Towards the Biosynthesis of the Ligustrones

Clarkson, Guy James (1990) Towards the Biosynthesis of the Ligustrones. PhD thesis, University of Glasgow.

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The synthesis of possible precursors of the ligustrone metabolites of Cercospora ligustrina was undertaken. These were postulated as hydroxy-substituted anthracenes with a fused pyrone ring. The best approach to the anthracene nucleus was via the fusion of two substituted benzenes in such a way as to produce the central ring of the anthracene. Lithiation of N,N-diethy 1-2,4-dimethoxybenzamide and reaction of the anion with 3,5-dimethoxybenzaldehyde gave a substituted phthalide. Hydrogenation cleaved the lactone ring to yield a benzylbenzoic acid which was cyclised to give 1,3,6,8-tetramethoxy-9-anthranol. 1,3,6,8,9-pentamethoxyanthracene was produced by a two stage methy-lation process from 9-acetoxy-1,3,6,8-tetramethoxyanthracene. Reaction of the lithiated amide with methyl 2,6-dimethoxy-4-formylbenzoate and reduction of the intermediate phthalide gave a carboxymethyl-substituted benzylbenzoic acid. Attempted ring closure gave 2-carboxymethyl-1,3,6,8-tetramethoxy-9,10-anthraquinone rather than the desired anthracene. Various approaches to the pyrone ring of the required precursor were also investigated. In model reactions, the best approach involved the treatment of an o-acetoxyacetophenone with base. The fungal metabolites ligustrone A and B were isolated from cultures of Cercospora ligustrina. The metabolite ligustrone C was never detected. [1-14C]Acetate feedings of C. ligustrina were investigated however incorporations were very low.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78159
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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