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Durham e-Theses
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Biosynthetic studies on tropic acid and piliformic acid

Chesters, Nicola C.J.E. (1995) Biosynthetic studies on tropic acid and piliformic acid. Doctoral thesis, Durham University.



This thesis is divided into two parts and covers biosynthetic studies on two secondary metabolites, tropic acid in Part I and piliformic acid, in Part II.(S)-Tropic acid is the acid moiety of the alkaloids hyoscyamine and scopolamine, which are produced by a number of plants of the Solanacae family. An intriguing rearrangement of the L-phenylalanine side chain gives rise to the isopropanoid (S)-tropic acid skeleton. The detailed nature of the rearrangement has however remained elusive despite continued interest over the years. In chapter two the identification of intermediates between L-phenylalanine and (S)-tropic acid is discussed, which has placed (R)-D-phenyllactic acid as an immediate precursor. The stereochemical features of the rearrangement are described in chapter 3 and finally in chapter 4 a mechanism for the rearrangement is proposed. This is based on information obtained from the incorporation of various isotopically labelled precursors to tropic acid into two of the minor alkaloids, 3a-2'-hydroxyacetoxytropane and 3a- phenylacetoxytropane. This work was carried out in collaboration with Dr Richard Robins at the AFRC Institute of Food Research in Norwich. Piliformic acid is elaborated by the slow growing fungus Poronia piliformis. The incorporation of a number of isotopically labelled substrates into piliformic acid has revealed a mixed biosynthetic origin, comprising C(_8) and C(_3) fragments. These have been shown to be of acetogenic and citric acid cycle origins respectively. The C(_8) fragment has been further demonstrated to be a degradation product of a longer chain fatty acid. The mode of coupling of the two fragments has been investigated and suggests the intermediacy of a novel a-carboxyoctanoate. A pathway for the assembly of piliformic acid, involving a 1,3-hydrogen shift, is proposed, consistent with the above findings. These results are the subject of chapter 6.

Item Type:Thesis (Doctoral)
Award:Doctor of Philosophy
Thesis Date:1995
Copyright:Copyright of this thesis is held by the author
Deposited On:09 Oct 2012 11:51

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