Mimics of the copper active site of LPMO’s using rotaxanes

Details

Supervisors

Singleton, Michael L.

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité approfondie

Abstract

enLytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes found in fungi, bacteria, and plants, known for disrupting polysaccharide crystallinity. Initially identified for chitin degradation, they were later shown to act on other substrates, including cellulose, making them valuable in sustainable applications such as bioethanol production. LPMOs cleave glycosidic bonds by oxidizing strong C-H bonds (~100 kcal/mol), a reactivity attributed to their unique T-shaped N3 copper coordination, known as the histidine brace. Due to the complexity of working with enzymes, synthetic models have been developed to study their mechanism, properties and reactivity. Among them, Itoh’s group reported the best performing model to date, attributing its success to a large torsional angle between imidazole ligands. This master’s thesis aimed to design and synthesize a copper-complexed rotaxane that mimics the histidine brace while offering greater conformational flexibility than previous models based on rigid linkers. The target architecture involved three components: pyridine-based macrocycles (successfully synthesized), imidazole-based macrocycles (not obtained due to solubility issues despite a promising new synthetic approach), and a rod bearing imidazole and amine functions. A pseudorotaxane was successfully formed with the larger pyridine-based macrocycle, offering insights into the role of cavity size in rotaxane formation. Although the pseudorotaxane could not be isolated due to dynamic equilibrium in solution, copper complexation was attempted via a one-pot assembly strategy. A copper complex was obtained, but the desired compound was not isolated and the N4 geometry does not fully replicate the histidine brace environment. UV-Vis studies showed the formation of new species in solution, while catalytic assays using the PNPG model substrate revealed enhanced reactivity in the presence of copper complex, though solubility limited direct comparisons. Future work should focus on developing imidazole-based macrocycles and employing capping or template-directed strategies to isolate stable, copper-complexed, rotaxanes. These systems hold promise for more accurately mimicking the structure and reactivity of enzymatic copper sites.