Late-Stage Functionalisation of Peptides via Photocatalytic Modification of Tryptophan

可以对多肽进行修饰，使其显示出比其原始类似物更有利的特性，从而使它们在制药工业中被用于许多应用，包括生产新药、辅助药物输送以及提供洞察生物系统的技术。然而，由于天然生物分子的复杂性，为了使多肽或蛋白质功能化，通常需要对单一氨基酸进行修饰，这是很困难的。经常使用的是半胱氨酸(Cys)的修饰，因为它的丰度很低(整个蛋白质组的相对丰度为~2%)，但Cys残基往往是蛋白质折叠的关键，和/或参与酶的活性部位，因此功能化可能会阻碍蛋白质的活性。一种新的策略是针对低丰度和蛋白质中不太重要的残基，例如相对丰度为1.4%的Trp，需求很高。光氧化还原化学领域的最新进展揭示了在温和和更可持续的条件下氨基酸选择性官能化的新方法；然而，这种化学在生物分子中的应用仍然相对不发达。与这种化学相关的条件通常遵守多个绿色原则；例如，催化、使用节能的单波长LED和更安全的溶剂。然而，尽管在这一领域取得了进展，但由于过度使用添加剂和/或某些成分造成浪费，一些程序存在缺陷。此外，这些方法往往使用贵金属催化剂，这在较长时间内是不可持续的。开发一种温和的光化学方法来实现色氨酸的功能化将具有广泛的价值，并可能在一系列领域中得到应用。建议的解决方案和方法本项目将开发一种温和而有效的光催化策略来选择性地修饰多肽和蛋白质中的色氨酸，扩大目前实现这种转化的有限方法的数量。一个关键目标是确保化学与绿色原则保持一致，以进一步增强研究的影响。最终，这些产品(小分子-多肽结合物)将在药物输送和活体成像中得到应用。该项目将建立在现有的利用可见光修饰吲哚部分的方法的基础上，最初的目标是确定能够使小分子与色氨酸结合的可持续和生物相容的条件。尽管存在干扰/竞争氨基酸，但该反应必须对多肽中的色氨酸具有选择性。该反应将应用于各种更复杂的含Trp的多肽(大于或等于5个氨基酸)，以了解其化学选择性。为了扩大我们制造的偶联物的数量，并使产品能够进一步应用，小分子也将被改变，以创建每个具有不同性质的修饰多肽的库。从廉价、容易获得的原料可以合成一系列小分子。通过更可持续的光催化路线合成的小分子-多肽结合物可以作为生物工具，这将被探索。根据所附着的小分子的不同，预计会有广泛的应用。例如，对产品进行生物测试，以确定修饰是否影响了多肽的活性。或者，这种化学可以用于蛋白质谱分析，以探测细胞中所有反应性色氨酸残基。

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 methodologyThis 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.