Thesis
Assessment of the bioorthogonality of the nitrile imine 1,3-dipole
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2025
- Thesis identifier
- T17213
- Person Identifier (Local)
- 202067175
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The nitrile imine (NI) 1,3-dipole is a highly reactive and readily accessible synthetic tool. Its ability to participate in 1,3-dipolar cycloadditions has enabled its utility in a variety of synthetic applications. Of note, NIs have found application in bioorthogonal chemistry due to their proclivity towards cycloadditions. This species also exhibits broad reactivity with a range of nucleophilic functionalities, such as, carboxylic acids, thiols, and amines, therefore posing possible selectivity issue for NI-mediated photoclick protocols. An exploration into the reactivity profile of the NI species with a library of coupling partners has allowed its range of reactivity to be quantified. This work has been expanded to assess the bioorthogonality of the dipole through the competition of an electronically activated dipolarophile versus a highly reactive fluorinated carboxylic acid. A range of NI species were generated through photolysis of a 2,5-disubstituted tetrazole and their reactivity with a model substrate was quantified. The selectivity observed has demonstrated the potential of low pKa carboxylic acids as bioorthogonal handles for future photoclick reactions. Additionally, a suitable NI precursor has been identified which enhances chemoselectivity for the bioorthogonal handle enabling selective labelling of a biomolecule (Figure 1). [See figure in PDF file]. Figure 1: The assessment of NI bioorthogonality with a low pKa carboxylic acid handle A bespoke amino acid monomer was designed to exemplify the bioorthogonal potential of this system in a biological setting. 2,2-Difluoroglutamic acid was synthesised on a multigram scale from a simple chiral building block in 5 steps. Extensive exploration of orthogonal protection strategies was conducted to enable incorporation of this species into a model peptide system via SPPS. While an appropriate route towards the orthogonal protection of 2,2-difluoroglutamic acid was established, insufficient quantities were obtained for SPPS. During the course of this work, an alternative low pKa carboxylic acid handle was designed which could be accessed in two synthetic steps from a protected lysine residue (Figure 2). [See figure in PDF file]. Figure 2: Orthogonally protected low pKa carboxylic acid handles for NI photoclick chemistry. Incorporation of the α-oxo carboxylic acid handle enabled a proof-of-concept NI photoclick protocol to be developed enabling the assessment of NI chemoselectivity in a model system. Optimisation of this methodology enabled selective labelling of the desired low pKa carboxylic acid handle with the NI of choice in a simple peptide motif (Figure 3). [See figure in PDF file]. Figure 3: Modification of the α-oxo acid handle in a model system Following extensive experience with the promiscuous reactivity of the nitrile imine, work sought to incorporate this species onto the peptide sequence itself to improve the selectivity of the photoclick reaction. A number of small molecule covalent modifiers were developed bearing the low pKa carboxylic acid motif required to enable chemoselective labelling of the NI. Based on this work, efficient and selective labelling of the NI was enabled, demonstrating the potential of this technique as a novel bioorthogonal labelling protocol (Figure 4). [See figure in PDF file]. Figure 4: Modification of a tethered tetrazole with low pKa carboxylic acid warhead.
- Advisor / supervisor
- Jamieson, Craig, 1973-
- Resource Type
- DOI
- Embargo Note
Relations
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File | 2025-03-20 | Embargo |