Development and Application of Protected Amino Acids for the Installation of Stable Post-translational Modifications Using Solid-Phase Peptide Synthesis

Abstract

This thesis describes the synthesis of non-canonical amino acid building blocks and their use in solid-phase peptide synthesis (SPPS) to explore peptidic drug analogues based on natural products. We replaced sensitive functionalities found in the structure of naturally produced peptides with carbon bridges to develop semi-synthetic, biologically active peptides. These include neopetrosiamide analogues against cancer metastasis and truncated nisin lipopeptides against bacterial infection. Neopetrosiamide is a 28 amino acid peptide found to have potential anti- metastatic activity against breast-cancer cells. However, it contains three disulfide bridges, which complicate it’s synthesis and may limit its in vivo stability. We developed synthetic routes for seven different orthogonally protected carbon-bridge containing amino acids amenable to solid-phase, one of which is a bioisostere of disulfide bridges. By utilizing this diaminosuberic acid derivative in SPPS, we synthesized three neopetrosiamide analogues, each with a single disulfide bridge replaced with methylenes. These analogues showed similar anti-metastatic activity to native neopetrosiamide. Nisin A is a 34 amino acid peptide effective against methicillin- resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE) at nanomolar concentrations. A synthetic route for six amino acid derivatives was used to replace different modifications present in nisin A via SPPS. The total synthesis of nisin using these derivatives was also investigated. As a more accessible alternative to nisin, we explored the synthesis and biological activity of truncated nisin lipopeptide analogues. The lipopeptides may overcome the propensity of nisin to deteriorate under biologically relevant conditions. Using SPPS- amenable precursors from our work on neopetrosiamide and nisin A, we synthesized four different nisin lipopeptide analogues. Preliminary tests indicate that these analogues are active against Gram-positive bacteria.