Chemical Synthesis of Peptides & Proteins with Post-Translational Modifications

This thesis describes efforts aimed at the synthesis of peptides and proteins bearing homogeneous carbohydrate and sulfate modifications for interrogation of the structural and functional roles of these post-translational modifications. This thesis is divided into two parts. The first section (Chapter Two and Chapter Three) describes efforts toward the synthesis of glycopeptides. Chapter Two describes the synthesis of rare S-linked glycopeptide sublancin-168 and its glycosylated variants, along with structural studies to understand the effect of S-glycosylation. Chapter Three outlines the isolation of N-linked oligosaccharides from a natural source in large quantity, and the study towards the utility of these isolated N-linked glycans to the synthesis of N-linked glycopeptides using a solid-phase aspartylation approach. The second section (Chapter Five and Chapter Six) of this thesis is devoted to the total synthesis of hirudin P6 peptide fragments and proteins bearing homogeneous carbohydrate and sulfate modifications. Inhibitory assays of these peptides and proteins against thrombin confirmed the importance of tyrosine sulfation for fibrinogenolytic activity via binding to exosite I of the protein. Introduction of both sulfation and/or O-glycosylation was shown to have a detrimental effect on binding and inhibition of the amidolytic activity of thrombin.