Natural products as sources of novel therapeutic agents experienced a steady increase from around the turn of the twentieth century until it peaked in the 1970s and 1980s. However since this time pharmaceutical research in natural products has experienced a decline. Despite this trend the natural products industry now seems to be experiencing a revival of sorts. This thesis represents a continuation of the work on the isolation and structure elucidation of potential drug leads from terrestrial fungal sources that the natural products group at the University of Canterbury is engaged in. The known compound, pseurotin A (2.7) and two novel diastereomers, pseurotin A2 (2.8) and pseurotin A3 (2.9) were isolated from the extract of a Penicillium sp. of fungus collected from the foreshore of a beach in Vancouver, Canada. The absolute stereochemistry of pseurotin A2 and proposed absolute stereochemistry for A3 were elucidated using a combination of X-ray crystallography (A2 only), circular dichrosim, oxidative cleavage reactions, and J2-resoved 2D NMR experiments. The extract of an as yet unidentified endophytic fungus has yielded eight novel compounds related to the spirobisnaphthalene class of compounds. These eight compounds fall into to distinct groupings. The spiro-mamakones, distinguished by a structurally unprecedented oxygenated spiro-nonene skeleton, comprise five compounds, spiro-mamakones A-E (3.11, 3.15-3.18). In addition to these naturally occurring compounds, the semi-synthetic compounds, 4-oxo-spiro-mamakone A (3.12) and O-acetyl-spiro-mamakone A (3.21), were also synthesised. spiro-Mamakone A was found to be racemic, while X-ray crystallography and optical rotation revealed spiro-mamakone C (3.15) to be present as an enantiomeric mixture (4S*, 5S*, 9R*). Unfortunately the enantiomeric excess was unable to be elucidated. NOE experiments revealed spiro-mamakone B (3.16) to have the relative stereochemistry 4S*, 5S*, 9S*. The relative stereochemistry of spiro-mamakones D (3.17) (4S*, 5S*, 8S*, 9S*) and E (3.18) (4S*, 5S*, 8S*, 9R*) was proposed from comparison of coupling constant calculations from energy-minimised models with those of the experimentally determined values. The second group, comprising three novel compounds named the mamakunoic acids, mamakunoic acid A-C (3.8, 3.7, 3.10), are characterised by their acid substituted dihydro benzofuran system. The low yield obtained of these compounds, unfortunately prevented their stereochemical elucidation. In addition to structure elucidation, biosynthetic studies on spiro-mamakone A and mamakunoic acid B were also carried out. Analysis of the NMR spectra derived from spiro-mamakone A, labelled with isotopic acetate, revealed a situation complicated by the presence of isotopomers and racemisation, resulting in NMR spectra that were somewhat anomalous in appearance. These irregularities however, were resolved leading to the proposal that spiro-mamakone A was derived from a dihydroxynaphthalene (DHN) intermediate, which proceeds through to spiro-mamakone via an epoxide intermediate. Despite problems with purity and low yields of isotopically labelled mamakunoic acid B, it was proposed that like spiro-mamakone A, it proceeded via a DHN intermediate. The extract derived from a Malaysian Scleroderma sp. was found to contain a new dichlorinated pulvinic acid derivative, methyl-3',5'-dichloro-4,4'-di-O-methylatromentate (4.14), the structure of which was confirmed by X-ray crystallography. In addition three previously reported compounds, 4,4'-dimethoxyvulpinic acid (4.11), methyl-3'-chloro-4,4'-di-O-methylatromentate (4.12) and methyl-4,4'-dimethoxyvulpinate (4.13), were also isolated. The extract of another, as yet unidentified endophytic fungus was found to contain the new acetogenin, 1,5-dihydroxy-6-(2-hydroxyethyl)-3-methoxyacetophenone (5.7), differing from the known compound, 2,4-dihydroxy-6-(2-hydroxyethyl)-3-methoxyacetophenone (5.8) only by virtue of the substitution pattern. The structure of 5.7 was confirmed by X-ray crystallography. The implementation of efficient dereplication procedures is paramount for those working in the field of natural products. The recent advances that have been made in the dereplication process in the natural products group at the University of Canterbury are given using examples from this research and where necessary from other group members.

Tetrahydrofuran (THF) and tetrahydropyran (THP) rings are commonly found in a wide range of natural products and biologically active compounds. In total synthesis, the formation of THF/THP motifs is often the key step but existing methods often involve numerous steps and low overall efficiencies. Part one of this thesis details the development of a practical method for the synthesis of THF rings by the controlled mono-addition/cyclisation of organolithium species to C2-symmetric diepoxides (Scheme A-1). This method can also be applied to the synthesis of bis-THF rings from triepoxides and has potential applications in more complex cascade reactions. A similar cyclisation process providing THF rings from epoxyaldehydes is also described. Part two of this thesis details our efforts towards the synthesis of the marine macrolide neopeltolide. Wright and co-workers reported the isolation of neopeltolide 211 from a deep-water sponge of the family neopeltidae off the north coast of Jamaica. The structure, which was assigned by NMR and HRMS studies and reassigned by total synthesis, contains a 14-membered macrolactone, a 2,6-cis THP ring and an unsaturated oxazole side-chain. Chapter four describes the synthesis of the C2-C8 and C9-C16 fragments (Scheme A-2). Chapter five details our initial attempts in the coupling of subunits 268 and 320, as well as a revised synthetic strategy that allowed us to successfully couple C2-C9 alkyne 347 with C10-C16 aldehyde 348 and the preparation of an advanced intermediate 364 (Scheme A-3).

Manumycin antibiotics represent an important class of secondary metabolites produced by Streptomyces bacteria. They belong to a big class of polyketide metabolites and posses significant antimicrobial, anti-inflammatory, antitumor, and many other biological activities. They are characterized by two short polyketide chains, which are attached to a central subunit. Polyketide chains are synthesized by enzymes of the iterative type II polyketide-synthase. Mechanism of regulation of the polyketide chains length has not been known yet. Understanding mechanism can lead to biosynthesis of novel manumycin antibiotics with predetermined chain lengths what may improve their biological activities in favour of a practical use of these compounds. We prepared a mutant strain of asukamycin producer Streptomyces nodosus ssp. asukaensis with deletion of genes coding for type I/II β-ketoacylsynthase and protein AsuC14, which is a potential factor affecting lower polyketide chain length, for the identification of the chain length factor in manumycin antibiotics producers. Next, the genes for type I/II β-ketoacylsynthase and potential chain length-affecting factor C14 from strains producing manumycins with variable length of the lower polyketide chains were expressed in this mutant strain. Our results demonstrate...

Cosmomicina é um antibiótico antitumoral produzido pela bactéria Streptomyces olindensis DAUFPE 5622. Estudos de expressão gênica demonstraram que genes cuja expressão esta relacionada a condições de estresse (dnaJ e 18hsp), assim como genes associados a via biossintética de cosmomicina, são expressos sob condições de produção do antibiótico. Genes que ainda tinham a função desconhecida foram selecionados (cosS e cosY) e foram realizados análises bioinformáticas destes atribuindo-lhes a função de regulador transcricional e ornitina ciclodesaminase, respectivamente. Um cassete para inativação desses genes foi construído visando a futura obtenção de mutantes nulos. Genes de glicosiltransferase (cosK e cosG) também apresentaram diferenças na expressão na presença do antibiótico. Neste trabalho, foi revelada a presença de uma hipotética glicosiltransferase que tem homologia com a B-daunosamine daunomy, glicosiltransferase envolvida na transferência de açúcares na biossíntese do antibiótico daunomicina. / Cosmomycin is an antitumoral antibiotic produced by the soil bacteria Streptomyces olindensis DAUFPE 5622. Gene expression studies established that stress condition genes like dnaJ and 18hsp, and cosmomycin biosynthetic pathways genes are expressed under antibiotic production. Also the genes cosS and cosY (unknowns function), were selected and analyzed by bioinformatics techniques attributing a transcriptional regulator and ornithine cyclodeaminase functions, respectively. A cassette was constructed in order to inactivate these two selected genes and generating void mutants. Another gene cosK, with glycosiltransferase function, also presented differences in its expression when the antibiotic is produced. We described in this work the presence of a hypothetical glycosiltransferase related with B-daunosamine daunomy, which transfers sugar molecules in the biosynthesis of daunomycin antibiotic.

Total synthesis of natural products with diverse architecture and varying degree of complexity is an area that has not only inspired and attracted several generations of organic chemists but also continues to enrich and refresh the foundations of organic chemistry itself, by offering new ideas and directions. Synthetic organic chemistry is perhaps the most formative and expressive enterprise of science in terms of its creative power and unlimited scope. Its impact on present day life and prosperity gets manifested when we see this science as the bedrock behind the production of pharmaceuticals, pesticides, fertilizers, nutritional products, high tech materials, polymers, cosmetics, plastics and clothing. Science of synthesis is also going to play an important role in the evolution of future societies based on the principles of the sustainable development. Being a precise science and a fine art, the endeavor of total synthesis is in a constant state of effervescence. Most significantly, the discipline is being continually challenged by new structures unraveled from the Nature’s bosom. The practice of total synthesis is being enriched constantly by new tools such as new reagents and catalysts as well as by analytical techniques. In fact, there has been a dramatic advancement in the recent past in the development of new synthetic protocols with high regio-, streo-, and enantiocontrol, which makes it possible to target natural product of any complexity. The demand for enantiomerically pure drugs, agrochemicals and food additives is growing, since pure enantiomers are often more target-specific and have fewer side effects than the recemic mixtures. As a result, synthesis of natural products in an enantioselective manner has been receiving increasing attention from synthetic chemists in recent years. Nature synthesizes a vast array of novel molecular structures in enantioselective fashion through several well-established biosynthetic pathways utilizing a few key building blocks. Among them mevalonate pathway to terpenes, shikimate pathway to aromatics, alkaloids and the polyketide pathway to aromatics, macrolides and related compounds are the most noteworthy. Polyketides, constitutes a large family of natural products built from acyl coenzyme A monomers and exhibit remarkable diversity both in terms of their structure and function. These natural products display a wide range of medicinally important activities such as antibiotic, anticancer, antifungal, hypolipidemic and immunosuppressive properties. In recent years, polyketide derived natural products embodying an epoxyquinone core, have been surfacing with increasing frequency from diverse natural sources. Both on account of their structural diversity and promising biological activity, polyketide derived epoxyquinoid natural products have evoked considerable attention from the synthetic community during the past few years. We too got enticed towards these natural products as an offshoot of ongoing research activity in the group. The present thesis entitled “Enantioselective Total Synthesis of Bioactive Epoxyquinoid Natural Products” is described in four chapters. Chapter 1: Enantioselective total synthesis of (+)-eupenoxide, (+)-6-epi-eupenoxide and (+)-phomoxide; Chapter 2: Enantioselective total synthesis of (−)-EI-1941-2; Chapter 3: Enantioselective total synthesis of (+)-integrasone. Chapter 4: Enantioselective total synthesis of (+)-hexacyclinol. It’s quite tempting to highlight the fact that while Nature might have used entirely different biochemical machinery to build up all these diverse natural products; but in the chemical laboratory all the syntheses have emanated from a single starting material, symbolizing the intrinsic power and versatility of chemical synthesis.

Diverse biological activities of polyketide natural products are often associated with specific structural motifs, biosynthetically introduced after construction of the polyketide core. Therefore, investigation of such "post-polykektide synthase (PKS)" modifications is important, and the accumulated knowledge on these processes can be applied for combinatorial biosynthesis to generate new polyketide derivatives with enhanced biological activities. In addition to the practical value, a lot of unprecedented chemical mechanisms can be found in the enzymes involved therein, which will significantly advance our understanding of enzyme catalysis. The works described in this dissertation focus on elucidating a number of post-PKS modifications involved in the biosynthesis of an insecticidal polyketide, spinosyn A, in Saccharopolyspora spinosa. First, three methyltransferases, SpnH, SpnI, and SpnK, responsible for the modification of the rhamnose moiety, have been investigated to verify their functions and to study how they are coordinated to achieve the desired level of methylation of rhamnose. In vitro assays using purified enzymes not only established that SpnH, SpnI, and SpnK are the respective rhamnose 4ʹ-, 2ʹ-, and 3ʹ-O-methyltransferase, but also validated their roles in the permethylation process of spinosyn A. Investigation of the order of the methylation events revealed that only one route catalyzed by SpnI, SpnK, and SpnH in sequence is productive for the permethylation of the rhamnose moiety, which is likely achieved by the proper control of the expression levels of the methyltransferase genes involved in vivo. The key structural feature of spinosyn A is the presence of the unique tetracyclic architecture likely derived from the monocyclic PKS product. To elucidate this "cross-bridging" process, which had been hypothesized to involve four enzymes, SpnF, SpnJ, SpnL, and SpnM, the presumed polyketide substrate was chemically synthesized using Julia-Kocienski olefination, Stille cross-coupling, and Yamaguchi macrolactonization as key reactions. Incubation of the synthesized substrate with SpnJ produced a new product where the 15-OH group of the substrate is oxidized to the ketone. Next, it was demonstrated that incubation of this ketone intermediate with SpnM produces a tricyclic compound, via a transient monocyclic intermediate with high degree of unsaturation. Whereas it was initially thought that SpnM catalyzes both dehydration and [4+2] cycloaddition in sequence, detailed kinetic analysis revealed that SpnM is only responsible for the dehydration step, and the [4+2] cycloaddition step is indeed catalyzed by SpnF. Finally, successful conversion of the tricyclic intermediate to the tetracyclic core was demonstrated using SpnL. Proposed chemical mechanisms of SpnF and SpnL, Diels-Alder and Rauhut-Currier reactions, respectively, are interesting because enzymes capable of catalyzing these reactions have yet to be characterized in vitro. This work not only establishes the biosynthetic pathway for constructing the spinosyn tetracyclic core, but also epitomizes the significance of the post-PKS modification as a rich source of new enzyme catalysis. / text

Natural products as sources of novel therapeutic agents experienced a steady increase from around the turn of the twentieth century until it peaked in the 1970s and 1980s. However since this time pharmaceutical research in natural products has experienced a decline. Despite this trend the natural products industry now seems to be experiencing a revival of sorts. This thesis represents a continuation of the work on the isolation and structure elucidation of potential drug leads from terrestrial fungal sources that the natural products group at the University of Canterbury is engaged in. The known compound, pseurotin A (2.7) and two novel diastereomers, pseurotin A2 (2.8) and pseurotin A3 (2.9) were isolated from the extract of a Penicillium sp. of fungus collected from the foreshore of a beach in Vancouver, Canada. The absolute stereochemistry of pseurotin A2 and proposed absolute stereochemistry for A3 were elucidated using a combination of X-ray crystallography (A2 only), circular dichrosim, oxidative cleavage reactions, and J2-resoved 2D NMR experiments. The extract of an as yet unidentified endophytic fungus has yielded eight novel compounds related to the spirobisnaphthalene class of compounds. These eight compounds fall into to distinct groupings. The spiro-mamakones, distinguished by a structurally unprecedented oxygenated spiro-nonene skeleton, comprise five compounds, spiro-mamakones A-E (3.11, 3.15-3.18). In addition to these naturally occurring compounds, the semi-synthetic compounds, 4-oxo-spiro-mamakone A (3.12) and O-acetyl-spiro-mamakone A (3.21), were also synthesised. spiro-Mamakone A was found to be racemic, while X-ray crystallography and optical rotation revealed spiro-mamakone C (3.15) to be present as an enantiomeric mixture (4S*, 5S*, 9R*). Unfortunately the enantiomeric excess was unable to be elucidated. NOE experiments revealed spiro-mamakone B (3.16) to have the relative stereochemistry 4S*, 5S*, 9S*. The relative stereochemistry of spiro-mamakones D (3.17) (4S*, 5S*, 8S*, 9S*) and E (3.18) (4S*, 5S*, 8S*, 9R*) was proposed from comparison of coupling constant calculations from energy-minimised models with those of the experimentally determined values. The second group, comprising three novel compounds named the mamakunoic acids, mamakunoic acid A-C (3.8, 3.7, 3.10), are characterised by their acid substituted dihydro benzofuran system. The low yield obtained of these compounds, unfortunately prevented their stereochemical elucidation. In addition to structure elucidation, biosynthetic studies on spiro-mamakone A and mamakunoic acid B were also carried out. Analysis of the NMR spectra derived from spiro-mamakone A, labelled with isotopic acetate, revealed a situation complicated by the presence of isotopomers and racemisation, resulting in NMR spectra that were somewhat anomalous in appearance. These irregularities however, were resolved leading to the proposal that spiro-mamakone A was derived from a dihydroxynaphthalene (DHN) intermediate, which proceeds through to spiro-mamakone via an epoxide intermediate. Despite problems with purity and low yields of isotopically labelled mamakunoic acid B, it was proposed that like spiro-mamakone A, it proceeded via a DHN intermediate. The extract derived from a Malaysian Scleroderma sp. was found to contain a new dichlorinated pulvinic acid derivative, methyl-3',5'-dichloro-4,4'-di-O-methylatromentate (4.14), the structure of which was confirmed by X-ray crystallography. In addition three previously reported compounds, 4,4'-dimethoxyvulpinic acid (4.11), methyl-3'-chloro-4,4'-di-O-methylatromentate (4.12) and methyl-4,4'-dimethoxyvulpinate (4.13), were also isolated. The extract of another, as yet unidentified endophytic fungus was found to contain the new acetogenin, 1,5-dihydroxy-6-(2-hydroxyethyl)-3-methoxyacetophenone (5.7), differing from the known compound, 2,4-dihydroxy-6-(2-hydroxyethyl)-3-methoxyacetophenone (5.8) only by virtue of the substitution pattern. The structure of 5.7 was confirmed by X-ray crystallography. The implementation of efficient dereplication procedures is paramount for those working in the field of natural products. The recent advances that have been made in the dereplication process in the natural products group at the University of Canterbury are given using examples from this research and where necessary from other group members.

Le polymère de sporopollénine est un constituant majeur de l’exine, la partie externe de la paroi du grain de pollen. Son exceptionnelle résistance permet de les protéger des stress environnementaux de nature mécanique ou chimique. Il constitue une des clefs de la colonisation du milieu terrestre par les plantes. Au cours de ma thèse, j’ai caractérisé deux Polykétide Synthases (PKS-A et PKS-B) et deux Tétrakétide α-Pyrone Réductases (TKPR1 et TKPR2) d’Arabidopsis thaliana. Par immunolocalisation, hybridation in situ et des études de microscopie j’ai montré que ces protéines intervenaient dans la synthèse de la paroi pollinique. In vitro, les deux PKS catalysent la condensation de 2 ou 3 molécules de malonyl-CoA sur différents esters de CoA d’acide gras pour former les tri et tétrakétide α-pyrones correspondants, substrat de TKPR1 et TKPR2. In vitro, celles-ci réduisent la fonction cétone en alcool secondaire formant des composés hydroxylés, précurseurs du polymère de sporopollénine. Dans les cellules du tapétum, la synthèse des monomères de sporopollénine se déroule en quelques heures seulement. Par immunodétection et en fusionnant les protéines à la GFP, j’ai montré que ces enzymes se trouvent à la surface du réticulum endoplasmique à l’exception de TKPR2. Des expériences de HIS-pull-down, de FLIM-FRET et de double hybride nous ont ensuite permis de suggérer que ces protéines forment un métabolon. L’identification de gènes homologues dans de nombreuses espèces végétales y compris une mousse révèle que nous avons identifié une voie métabolique très ancienne conservée au sein des angiospermes. / .onferes a high degree of resistance to various mechanical and chemical stresses. During the evolution, this properties enabled the plant to adapat to land conditions. We caracterized two Polyketide Sythases (PKSA and PKSB) and two Tetraketide -pyrone Reductases (TKPR1 and TKPR2). By immunolocalisation, in situ hybridization and microscopy analysis we showed those proteins are involved in the pollen wall synthesis.We investigated the in vitro activity of the recombinant proteins and showed that the two PKS catalyzed the condensation of 2 or 3 malonyl-CoA with various fatty acid CoA esters, producing the corresponding tri and tetraketides. We also demonstrated that the tetraketides produced by PKS were substrates of the TKPR1 and TKPR2. In vitro, they reduced the cetone function of the lateral chain to a secondary alcohol forming hydroxylated compounds involved in the polymerization of sporopollenin.In tapetum cells, the synthesis of sporopollenin monomers is achieved in a few hours. To explain the underlying metabolic rate, I studied the cellular organization of the metabolic pathway. By immunodetection and GFP fusion experiments I localized PKSA, PKSB and TKPR1 to the endoplasmic reticulum while TKPR2 was mainly cytosolic. Then, interaction studies by HIS pull-down, FLIM-FRET and double hybride experiments showed the occurrence of a metabolon localized to the ER. Finally, by phylogenetic analysis, we showed the conservation of the genes involved in sporopollenin biosynthesis pathway, from mosses to higher plants.

Cosmomicina é um antibiótico antitumoral produzido pela bactéria Streptomyces olindensis DAUFPE 5622. Estudos de expressão gênica demonstraram que genes cuja expressão esta relacionada a condições de estresse (dnaJ e 18hsp), assim como genes associados a via biossintética de cosmomicina, são expressos sob condições de produção do antibiótico. Genes que ainda tinham a função desconhecida foram selecionados (cosS e cosY) e foram realizados análises bioinformáticas destes atribuindo-lhes a função de regulador transcricional e ornitina ciclodesaminase, respectivamente. Um cassete para inativação desses genes foi construído visando a futura obtenção de mutantes nulos. Genes de glicosiltransferase (cosK e cosG) também apresentaram diferenças na expressão na presença do antibiótico. Neste trabalho, foi revelada a presença de uma hipotética glicosiltransferase que tem homologia com a B-daunosamine daunomy, glicosiltransferase envolvida na transferência de açúcares na biossíntese do antibiótico daunomicina. / Cosmomycin is an antitumoral antibiotic produced by the soil bacteria Streptomyces olindensis DAUFPE 5622. Gene expression studies established that stress condition genes like dnaJ and 18hsp, and cosmomycin biosynthetic pathways genes are expressed under antibiotic production. Also the genes cosS and cosY (unknowns function), were selected and analyzed by bioinformatics techniques attributing a transcriptional regulator and ornithine cyclodeaminase functions, respectively. A cassette was constructed in order to inactivate these two selected genes and generating void mutants. Another gene cosK, with glycosiltransferase function, also presented differences in its expression when the antibiotic is produced. We described in this work the presence of a hypothetical glycosiltransferase related with B-daunosamine daunomy, which transfers sugar molecules in the biosynthesis of daunomycin antibiotic.

As the battle against ever-increasing drug resistence bacteria rages on, novel and sometimes more complex natural products can be used to combat this. In this study, two-dimensional NMR techniques were utilized to collect a complete spectral data set for two natural products. The first structure, a synthesized Pyrrolobenzodiazepine alkaloid natural product was confirmed through these methods. The second, a strain of Rhodococcus, MTM3W5.2, produces a novel antibacterial molecule in broth cultures and the active compound was fractionated using a Sephedex LH-20 column. Chromatographic purification yielded a pure sample at 58.90 minutes, RT.58. HRMS data deduced an exact mass of 911.5490 Da, equivalent to a molecular formula of C52H78O13. Several major spin systems were constructed from the 2D-NMR spectra. However, due to limited sample quantity in compound with a large molecular weight and product instability, the long range HMBC signals needed to connect these fragments have not yet been obtained.