Methodology development and synthesis of a biologically relevant natural product and targeted scaffold discovery for serine hydrolase inhibition

Thesis

The phenomenal potential of synthetic chemistry to influence small molecule therapeutic development represents my overarching theme. The goal of designing or discovering a novel clinical candidate or biological target can be achieved through a variety of avenues available to synthetic organic chemists. The potential of natural product total synthesis and inhibitor development as impactful projects were pursued with the use and development of methodology.

The natural product streptonigrin, a potent antitumor antibiotic, showed promise in clinical trials ultimately terminated in the 1970s. The underexplored mechanism of action prompted a reexamination of this potential therapeutic. The Donohoe group successfully designed a modular total synthesis accessing streptonigrin in 11 steps and 14% yield. The introduction of an asymmetric Suzuki– Miyaura reaction yielded a key intermediate in 42% ee and 65% yield, which represents the first example of purely synthetic access to enantioenriched late-stage streptonigrin analogues.

The "hydrogen-borrowing" method allows the functionalization of ketones with methanol and transition metal catalysts, but examples lacked application to further α-functionalization. The successful development of a novel "interrupted- hydrogen-borrowing" method allowed the use of iridium and methanol to trap the reactive enone intermediates by preventing the subsequent "hydrogen returning". Thus, this enabled these reactive intermediates to be subjected to a 1,4-conjugate addition with a nucleophilic ketone enolate and subsequent cyclization and oxidation to form highly substituted pyridines from simple ketones.

The exploration of serine hydrolases, an important mammalian enzyme class with a large portion still uncharacterized, requires inhibitors with new chemotypes that can covalently and irreversibly bind. The small library of urea- and carbamate- containing scaffolds with varied aromatic backbone substitutions was subjected to activity-based protein profiling to allow expedient examination of the whole serine hydrolase family. The predicted strong electronic effect of the p-substituent was confirmed, modulating the reactivity of the electrophilic urea or carbamate moiety. MudPIT analysis of a subset supported the demonstrated reactivity profile and identified the uncharacterized serine hydrolase PNPLA4 as a selective target of one inhibitor. This potent and selective inhibition was verified by in vitro and in cell assays and validates this chemotype as a family of serine hydrolase inhibitors.

Authors: Kornahrens, A

• DOI: 10.5287/ora-zbrgdnxrq
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford