Design and synthesis of conformational switches and β-turn mimics through chemical ligation

Crecente García, Selma (2021) Design and synthesis of conformational switches and β-turn mimics through chemical ligation. PhD thesis, University of Glasgow.

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The control of peptide conformation is crucial to facilitate further understanding of peptide and protein folding and activity. This thesis focuses on the control and mimicry of peptide secondary structure through two strategies: the design of conformational switching systems and the mimicry of β-turns through chemical ligation.

Chapter 1 describes the forces that determine protein structure and the conformations adopted by these biological systems. Strategies towards the design of β-hairpins, including β-turn mimics and their applications are described, followed by a survey of the current state of the literature regarding bioconjugation and ligation strategies.

Chapter 2 focuses on the design of tertiary amide-based conformational switches actuated through disulfide formation. The sequence Ac-GWPQG-NH2 was studied through a double mutant cycle, making use of nuclear magnetic resonance (NMR) to evaluate the cis Pro content of the sequences and the cooperativity between the Trp and Gln residues. This information was then used to design two generations of disulfide-actuated switches, the conformations of which were studied through NMR.

Chapter 3 explores the design of novel β-turn mimics installed through chemical ligation. Hydrazide formation was employed in the design of three mimics, which are synthesised through a reductive amination step that allows the use of two unprotected peptide partners and mild conditions. The mimics were implemented in tripeptides and within the Tryptophan Zipper β-hairpin. NMR and circular dichroism (CD) analysis showed that the tripeptide systems adopted a turn-like conformation in solution, and that the full-sized conjugates successfully mimicked the β-turn and β-hairpin conformation in the control system.

Chapter 4 details the design, synthesis and evaluation of a cyclic peptide inhibitor of the MDM2/p53 protein-protein interaction, which contains one of the β-turn mimics designed in Chapter 3 and is synthesised by means of a ligation step that cyclises the peptide. The activity of the peptide was evaluated through surface plasmon resonance (SPR) assays, which showed an improvement in comparison to the control system, which contains a (D-Pro)-(L-Pro) β-turn.

Chapter 5 explores oxime ligation as a strategy to install β-turn mimics within β-hairpin backbones. One of the targets explored contained a β-turn mimic based on a meta-substituted aromatic ring, which afforded one stereoisomer that adopted a largely unfolded conformation, while the other showed successful mimicry of the turn and hairpin structure through CD analysis. An aliphatic oxime linkage was also explored, and although it provided less preorganisation it gave rise to two stereoisomers that successfully mimicked the conformation of the control system. The reduction of the oxime to generate an N-alkoxy amine junction was also studied through CD, which showed a higher degree of folding and stability in comparison to its oxime precursor.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QD Chemistry
Colleges/Schools: College of Science and Engineering > School of Chemistry
Supervisor's Name: Thomson, Dr. Drew
Date of Award: 2021
Depositing User: Theses Team
Unique ID: glathesis:2021-82515
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Oct 2021 10:24
Last Modified: 26 Oct 2021 14:37
Thesis DOI: 10.5525/gla.thesis.82515
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