Abstract
Synthetic approaches to protein functionalisation and sensing, in particular the S-arylation of cysteine residues mediated by organometallic complexes of palladium and gold, have been investigated.Firstly, the arylation of canonical amino acids using transition metals in biologically compatible conditions is reviewed. Despite transition metal catalysis being the obvious choice for the arylation of small molecules in modern organic chemistry, its application in bioconjugation chemistry is limited. This has led to the rapidly growing number of organometallic strategies for the arylation of canonical amino acids in biomolecules.
The synthesis and application of Pd(II) complexes prepared via C-H activation towards cysteine S-arylation is then described. It was found that synthesis of organometallic Pd(II) complexes via a C-H activation approach offers usability advantages compared to the oxidative addition approach currently prevalent in the literature. Isolated C-H activation complexes showed excellent bioconjugation efficiency and cysteine selectivity, and their generation in situ enabled cysteine functionalisation with aryl groups adorned with a wide range of functionalities with a rapid and user-friendly protocol. Further application of C-H activation complexes revealed their high selectivity towards exposed cysteine when arylating intact proteins.
Further investigation applied Pd(II) C-H activation complexes of amino acids bearing aromatic side chains towards the formation of cysteine-amino acid side chain-side chain linkages. Synthesis of Pd(II)-amino acid complexes from ammonium salts was found to be affected by the nature of the anion, and their subsequent ability to S-arylate cysteine was dependant on the phosphine ligand. The methodology was scaled up, allowing full characterisation of a bioconjugate, and exposed cysteine on an intact protein was functionalised. Initial investigations revealed potential applications of the chemistry towards the formation of macrocyclic peptides.
Finally, the S-arylation kinetics of organometallic Au(III) complexes in biologically relevant conditions were studied. Using a combination of competition experiments and stopped-flow kinetics experiments, the effect of the environment around Au(III) on the bioconjugation kinetics was probed. It was found that ligand and substrate both significantly affect the kinetics and revealed information about the mechanism of the process. Insights gained were then used to synthesise a bimetallic Au(III) reagent which enabled the synthesis of cross-coupled biomolecules.
| Date of Award | 24 May 2023 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Christopher Frost (Supervisor), A T Lubben (Supervisor) & James Taylor (Supervisor) |