Haynes, Stuart W. (2010) Mutasynthesis approaches to the preparation of streptorubin B analogues. PhD thesis, University of Warwick.

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Abstract

Prodiginines are a large family of red-pigmented tripyrrole-based antibiotics.
Their biosynthesis in Streptomyces coelicolor A3(2), by enzymes encoded in the
red gene cluster, involves the condensation of 4-methoxy-2,2′-bipyrrole-5-
carboxaldehyde (MBC) and 2-undecylpyrrole, catalysed by the RedH enzyme to
give undecylprodiginine. This is followed by the mechanistically interesting
oxidative carbocyclisation, catalysed by RedG to give streptorubin B.
In this thesis prodiginine analogues have been generated by a mutasynthetic
approach, in which chemically synthesised analogues of intermediates MBC and
2-undecylpyrrole were fed to mutant strains of S. coelicolor in which one of the
genes required to biosynthesise MBC or 2-undecylpyrrole (redM or redL
respectively) have been deleted. RedH and RedG have been shown to display
relatively broad substrate tolerances and several analogues of both
undecylprodiginine and streptorubin B have been generated by this approach. A
variety of factors which are potentially limiting to substrate tolerances have been
probed, including the steric size, alkyl chain hydrophobicity and introduction of
π-electrons.
The absolute stereochemistry of streptorubin B has been investigated by a
mutasynthetic approach in which 2-undecylpyrrole, stereospecifically labelled
with deuterium, is fed to a mutant strain of S. coelicolor unable to biosynthesise
2-undecylpyrrole. During the course of the investigation streptorubin B was
analysed on a homochiral stationary phase HPLC and evidence of both ent- and
dia-streptorubin B was discovered in the natural product isolated from S.
coelicolor. When the position of the deuterium label from the mutasynthesis
experiment was investigated by 1H-NMR and 2H-NMR the partial epimerization
of the synthetic material became apparent. This made the definitive
determination of the absolute stereochemistry of streptorubin B impossible.
However, a tentative assignment of the absolute stereochemistry was possible.
This was supported by comparison with the related natural products
metacycloprodigiosin, the stereochemistry of which was established here by CD
spectroscopy and chiral HPLC analyses, and roseophilin.

Item Type:	Thesis (PhD)
Subjects:	Q Science > QD Chemistry
Library of Congress Subject Headings (LCSH):	Antibiotics, Streptomyces coelicolor, Biosynthesis, Stereochemistry
Official Date:	March 2010
Dates:	Date Event March 2010 Submitted
Institution:	University of Warwick
Theses Department:	Department of Chemistry
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Challis, Gregory L.
Extent:	xxix, 243 leaves : ill., charts
Language:	eng

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