Peptides are useful modulators of protein-protein interactions (PPIs) and cellular membranes, both of which are traditionally challenging to target using small molecules. Often therapeutic peptides suffer from issues including poor proteolytic stability. Two-component peptide stapling can improve stability and enable facile peptide functionalisation. This thesis describes the development of functionalised stapled peptides for two biological applications.

1. The development of stapled peptides as chemical tools to investigate PPIs in human platelets Platelets are a vital, anuclear component of blood. The Bcl-2 family of proteins are known to be key mediators of apoptosis in nucleated cells, however the role of each Bcl-2 protein in platelet apoptosis and activation is unknown. Recently, stapled peptides were deemed useful chemical tools for studying PPIs in platelets. In this section, three polyarginine-functionalised stapled peptides were developed as Bcl-2 PPI inhibitors. These novel chemical tools are anticipated to provide valuable insight into the roles of Bcl-2 PPIs in platelet modulation, which could ultimately lead to new therapeutic targets.
2. The development of cleavable stapled peptide-drug conjugates to target Pseudomonas aeruginosa Antimicrobial resistance (AMR) is a major healthcare threat, and Gram-negative bacteria such as Pseudomonas aeruginosa pose a significant therapeutic challenge. Antimicrobial peptides disrupt bacterial membranes, however functionalised two-component stapled antimicrobial peptides (STAMPs) are underexplored. This section describes the development of a STAMP-drug conjugate, constructed by functionalisation of the STAMP staple with a small molecule antibiotic, attached via a β-lactamase-cleavable motif. The resulting conjugate combines two mechanisms of action, which is a validated strategy for overcoming AMR. To this end, two novel, unfunctionalised STAMPs were identified that exhibited good minimum inhibitory concentrations against P. aeruginosa (64 μg/mL) and selectivity over a Gram-positive strain, from a panel of seven novel STAMPs. Subsequently, a tractable synthesis of the proposed functionalised STAMP was investigated. It is hypothesised that the cleavable STAMP-drug conjugate will enable infection-controlled drug-release and dual-targeting of P. aeruginosa.