Towards the Biosynthesis of the Ligustrones

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

Abstract

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
• URI: https://theses.gla.ac.uk/id/eprint/78159