Synthesis and biological activity of peptidic macrocycles, trithiazoles and Hsp27 fragments

This thesis describes the synthesis and biological evaluation of Sanguinamide B-14 (SanB-14) analogues, trithiazole analogues, and peptides based on the structure of heat shock protein 27 (Hsp27), as potential anti-cancer agents. SanB-14, described in Chapter 2, is a natural product-derived macrocycle with low micromolar cytotoxicity against the human colon cancer cell line HCT-116. Structure activity relationship (SAR) studies were undertaken on SanB-14, to determine if compound activity is affected by the positioning and stereochemistry of the amino acids around the macrocyclic backbone as well as the configuration of proline residues. The SAR study showed the incorporation of a carboxylbenzyl lysine group, and the stereochemistry of phenylalanine residues was essential to compound cytotoxicity. The configuration of proline residues, however, did not impact activity. Trithiazoles are an important scaffold in anti-cancer macrocycles including Urukthapelstatin A and Marthiapeptide A. Chapter 3 describes the synthesis of trithiazole analogues with different terminal groups, and side chain functionality varying in size and stereochemistry. Three trithiazole esters 85d, 85e and 85h exhibited cytotoxic activity at low micromolar concentrations against HCT-116 and were as effective as the cytotoxic compound RITA in inducing cellular apoptosis. Mechanistic studies showed that while RITA increased the expression of the pro-apoptotic protein p53 while reducing expression of oncogenic proteins Mcl-1 and c-Myc, 85h reduced the expression level of Mcl-1 independently of p53. Hsp27 is a protein that is upregulated in tumours and also plays a role in certain neurodegenerative diseases. Dimerization is important for Hsp27 to effectively function and the cysteine residue C137 may facilitate this. To better understand the mechanism of Hsp27 dimerization through mass spectrometry and fluorescence polarization (FP) assays, Chapter 4 describes the synthesis of six peptides as probes, based on the structure of the Hsp27 amino acid sequence and containing the C137 residue. To evaluate peptide-protein binding through FP, three peptides were tagged with the fluorophore fluorescein isothiocyanate (FITC). The synthesised probes will provide insights into the amino acids involved in Hsp27 dimerization and confirm the role of C137