Enantioselective Total Synthesis of Galbulimima Alkaloids GB13 and Himgaline PDF Download
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Author: Unmesh Shah
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 532
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Book Description
Author: Unmesh Shah
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 532
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Author: Drew James Adams
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 502
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Author: Meiliana Tjandra
Publisher:
ISBN:
Category :
Languages : en
Pages : 299
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I. Total Synthesis of All Class III Galbulimima Alkaloids We describe the total synthesis of (+)- and (-)-galbulimima alkaloid 13, (-)-himgaline anad (-)-himbadine. The absolute stereochemistry of natural (-)-galbulimima alkaloid 13 is revised to 2S. Sequential use of catalytic cross-coupling and cross-metathesis reactions followed by an intramolecular Diels-Alder reaction provided the required trans-decalin AB-ring system and masked the Cl 6-carbonyl as an N-vinyl carbamate for late stage unveiling in the form of the necessary C16-enone. A vinyl-radical cyclization secured the C-ring while successful execution of our strategy for introduction of the CDE-ring system in complex galbulimima alkaloids provided the target pentacycle with complete diastereoselection. II. Total Synthesis of (-)-Himandrine We describe the first total synthesis of (-)-himandrine, a member of the class II galbulimima alkaloids. Noteworthy features of this chemistry include a diastereoselective Diels- Alder reaction in the rapid synthesis of the tricycle ABC-ring system in enantiomerically enriched form, the use of a formal [3+3] annulation strategy to secure the CDE-ring system with complete diastereoselection, and successful implementation of our biogenetically inspired oxidative spirocyclization of an advanced intermediate. The successful and direct late-stage formation of the F-ring in the hexacyclic core of himandrine drew on the power of biogenetic considerations and fully utilized the inherent chemistry of a plausible biosynthetic intermediate.
Author: Kimberly Katherine Larson
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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This dissertation describes our strategy for the total synthesis of Galbulimima alkaloid ()-G.B. 13. First, an overview of the isolation and structural classification of the twenty-eight alkaloids in the Galbulimima family is presented. Proposals for the biosyntheses of these natural products as well as the determination of their absolute stereochemical relationships are discussed. Additionally, the biological and medicinal properties of himbacine, another Galbulimima alkaloid, are presented. The four total syntheses of alkaloid G.B. 13 that have been completed by research groups other than our own are briefly examined. Our own total synthesis of ()-G.B. 13 was accomplished in eighteen linear steps from commercially available starting materials. A detailed account of our synthetic endeavors, which include the rational development of both an allylic alcohol transposition under modified Parikh-Doering conditions and an unprecedented rhodium(I)-catalyzed addition of an aryl boronic ester into an unactivated ketone carbonyl, is described. The completion of this synthesis demonstrates the synthetic utility of a pyridine moiety as a piperidine surrogate. The last section of this dissertation conveys our work developing a novel palladium(0)-mediated transformation that provides stereochemically-defined enals, enones, and dienones through the union of aryl and vinyl halides with divinyl and enyne carbinol coupling partners. This reaction is believed to proceed through a cyclopropanol intermediate and to involve a novel skeletal reorganization. Experimental observations in support of our proposed mechanism, as well as a complete substrate scope, are presented.
Author: Diana Katharine Hunt
Publisher:
ISBN:
Category :
Languages : en
Pages : 413
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I. Total Synthesis of Galbulimima Alkaloids. The total synthesis of enantiomerically enriched (+)- and (-)-galbulimima alkaloid 13 is outlined. Sequential use of catalytic cross-coupling and cross-metathesis reactions followed by an intramolecular Diels-Alder reaction provided the required trans-decalin AB ring system and masked the C16-carbonyl as an N-vinyl carbamate for late stage oxidative unveiling as the corresponding C16-enone. Completely diastereoselective introduction of the C-ring via radical cyclization chemistry followed by an enamine-ketone addition for construction of the CDE-ring system allowed rapid entry to the pentacyclic core of these alkaloids. The absolute stereochemistry of natural (-)-galbulimima alkaloid 13 is now unambiguously revised to 2S.
Author: Vivek Badarinarayana
Publisher:
ISBN: 9780542722608
Category : Chemistry, Organic
Languages : en
Pages :
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This dissertation consists of two parts. The first part describes the enantioselective total synthesis of martinellic acid. The Martinella alkaloids have attracted considerable attention in the synthetic community over the past few years. This interest is due in large part to their unique structure and useful biological activity (bradykinin receptor antagonist). In model systems we have successfully used the [3+2] azomethine ylide-alkene cycloaddition to construct the heterocyclic core of these alkaloids. The enantioselective approach described herein also involves the azomethine ylide-alkene cycloaddition as a key step in the total synthesis. The pyrrolo[3,2-c]quinoline core of this alkaloid was constructed in an enantioselective fashion by the elaboration of an N-aryl pyrrolidinone, which was obtained via Pd-catalyzed aryl amination reaction using a non-racemic lactam. Pirkle's chiral solvating agent was successfully used to demonstrate the stereochemical integrity of not only the N-aryl lactam (obtained by Pd-catalyzed cross-coupling) but also the cycloaddition precursor and the cycloaddition product (tetracyclic pyrroloquinoline core). The tetracyclic compound obtained via the azomethine ylide-alkene cycloaddition was elaborated to ( - )-martinellic acid in 11 steps and 6% overall yield. The second part of this dissertation describes application of several novel organometallic complexes for carrying out various organic transformations. A fluorinated tris(pyrazolyl)borato silver(I) complex catalyzes the addition of ethyl diazoacetate to benzene rings, providing norcaradienes, which undergo electrocyclization to provide the corresponding cycloheptatriene (the Bu & huml;chner reaction). These reactions are surprisingly selective for addition to the aromatic moiety rather than C-H insertion. A copper complex containing a fluorinated triazapentadienyl ligand has been used to catalyze some carbene and nitrene addition and insertion chemistry. Nitrene addition occurs rapidly and with both aryl and alkyl substituted olefins providing the corresponding aziridine. The carbene transfer reactions that were attempted include C-H insertion, O-H insertion and N-H insertion, of which the latter two were very efficient.
Author: Alec Donald Lebsack
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 622
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Author: Phillip Conrad Knutson
Publisher:
ISBN:
Category :
Languages : en
Pages : 1108
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The Gelsemium alkaloids represent a diverse class of natural products that have displayed interesting biological and medicinal properties. Because of their pharmacological interest as well as inherent synthetic challenges, chemists have been tackling the construction of these molecules for decades. Many of the Gelsemium alkaloids share a characteristic oxabicyclic core that is both densely packed and relatively unfunctionalized. We noticed that this core could be generated rapidly through a tandem cycloisomerization/Cope rearrangement. Through our execution of this methodology we were able to accomplish the total syntheses of Gelsenicine and Gelsedine. These total syntheses represent an entry into a divergent total synthesis program. Through the synthesis of a common core through the tandem cycloisomerization/Cope rearrangement, we envision access to other members of the Gelsemium alkaloid family, such as Gelsemoxonine. We have also demonstrated the enantioselective total synthesis of Gelsenicine through an enantioselective gold-catalyzed cycloisomerization. This was accomplished by using chiral ligands such as phosphoramidites and bisphosphines. We found that bisphosphine ligands bearing electron rich and bulky aryl substituents on phosphorous worked well to give high levels of asymmetric induction in the cycloisomerization product. Lastly, a convenient Cadiot8́2Chodkiewicz protocol that facilitates the use of low molecular weight alkyne coupling partners is described. The method entails an in situ elimination from a dibromooleƠ̐1n precursor and immediate subjection to copper-catalyzed conditions, circumventing the hazards of volatile brominated alkynes. The scope of this method is described, and the internal 1,3-diyne products are preliminarily evaluated in ruthenium-catalyzed azide-alkyne cycloadditions.
Author: Cheryl Faye Lichti
Publisher:
ISBN:
Category : Alkaloids
Languages : en
Pages : 186
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Author: Sunkyu Han
Publisher:
ISBN:
Category :
Languages : en
Pages :
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I. Total Synthesis of the (-)-Agelastatin Alkaloids The pyrrole-imidazole family of marine alkaloids, derived from linear clathrodin-like precursors, constitutes a diverse array of structurally complex natural products. The bioactive agelastatins are members of this family that possess a tetracyclic molecular framework incorporating C4-C8 and C7-N12 bond connectivities. We provide a hypothesis for the formation of the unique agelastatin architecture that maximally exploits the intrinsic chemistry of plausible biosynthetic precursors. We report the concise enantioselective total syntheses of all known agelastatin alkaloids including the first total syntheses of agelastatins C, D, E, and F. Our gram-scale chemical synthesis of agelastatin A was inspired by our hypothesis for the biogenesis of the cyclopentane C-ring and required the development of new transformations including an imidazolone-forming annulation reaction and a carbohydroxylative trapping of imidazolones. II. Total Synthesis of the (-)-Trigonoliimine Alkaloids The concise and enantioselective total syntheses of (-)-trigonoliimines A, B, and C are described. Our unified strategy to all three natural products is based on asymmetric oxidation and reorganization of a single bistryptamine, a sequence of transformations with possible biogenetic relevance. We revise the absolute stereochemistry of (-)-trigonoliimines A, B, and C.
