Part one of this two-part thesis describes my efforts toward the total syntheses of the complex polycyclic alkaloids himeradine A and fastigiatine, which are members of the Lycopodium family of natural products. A cascade reaction sequence featuring a biosynthesis-inspired transannular Mannich reaction was planned to construct the strained and densely functionalized pentacyclic cores of the molecules from acyclic starting materials. After difficulties were encountered in a first-generation synthesis plan toward himeradine A, a second-generation synthesis plan was eventually successful in accomplishing the first total synthesis of fastigiatine via a formal [3+3]-cycloaddition reaction and a retro-aldol tandem transannular Mannich reaction sequence. In part two of this thesis, syntheses of the hibarimicin aglycons, including HMP-Y1, atrop-HMP-Y1, hibarimicinone, atrop-hibarimicinone, and HMP-P1, are reported. These natural products are amongst the largest and most complex type-II polyketides isolated. A novel benzylic fluoride Michael-Claisen reaction sequence was developed to construct the complete carbon skeleton of HMP-Y1 and atrop-HMP-Y1 via a symmetrical bidirectional double annulation reaction. Through efforts to convert HMP-Y1 derivatives to hibarimicinone and HMP-P1, a biomimetic mono-oxidation to desymmetrize protected HMP-Y1 was realized. A bidirectional unsymmetrical double annulation and biomimetic etherification were developed to construct the polycyclic and highly-oxidized skeleton of hibarimicinone, atrop-hibarimicinone, and HMP-P1. Lastly, a pH-dependent rotational barrier about the C2-C2' bond of hibarimicinone was discovered, which provides valuable information for achieving the syntheses of the glycosylated congeners of hibarimicinone. / Chemistry and Chemical Biology

A stereoselective approach toward the synthesis of 8-methyl-pyridoxatin using an intramolecular carbolithiation strategy is discussed. Model studies have proven this approach is not feasible for the synthesis of 8-methyl-pyridoxatin. / text

No description available.

The project focused on the isolation, characterization and synthesis of secondary metabolites of Gunnera perpensa L. (Gunneraceae), a South African medicinal plant used by many South African women to induce or augment labour and as an antenatal medication to tone the uterus. From the methanol extracts of the rhizomes we have isolated the compounds Z-venusol, methyl lespedezate, 4-6>-/?-D-glucopyranosyl-3,3',4'-tri-0- methylellagic acid and punicallagin. Structural elucidation of the compounds was performed using NMR spectroscopy. The presence of ellagic acid derivatives and hydrolysable tannins have not previously been reported from the family Gunneraceae. The study also focuses on the development of an HPLC analytical method to fingerprint the crude extracts of G perpensa. This method was used to determine the chemical composition of the rhizomes of the G. perpensa collected in different parts of South Africa. It is clear from the HPLC study that the rhizomes contain large concentrations of the hydrolysable tannin punicalagin and the second most abundant metabolite was Z-venusol. However, it was observed from plants collected in different regions that the ratio between punicalagin and Z-venusol differs substantially in the different extracts. An ellagic acid derivative isolated from G. perpensa contains a biaryl structure derived from gallic acid. The synthesis described in this thesis focused on reaction methods to access unsymmetrical biaryls and two synthetic routes were investigated - one that relies on the Ullmann reaction and the second that uses the Heck coupling reaction. Success of this coupling reaction towards the formation of ellagic acid derivatives was accomplished by the Heck coupling reaction method. One of the most important considerations towards the synthesis was the manipulation of hydroxyl groups of gallic acid by selective protection reactions that provide entry to the aforementioned preparation of unsymmetrical ellagic acid derivatives. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

The work undertaken explored the potential for discovery of new bioactive metabolites from soil fungi. The research developed selective mycological isolation techniques and maximised metabolite production from active selected fungi by application of the OSMAC approach and concept of hormesis. Novel active compounds were discovered and many other known compounds characterised.

Macrocyclization is a synthetically challenging step in the total synthesis of natural products. The success of chemical approaches such as the Corey-Nicolaou, Yamaguchi and Keck macrolactonization is heavily based on the confirmation and stereochemistry of the substrate. While there have been some advances in computational modeling, it has been difficult to predict whether the above-mentioned reactions will work. We have begun characterizing polyketide thioesterase catalytic activity and substrate tolerance to find more efficient and dependable routes towards macrolactonization and macrolactamization.

This work can be separated into two parts; the first will encompass chapters one and two, which discuss the use of the Catellani reaction to access different heterocycles. The second part will encompass the remaining chapters and deals with stereoselective reactions of arynes. Chapter one outlines the development of a general and high yielding synthesis of the phenanthridine nucleus via a palladium-catalyzed domino reaction of aryl iodides with N-H or N-trimethylsilyl imines. This strategy was applied in a succinct synthesis of benzo[c]phenanthridine alkaloids nitidine and NK109. Chapter two details the development of a Catellani-type reaction of aryl iodides with 2H-azirines. Conditions were found to selectively provide access to either the indole nucleus or unusual dihydroimidazoles. The yields of the products ranged from moderate to good, however, the success of the reaction is highly dependent on the structure of the 2H-azirine. A mechanism was proposed involving oxidative addition of the azirine to generate an azaalyl intermediate. In Chapter three the foray into the area of aryne chemistry begins. A stereoselective nickel- catalyzed [2+2+2] cycloaddition of 1,6-enynes with aryne intermediates was developed. Attempts were made at the development of an asymmetric variant of the reaction, however, only low enantiomeric excess was observed. Good diastereoselectivity could be obtained when an allylic substituent was present. The yields of the products ranged from moderate to excellent. However, the yields vary greatly and in a number of cases the reactions were unsuccessful. Finally, in chapter four the development of a general and high yielding annulation strategy for the synthesis of various carbo- and heterocycles, based on an intramolecular aryne ene reaction is described. It was found that the geometry of the olefin is crucial to the success of the reaction and it that regioselective hydrogen migration occurs. Furthermore, the electronic nature of the aryne was found to be important to the success of the reaction. Deuterium labeling studies and DFT calculations provided insight into the reaction mechanism. The data suggested a concerted asynchronous transition state, resembling a nucleophilic attack on the aryne. This strategy was successfully applied to the formal synthesis of the ethanophenanthridine alkaloid (±)-crinine. In a similar vein, preliminary results demonstrating an intramolecular, formal [2+2] cycloaddition of an aryne with an S, O-ketene acetal to give interesting tricyclic benzocyclobutene products are disclosed.

The Kingston group's engagement in an International Cooperative Biodiversity Group (ICBG) program and a collaborative research project established between Virginia Tech and the Institute for Hepatitis and Virus Research (IHVR) has focused on the search for bioactive natural products from tropical forests in both Madagascar and South Africa. As a part of this research, a total of four antiproliferative extracts were studied, leading to the isolation of fourteen novel compounds with antiproliferative activity against the A2780 human ovarian cancer line. One extract with antimalarial activity was studied, which led to the isolation of two new natural products with antiplasmodial activity against a drug-resistant Dd2 strain of Plasmodium falciparum. The plants and their secondary metabolites are discussed in the following order: two new antiproliferative acetogenins from a Uvaria sp. (Annonaceae); two new antiproliferative calamenene-type sesquiterpenoids from Sterculia tavia (Malvaceae); two new antiproliferative triterpene saponins from Nematostylis anthophylla (Rubiaceae); six new antiproliferative homoisoflavonoids and two new bufatrienolides from Urginea depressa (Asparagaceae); and two new antiplasmodial anthraquinones from Kniphofia ensifolia (Asphodelaceae). The structures of all these compounds were determined by analysis of their mass spectrometric, 1D and 2D NMR, UV and IR spectroscopic and optical rotation data. Other than structural elucidation, this work also involved bioactivity evaluations of all the isolates, as well as total synthesis of the two antiproliferative sesquiterpenoids, and a structure-activity relationship (SAR) studies on the antiplasmodial anthroquinones. / Ph. D.

This thesis describes the first total synthesis of ancistrotanzanine A, a member of the naphthylisoquinoline class of natural products. In Chapter 1 the synthetic challenges presented by the naphthylisoquinoline alkaloids are discussed and strategies that have been adopted in previous syntheses of naphthylisoquinoline alkaloids overviewed. Chapter 2 describes the preparation of the key 5,3'-biaryl linkage via the Pinhey-Barton reaction. Studies into forming the linkage atropselectively were investigated using chiral hydrobenzoin acetal auxiliaries. This was found to have limited success with an atropisomeric ratio of 65:35 obtained. Changing the base from the achiral pyridine to the chiral brucine was also investigated and found to give no enhancement in the diastereoselectivity. From the results presented in Chapter 2, it was concluded that hydrobenzoin acetal auxiliaries were not appropriate for the diastereoselective synthesis of the key biaryl linkage of ancistrotanzanine A. As the chiral acetal strategy outlined in Chapter 2 failed to yield an atropselective process, efforts were re-focused on a new approach to the naphthylisoquinolines. In Chapter 3, an overview of all the methods available for the synthesis of chiral 3,4-dihydroisoquinolines is provided. From this, it was decided to apply the alkylation of o-tolylnitriles with chiral sulfinimines, as originally developed by Davis, to the synthesis of naphthylisoquinolines. Synthesis of the o-tolylnitrile lead reagent was readily achieved, but it was found that the amount of lead tetraacetate had to be carefully controlled to avoid side-reactions in the Pinhey-Barton reaction. After careful optimisation, the key 5,3'-biaryl linkage was prepared in high yield. Application of the Davis methodology to the MOM protected biaryl failed, with no reaction resulting. After much experimentation, it was established that the reaction was very sensitive to steric hindrance. A successful reaction was finally achieved by changing the base to lithium diethylamide. However, it was found the diastereoselection of the alkylation was quite low when p-tolyl sulfinimine was used. The use of the t-butane sulfinimine meant that the diastereoselection was significantly improved, with a ratio of 85:15 being obtained. After 3 more steps, the total synthesis was completed and ancistrotanzanine A was obtained, as a 1:1 mixture of atropisomers. Efforts to separate the atropisomers formed failed and even the use of chiral HPLC failed to resolve the material. To complete the Chapter, two analogues of ancistrotanzanine A were prepared – the tetrahydroisoquinoline and the methoxy ether. Chapter 4 summarises the above results and discusses the future potential of this research. / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2010

In this thesis, synthetic chemistry was used as a tool in the exploration of various aspects of natural products discovered by the natural products research group at the University of Canterbury. Work on the constituent amino acids and connectivity of the pteratides, a potently cytotoxic series of cyclodepsipeptides, had been completed before the beginning of this work (carried out by Miss C. Chen). The elucidation of the stereochemistry of the constituent amino acids was undertaken in this present work. The synthesis of all stereochemical entities of a number of unusual amino acids, which were either not available commercially or were expensive, was carried out, providing reference materials for comparison to the natural products. The synthesis of the diastereoisomers of one of these amino acids, 4-methylproline, was carried out by modification of literature procedures, which led to the development of an improved, concise and stereoselective synthesis. The hydrolysis of the natural products, derivatisation of the resultant hydrolysates, synthetic and commercial reference amino acids and HPLC analysis allowed the full stereochemical assignment of the pteratide series. The total synthesis of spiro-mamakone A, a cytotoxic polyketide isolated by Dr S. van der Sar, was undertaken. The synthesis was not successfully completed due to difficulties in the late-stage formation of a crucial enedione motif. However, very advanced intermediates were successfully synthesised. These synthetic analogues of the natural product were analysed for biological activity, allowing valuable insight into the structure-activity relationship, for example, demonstrating the importance of the enedione moiety to biological activity.