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Title: Design and synthesis of farnesyl diphosphate analogues for modulating the chemistry of aristolochene synthase
Author: Yu, Fanglei
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2007
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Abstract:
A variety of farnesyl pyrophosphate (FPP) analogues were prepared by both published protocols and novel methodology, which was developed by modification and improvement of the traditional Suzuki-Miyaura coupling. These compounds were incubated with aristolochene synthase in order to probe its mechanism of action and resulted in many interesting results. The synthesis 12,13-difluoro farnesyl pyrophosphate was achieved in 13 steps using Suzuki-Miyaura chemistry. It proved to be a potent inhibitor of aristolochene synthase (AS), which revealed that the initial cyclisation to germacryl cation occurs in a concerted fashion. Analogue 2-fluoro FPP was synthesized and upon incubation with aristolochene synthase was converted to a single pentane extractable product according to GC/MS analysis. On the basis of NMR-analyses and GC-MS experiments this product was identified as 2-fluorogermacrene A. This work suggests that after an initial concerted cyclisation of FPP to germacryl cation, deprotonation leads to the formation of germacrene A and provides compelling evidence that germacrene A is indeed an on-pathway product of catalysis by aristolochene synthase. Analogue 6-fluoro FPP was prepared using the Weiler's chain extension method in 10 steps, and has been postulated to be give 6-fluoro germacrene A as product, which is consistent with published results on Epi-aristolochene synthase. 10-Fluoro FPP was made with sulfonylation-alkylation-desulfonylation methodology and it was found not to act as substrates of the AS. This result is fully consistent with the conclusions drawn from the results with 12,13-difluoro FPP. FPP analogues with one fluoro substituent at position C14 and CI5 were made using methodology employing the Horner-Emmons Wittig condensation as a key step. These two compounds were tested with AS and both gave one major extractable terpene product according to GC/MS analysis. These two products are postulated as two different compounds—14-fluoro aristolochene and 15-fluoro germacrene A respectively, because of the destabilizing effect of the p-substituted fluorine atom on the carbocation in their vicinity. Analogues of farnesyl pyrophosphate containing phenyl substituents in place of methyl groups have been prepared in syntheses that feature use of Suzuki-Miyaura reactions as key steps. These analogues were found not to act as substrates of the aristolochene synthase. However, they were potent competitive inhibitors of AS, which indicate that the active sites of terpene synthases are sufficiently flexible to accommodate even substrate analogues with large substituents suggesting a potential way for the generation of non-natural terpenoids.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.584108  DOI: Not available
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