Total Synthesis of Bioactive Peptides and Whole Proteins

Abstract

Total chemical synthesis is an essential tool for the validation of natural product structures and the discovery and elaboration of novel therapeutic scaffolds. Chapter 1 (Part I) surveys existing treatments for trypanosomatid neglected tropical diseases, and the synthesis of a novel class of antiparasitic cyclic depsipeptides is reported (Chapter 2) alongside a full NMR assignment and structure calculation using NMR-derived distance restraints. The synthetic peptides exhibit activity profiles in agreement with published results, and a series of ester-to-amide substitution analogues also synthesized show similar low micromolar potency. Chapter 3 describes the synthesis of lassomycin, a tuberculocidal lasso peptide reported to exhibit a unique unthreaded topology. The naturally occurring peptide was synthesized alongside C-terminally amidated and truncated analogues, but none were biologically active. Given clear differences observed in the two-dimensional NMR data for synthetic lassomycin, it is suggested that the reported natural product in fact exists in the threaded form. The chemical synthesis of whole proteins is addressed in Part II, and current progress in the field is reviewed (Chapter 4). Work towards the total chemical synthesis of acyl carrier protein using a two fragment approach is described in Chapter 5. The N-terminal fragment was synthesized using the sulfonamide linker, and while the C-terminal fragment presented difficulties due to extremely low solubility, solubilization using backbone protection was demonstrated. The development of a modified Dawson linker for the synthesis of peptide N-acylureas without overacylation is also described. Finally, Part III details the synthesis of tumor targeting peptides used for imaging and inhibition of cancer cell growth, and which cause tumor size reduction in vivo. A novel web utility used for the automated assignment of peptide mass spectra throughout this thesis is also presented.