Over the last two decades, the functionalisation of proteins through bioconjugation reactions (often in a therapeutic setting) has been of great interest in the field of chemical biology and within the pharmaceutical industry. Novel strategies for the modification of cysteine residues are of major relevance to the field of protein bioconjugation due to the pharmacokinetically superior nature of the homogenous products that can be formed through site-selective methodologies. Researchers have strived to enable stable, covalent modification of cysteine residues, which has been the driver behind forming leading biologics (e.g. in the formation of antibody-drug conjugates (ADCs)). In recent years, the cysteine reactive pyridazinedione (PD) scaffold has been developed to facilitate the efficient formation of stable, homogenous and multi-functional bioconjugates. However, whilst the PD scaffold is a highly promising reagent for bioconjugation (especially when modifying antibodies and antibody derived proteins), this is still considered an early technology; the full potential of this scaffold as a next generation bioconjugation reagent has yet to be unlocked. This work aimed to provide greater accessibility and deepen current knowledge surrounding the PD functionalisation technology. This was achieved through the optimisation of synthetic routes to form PDs as well as providing an assessment of the extent of PD modification on native antibody function. Furthermore, novel applications that stemmed from novel fundamental PD-based chemistry were developed to provide a platform for site-selective tri-functionalisation of proteins, as well as dynamic reversible cysteine modification
