Studies on the Biosynthesis of Spirotetronate Polyketides

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Spirotetronate polyketides possess complex polycyclic structures and display a wealth of promising biological properties. Spirotetronate biosynthesis incorporates many intriguing biotransformations and the investigation of these enzymatic processes is the focus of this thesis.
Chapter 2 focusses on the spirotetronate antibiotic abyssomicin C and details three discrete projects. Chapter 2.2 describes the functional characterisation of the cytochrome P450 enzyme AbyV from the aby biosynthetic gene cluster. Through the synthesis of the proposed substrate, and in vitro assays with AbyV, the enzyme was shown to catalyse a key late-stage epoxidation of the spirotetronate scaffold 31. Our studies included the development of a 13Clabelling strategy, which allowed the enzymatic transformation to be monitored directly by 13C NMR. Chapter 2.3 describes studies on the putative tetronate synthase AbyA1. Two pantetheine thioester analogues (111 and 98) of the enzyme’s putative ACP-bound substrates were synthesised. Technical challenges were encountered with our proposed assay system which led us to investigate alternative ACP candidates. Chapter 2.4 describes the isolation of abyssomicin C and atrop-abyssomicin C from mutant strains of the natural producer Micromonospora maris. The natural products were isolated from two strains of M. maris, however, in both cases they were obtained as a mixture of atropisomers and in low titres (1.2-2.6 mg/L).
Chapter 3 focusses on the [4+2]-cyclisation cascade that forms the pentacyclic core of the class II spirotetronates. The synthesis of the linear precursor 187 was completed in 6% yield over 12 steps.187 was used in in vitro assays to probe the function of the chlorothricin [4+2]-cyclases, ChlE3 and ChlL. Studies toward the synthesis of the partially-cyclised decalin intermediate 188 are also described.
Date of Award20 Jun 2023
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorPaul Race (Supervisor) & Chris L Willis (Supervisor)

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