Merrilactone A (1) and the epimeric anislactones A (2) and B (3) are sesquiterpene natural products that were first isolated from the dried pericarps of Illicium merrillianum (Fukuyama in 2000) and Illicium anisatum (Kouno in 1990), respectively. Merrilactone A (1) was identified as a potent nonpeptidal neurotrophic factor that strongly promotes neurite outgrowth in the culture of foetal rat cortical neurons and is a potential small molecule lead for the treatment of neurodegenerative disorders. Merrilactone A (1) together with 2 and 3, are highly complex cage-like structures that have established themselves as challenging and attractive targets in natural product synthesis. Presented in this research is a regiodivergent approach to both sets of natural products via the first known application of the defining transformation, an intramolecular tandem cyano-aldol cyclisation. We demonstrated an efficient route to the cyano-aldol product 303, which acted as the common intermediate to either natural product by orthogonal lactonisation sequences. This culminated in the successful synthesis of known intermediate 320, which represents the formal total synthesis of 1, and advanced tetracyclic intermediate 309, that is the full carbon skeleton of 2 and 3.

Naturally occurring quinones have attracted considerable interest due to their widespread occurrence, structural diversity and often potent biological activities. The research outlined in this thesis involves the development of synthetic approaches to two novel naphthoquinone derivatives, both of which were discovered during investigations into the bioactive constituents of tropical plant species. Chapter 1 introduces the family of quinonoid compounds and also considers the important role that natural product synthesis can play in structural confirmation and in providing an adequate supply of compounds for further research. Chapter 2 describes the synthesis of elecanacin 36, an unusual cyclobuta-fused naphthalene-1,4-dione derivative which has been isolated from the bulbs of the iris Eleutherine americana Merr. et Heyne (Iridaceae), along with the isomeric and well-known pyranonaphthoquinones eleutherin 38 and isoeleutherin 39. Chapter 3 focuses on an approach to 3-hydroxymethylfuro[3,2-b]naphtho[2,3-d]furan-5,10-dione 37, which has been isolated from the wood of the tropical tree Crescentia cujete L. (Bignoniaceae) and incorporates a rare fully aromatic furofuran moiety.

Protection from the negative effects of solar radiation can be achieved by wearing protective clothing, avoiding exposure to sunlight or by the application of topical sunscreens. In this thesis, a number of studies were designed to determine if quercetin is suitable for use as a topical sunscreen.<p> The first objective was to determine if quercetin could protect against UV-induced lipid oxidation. Quercetin is twice as effective at preventing UVB-induced oxidation as preventing UVA-induced oxidation.The difference between UVA- and UVB- induced oxidation is believed to be due to the presence of an excited state form of quercetin in the UVA system. <p> The second objective was to determine the UV photostability of quercetin in solution. Three photoproducts of quercetin form regardless of whether UVA or UVB radiation is used. These photoproducts are 2,4,6-trihydroxybenzaldehyde, quercetin depside and hydroxytyrosol. . The slow rate of formation, less than 20% loss of starting material over 11 hours, and non-toxic nature of the photoproducts indicate that photostability of quercetin is not an obstacle to its use as a sunscreen.<p> The third objective was to determine the ability of quercetin to inhibit photosensitization by ketoprofen. Quercetin was shown to be effective in preventing decomposition of ketoprofen until it was consumed in the formation of the three quercetin photoproducts. This abilty of quercetin to prevent ketoprofen photosensitization indicates a beneficial effect for the use of quercetin as a topical sunscreen.<p> The fourth objective was to determine if quercetin can prevent UV-induced damage in a biological system. Quercetin was found to significantly reduce secretion of matrix metalloprotease 1 (MMP-1) upon UVA or UVB exposure, but had no effect on secretion of tumor necrosis factor á (TNF-á) in HaCaT cells. , Topical application of quercetin to UVA or UVB exposed EpiDerm skin mimics significantly reduced both MMP-1 and TNF-á secretion.<p> These results indicate that quercetin is effective in decreasing or eliminating several harmful effects of UVA and UVB radiation in the skin without major loss of starting material and without formation of toxic photoproducts. As such, quercetin appears to be a good candidate for inclusion into topical sunscreen formulations.

Protection from the negative effects of solar radiation can be achieved by wearing protective clothing, avoiding exposure to sunlight or by the application of topical sunscreens. In this thesis, a number of studies were designed to determine if quercetin is suitable for use as a topical sunscreen.<p> The first objective was to determine if quercetin could protect against UV-induced lipid oxidation. Quercetin is twice as effective at preventing UVB-induced oxidation as preventing UVA-induced oxidation.The difference between UVA- and UVB- induced oxidation is believed to be due to the presence of an excited state form of quercetin in the UVA system. <p> The second objective was to determine the UV photostability of quercetin in solution. Three photoproducts of quercetin form regardless of whether UVA or UVB radiation is used. These photoproducts are 2,4,6-trihydroxybenzaldehyde, quercetin depside and hydroxytyrosol. . The slow rate of formation, less than 20% loss of starting material over 11 hours, and non-toxic nature of the photoproducts indicate that photostability of quercetin is not an obstacle to its use as a sunscreen.<p> The third objective was to determine the ability of quercetin to inhibit photosensitization by ketoprofen. Quercetin was shown to be effective in preventing decomposition of ketoprofen until it was consumed in the formation of the three quercetin photoproducts. This abilty of quercetin to prevent ketoprofen photosensitization indicates a beneficial effect for the use of quercetin as a topical sunscreen.<p> The fourth objective was to determine if quercetin can prevent UV-induced damage in a biological system. Quercetin was found to significantly reduce secretion of matrix metalloprotease 1 (MMP-1) upon UVA or UVB exposure, but had no effect on secretion of tumor necrosis factor á (TNF-á) in HaCaT cells. , Topical application of quercetin to UVA or UVB exposed EpiDerm skin mimics significantly reduced both MMP-1 and TNF-á secretion.<p> These results indicate that quercetin is effective in decreasing or eliminating several harmful effects of UVA and UVB radiation in the skin without major loss of starting material and without formation of toxic photoproducts. As such, quercetin appears to be a good candidate for inclusion into topical sunscreen formulations.

For many years, natural products have been a primary source of new molecules for the treatment of disease, and microorganisms have been a prolific source of these molecules. Recent studies have indicated, however, that many biosynthetic pathways are present in organisms for which no natural product can be associated, and only a small fraction of the microbial life present in the environment can be grown in culture. This indicates that if methods could be developed for the isolation of these pathways and production of their target molecules in heterologous hosts, great numbers of potentially valuable compounds might be discovered. In these investigations, large insert libraries of two microorganisms were constructed, one a bacterial artificial chromosome (BAC) library, the other a fosmid library, and two large insert fosmid libraries were constructed with DNA isolated from marine environmental samples. A mathematical formula was derived to estimate probabilities of cloning intact biosynthetic pathways with large insert genomic libraries and tested with a computer simulation. This indicated that even large pathways could be cloned intact in large insert libraries, provided there was an adequate size difference between the target pathway and the library inserts, and there was a concomitant increase in the size of the library with the targeting of these larger pathways. In addition, an investigation into a mixed marine culture sample lead to the identification of an unusual relationship between two bacteria for which extended co-culture leads to the production of pyocyanin. However, no useful biosynthetic pathways were located within the genomic libraries. It is concluded that significant improvements would be required to make this approach feasible for larger scale investigations. It is further concluded, on the basis of recent developments in the field, including a reduction in the cost of sequencing, improvements in techniques of whole-genome shotgun sequencing, and the development of recombination based cloning, that the employment of mass sequencing efforts and sequence-driven, recombinationbased cloning, might prove to be a more fruitful and efficient alternative to large-insert library construction for the isolation and expression of these pathways. A possible paradigm for the cloning of pathways on the basis of this technology is proposed.

New structurally diverse natural products can be discovered when carefully designed screening procedures have been applied and when a prolific organism from a different biological source is examined, such as, rare actinobacteria from an untapped environment. Chapter 3 describes the isolation and structure characterisation of eight compounds from the rare actinobacterum, Saccharothrix xinjiangensis (NRRL B-24321), including, two new 16-member macrolides, Tianchimycin A and B, respectively. OSMAC (One Strain - Many Compounds) is used to search bioactive compounds from the metabolic profile of S. xinjiangensis, isolated from a semi-arid or desert area, Tanchi, Xinjiang in the study. Isolated compounds were characterised by NMR spectroscopy and accurate mass spectrometric analysis. Investigations of the natural products at all levels, from genes, to enzymes, to molecules has revealed insights into differentiating features of the biosynthetic pathways that lead to structural diversity of natural products. The presence of a halogen substituent in natural products profoundly influences their biology activity. Actinomycins are a well-known class of antibiotics/anticancer agents. Here, the gene cluster directing chlorinated actinomycin G biosynthesis in Streptomyces iakyrus (DSM 41873) has been identified and sequenced. It contains one actinomycin synthetase I (ACMS I) gene and two copies of ACMS II and III genes. Genetic analysis demonstrates a unique partnership between the putative hydroxylation and chlorination activities as both acm8 and acm9 genes need to be transcribed for the biosynthesis of actinomycin G2 and actinomycin G3, respectively. In chapter 5, I descries a possible metabolic flux rebalancing pathway for increasing phenazinomycin production in S. iakyrus (DSM 41873) after interruption of the methyltrasfer gene (acmG5') in actinomycin G gene cluster. The gene cluster of phenazinomycin was identified by in silico analysis and by comparison with a known phenazine gene cluster from S. iakyrus (DSM 41873).

Thesis (M.Sc.)--Victoria University of Wellington, 2008. / Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 136-148). Also available on the World Wide Web.

Biomimetic synthesis is the branch of synthetic organic chemistry which attempts to learn from nature into order to solve the challenges of chemical synthesis. This thesis describes application of biomimetic principles to the total synthesis of three phenylethanoid alkaloid natural products: incargranine B; millingtonine and incargranine A. Chapter 1 provides a general introduction to the area. Specific introductions can be found at the start of each chapter. Chapter 1 introduces the concept of biomimicry and provides a brief overview of the development of the underlying concepts and terminology. The major biosynthetic pathways involved in the production of incargranine B, millingtonine and incargranine A (shikimic acid, ornithine alkaloids) are also introduced. Chapter 2 discusses the synthesis of incargranine B. Biosynthetic analysis of this dimeric alkaloid led us to question its structural assignment and suggest a structural revision. This speculative reassignment was validated through a biomimetic total synthesis of our proposed structure. Incargranine B was successfully prepared in a longest linear sequence of six steps, forming three new rings, four bonds and three contiguous stereocentres in a single biomimetic domino condensation/Mannich/SEAr sequence. Chapter 3 describes the synthesis of millingtonine. We proposed that millingtonine is biosynthetically related to incargranine B through a divergent/re-convergent network of pathways. Synthetic exploration of this hypothesis culminated in the total synthesis of millingtonine and discovery of an unanticipated biosynthetic intermediate, dia-millingtonine, which we propose as a previously unidentified natural product. . Chapter 4 details the synthesis of incargranine A. Incorporating dia-millingtonine into our biosynthetic hypothesis allowed the development of a four step bioimimetic total syntheses of incargranine A which was scaled-up to provide over one gram of natural product. Chapter 5 summarises the work presented and provides a perspective on its contribution to the field.

Resumo: Este trabalho relata o estudo dos constituintes químicos de quatro espécies do gênero Casearia, bem como a avaliação das atividades antioxidante, anticolinesterásica, antifúngica e citotóxica de extratos e substâncias isoladas. O estudo da constituição química de C. gossypiosperma resultou no isolamento de três substâncias do extrato etanólico das folhas, sendo dois flavonóides: (+)-taxifolina (1) e quercetina (3) e um novo ciclitol: rel-(2R, 3S, 4R, 5R)-3,4,5-trihidroxi-2-etóxi- ciclohexanona (2). A partir do extrato hexânico das folhas de C. obliqua isolou-se quatro substâncias: o esteróide sitosterol (4) e três diterpenos clerodânicos: (rel)-2- benzoato-6-hidroxizuelanina + (rel)-6-benzoato-2-hidroxizuelanina (5+6) e 6- cinamato-2-hidroxizuelanina (7). Da fase etérea oriunda do extrato etanólico dos galhos foram isoladas cinco substâncias, sendo dois diterpenos clerodânicos inéditos: caseobliquina A (8) e caseobliquina B (9), um ácido fenólico simples: ácido cinâmico (10) e duas amidas: N-trans-p-cumaroiltiramina (11) e N-trans- feruloiltiramina (12). De C. rupestris foram isolados, a partir do extrato hexânico das folhas, quatro substâncias, sendo uma mistura de esteróide e diterpeno: sitosterol + E-fitol (4+13) e dois novos diterpenos clerodânicos, a casearupestrina B (16) e a casearupestrina D (18) e da fase hexânica do extrato EtOH das folhas foi isolado o diterpeno E-fitol (13). A partir da fase etérea também deste mesmo extrato foram isolados cinco diterpenos clerodânicos inéditos, as casearupestrinas A, B, C, D e G (14-18). A partir da casearupestrina A (14) e D (18) foram obtidos, por acetilação, mais dois diterpenos inéditos, as casearupestrinas E (14a) e F (18a), respectivamente. De C. decandra foi isolada a hidroquinona (19) a partir das fases hexânica, acetato de etila e hidroalcoólica, todas obtidas do extrato ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract:This work describes the study of the chemical constituents from four Casearia species, as well as the evaluation of antioxidant, anticholinesterasic, antifungal, and cytotoxic activities of extracts and the isolated chemical contituents. The study of the chemical constituents of C. gossypiosperma resulted in the isolation of three substances from ethanolic extract of the leaves, two flavonoids: (+)-taxifolin (1) and quercetin (3), and a new ciclitol: rel-(2R, 3S, 4R, 5R)-3,4,5-trihydroxy-2-ethoxy- cyclohexanone (2). From hexane extract of the leaves from C. obliqua were isolated four substances, the steroid sitosterol (4) and three clerodane diterpenes: (rel)-6- hydroxyzuelanin-2-benzoate + (rel)-2-hydroxyzuelanin-6-benzoate (5+6) and 2- hydroxyzuelanin-6-cinnamate (7). From ether phase obtained of the ethanolic extract from twigs of C. obliqua were isolated five substances, two new clerodane diterpenes: caseobliquin A (8) and caseobliquin B (9), one phenolic acid: cinnamic acid (10) and two amides: N-trans-p-coumaroyltyramine (11) and N-trans- feruloyltyramine (12). In C. rupestris four substances were isolated from hexane extract of leaves a mixture of a steroid and diterpene: sitosterol+E-phytol (4+13) and two new clerodane diterpenes: casearupestrin B (16) and casearupestrin D (18) and from hexane phase was isolated the diterpene E-phytol (13). Other five new clerodane diterpenes were isolated from ether phase obtained from ethanolic extract of leaves: casearupestrin A, B, C, D, and G (14-18). By acetylation, more two new clerodane diterpenes casearupestrin E (14a) and F (18a) were obtained from casearupestrin A (14) and D (18), respectively. From C. decandra was isolated the hidroquinon (19) of the hexane, ethyl acetate, and hydroalcoholic phases, every phases obtained from ethanolic extract of leaves. The structures of isolated compounds were determined by ... (Complete abstract click electronic access below) / Orientador: Alberto José Cavalheiro / Coorientador: Nivaldo Boralle / Banca: Isabele Rodrigues Nascimento / Banca: Antonio Gilberto Ferreira / Banca: Maria das Graças Lins Brandão / Banca: Mariana Helena Chaves / Doutor