Synthesis and Biological Evaluation of a Potential Anticancer Agent and the Development of New Methods

UoM administered thesis: Phd

  • Authors:
  • Ilma Amalina

Abstract

Bub1 is a serine/threonine kinase proposed to play a role in the Spindle Assembly Checkpoint (SAC) and chromosome alignment. However, its role remains controversial. Bub1 kinase is suggested to have two substrates, histone 2A (H2A) and Cdc20, and inhibits the anaphase process before all kinetochores bind to microtubules in the mitosis cycle. Bub1 kinase was also discovered to be a major kinase that provides a scaffold protein to recruit other SAC proteins and could be used as a target to cure cancer. Two Bub1 kinase inhibitors based on the pyrazole core, cyclopropylbenzylpyrazole (BAY-320) and methoxybenzylpyrazole (BAY-524), have been synthesised by Hitchcock et al. The cyclopropylbenzylpyrazole showed selective binding to Bub1 kinase in assays, therefore the synthesis of the Bub1 kinase inhibitor could be used as a tool to address the role of Bub1 kinase. Synthesis of cyclopropylbenzylpyrazole in eight steps was achieved using the route and modified procedures of Hitchcock et al. The approach involves several steps: 1) a Weinreb amide to form a ketone; 2) 1,3-dicarbonyl formation and condensation to generate a pyrazole; 3) amidine formation; 4) pyrimidine ring formation; and 5) palladium-catalyzed Buchwald-Hartwig amination. The biological assay activity showed that Bub1 kinase activity is not essential for SAC function, but it did suggest that Bub1 plays a role in the scaffolding of SAC proteins. Comparison with another Bub1 kinase inhibitor, 2OH-BNPP1, showed that cyclopropylbenzylpyrazole (BAY-320) could inhibit Bub1 kinase activity in vitro and in vivo by inhibition of H2A phosphorylation, Sgo1 delocalisation and colony growth, whereas the 2OH-BNPP1 could only inhibit in vitro. Anticancer agent, BGC945, inhibits Thymidilate Synthase (TS). We proposed to synthesise the cyclopenta[g]quinazalone core of BGC945 using a new strategy based around a SmI2-mediated step. It was proposed that BCG945's core could be generated from a cyclopropyl benzoate substrate using a cascade reaction mediated by SmI2. However, after the formation of key starting materials, a cyclopropane, an a,b-unsaturated ketone and an alkyl halide, and many synthesis attempts, we could not generate the core of target compound. Building on our studies with SmI2, we discovered an unprecedented SmI2-mediated 1,4-ester shift that proceeds via the 5-exo trig cyclisation of a ketyl radical formed from an ester by SmI2. A five step synthesis was carried out to generate lactone substrates. The route started from dimethyl malonate and involved a Michael addition, cross metathesis, and SmI2-H2O-mediated ketone reaction. The novel 1,4-ester shift was mediated by SmI2-HMPA-H2O. The scope has been explored and the 1,4-ester shift was seen to proceed in moderate to good yield and with complete diastereocontrol. The substituent at the 5-position of the lactone ring is thought to play a key role in controlling the conformation of the lactone and favouring the 1,4-ester shift.

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Original languageEnglish
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Award date31 Dec 2020