be synthesised from cheap, readily available starting materials.
Small molecule-peptide conjugates synthesised via the more sustainable photocatalytic route can act as biological tools and this will be explored. A wide range of applications are envisaged depending on the small molecule attached. Examples include biological testing of products to determine if the modification has affected the peptide's activity. Alternatively, the chemistry could be used for protein profiling to probe all reactive Trp residues in a cell.

Planned Impact

This CDT will deliver impact aligned to the following agendas:

A2P will provide over 60 PhD graduates with the skill sets required to deliver innovative sustainable products and processes into the UK chemicals manufacturing industry. A2P will inspire and develop leaders who will:
- understand the needs of industrial end-users;
- embed sustainability across a range of sectors; and
- catalyse the transition to a more productive and resilient UK economy.

A2P will promote a step change towards a circular economy that embraces resilience and efficiency in terms of atoms and energy. The benefits of adopting more sustainable design principles and smarter production are clear. For example, the global production of active pharmaceutical ingredients (APIs) has been estimated at 65,000-100,000 tonnes per annum. The scale of associated waste is > 10 million tonnes per annum with a disposal cost of more than £15 billion. Consequently, even a modest efficiency increase by applying new, more sustainable chemical processes would deliver substantial economic savings and environmental wins. A2P will seek and deliver systematic gains across all sectors of the chemicals manufacturing industry. Our goals of providing cross-scale training in chemical sciences with economic and life- cycle awareness will drive uptake of sustainable best practice in UK industry, leading to improved economic competitiveness.

This CDT will deliver significant new knowledge in the development of more sustainable processes and products. It will integrate the philosophy of sustainability with catalysis, synthetic methodology, process engineering, and scale-up. Critical concepts such as energy/resource efficiency, life cycle analysis, recycling, and sustainability metrics will become seamlessly joined to what is considered a 'normal' approach to new molecular products. This knowledge and experience will be shared through publications, conferences and other engagement activities. A2P partners will provide efficient routes to market ensuring the efficient translation and transferal of new technologies is realised, ensuring impact is achieved.

The chemistry-using industries manufacture a rich portfolio of products that are critical in maintaining a high quality of life in the UK. A2P will provide highly trained people and new knowledge to develop smarter, better products, whilst increasing the efficiency and sustainability of chemicals manufacture.
To amplify the impacts of our CDT, effective public engagement and technology transfer will become crucially important. As a general comment, 'sustainability' styled research is often regarded in a positive light by society, however, the science that underpins its effective implementation is often poorly appreciated. The University of Nottingham has developed an effective communication portfolio (with dedicated outreach staff) to tackle this issue. In addition to more traditional routes of scientific communication and dissemination, A2P will develop a portfolio of engagement and outreach activities including blogs, webpages, public outreach events, and contribution of material to our award-winning YouTube channel,

A2P will build on our successful Sustainable Chemicals and Processes Industry Forum (SCIF), which will provide entry to networks with a wide range of chemical science end-users (spanning multinationals through to speciality SMEs), policy makers and regulators. We will share new scientific developments and best practice with leaders in these areas, to help realise the full impact of our CDT. Annual showcase events will provide a forum where knowledge may be disseminated to partners, we will broaden these events to include participants from thematically linked CDTs from across the UK, we will build on our track record of delivering hi-impact inter-CDT events with complementary centres hosted by the Universities of Bath and Bristol.


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