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Studies on the synthesis of biologically active, small molecule natural products

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Molesworth, PP (2010) Studies on the synthesis of biologically active, small molecule natural products. PhD thesis, University of Tasmania.

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Abstract

Common potato scab affects potato farmers worldwide and costs the Tasmanian
potato farming industry approximately $5 million dollars a year. The disease is caused
in white potatoes by the common soil bacterium streptomyces scabies, from which
several secondary metabolites have been isolated; these are known as the thaxtomin
class of phytotoxins. These compounds have been shown to cause scabs in
potatoes in sterile conditions and are phytotoxic to cellulose based plants.
Several approaches to the total synthesis of the thaxtomins have been investigated.
The most successful proceeds via the synthesis of 4-nitrotryptophan, followed by
peptide coupling and cyclisation to give two of the three dehydroxy-thaxtomins. Other
routes starting from glycine anhydride using condensation chemistry to build the three
ring system have provided a series of analogues for structure activity testing.
Toxicity of the analogues and synthetic thaxtomins has been analysed using
Arabidopsis thaliana. Two analogues showed activity approaching thaxtomin A and
show promise as potential new herbicides. Non-toxic analogues have been tested
for their ability to ameliorate or negate the effects of thaxtomin A using a variety of
models. These compounds provide a possible solution to the scab problem.
Current methods for the synthesis of the pyrrolidine antibiotic anisomycin are
complicated and rely on the preparation of a 3-pyrroline intermediate. Two novel
methods to target this advanced intermediate are discussed, firstly use of a Zn/HCI
reduction of a a-ketopyrrole, and secondly the reduction of N-tosyl pyrroles with
TFA/NaCNBH3 . The use of N-toysl protected 3-pyrrolines as building blocks towards
hydroxyl substituted pyrrolidines is also explored.
Synthesis of gram quantities of the C19 and C21 triene sex pheromones of the
autumn gum moth (Mnesampe/a private) has proved difficult because of the tendency
of the trienes to decompose through auto oxidation. We present an approach to the
synthesis of these compounds by spiking the starting material with the antioxidant
BHT and carrying it through the reaction scheme. This enables a significant
improvement in the overall yield of the desired product, which increased from 20%
without the antioxidant to 86% with.

Item Type: Thesis (PhD)
Keywords: Potatoes, Potato scab, Bacterial diseases of plants
Copyright Holders: The Author
Copyright Information:

Copyright 2010 the Author

Additional Information:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Available for use in the Library but NOT for copying until 18 June 2012. After that date, available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2010. Includes bibliographical references. Ch. 1. Synthesis of thaxtomin compounds and analogues -- Ch. 2. Biological testing of thaxtomins and thaxtomin analogues -- Ch. 3. Using pyrrole as a template to prepare anisomycin -- Ch. 4. Improving the synthesis of pheromone components of the Autumn Gum moth

Date Deposited: 03 Feb 2015 03:04
Last Modified: 18 Apr 2016 23:08
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