Development of tunable electrochemical methods for late-stage peptide modifications

Abstract

Residue-specific peptide modification strategies, especially those which can provide high regio- and chemoselectivity, are imperative for advancing the therapeutic capacity of peptides. Over the past few years, electro-organic chemistry has become a trending synthetic platform by offering programmable and precise modifications through environmentally-friendly and sustainable protocols. In this thesis, the applicability of an anodic oxidation reaction is demonstrated in the context of peptide modifications targeting underutilized amidic side-chains, affording access to high-value functionalized peptide products. In addition, the first electrochemical peptide macrocyclization, and tunability-based iterative and orthogonal modifications of peptides are accomplished. Chapter One aims to provide a general background on the existing approaches for residue-specific late-stage peptide modifications, approaches available for amidic side-chain modifications and advances in modern preparative electro-organic chemistry. This chapter also focuses on the electrochemical concept employed for tunable modification strategies. Chapter Two showcases the synthesis of model electro-active substrates (N,S-acetals of propionamide), cyclic voltammetry studies and optimization of electrochemical modifications. The suitable model N,S-acetals for developing a tunable electrochemical method were selected based on the oxidation peak potentials obtained from cyclic voltammograms and were optimized by screening diverse reaction conditions. Moreover, glutamine building blocks bearing designer electro-active N,S-acetals were successfully synthesized for incorporation into peptides. Chapter Three details the solid phase synthesis of electro-active peptides bearing electro-active N,S-acetals and develops an electrochemical protocol for the generation of several peptides with invaluable N,O-acetal functional handles. The extension to intramolecular nucleophiles establishes proof-of-principle for an electrochemical peptide stapling protocol, and the functionalization of a bioactive substrate displayed the applicability of the method on larger, more intricate peptide systems. Finally, a strategy for tunable and sequential electrochemical modifications was developed. Chapter Four introduces second-generation N,S-acetal building blocks which improve the efficacy of the developed tunable electrochemical method. It outlines the limitations of first-generation building blocks and examines the broader electrochemical reactivity of diverse peptides bearing second-generation building blocks. Chapter Five summarizes the electrochemical methodologies implemented for modifications of amidic side chains within complex peptide settings. Future studies, including the incorporation of electro-active building blocks into proteins and the execution of tunable modifications, are discussed. Show more