Synthesis of Novel Substrates to Probe the Specificities of Mupirocin Enzymes

  • Abigail M C Mountford

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Mupirocin, produced by Pseudomonas fluorescens, displays antibiotic activity against a wide range of Gram positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). It is a mixture of pseudomonic acids A, B and C as described in chapter one. Biosynthetic studies have provided an insight into the assembly of the polyketide backbone and post assembly modifications. However, some features of the biosynthetic pathway remain unknown including the timing and mechanism of 6-hydroxylation and the mechanism of tetrahydropyran (THP) ring formation.

Chapter two describes investigations into the gene responsible for 6-hydroxylation, tentatively assigned as mupA in mupirocin biosynthesis. Thioester 28 was prepared in 11 steps via a key cross metathesis step to install the 10,11-alkene (pseudomonic acid numbering), followed by an aldol reaction to install the stereocentre at C-7. The synthesis of pantetheinic substrate 29 utilised a hydroboration to install the stereocentre at C-8, followed by a Suzuki cross coupling to establish the E alkene. Enzyme assays of these substrates were carried out with MupA, the results of which are discussed herein.

Chapter three describes the synthesis of linear substrates 161 and 187, and studies towards the preparation of amine 196, to probe the specificities of MupW and MupZ, the enzymes responsible for the formation of the THP ring. The synthetic route to thioester 29 was adapted to introduce the fatty acid side chain of substrates 161 and 187 via a Mukaiyama aldol reaction. Bioassays of substrates 161 and 187 were carried out to provide insight into both the mechanism of the ring closure and the specificities of MupW and MupZ.
Date of Award12 May 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorChris L Willis (Supervisor) & Laura M Chavda (Supervisor)

Keywords

  • Natural Products
  • Organic chemistry
  • Biosynthesis

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