Perophoramidine 1 is a halogenated natural product which contains two contiguous quaternary centres within its structure. In this thesis, approaches towards the synthesis of perophoramidine are described. In particular, the synthesis of the tetracyclic core structure and the formation of the quaternary centres have been examined. In Chapter 1, the natural product perophoramidine 1 is introduced and its isolation, structure and biological activity is discussed. The structurally related communesin family of natural products are also introduced before the literature published on both the biosynthesis and laboratory synthesis of perophoramidine 1, is reviewed. Finally the Westwood group's approach towards the synthesis of perophoramidine 1 is introduced with a summary of non-halogenated model system investigations previously carried out within the group being provided. Chapter 2 describes studies towards the synthesis of an appropriately halogenated indolo[2,3-b]quinoline core structure of perophoramidine 1. This then allowed methodology previously developed within the group on model system substrates to be applied to the formation of the first of the two quaternary centres required for the synthesis of perophoramidine 1. Chapter 3 describes the attempted formation of the second quaternary centre using an ester alkylation approach. After initial studies failed to generate the desired quaternary centre, non-halogenated model system studies were carried out in an attempt to develop an alternative approach. In Chapter 4, model system studies were continued with cyclic ether compounds investigated as potential intermediates towards the synthesis of perophoramidine 1. The results obtained in this chapter provided a novel route to the formation of the second quaternary centre and led to a redesigned approach towards perophoramidine 1 being developed. In Chapter 5, this redesigned approach was applied to the halogenated intermediates synthesised in Chapter 1. This led to the formation of the first halogenated intermediate synthesised within the group which contained the two contiguous quaternary centres required for the synthesis of perophoramidine 1.

Leishmaniasis is a disease caused by obligate intracellular parasites of the genus Leishmania, including 20 species that are pathogenic to humans. Female sand fly is the known vector that can transmit the disease. Visceral leishmaniasis is the severe form of the disease that affects internal organs and can be fatal with inappropriate diagnosis or treatment. Leishmania donovani is the causative agent of visceral leishmaniasis. Approximately 350 million in 89 countries are at risk of infection. Around 2 million new cases are reported annually with 500,000 of these are visceral leishmaniasis. Current drug therapies are inadequate due to their toxicity, high cost, severe adverse reaction, limited availability, and the emergence of resistance. With all these limitations, the need for new drugs is urgent. Pentavalent antimonials are the first line of treatment for leishmaniasis since the 1940s. Although amphotericin B, pentamidine and paromomycin are current drugs that treat leishmaniasis, they were discovered initially as a treatment for other pathogens. Furthermore, miltefosine the only available oral drug for leishmaniasis is an anticancer drug that found to be active against Leishmania. Therefore, we used our quantitative Leishmania donovani axenic amastigote assay and the clinically relevant infected macrophage assay to identify new antileishmanial hits from unstudied or understudied natural product sources such as mangrove endophytic fungi, Antarctic deep-sea coral, and terrestrial plants. We also used the same assays to screen synthetic compounds form multiple chemical scaffolds. Our well-established assays led to the identification of new antileishmanial hits from unstudied natural products and the discovery of new classes of molecules from synthetic compounds that possess potent activity against Leishmania donovani. Finally, we conducted an in vivo hamster study on an active hit that revealed high efficacy against Leishmania donovani in this severe model leading to promising antileishmanial drug development.

Lomaiviticin A (1) and B (2) are natural products with remarkably complex C2-symmetric structures and potent antiproliferative properties. Achieving total syntheses of 1 and 2 has been a long-standing project in the Shair group and part one of this thesis describes our first successful synthesis of the C4-epi-lomaiviticin A and B core structures. A key stereoselective oxidative enolate dimerization of an oxanorbornanone system was employed to establish the highly hindered C2-C2' bond. Crucial to our completion of the lomaiviticin core structures was the discovery of subtle yet far-reaching stereoelectronic effects imparted by the C4/C4'-stereocenters. The Lycopodium alkaloids are a family of complex polycyclic alkaloid natural products that have long served as popular targets for developing synthetic chemistry. More recently, select members have been reported to exhibit neurological effects. Part two of this thesis presents the development of a biomimetic, unified strategy for the synthesis of 7-membered ring-containing Lycopodium alkaloids and its successful application toward the first total syntheses of the proposed structure of (-)-himeradine A (38), (-)-lycopecurine (39), and (-)-dehydrolycopecurine (199), and the syntheses of (+)-lyconadin A (31) and (-)-lyconadin B (32). A biosynthetically inspired one-pot cascade reaction sequence was developed to construct the strained polycyclic core structure shared amongst these alkaloids. Additionally, the syntheses of 38, 39, and 199 featured a biomimetic intramolecular Mannich reaction to furnish the tetracyclic ring system. The successful application of our unifying strategy toward the synthesis of a diverse set of alkaloids lends support to our biosynthetic hypothesis that 7-membered ring-containing Lycopodium alkaloids arise from a common precursor. Our synthetic approach can potentially provide access to all such natural products. / Chemistry and Chemical Biology

An improved second generation approach to pestalotiopsin A and 6-epitaedolidol has been developed. A silicon group bonded directly to carbon has been used as a stereocontrol element in cyclisation substrates for a SmI2 – mediated 4-exo-trig radical cyclisation. The silicon groups acts as a steric block to set up three new stereocentres in high to complete diastereocontrol. Several approaches to the cyclisation substrates are outlined, including a silyl transfer/aldol cascade and a novel C2-symmetric N-heterocyclic carbene – copper catalyst to asymmetrically install a C-Si bond. The silicon group is a versatile handle for further manipulation and has been oxidised using Fleming oxidation conditions to install the hydroxyl functionality required in the target compounds. The silicon group also simplifies the alcohol protecting group strategy in the approach to pestalotiopsin A and 6‐epitaedolidol. The first application of N-heterocyclic carbene – copper catalysed silyl transfer in natural product synthesis and the first use of a SmI2 – mediated cyclisation directed by a C-Si stereocontrol element are described.

Fungal polyketides are a diverse class of natural products that possess many pharmacological properties, including anticancer properties. These properties are evident in the resorcylic acid lactones, a family of polyketides, including zearalenone and radicicol, which shows potent inhibition of tumour cell growth. The key step in the biosynthesis of these lactones is macrocyclization of a linear carboxylic acid into the macrolactone. This reaction is catalyzed by a polyketide synthase (PKS) thioesterase enzyme. Bacterial PKS thioesterases (TEs) have been extensively studied and their substrate specificity has been characterized in vitro. They are highly substrate selective for the macrocyclization reaction. Since Fungal PKS TEs show little sequence homology to bacterial TEs, we have begun investigating their substrate specificity. In particular we are examining the ability of fungal TEs to macrocyclize compounds with varying ring sizes, stereogenic configuration, and nucleophiles. Herein we present the synthesis of a number of diverse TE substrates and the in vitro macrocyclization results for the TEs from zearalenone and radicicol biosynthetic pathway with these substrates.

The field of metal-catalyzed C–H bond functionalizations is an incredibly vibrant and spans beyond the formations of biaryl motifs. The introduction chapter will cover the mechanistic aspects of the C–H bond functionalization with metal-carboxylate complexes. The mechanistic facets of this reaction will be the main conducting line between the different sections and chapters of the first part of this thesis. In the second chapter, will be described additives that can readily promoted C–H bond arylation of poorly reactive substrates. More specifically, we will revisit the intramolecular direct arylation reaction we will demonstrate the effect of pivalic acid as a co-catalyst by developing milder reaction conditions. In the third chapter we be described experimental and computational studies which suggested that the a single pathway might be involved in the palladium-catalyzed C–H bond functionalization of a wide range of (hetero)arene. Following this we will describe a general set of conditions for the direct arylation of wide range of heteroarenes. Also, we will present two different strategies to selectively and predictably arylate substrates containing multiple functionalizable C–H bonds. In the fourth chapter will be presented our efforts toward the development of new C–H bond functionalization methods in which we could apply our knowledge on the C–H bond cleavage and apply it to the formation of new scaffolds. The development of two new palladium-catalyzed methods were also described. In the fifth chapter, our effort toward the development of ligands to specifically promoted C–H bond cleavage will be presented. In the sixth chapter will be presented the latest results on the study of the mechanism of the C–H bond cleavage combining experimental and computational studies. In part B of this thesis will be presented our strategy toward the total synthesis of ginkgolide C that included two gold(I)-catalyzed reactions as key steps in the preparation of the spiro[4.4]nonane core of this natural product. The first studies on the feasibility of the key steps of the synthesis will be described.

Within this thesis are described synthetic approaches towards the phomactins which are novel platelet activating factor antagonists. The synthesis of known alcohol 162 is described, the two key intermediates being aldehyde 160 and vinyl iodide 161. The key step of the synthesis of aldehyde 160 is a [2,3]-Wittig-Still rearrangement of stannane 159 which introduces the hindered C1-C2 bond present in the phomactins. The vinyl iodide 161 is made in four steps from 4-pentyn-1-ol. Addition of the vinyl ytterbium species derived from the vinyl iodide to aldehyde 160 gave secondary alcohol 162. Subsequent transformations furnished the bisprotected macrocyclic sulfone 174 in four steps from alcohol 162 to give the C2 SEM protected macrocycle. Elaboration of the macrocycle to ketoaldehyde 206 was made possible by the TPAP oxidation/rearrangement reaction. Reduction with DIBAL-Hgave diol 175. Attempts at removing the sulfone appendage proved difficult so the diol was protected as the bis-acetate to attempt a selective epoxidation of the D3,4 olefin in the presence of the D1,15 olefin. Although this looked promising with the formation of the mono-epoxide 213, the inefficiency of removing the SEM group at C2 prior to the epoxidation meant the route was not viable. Removing both protecting groups from macrocycle 174 was possible with refluxing TBAF and after incorporating the epoxide of the D3,4 olefin, the macrocycle was elaborated to the benzyl ether 217. Applying the TPAP oxidation/DIBAL-H reduction sequence furnished advanced intermediate 179 which has the full carbon skeleton found in phomactin A and also had oxygen functionality at all the required positions.

The terpene and terpenoid family of compounds is considered to be the largest group of natural products. These compounds not only display great diversity in their structural features but are also known to have a multitude of biological activities including but not limited to anti-bacterial, anti-cancer, anti-inflammatory, and anti-HIV properties. Remarkably, all the terpenoids formed in nature come from two molecules viz. isopentenyl pyrophosphate and its isomer, dimethylallyl pyrophosphate both consisting of just five carbons but assembled in many ways. Nature utilizes highly efficient, enzyme-mediated cascade reactions to transform simple linear molecules to more complex cyclic scaffolds. Cascade or domino reactions are organic chemistry’s most powerful tools that, if executed correctly, mimic the extreme complexity of reactions occurring in nature. Our group has successfully utilized cationic cascade cyclization reactions, to prepare a large library of natural products along with their analogues. It was during the synthesis of one such natural product that it was discovered that a methoxymethyl (MOM) “protecting group” had been transferred within the same molecule. The optimization of this process not only allowed the synthesis of the desired tricyclic framework but also resulted in the liberated MOM group doing an EAS reaction which gave a new C-C bond. This transferred MOM group was further elaborated to different functional groups. Use of the tandem reaction sequence in an attempt to prepare radulanin E has been described. Total syntheses of two chalcone-based analogous meroterpenoids have been successfully completed using the aforementioned sequence. An advanced intermediate for an entire new class of acridine-based schweinfurthins has been elaborated. The results will be discussed in detail.

This dissertation is focused on exploring the potential of bacteria for the biosynthesis of natural products with the purposes of generating novel natural product derivatives and of improving the titer of pharmaceutically important natural products. A wide variety of compounds from various sources have been historically used in the treatment and prevention of diseases. Natural products as a major source of new drugs are extensively explored due to their huge structural diversity and promising biological activities such as antimicrobial, anticancer, antifungal, antiviral and antioxidant properties. For instance, penicillin as an early-discovered antimicrobial agent has saved millions of lives, indicating the historical importance of natural products. However, the alarming rise in the prevalence of drug resistance is a serious threat to public health and it has coincided with the decreasing supply of new antibiotics. Bacteria with a tremendous undiscovered potential have still been one of the richest sources of bioactive compounds to tackle the growing threat of antibiotic-resistant pathogens. Nevertheless, the production level of those important compounds is often quite low, and often undetectable using current analytical techniques. To expand the chemical repertoire of nature and to increase the titer of the natural products, researchers have developed various strategies, such as heterologous expression, co-cultivation of different bacteria, optimization of fermentation conditions, discovery of new species, engineering of biosynthetic enzymes, and manipulating regulatory elements. Thus, in my dissertation research, I have exploited a few of these strategies. First, I heterologously expressed some of the biosynthetic genes from the sch biosynthetic gene cluster, resulted in the production of a novel glycosylated angucycline. I was also able to generate another new glycosylated derivative of angucycline through gene disruption of tailoring enzymes. In this research, I isolated two novel angucycline derivatives and gained new insights into the glycosylation steps in the biosynthesis of Sch47554 and Sch47555. Next, I engineered the regulatory elements in Streptomyces sp. SCC-2136 through the overexpression and targeted gene disruption approaches for enhanced production of pharmaceutically important angucyclines. The highest titer of Sch47554 was achieved in Streptomyces sp. SCC-2136/ΔschA4 (27.94 mg/L), which is significantly higher than the wild type. This work thus provides an initial understanding of functional roles of regulatory elements in the biosynthesis of Sch47554 and Sch47555 and several engineered strains with enhanced production of Sch47554. Last, I isolated a carotenoid-producing endophytic bacterium from the leaves of the yew tree and optimized the fermentation conditions for an improved yield of zeaxanthin diglucoside up to 206 ± 6 mg/L. With the introduction of an additional copy of the Pscrt gene cluster through an expression plasmid, the engineered strain Pseudomonas sp. 102515/pOKF192 produced zeaxanthin diglucoside at 380 ± 12 mg/L, which is 85% higher than the parent strain. This strain holds a great potential for the production of pharmaceutically important antioxidant agent, zeaxanthin diglucoside.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18100号 / 理博第3978号 / 新制||理||1573(附属図書館) / 30958 / 京都大学大学院理学研究科化学専攻 / (主査)教授 丸岡 啓二, 教授 大須賀 篤弘, 教授 時任 宣博 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM