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Pryyma, Alla

University of British Columbia

This thesis describes my contribution to the development of synthetic methods directed at accessing bicyclic toxic peptides, amatoxins, as well as amatoxin-based bioconjugates for targeted treatment of cancer. Alpha-amanitin, the principal toxin of the amatoxin family and a potent transcription inhibitor, is of significant interest for applications in cancer therapy in a form of conjugates targeting cancer-specific receptors. Despite being known for over 70 years, the complex structure of α-amanitin has challenged the development of synthetic methods. In Chapter 2, C-3a-halopyrroloindolines are successfully employed as precursors to a tryptathionine crosslink, a key structural feature shared by amatoxins. Notably, fluoropyrroloindoline (FPI) was utilized to access previously inaccessible, oxidation-sensitive 6'-hydroxy-tryptahtionine found in α amanitin. Furthermore, the distinct reactivity of FPIs under H-bonding conditions was explored whereby hexafluoroisopropanol was used to ionize the C-F bond for nucleophilic attack yielding C-2-thiol-substituted tryptophans and C-3a-functionalized pyrroloindolines. Chapter 3 describes the synthesis and evaluation of (RSO)-5'-hydroxy-6'-deoxy-amanitin, a novel, bioactive analog of α-amanitin for use as a payload in targeted therapies. This synthesis employs naturally abundant 5-OH-tryptophan to incorporate an indole conjugation handle in three steps, in contrast to the synthetically challenging 6-OH-tryptophan. In vitro cell viability and RNA polymerase II transcription inhibition assays complete the biological evaluation of (RSO)-5'-hydroxy-6'-deoxy-amanitin and sulfur-modified analogs thereof. Chapter 4 describes two diastereoselective sulfoxidation methods providing access to amatoxins with the biologically active (R)-sulfoxide, thereby solving the last-standing challenge in the synthesis of amatoxins. The late-stage sulfoxidation approach utilizes Ti(IV)/L-DET-based system and is applied to the bicyclic precursor as the last step of the synthesis yielding the (R)-sulfoxide in large excess ((R:S) 19:1). Additionally, facile and cost-effective early-stage sulfoxidation employing meta-chloroperoxybenzoic acid in dimethylformamide is described. In Chapters 5 and 6, two synthetic amanitin analogs, conjugated at different sites, are used to assemble peptide drug conjugates targeted to cancer-specific receptors. The development of a modular synthetic platform for the construction of cleavable and non-cleavable amanitin-peptide conjugates that can be adapted to various targeting moieties is reported. In vitro cell proliferation studies on antigen-positive cell line revealed target-specific toxicity of conjugates with up to 1000-fold bioactivity enhancement.

Text

2022-02-16

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/80841

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/