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1
Liu, Yunqi. "Synthetic approaches toward natural product synthesis." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187050.
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1,2-Dithiolan-3-one-1-oxide exists in antihumor antibiotic leinamycin and can cause DNA cleavage in the presence of thiols. Diastereoselective synthesis of this unique ring system has been achieved by low temperature oxidation of the corresponding 1,2-dithiolan-3-ones with 3,3-dimethyldioxirane. 5-Methyl-1,2-dithiolan-3-one-1-oxides were synthesized by oxidation of 5-methyl-1,2-dithiolan-3-one with 3,3-dimethyldioxirane. Eu(fod)₃ and C₆D₆ induced proton chemical shift studies showed that the major isomer in the product has a trans sulfoxide relative to the 5-methyl group. Low temperature oxidation of 4-substituted-amino-5,5-dimethyl-1,2-dithiolan-3-ones by 3,3-dimethyldioxirane preferentially led to the corresponding trans-1,2-dithiolan-3-one-1-oxides. This assignment was made on the basis of a X-ray crystallographic structure study. Formation of azlactones as well as 1,2-dithiolan-3-one-1,1-dioxide were also observed when some substituted 1,2-dithiolan-3-ones were oxidized by 3,3-ditnethyldioxirane. Three 2,2-dimethyl-1,3-dithian-4-ones were synthesized by SnCl₄ mediated condensation of β-mercaptothioacids and acetone. Oxidation of 2,2,6-trimethyl-1,3-dithian-4-one with Ce(IV) did not give 1,2-dithiolan-3-one or 1,2-dithiolan-3-one-1-oxides as anticipated; 1,3-dithian-5-en-4-one was detected as the product instead. Synthetic approaches toward loline were explored. Intramolecular photoaddition of bicyclic olefinic N-nitrosamine did not give the desired product. An epoxide approach did not furnish loline due to unsuccessful epoxide ring opening by azide ion. In the urea approach, the tertiary nitrogen of the bicyclic urea preferentially undergoes a transannular iodocyclization. The same results were obtained by halocyclizing bis-silylimidate or mono-silylimidate of the bicyclic urea.
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Li, I. C. K. "Natural product syntheses." Thesis, University of Southampton, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375675.
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Vollmer, Heidi R. "Biologically active natural product synthesis." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365780.
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Merifield, Eric. "Aspects of natural product synthesis." Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258148.
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Longbottom, Deborah Anne. "Polyenoyltetramic acid natural product synthesis." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620206.
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Hunter, Ruth F. "Benzynes in natural product synthesis." Thesis, University of Manchester, 1989. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.655226.
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Foot, Jonathan Stuart. "New synthetic methodology and antiviral natural product synthesis." Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412621.
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Thite, Aniket Mohan. "Direct approaches toward natural product synthesis." [Ames, Iowa : Iowa State University], 2007.
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Sperry, Jonathan. "Biomimetic oxidations in natural product synthesis." Thesis, University of Exeter, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425500.
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Hinks, Jeremy David. "Metal carbenes in natural product synthesis." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393940.
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Elsworth, Jon D. "Prins cyclisations in natural product synthesis." Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445810.
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O'Neil, Ian Anthony. "Novel methods in natural product synthesis." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38124.
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Bolton, R. E. "Azide decomposition in natural product synthesis." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37947.
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Durbin, Matthew J. "Palladium catalysis for natural product synthesis." Thesis, University of Bath, 2007. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519010.
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This thesis details investigations towards the total synthesis of the naturally occurring alkaloid hodgkinsine, utilising palladium catalysis to achieve desymmetrisation of a meso-chimonanthine derivative. Initially, a Suzuki cross-coupling approach was envisaged. Meso-chimonanthine is functionalised as its C-7 bisiodide derivative by directed ortho-lithiation. Suitable electrophiles are screened for the successful preparation of additional bisbromide and bistriflate derivatives to broaden the scope of the cross-coupling. The synthesis of a suitable indole-3-boronic ester coupling partner is also achieved. Investigations into the post-Suzuki coupling elaboration of the indole moiety were conducted with model substrates to assess the viability of a proposed alkylation-cyclisation procedure. C-3 alkylation of various N-protected C-3 phenylindole derivatives was unsuccessful when employing aziridines, sulfamidites and sulfamidates as electrophilic two carbon fragments. Therefore a second generation boronic ester with latent enolate functionality for increased nucleophilicity was prepared in six high yielding steps from oxindole, via trapping 3-bromo-N-BOC-oxindole as the TIPS enol ether and subsequent C-3 palladium catalysed borylation. The Suzuki coupling of the new boronic ester with meso-chimonanthine derivatives was shown to be unsuccessful in a broad range of anhydrous and aqueous solvent systems. Palladium catalysts, ligands, bases and measures to reduce steric interactions were all screened in an attempt to achieve coupling. Subsequently the palladium catalysed arylation of N-protected oxindole enolates is developed; aryl bromides, chlorides and triflates are all suitable coupling partners, whilst a broad range of ortho, meta and para functionalised arenes are well tolerated providing C-3 aryl oxindoles in high yield. Extension of this methodology to a C-7 bisbromo meso-chimonanthine substrate was successful, furnishing the desymmetrised product under racemic conditions in 45% yield with the dicoupled product also observed in 20% yield.
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Rodger, Robert. "Fused ring systems in natural product synthesis." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/27645.
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On the instigation of A/Prof C. S. P. McErlean I investigated the rapid synthesis of fused ring compounds by a key polyene cyclisation.
Chapter 1 sets the scene by highlighting deficiencies in literature syntheses of selected fused-ring compounds, where synthetic strategies are often suboptimal. In particular, the scarcity of reported syntheses involving a direct cyclisation method is noted.
Chapter 2 discusses the taiwaniaquinoids and previous synthetic approaches including McErlean group efforts which delivered the non-natural stereochemistry. A method to produce the desired trans stereochemistry of ()-taiwaniaquinone G was developed. Attempts to apply this methodology to a divergent synthesis of the taiwaniaquinoids are detailed.
Chapter 3 extends this strategy to the attempted synthesis of compounds with a greater number of rings: the dasyscyphins, pelorol, atomarianone B and disidein. The successful partial cyclisation and subsequent full cyclisation of two farnesylarenes was reported. Larger architectures remain an elusive goal.
Chapter 4 discusses efforts in the synthesis of a different class of fused-ring compounds: the marine polycyclic ethers. The application of newer methodologies to the synthesis of the polycyclic ethers is described, however this did not lead to a viable strategy to these compounds.
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Catterick, David. "The parallel synthesis of natural product families." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299756.
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Gallagher, Oliver Paul. "Structure and synthesis in natural product chemistry /." [St. Lucia, Qld. : s.n.], 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16653.pdf.
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Torssell, Staffan. "Stereoselective Synthesis of Amino Alcohols : Applications to Natural Product Synthesis." Doctoral thesis, Stockholm : Kemi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4472.
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Yu, Miao. "Stereoselective Olefin Metathesis Reactions for Natural Product Synthesis." Thesis, Boston College, 2014. http://hdl.handle.net/2345/3861.
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Thesis advisor: Amir H. HoveydaChapter 1. The first examples of highly Z- and enantioselective ring-opening/cross-metathesis reactions are disclosed. Transformations involve meso cyclic olefin substrate and styrenes or enol ethers as olefin cross partners. A stereogenic-at-Mo monoaryloxide monopyrrolide (MAP) complex, prepared and used in situ, is discovered for the efficient formation of Z olefins. Such complex, bearing a relatively smaller adamantylimido and a larger chiral aryloxide ligand, leads to kinetic Z-selectivity due to the size differential. In most cases, the resulting disubstituted Z olefins are formed with excellent stereoselectivity (>95% Z). Chapter 2. The protocols for efficient Z-selective formation of macrocyclic disubstituted alkenes through catalytic ring-closing metathesis (RCM) is described. Stereoselective cyclizations are performed with either Mo- or W-based monoaryloxide monopyrrolide (MAP) complex at 22 oC. Synthetic utility of such broadly applicable transformation is demonstrated by synthesis of several macrocyclic natural products: relatively simpler molecules such as epilachnene (91% Z) and ambrettolide (91% Z), as well as advanced precursors to epothilones C and A (97% Z) and nakadomarin A (94% Z). Several principles of catalytic stereoselective olefin metathesis reactions are summarized based on the studies: 1) Mo-based catalysts are capable of delivering high activity but can be more prone to post-RCM isomerization. 2) W-based catalysts, though furnish lower activity, are less likely to cause the loss of kinetic Z selectivity by isomerization. 3) Reaction time is critical for retaining the stereoselectivity gained from kinetic, which not only applicable with MAP complexes but potentially with other complexes as well. 4) By using W-based catalyst, polycyclic alkenes can be accessed with sequential RCM reactions, without significant erosion of the existing Z olefins in the molecule. Chapter 3. An enantioselective total synthesis of anti-proliferative agent (+)-neopeltolide is presented. The total synthesis is accomplished in 11 steps for the longest linear sequence and 28 steps in total, including 8 catalytic reactions. Particularly, several Mo- or Ru-catalyzed stereoselective olefin metathesis reactions as well as N-hetereocyclic carbene (NHC)-catalyzed enantioselective boron conjugate addition to an acyclic enoate have proven to be effective for convergent construction of the molecule. The most important novelty of the study incorporates the explorations of feasibility of Z-selective cross-metathesis reactions to solve the challenge of installing two Z olefins with excellent selectivity
Thesis (PhD) — Boston College, 2014
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Yu, Elsie. "Catalytic Stereoselective Olefin Metathesis for Natural Product Synthesis." Thesis, Boston College, 2018. http://hdl.handle.net/2345/bc-ir:107714.
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Thesis advisor: Amir H. HoveydaChapter 1. Efficient Z-Selective Synthesis of Allylic- and Alkenyl Boronates by Catalytic Cross-Metathesis Efficient Z-selective cross-metathesis reactions to furnish Z-(pinacolato)-allylboron and Z-(pinacolato)alkenylboron compounds through catalytic cross-metathesis are disclosed. Z-allylic boron compounds are generated by the use of catalytic amounts of a W-based monoaryloxide monopyrrolide (MAP) complex in up to 91% yield and 96:4 dr after allylation to benzaldehyde. Alkenylboron compounds are prepared in high yields and high Z selectivity in up to 93% yield and 97:3 Z:E. Cross-metathesis reactions with 1,3-dienes and aryl olefins are efficient and highly Z-selective. Combination of cross-metathesis and cross-coupling to synthesize anticancer agent combretastatin A-4 highlights the utility of this approach. Chapter 2. Synthesis of Macrocyclic and Acyclic Z-Enoates and (E,Z) or (Z,E) Dienoates by Catalytic Cross-Metathesis The first examples of kinetically controlled catalytic olefin metathesis reactions to generate Z-α,β-unsaturated macrocyclic and acyclic esters are disclosed. The synthesis of (E,Z) or (Z,E)-dienoates are also presented. Reactions promoted by 3.0–10 mol % of Mo-based monoaryloxide monopyrrolide complex proceed to completion to the desired macrocycles within 2–6 h at room temperature. Macrocycles of diverse ring sizes are formed in 79:21 to >98:2 Z:E selectivity. Pure Z isomers can be obtained after purification in up to 75% yield. Acyclic Z-α,β-unsaturated esters are prepared in the presence of acetonitrile to avoid using excess amounts of the more valuable cross-partner substrate. Spectroscopic investigations and X-ray analysis rationalize the positive effect of acetonitrile in the reaction system. Linear (Z)-enoates are generated in up to 71% yield and up to >98:2 Z:E. (E,Z)-Dienoates are generated with high Z selectivity as well. The utility of the ring-closing metathesis and cross-metathesis is highlighted by the synthesis of an (+)-aspicilin precursor and the C1–C12 fragment of biologically active natural product (–)-laulimalide. Chapter 3. Application of E-Selective Catalytic Ring-Closing Metathesis in the Total Synthesis of Dolabelides A, B, C and D Efforts towards the enantioselective synthesis of the dolabelide family of anti-cancer macrolides is presented. Development of a total synthesis incorporating a late-stage kinetically E-selective RCM is illustrated. Previous attempts to synthesize the macrolide by ring-closing metathesis (RCM) have demonstrated poor efficiency and low selectivity for the E isomer. Methodology developed in our group with acyclic trisubstituted cross-metathesis demonstrates that high selectivity can be achieved with stereodefined 1,2-disubstituted and trisubstituted olefins by the use of the proper catalyst and reaction design. Modern catalytic and stereoselective approaches towards the two main fragments of dolabelide are presented. More efficient and concise routes will be pursued to highlight the utility of the proposed disconnections and practicality of the total synthesis
Thesis (PhD) — Boston College, 2018
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Hutchinson, John Howard. "The use of camphor in natural product synthesis." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25830.
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(+)-9,10-Dibromocamphor 3̲7̲, prepared in three steps from (+)-3-e̲n̲d̲o̲-bromocamphor 1̲5̲a̲, was found to undergo facile ring cleavage to provide the cyclopentanoid ring systems 1̲5̲8̲, 1̲5̲9̲ and 1̲6̲1̲. The bromoacid 1̲5̲9̲ was readily lactonised to provide 1̲6̲0̲ in high yield.
The hydroxyacid 1̲6̲1̲ was converted into the hydrindenone 1̲9̲0̲ in three steps and a further six steps were required to complete the total enantiospecific synthesis of (-)-estrone e̲n̲t̲4̲1̲.
Studies directed toward the synthesis of vitamin D₃ (2̲1̲3̲) and metabolites have shown that diastereoselective alkylation of lactone 1̲6̲0̲ and ester 2̲8̲3̲ (derived from 1̲6̲1̲) can be accomplished in high yield and with almost complete stereoselectivity. As a result, diol 3̲2̲2̲, representing the structural sub-unit of ring D and side chain of vitamin D₃, has been synthesised.
Ring cleavage of the bromoketone 3̲5̲0̲ (derived from 1̲5̲9̲) gave 3̲5̲2̲ which was transformed into the aldehyde 3̲3̲2̲ and the trienols 3̲4̲0̲a̲ and 3̲4̲0̲b̲ to complete a formal synthesis of 3̲2̲7̲a̲, one of the components of the California Red Scale pheromone.
Methylation of camphor 1̲0̲ yielded the 3-e̲x̲o̲-methyI derivative 3̲6̲2̲b̲ as the major product. The thermodynamically most stable epimer was found to be 3-e̲n̲d̲o̲-methylcamphor 3̲6̲2̲a̲. In contrast, 3-methylcamphor 3̲6̲2̲a.̲b̲ undergoes preferential endo alkylation. The factors governing these results are discussed. (+)-3- e̲n̲d̲o̲-Bromocamphor 1̲5̲a̲ and (+)-3- e̲n̲d̲o̲-9-dibromocamphor 1̲8̲a̲ were found to rearrange to provide (-)-6- e̲n̲d̲o̲-bromocamphor 1̲7̲2̲ and (-)-6- e̲n̲d̲o̲-9-dibromocamphor 2̲6̲. Dehalogenation of 1̲7̲2̲ provided optically pure (-)-camphor e̲n̲t̲1̲0̲ while dehydrohalogenation gave (+)-5,6-dehydrocamphor 1̲7̲3̲.[formula omitted]Science, Faculty of
Chemistry, Department of
Graduate
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Nodwell, Matthew B. "Synthesis of biologically active marine natural product analogues." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/25745.
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Natural products have long been a source of inspiration for many drugs in human use. The Andersen lab examines compounds from marine sources that can be used as lead structures for drug discovery. Synthetic studies, structure-activity relationships (SAR) and biological findings of two such compounds are described in this thesis.
The first is pelorol, a meroterpene isolated from a tropical sponge Dactylospongia elegans. Pelorol is a small molecule activator of SHIP 1, a phosphatase that is a negative regulator of the P13K pathway in hematopoetic cells. Using a synthetic route from a previous co-worker, Lu Yang, a series of SHIP 1 activating compounds based on pelorol were synthesized. These compounds were evaluated for selectivity, potency, and efficacy in a series of biological studies, leading to the discovery of 2.27 as a preclinical lead compound. Water-soluble prodrugs of the SHIP 1-activating compounds were also synthesized and their properties reported.
The second compound examined is ceratamine A, an alkaloid isolated from the sponge Pseudoceratina sp. from Papua New Guinea. Ceratamines A and B are microtubule stabilizing antimitotic agents that may be useful in cancer chemotherapy. The core imidazo[4,5,d]azepine heterocycle of the ceratamines has no precedent among known synthetic or natural compounds. The relatively simple structure of the ceratamines and the novel antimitotic phenotype they generate makes them attractive targets. Desbromo ceratamine A (3.44) was synthesized by an efficient and scaleable route, confirming the structure of ceratamine A and validating the biological activity of the core pharmacophore. Synthetic efforts towards ceratamine A were ultimately thwarted by the inability to install the bromine atoms present in the natural product. A significant finding is that the bromine atoms in ceratamine A contribute significantly to the antimitotic potency of the compound necessitating a bioisosteric approach to more potent antimitotic ceratamine-based agents.
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Flasz, Jakub Tadeusz. "Total synthesis of the antitumour natural product, (-)- echinosporin." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601477.
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The following dissertation describes a collection of results that led to a successful formal total synthesis of a naturally-occurring antitumour antibiotic, (-)..echinosporin. To achieve that, various synthetic strategies were developed and examined, all of which relied on a cycloadditive event as a key step to prepare the [3.4.0J-bicyclic framework of (-)-echinosporin. The synthesis was eventually accomplished using the Padwa [3+2] cycloaddition-elimination of allenylphenylsulphone to a chiral sugar enone 6 as a key transformation. it provided the first recorded example of this reaction used in complex natural product total synthesis. Following a series of functional group interconversions on this cycloadduct, a mild new method for the C-carboxyalkylation of bromomagnesium ketone enolates was applied to install the C(11)~carboxylic group of (-)- echinosporin. The quaternary OH-bearing stereocentre was introduced via a substrate~directed osmylative dihydroxylation on a i3-keto ester enol 71 . The resulting ketone 77 was advanced into 70 via Barton deoxygenation. Following that, the crucial C(8)-C(9) unsaturation was introduced starting from the ketone 70 through a three-step sequence based on the Barton vinyl iodide synthesis and Pd(O)-mediated dehalogenation. Next, a TEMPO-based oxidation was used to bring the C(10)- position to a correct oxidation state. Following protection as the allyl ester, an E1cb silyloxy elimination installed the remaining C(4)-C(5) unsaturation. The allyl ester 90 was finally transformed into a primary amide and the C-2 ethyl glycoside was chemoselectively hydrolysed using aqueous HBF4 to reveal Smith's intermediate 1.
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Barry, Conor. "Clavosolide A : Prins cyclisation in natural product synthesis." Thesis, University of Bristol, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413614.
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Giampa, Geoffrey. "Investigations Into Carbon Nanotube And Natural Product Synthesis." ScholarWorks @ UVM, 2016. http://scholarworks.uvm.edu/graddis/552.
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This dissertation describes research into the synthesis of carbon nanotubes using traditional organic synthetic methods, as well as work on the fragmentation of β-hydroxy-α-diazoesters with a γ-hetero group and applications of their reactivity towards natural product synthesis.
Carbon nanotubes are unique structures that can exhibit different electronic properties based on their chiral vector, and are a potential future source of semiconductors. Current methods of synthesis are unable to be adapted to commercial synthesis, providing the opportunity for the application of organic synthetic methods to generate them more uniformly and on a larger scale.
The generation of tethered aldehyde ynoates and their utilization in 1,3-dipolar cycloadditions has been well developed by the Brewer group. Traditionally they have been generated from γ-siloxy-β-hydroxy-α-diazoesters, herein we explore utilizing an amino group as the fragmentation initializer. Additionally, application of the tethered aldehyde ynoate towards the synthesis of the natural products Demissidine and Aspidospermine are discussed.
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Källström, Jan Eddy Adolf. "Synthesis studies towards daphlongeranine B." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:638685a8-da64-488b-b65d-ba9a2111d4fb.
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This thesis describes the development of a synthetic route towards daphlongeranine B, an alkaloid isolated from the fruits of Daphniphyllum longeracemosum, by utilising an intramolecular Michael addition to form its unique tricyclic core. Chapter 1 gives a general introduction to the family of Daphniphyllum alkaloids together with some recent examples, from the literature, illustrating some synthetic attempts towards structurally similar alkaloids. This chapter also features our retrosynthetic analysis of daphlongeranine B. Chapter 2 details the synthesis of the model spirocyclic enone 72 which was the vital building block needed to investigate the key intramolecular Michael addition. This key reaction was then successfully validated and access to the unique tricyclic core 64 of daphlongeranine B was made possible. Chapter 3 expands the scope of the key intramolecular Michael addition step. This chapter first describes a synthetic route to the Î2-substituted spirocyclic enone 112 and subsequently validates the key intramolecular Michael addition step to give the tricyclic core 138 of daphlongeranine B. Chapter 4 details a synthetic route towards the spirocyclic fragment 141 by utilising a Baker's yeast reduction and a tandem addition/cyclisation reaction.
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Pepper, Adrian Gordon. "Asymmetric synthesis using acyl-nitroso cycloadditions : applications to natural product synthesis." Thesis, University of Salford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314011.
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Sadler, Matthew James. "Diastereoselective synthesis of 2,4,5 trisubstituted piperidines : application in natural product synthesis." Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/2901/.
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This thesis describes the diastereoselective synthesis of 2,4,5-trisubstituted piperidines using carbonyl-ene and Prins cyclisations and their application in natural product synthesis. Following on from previous work in the group, we investigated how a preinstalled substituent in the 2-position can help to control the sense of induction at the two newly forming stereocentres. We utilised the Prins reaction in the formal synthesis of pseudodistomin F, a marine alkaloid that posses a 2,4,5-tribsubstituted piperidine core. An initial first generation synthesis focused on the construction of a cyclisation precursor containing a crotyl-ene component, however, cyclisation with anhydrous hydrogen chloride at -78 °C resulted in side product formation, presumably resulting from the relative instability of the secondary carbocation. Changing the ene component to a prenyl group resulted in successful cyclisation to yield the trans, cis-2,4,5-trisubstituted piperidine, with diastereomeric ratios of up to 200:1. An improved second generation synthesis completed the formal synthesis of pseudodistomin F on a multi-gram scale. Progress towards the total synthesis of pseudodistomin F by a third generation synthesis was undertaken. An investigation into how varying the electronics of the Prins reaction would alter the diastereoselectivity was conducted with a range of para-substituted cinnamyl substrates. The results indicated that selectivity in favour of the trans diastereomer was favoured as the electron withdrawing power of the substituent increased.
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Thomas, A. "The enantiospecific synthesis of natural product analogues from carbohydrates." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356073.
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Carter, Catherine Frances. "The application of flow chemistry to natural product synthesis." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610524.
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Lancefield, Christopher Stuart. "Using molecular oxygen in synthesis : applications in lignin valorisation and natural product synthesis." Thesis, University of St Andrews, 2015. http://hdl.handle.net/10023/6959.
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The first part of this thesis describes my research towards the valorisation of lignin. Due to environmental and political pressures, there has been a drive to start the transition from a fossil fuel based economy to a renewable based one. This will require the development of novel routes to renewable chemicals, one source of which may be the biopolymer lignin. Through the synthesis of advanced lignin model compounds, the chemistry of real lignin is explored. This work culminates in the development of a novel method for the depolymerisation of real lignin to simple mixtures of aromatic chemicals that could be useful building blocks for the chemical industry. One of the key steps in this process is the oxidation of the β-O-4 linkages in lignin using catalytic amounts of DDQ and molecular oxygen as the terminal oxidant. The second part of this thesis details the first synthesis of melohenine B and O-ethyl-14-epimelohenine B, two medium sized ring containing natural products. The key step in the synthesis of these natural products was the photo-sensitised oxidative cleavage of an indolic substrate by molecular oxygen. Additionally, the use of residual dipolar coupling (RDC) analysis for the conformational analysis of these molecules in solution has been explored. Finally, the absolute configurational assignment of the natural products was established and their biological activities investigated.
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Wallace, Stephen. "A cascade approach towards the gephyrotoxins." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:1f7b55ec-0346-498c-be03-81f3b9fde2f5.
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The aim of this project was to develop a cascade approach towards perhydropyrrolo-[1,2-a]-quinolines and to apply this to the asymmetric synthesis of the gephyrotoxin alkoids. Chapters Two and Three outline the development of a synthetic route towards a range of cascade precursors, whilst Chapter Four outlines investigations into the enamine-Michael cascade. Central to understanding the cascade process was the discovery that the major product of the enamine-Michael cascade was the unusual tricyclic hydroquinium salt. This can subsequently be engaged in a diastereoselective inter- or intramolecular reduction to afford either a trans-perhydro-[1,2-a]-quinoline or a tetracyclic aminal in high overall yield depending on the C1 oxygen substituent.
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Harsh, Philip R. "Applications of asymmetric allylation reactions towards natural product synthesis." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=6029.
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Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains vi, 78 p. : ill. Includes abstract. Includes bibliographical references (p. 37-38).
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Ghirardi, Elena. "Enantio- and Diastereoselective Cyclocondensation Reactions. Stereocontrolled Access to Azabicycles and Application to Natural Product Synthesis." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/398789.
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The first objective of this Thesis was the study of the preparation of octhydro-1H-cyclopenta[b]pyridines and octahydro-1H-indoles, through the synthesis of (R)-phenylglycinol derived tricyclic lactams. Following the previous reported methodology a carbon substituent would be present at the carbocyclic ring and we planned to find the conditions for controlling its absolute configuration. Unfortunately, the reaction of ketoester 4 and ketoacid 7, provided undesired enamines 8 and 9. On the other hand, the reaction of ketoacid derivatives 16 and 17 with (R)-phenylglycinol led to a mixture of epimeric amides 18.
With the aim to extend the methodology, we planned to study the cyclocondensation reaction of (R)-phenylglycinol and (1S, 2R)-aminoindanol with C-3 and C-5 substituted cyclohexanepropionate derivatives. These reactions provided enantiopure tricyclic or pentacyclic lactams: in every run, a major lactam was isolated or identified, and a minor one was detected. The use of (1S, 2R)-aminoindanol resulted in better results. These tricyclic and pentacyclic lactams are precursors of C-8 (and C-6,8) substituted cis-decahydroquinolines. The conversion required the stereoselective reductive cleavage of C-O oxazolidine bond with simultaneous reduction of lactam carbonyl group, and debenzylation. A library of enantiopure cis-decahydroquinolines was obtained. To illustrate the usefulness of our method, we decided to undertake the synthesis of some alkaloids of Myrioneuron nutans family, which contain an 8-substituted cis-decahydroquinoline core. In particular, we prepared the enantiopure alcohol 82, which was described to be a common intermediate in the synthesis of various Mirioneuron nutans alkaloids. Our synthetic procedure greatly improved the previous results reported for the synthesis of this alcohol.
The cyclocondensation reaction of (R)-phenylglycinol and (1S,2R)-aminoindanol with 3-alkyl-2-oxo-cyclohexane-1-acetate derivatives was finally considered. Reaction of (R)-phenylglycinol and 3-alkyl-2-oxocyclohexaneacetate derivatives 97-100 and 107 provided with high yield and stereoselectivity tricyclic lactams 110, 112a, 114, 116 and 118, which incorporate an alkyl or aryl substituent at C-10, while (1S,2R)-aminoindanol did not furnish so good outcomes. These reactions stereoselectively provided an additional minor hexahydroindole by-product. The absolute configuration of these compounds 111a, 113a, 115a and 117a was confirmed by X-ray crystallography. In the case of any or aryl substituent at C-10 of the tricyclic lactam, no by products were detected. We demonstrated that these unsaturated products derived from the opening of the oxazolidine ring of the minor lactams, which are epimers at C-10 of the major lactams, in the presence of acids. The stereoselective opening of the oxazolidine ring of the major lactams, in the presence of strong acids provided unsaturated compounds 111b, 113b, 115b and 117b, in which H-7 and H-7a resulted in cis relative disposition. In the case of lactam 118, with an aryl substituent at C-10, provided the unsaturated compound 125, in which H-7 and H-7a are in relative trans disposition. This different relative configuration can be accounted for by considering the structure rigidity of this system.
Major tricyclic lactams were converted into C-7 exo substituted cis-octahydroindoles and cis-octahydroindolones, by selection of the appropriate reductive conditions. Hexahydroindolones 111b, 113b, 115b and 117b were converted stereoselectively into the corresponding enantiopure C-7 endo substituted cis-octahydroindolones, by catalytic hydrogenation of the carbon-carbon double bond, followed by elimination of the chiral inductor through reaction with sodium radical. Moreover, these hexahydroindolones and 125 were transformed into the corresponding trans-octahydroindolones 146c-149c and 126b by simultaneous reduction and debenzylation in sodium ammonia. The presence of the amide function allowed the stereoselective insertion of a new substituent by a-alkylation and a-amidoalkylation.
Finally, in order to demonstrate the utility of this methodology, (+)-a-Lycorane was synthesized in only four steps, starting from easily available ketone 171, in 35% of overall yield, which resulted an improvement with respect to previously reported synthesis.El primer objetivo de esta Tesis Doctoral ha sido el estudio de la preparación de octahidro-1H-ciclopentapiridinas y octahidro-1H-indoles, a través de la síntesis de lactamas tricíclicas derivadas del (R)-fenilglicinol. Desafortunadamente, la reacción del ceto-éster 4 y del ceto-ácido 7, proporcionó solamente las eniminas 8 y 9. Por otro lado, la reacción de los derivados de ceto-ácidos 16 y 17 con (R)-fenilglicinol rindió únicamente una mezcla de productos 18, amidas conjugadas epímeras en la posición C-7a. Se ha sido estudiado la reacción de ciclocondensación de derivados de 2-oxociclohexano propionato convenientemente sustituidos en C-3 o en C-3 y C-5 con (R)-fenilglicinol y (1S,2R)-aminoindanol. Esta reacción conduce estereoselectivamente a lactamas tricíclicas o pentacíclicas quirales: se aisló mayoritariamente una lactama y se detectó la presencia de otra minoritaria. Al utilizar (1S,2R)-aminoindanol se obtuvieron mejores resultados. Estas lactamas son precursoras de cis-decahidroquinolinas, con sustituyentes en la posición 8 o en la posición 6 y 8. Las etapas clave de esta transformación son la reducción con alano y la eliminación del inductor quiral. Con esta metodología se ha preparado la decahidroquinolina 82, precursor de numerosos alcaloides de la familia Mirioneuron nutans. Además, presentamos el estudio de las reacciones de ciclocondensación con (R)-fenilglicinol a partir de ciclohexanonas que poseen una cadena de acetato en la posición C-1 y diversos sustituyentes alquilo o arilo en la posición C-3. Esta reacción conduce estereoselectivamente a una sola lactama tricíclica de las ocho posibles. A partir de las cetonas con un sustituyente alquilo en la posición C-3 aislamos una cantidad variable de enamida. Las lactamas mayoritarias, fueron convertidas en cis-octahidroindoles y cis-octahidroindolonas, que presentan un sustituyente en la posición 7 o en las posiciones 7 y 7a del anillo carbocíclico. Además, estudiamos la reactividad de las lactamas tricíclicas en medio ácido: la reacción con TiCl4 en THF, proporciona lactamas insaturadas con elevada estereoselectividad y buen rendimiento. La presencia de la función enamida, nos permitió preparar selectivamente nuevas cis y trans octahidroindolonas. Esta metodología nos permitió sintetizar el (a)-Licorano, un metabolito de la familia de las Amaryllidaceae.
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Cordier, Christopher James. "The Diversity-oriented Synthesis of Natural Product-like Libraries." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485204.
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This thesis describes a novel approach to diversity-oriented synthesis. The approach involves the iterative assembly of building blocks onto a purification handle using temporary diisopropylsilylene tethers; this approach yields substrates for a ring-c1osing-ring-opening olefin metathesis cascade. The metathesis cascade results in a skeletal transformation and a range of scaffolds have been generated using only a few simple building blocks and a small number of common reactions. The use of a fluorous tag as a purification handle minimised labour-intensive purification steps and rendered the approach appropriate for library synthesis. The structures ofthe diverse final compounds are reminiscent ofpolyketide natural products. Chapter 1 describes alternative approaches for varying molecular scaffolds and places our generic approach in context. In Chapter 2, .the syntheses of.enant.iome~cally enriched building . blocks are described in· which an enzymatic desymmetrisation· is often used to induce asymmetry. Our investigations to conduct our methodology on solid support our described in Chapter 3. The potential of individual building blocks to participate in simple metathesis cascades is described in Chapter 4. In addition, this Chapter describes our studies to optimise the formation of unsymmetrical silaketals using diisopropylsilyl ethers as storable precursors. The thesis culminates with the preparation of36 metathesis substrates in which pairs of building blocks have been appended to the fluorous tag. The metatheses of some ofthese substrates are described and leads to natural product-like ligands.
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Teske, Jesse. "Natural Product Synthesis via [2+2+2] Cyclotrimerization Reactions." NCSU, 2009. http://www.lib.ncsu.edu/theses/available/etd-06202009-165943/.
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The transition metal mediated [2+2+2] cyclotrimerization reaction of alkynes is a highly convergent approach to the synthesis of polysubstituted carbo- and heterocyclic aromatic ring systems. However, few examples of the application of cyclotrimerization reactions in natural product synthesis have been reported. Here we explore the development of [2+2+2] cyclotrimerization reactions towards benzene derivatives applicable to the regioselective synthesis of indanone, isoquinoline, anthraquinone, cannabinoid, and neolignan based natural products. In addition, the development of [2+2+2] cyclotrimerization reactions towards pyridine derivatives applicable to the synthesis of the Streptomyces antitumor natural products streptonigrin and lavendamycin and several Lycopodium alkaloids has been explored. Optimization of the key cyclotrimerization events involved investigation of the alkyne (diyne or monoyne) and nitrile substitution pattern, the catalyst system employed, and conventional heating versus microwave irradiation.
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Liang, Huan. "Methodology for natural product synthesis : sordarin, himandrine and lepadiformine." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/14570.
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Fungal infection, of small concern in healthy individuals, can become problematic in immunosuppressed patients with illnesses such as AIDS, and the search for substances that exert antifungal action by new mechanisms continues. A noteworthy group of potent antimycotic natural products known as the sordarins meet this criterion. In order to investigate the effect of various functional and skeletal changes to sordarin on anti-pathogenic activity, we have devised practical, expeditious, and efficient routes to analogs of the natural product. The bioactivity of the new compounds against various pathogenic fungi was evaluated. This research constitutes the first half of my doctoral dissertation.
The second half of my work centers on the development of a practical method for the oxidative amidation of phenols. This reaction achieves the conversion of phenols into spirocyclic (sulfon)amido-dienones. The new methodology forms the centerpiece of envisioned syntheses of (±)-himandrine and (-)-lepadiformines. Himandrine, isolated from the bark of Galbulimima belgraveana, displays anticholinergic activity and is thus of potential interest for the treatment of a number of human ailments. Our himandrine skeleton synthesis centered on a tandem oxidative amidation and Diels-Alder reaction, using three different approaches. The alkaloid (-)-lepadiformines displays potency as a potassium channel blocker. Our synthetic study towards this substance utilizes the oxidative cyclization of a phenolic sulfonamide as the key step. The resulting dienone is then desymmetrized through a stereoselective Michael addition leading to an enantiopure tricyclic intermediate, to which hydrocarbon side chain was appended in high yield. Further elaboration will lead to the natural product.
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Hobson, Stephen. "Applications of the achmatowicz rearrangement in natural product synthesis." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1660/.
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The structurally related PM-94128 and Ajudazols A and B exhibit differing biological activities but share the isocoumarin core structure. PM-94128 belongs to a large family of compounds known as the aminodihydroisocoumarins and was isolated in 1997. It has been shown to be an inhibitor of DNA and RNA synthesis and have potent cytotoxic activity in vivo. The Ajudazols A and B were isolated in 2004 and have antifungal activity against several important food spoilers. The work that follows details the design and development of a novel method for the generation of the isocoumarin core from isobenzofuran utilizing the Achmatowicz rearrangement of a-hydroxyisobenzofurans. Spirocyclic pyrans such as Polymaxenolide are structurally complex molecules, containing large amounts of functionality. The biological activity of Polymaxenolide is unknown and there have been no total syntheses reported to date.
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Seden, Peter Timothy. "Application of the Prins Cyclisation to Natural Product Synthesis." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499891.
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Swift, Michael D. "Investigation of metal mediated reactions for natural product synthesis." Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/621/.
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During the course of the studies outlined in this thesis, an ether-directed Pd(II)-catalysed aza-Claisen rearrangement reaction that had previously been developed by the Sutherland group was expanded to include more functionalised rearrangement substrates. This methodology has been applied for the synthesis of several natural products including dihydroxylated-amino acids. Further investigation of substrates for the rearrangement led to the synthesis of other substituted trichloroacetimidates. Rearrangement of these compounds demonstrated the role of steric strain on the stereocontrol of the rearrangement and also highlighted the role that solvent can have upon the diastereoselectivity of ether-directed rearrangements. In addition to this, a novel tandem aza-Claisen rearrangement and ring closing metathesis reaction has been developed. This reaction allows the synthesis of cyclic allylic trichloroacetamides in excellent yields from simple allylic alcohols. The use of commercially available chiral rearrangement catalysts allowed a highly enantioselective tandem process to be developed. Further development of this process has provided an ether-directed tandem aza-Claisen rearrangement and RCM reaction which occurs with high yield and diastereoselectivity to provide functionalised cyclic products. The use of these compounds for the total synthesis of the amaryllidaceae alkaloid (+)-gamma-lycorane was also investigated.
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Moore, Rebecca J. "Novel approaches to natural product synthesis using organozinc intermediates." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362516.
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Hindley, Stephen. "Towards the total synthesis of the natural product tetronothiodin." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366274.
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Medeiros, Edna Faria de. "The use of pyrylium salts in natural product synthesis." Thesis, University of Essex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334742.
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Davies, Darren. "Approaches towards the synthesis of the natural product phorbol." Thesis, Loughborough University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392383.
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Peed, Jennifer. "Unsaturated aldols as useful substrates in natural product synthesis." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601674.
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This thesis focuses on the use of unsaturated aldols as useful substrates in natural product synthesis. Two methodologies have been investigated for the asymmetric synthesis of highly substituted lactones containing multiple contiguous stereocentres from unsaturated aldol precursors. These lactones have potential application as building blocks for natural product synthesis. Firstly, synthetic applications of the retro aldol reaction are reviewed. The second chapter describes a novel methodology for the asymmetric synthesis of highly substituted δ-lactones from syn-aldol cyclopropanes iii. Mercury mediated cyclopropane ringopening of the methyl ester cyclopropanes iv followed by concomitant cyclisation produced organomercurial δ-lactones v, which subsequently undergo reductive demercuration in basic sodium borohydride to afford the highly substituted δ-lactones vi in good yield and excellent diastereoselectivity. The scope of this method was investigated with variation of the R1 and R2 groups. The synthetic utility of this process was also demonstrated with the synthesis of a series of (+)-Prelactone natural products. The third chapter decribes a method of preparing hydroxy-γ-butyrolactones (viii-x) containing multiple contiguous stereocentres in high yield with good diastereoselectivity. Upjohn dihydroxylation conditions using catalytic osmium tetroxide were employed to β-alkenyl-β- hydroxy-N-acyloxazolidin-2-ones vii with different alkene substitution patterns. This resulted in the formation of triols that underwent spontaneous intramolecular 5-exo-trig cyclisation reactions to afford hydroxy-γ-butyrolactones viii, ix or x depending on the substitution pattern of the alkene precursor.
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Neal, Andrew. "Use of the Claisen rearrangement in natural product synthesis." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16129.
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Kumar, Rohitesh. "Design and Synthesis of Natural Product-Based Screening Libraries." Thesis, Griffith University, 2017. http://hdl.handle.net/10072/366694.
Full textAbstract:
Natural products (NPs) continue to have significant impact in the area of drug discovery and development. More than 50% of the approved drugs between 1981 and 2014 were either unaltered NPs, NP derivatives or synthetic drugs inspired by NP pharmacophores. NPs have also served as lead molecules in drug development programs; noteworthy example include the semi-synthetic antifungal drugs caspofungin, anidulafungin, and micafungin that were based on NP lead compounds isolated from the fermentation products of various fungus. Other notable examples include the sponge metabolite halichondrin B that was developed into the anticancer drug eribulin, and camptothecin, a plant NP that was developed into the oncology drugs, topotecan and irinotecan.
Many research groups are now utilizing isolated NPs as scaffolds for the generation of semi-synthetic analogue libraries rather than pursuing the total synthesis of a bioactive NP followed by classic medicinal chemistry. This approaches main advantage is the reduction in timelines and resource allocation, which is typically associated with de novo multi-step syntheses of a bioactive NP. Furthermore, once the NP scaffold has been isolated from the source biota rapid analogue generation and subsequent SAR data can be acquired. Thus the evaluation of a scaffold chemotype for potential lead optimization studies is quickly assessed.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Natural Sciences
Science, Environment, Engineering and Technology
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Lefranc, David. "Total synthesis of micrococcin P1." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/3626.
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This thesis describes the total synthesis of the thiopeptide antibiotic micrococcin P1.
It unambiguously elucidates its structure, which has been subject to controversy for over thirty years. The centerpiece of the route to the target molecule is a facile one-pot construction of the central thiazole/pyridine cluster developed in our laboratory. This highlyconvergent route entails a delicate Michael addition to yield a Hantzsch dihydropyridine intermediate, which undergoes further oxidation to the fully aromatised heterocycle. The synthesis was completed by the coupling of this core with a highly-modified sensitive peptide chain. The modular nature of the synthesis can also accommodate modifications for
SAR studies, contributing thereby to the fields of medicinal chemistry, pharmacology, and microbiology. At a purely chemical level, we remain confident that this work will serve as a valuable guide in the elaboration of other members of the thiopeptide family.
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Das, P. "Antimalarial natural product cladosporin: synthesis of stereoisomeric library, lead optimization, co-crystallization, and biological evaluation and synthesis of related macrocyclic natural products." Thesis(Ph.D.), CSIR-National Chemical Laboratory, 2021. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/5984.
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The work incorporated in this thesis is mainly focused on “Medicinal chemistry” and “Total synthesis”. Herein we have developed a unique and divergent synthetic scheme to access all the possible stereoisomers of a potent anti-malarial natural product, cladosporin and assessed their inhibitory potency through parasite-, enzyme- and cell-based assays. Based on the scores from biological assays, we categorized the entire set of stereoisomers in to three different potency classes, two of them (including cladosporin) being the most potent ones. X-ray diffraction study of co-crystals of the stereoisomers with target protein, PfKRS further gave an insight about the structural bases of enzymatic binding of the isomers. This exercise collectively helped us to decipher the role of stereochemical modifications on anti-malarial potency of cladosporin.
Natural products are mostly procured in substantial low quantities from natural sources, which often hinders, and sometimes, even eliminates the possibility of in depth biological assessment (mainly in vivo). Hence, we adopted a modified synthetic protocol to access more than two grams of cladosporin in a single batch process. Besides, the scheme adopted herein is amenable to further scale-up.
In the later part of this work, we have studied a systematic structure activity relationship (SAR) of a library of analogues, designed and synthesized based on cladosporin scaffold in anti-malarial potency through parasite-, enzyme- and cell-based assays. In this effort, we identified a lead compound (CL-2) having similar potency to that of cladosporin, but with improved drug-like properties (increased metabolic stability and hydrophilicity). Besides, the co-crystal structure of the most active compound (CL-2) with target protein PfKRS reveals new features of enzyme drug interactions.
Lastly, we have accomplished the total synthesis of three bio-active twelve membered resorcyclic acid lactones (RAL12) namely (R)-penicimenolide A, (R)-dihydroresorcyclide and (R)-trans-resorcyclide. These natural products bear an interesting structural compliance with cladosporin.AcSIR
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Plowright, Alleyn T. "Synthetic studies towards the marine natural product phorboxazole A." Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311837.
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