Development of a fluorine-thiol reaction platform for post-translational modification analysis and stapled peptide synthesis

Abstract

Post-translational modifications (PTMs) allot versatility to the biological functions of highly conserved proteins. Recently, modifications to non-histone proteins such as methylation, acetylation, phosphorylation, glycosylation, ubiquitination, and many more have been linked to the regulation of pivotal pathways related to cellular response and stability. Due to the broad spectrum of pathways PTMs are associated with, their dysregulation is often linked to oncogenesis and various autoimmune diseases. Proteins involved in the incorporation (writers), removal (erasers) and recognition (readers) of PTMs, and substrate proteins, are regarded as important biomarkers and potential therapeutic targets as a result of their role in detrimental pathways. Current methodologies to monitor PTM substrates rely on alkyne/azide-based chemical proteomics, which are inefficient due to their bulky nature. This steric hindrance has been shown to limit the metabolic incorporation of alkyne/azide tags via PTM writers on to substrate proteins and has limited the use of these chemical reporters to enzymes containing large active sites. One portion of this dissertation will focus on the development of a steric-free biorthogonal chemical tagging platform utilizing a fluorine-thiol displacement reaction. Fluorinated PTM cofactors/precursors are steric free and could be easily recognized and metabolized by PTM enzymes. Reaction development identified thiophenols as a suitable partner for the displacement reaction to convert fluorine to other useful functionalities, allowing for the labeling and enrichment of multiple acetylation substrates in cell lysates. Another goal of this dissertation was the synthesis of novel stapled peptide therapeutics with this FTDR platform. A library of unprotected peptides were cyclized with this methodology, and were found to promote sufficient levels of alpha helical stability. Biological evaluation of FTDR-based stapled peptides showed that this methodology produced compounds with enhanced stabilities, which were a significant upgrade to ring-closing metathesis-based peptides in regard to solubility and cell permeability. The final goal of this dissertation focuses on the synthesis of a novel PET imaging probe. Immuno-PET imaging is a rising field in cancer prognosis and therapy, yet current probes utilize full-length IgGs and random conjugation methods, that lead to conjugates with random stabilities and activities. In conjunction with biologist in our lab, a 64Cu chelating NOTA linker, tethered to a BCN moiety was site-specifically conjugated to Fab fragments. The smaller unnatural amino acid containing Fab fragments, specifically mutated with p-azidophenylalanine (pAzF), boasted improved pharmacokinetic profiles and allowed for site-specific conjugation via strain-promoted cycloaddition.