This thesis is divided into two parts. Part 1 covers the biosynthesis of the fungal metabolite tenellin, and Part 2 the metabolism of β-aminoisobutyrate m Streptomyces sp. Tenellin is a yellow pigment of the fungus Beamaria bassiana. It is of mixed biosynthetic origin, being derived from a polyketide moiety and the amino acid L-phenylalanine. The timing of the C-methylations of the polyketide chain is discussed in Chapter 2, which describes attempts to incorporate deuterium labelled partially assembled putative intermediates into the polyketide. The biosynthesis of the pyridone ring of tenellin requkes the condensation of the polyketide moiety with a rearranged phenylpropanoid unit derived from phenylalanine. The nature of this intriguing intramolecular rearrangement is discussed in Chapters 3 and 4. A phenylalanine derived tetramic acid, proposed as an intermediate in the biosynthesis, has been synthesised, and used in biosynthetic investigations. The results of these investigations and the subsequent identification of tyrosine as a closer precursor to tenellin argue against its intermediacy. The failure of [2-(^13)C(^2)H(^15)N]-phenylalanine to become incorporated intact suggests a transamination process for phenylalanine / tyrosine prior to incorporation. Preliminary investigations suggest para-hydroxy phenyllactate may be die substrate for the rearranging enzyme and a more direct precursor to tenellin. β-Aminoisobutyrate, the end product of reductive thymine catabolism, contributes to both the propionate and butyrate pools in Streptomyces sp. The pathway of incorporation into the isobutyrate / butyrate pool has been investigated, and confirmed to be the reverse of that known to occur in L-valine metabolism. A mutant strain of Streptomyces avemitilis, unable to produce isobutyrate, was used due to low level incorporations into the branched-chain fatty acids. This work was carried out in collaboration with Dr. Hamish McArthur, Pfizer Central Research Division, Groton, USA, and Dr. Kevin Reynolds, Department of Pharmaceutical Science, University of Maryland.

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Doctor of Philosophy (PhD) / This thesis describes synthetic studies towards the HIV-1 integrase inhibitory natural products lithospermic acid and integramycin, resulting in a formal total synthesis of the former. A modular, flexible and convergent synthetic strategy to lithospermic acid was devised. In this approach, a Sonogashira coupling was used to unite the C1–C7 and C20–C27 fragments that were subsequently manipulated to then participate in the key step of the synthesis, a palladium-mediated carbonylative annulation. Reduction of the benzofuran nucleus with magnesium in methanol then provided the desired dihydrobenzofuran core of lithospermic acid. Various protecting group strategies were investigated to complete this sequence in an efficient manner. Further synthetic manipulations afforded the complete C1–C9/C19–C27 fragment, which was united with the C10–C18 fragment to deliver the entire carbon skeleton of lithospermic acid. A two step deprotection sequence was undertaken, however, complications with the final deprotective step prevented definitive proof that the total synthesis of lithospermic acid had been achieved. An alternate protecting group strategy was sought, and a formal total synthesis of lithospermic acid was achieved by intercepting an advanced intermediate from a previous total synthesis. Several strategies for the enantioselective synthesis of the dihydrobenzofuran core of lithospermic acid were evaluated, however, none proved successful. A synthetic route towards the tetramic acid subunit of integramycin was also investigated. 3- Methoxymaleimide was constructed using known chemistry, and the regioselective reduction of this ring system was developed. Attempts to further functionalise this ring system were thwarted by difficulties associated with handling. The scope of the regioselective reduction was investigated on an array of N- substituted methoxymaleimides with the procedure found to be generally high yielding and highly regioselective.

Doctor of Philosophy (PhD) / This thesis describes synthetic studies towards the HIV-1 integrase inhibitory natural products lithospermic acid and integramycin, resulting in a formal total synthesis of the former. A modular, flexible and convergent synthetic strategy to lithospermic acid was devised. In this approach, a Sonogashira coupling was used to unite the C1–C7 and C20–C27 fragments that were subsequently manipulated to then participate in the key step of the synthesis, a palladium-mediated carbonylative annulation. Reduction of the benzofuran nucleus with magnesium in methanol then provided the desired dihydrobenzofuran core of lithospermic acid. Various protecting group strategies were investigated to complete this sequence in an efficient manner. Further synthetic manipulations afforded the complete C1–C9/C19–C27 fragment, which was united with the C10–C18 fragment to deliver the entire carbon skeleton of lithospermic acid. A two step deprotection sequence was undertaken, however, complications with the final deprotective step prevented definitive proof that the total synthesis of lithospermic acid had been achieved. An alternate protecting group strategy was sought, and a formal total synthesis of lithospermic acid was achieved by intercepting an advanced intermediate from a previous total synthesis. Several strategies for the enantioselective synthesis of the dihydrobenzofuran core of lithospermic acid were evaluated, however, none proved successful. A synthetic route towards the tetramic acid subunit of integramycin was also investigated. 3- Methoxymaleimide was constructed using known chemistry, and the regioselective reduction of this ring system was developed. Attempts to further functionalise this ring system were thwarted by difficulties associated with handling. The scope of the regioselective reduction was investigated on an array of N- substituted methoxymaleimides with the procedure found to be generally high yielding and highly regioselective.

An understanding of the underlying mechanisms by which proteins engage and communicate within the complex cellular environment is critical to the elucidation of the molecular basis of disease states and the development of safer, more efficacious drug therapies. Diverse cellular functions, including replication, transcription, cell growth and intracellular signal transduction, are governed by extensive networks of protein-protein interactions (PPIs). Disruption of the finely-tuned cellular networks due to the formation of aberrant or unregulated PPIs is implicated in the development and progression of cancer. As a result, over the last decade, PPI modulation has developed as an attractive molecular target for novel cancer therapies and as a powerful research tool in chemical biology to provide insight into the cellular transformations involved in carcinogenesis. Chapter 1 provides a review of the physiological importance of PPIs and the role they play in the development and progression of cancer. A summary of the challenges associated with targeting PPIs is given, highlighting the changing perception regarding the drugabbility of PPIs and the technological and conceptual advances driving this transformation. A brief overview of the approaches used to identify PPI modulators links the reader to the appropriate chapter for further discussion and utilisation of a selection of these methods. Chapter 2 describes the application of a virtual screening approach to discover PPI modulators. In particular, the development of an in silico – in vitro screening method to identify modulators of the protein interactome of the AAA+ protein reptin. The synthesis and optimisation of two hit compounds is outlined, with a discussion of their predicted binding modes, mode of action, potential as chemical tools and lead molecules for an anti-cancer drug discovery programme. Chapter 3 highlights the potential to discover PPI modulators from Nature's rich source of structurally complex, bioactive molecules. A synthetic approach to a sub-family of tetramic acid natural products is outlined, involving the development of a short, asymmetric synthesis of unnatural 4,4-disubstituted glutamic acid derivatives. The first total syntheses of the potent siderophore harzianic acid and the PAC3 PPI inhibitor JBIR-22 are reported. In addition, the potential role of a Diels-Alderase enzyme in the biosynthesis of JBIR-22 and the development of a chiral catalysed intramolecular Diels-Alder of an advanced JBIR-22 intermediate is investigated. Chapter 4 discusses the use of structure based design techniques in the development of PPI modulators. The process involved in the design of two series of inhibitors of PICK PDZ domain mediated interactions is outlined. This leads to the development and optimisation of synthetic routes to both series of inhibitors, including the utilisation of a strategic sp3-sp2 cross coupling reaction. Finally, preliminary biological assessment of the inhibitors is reported. Chapter 5 gives a brief overview of high-throughput screening (HTS) methods used to identify PPI modulators. The utilisation of a forward chemical genetics screen to identify the p53 activator MJ05 is described. A racemic and asymmetric route to MJ05 is developed and biochemical analysis of the two enantiomers of MJ05 is reported including the investigation of MJ05 as an adjuvant therapy for the treatment of cancer. Chapter 6 provides a general overview of the outcome of the different approaches used in this research to discover PPI modulators. Particular emphasis is placed on the development of chemical tools for the elucidation and dissection of the physiological role of protein-protein interactions and the identification of novel drug targets, in addition to the identification of lead molecules for PPI drug development programmes.