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Title: Towards the biosynthesis of the ligustrones
Author: Clarkson, Guy James
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1990
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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.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available