Total Synthesis of (±)-bostrycin, Synthesis of a Chiral Catechol-based C2-symmetric Ligand and Studies Directed Towards the Synthesis of Dienoyl Tetramic Acid Section of Tirandamycin PDF Download
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Author: Jayanta Kumar Saha
Publisher:
ISBN:
Category : Antibiotics
Languages : en
Pages : 364
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Book Description
Author: Jayanta Kumar Saha
Publisher:
ISBN:
Category : Antibiotics
Languages : en
Pages : 364
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Book Description
Author:
Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 734
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Book Description
Author: American Chemical Society, Committee on Professional Training Staff
Publisher:
ISBN: 9780841214187
Category : Science
Languages : en
Pages : 1390
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Author: Ruowei Mo
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Two efficient, regio- and stereo controlled synthetic approaches to the synthesis of racemic analogs of pancratistatin have been accomplished and they serve as the model systems for the total synthesis of optically active 7-deoxy-pancratistatin. In the Diels-Alder approach, an efficient [4+2] cycloaddition of 3,4-methylenedioxyco- nitrostyrene with Danishefsky's diene to selectively form an exo-nitro adduct has been developed as the key step in the construction of the C-ring of the target molecule. In the Michael addition approach, the key step was a conjugate addition of an organic zinc-cuprate to the 3,4-methylenedioxy-(B-nitrostyrene, followed by a diastereocontroUed closure to form the cyclohexane C-ring of the target molecule via an intramolecular nitro-aldol cyclization on a neutral alumina surface. A chair-like transition state for such a cyclization has been established and such a chelation controlled transition state can be useful in the prediction of diastereoselectivity in other related 6-exo-trig nitroaldol reactions. Cyclization of the above products fi^om both approaches by using a Bischler-Napieralski type reaction afforded two lycoricidine derivatives 38 and 50 in good yields. The initial results from the above modeling studies as well as the analysis of the synthetic strategy were directed to a chiral pool approach to the total synthesis of optically active 7-deoxy-pancratistatin. Selective monsilylation and iodination of Ltartaric acid provided a chiral precursor for the proposed key Michael transformation. The outlook for the total synthesis of 7-deoxy-pancratistatin by this approach is very promising.A concise synthesis of novel designed, optically pure, Cz-symmetrical disulfonylamide chiral ligands starting from L-tartaric acid has also been achieved. This sequence employs the metallation of indole followed by Sfj2 replacement of a dimesylate as the key step. The activity for this Cz-symmetric chiral disulfonamide ligand in the catalytic enantioselective reaction has been confirmed by nucleophilic addition to benzaldehyde in the disulfonamide-Ti (0-i-Pr)4-diethylzinc system with a 48% yield and a 33% e.e. value. Such a ligand tethered with a suitable metal complex should be also applicable towards the total synthesis of 7-deoxy-pancratistatin.
Author: Kevin B. Albertson
Publisher:
ISBN:
Category :
Languages : en
Pages : 224
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Author: Jie Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 834
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Abstract: Research projects have involved the development of enantioenriched crotylsilane reagents and their application in natural product synthesis. These novel crotylsilanes were generated through Rh(II) or Cu(I) catalyzed asymmetric carbenoid Si-H insertion. Jacobsen's C2-symmetric copper(I) diimine complexes were applied to carbenoid Si-H insertions with a-diazovinylacetates, which resulted in the formation of crotylsilanes bearing C-centered chirality with high enantioenrichment. A comparison of chiral Cu(I) and Rh(II) catalysis was also detailed in this study. The generated organosilane products were then utilized in a Lewis acid-promoted crotylation with aldehydes and imines to provide stereochemically well-defined homoallylic ethers and carbamates. In some cases, [3 + 2] annulation products were formed through a [1,2]-silyl rearrangement pathway. (—)-Virginiamycin M2 belongs to a class of naturally occurring antibiotics known as virginiamycins. Derivatives of virginiamycins displayed potent antibiotic activity against methicillin-, erythromycin-, and vancomycin-resistant S. aureus. The unique chemical structure of (—)-virginiamycin M2 and its potential bioactivity motivated us to initiate a study towards its total synthesis. Notable features of our synthetic strategy included the application of the novel crotylsilane to address stereochemical features of the syn vinylogous aldol product; the use of an alkoxide-directed reductive coupling to assemble the ( E,E)-diene; and a SmI2-promoted Barbier-type macrocyclization to construct the 23-membered macrocycle. A sequential transformation involving an asymmetric crotylation followed by metal carbenoid reactions has been developed to access novel bicylic and tricyclic chemotypes. By subsequent pairing of installed functional groups using Heck cyclization or [2 + 2] photo-cycloaddition, the syntheses of tetracycles, pentacycles, and condensed polycycles were achieved with high stereochemical and skeletal variation. Densely functionalized chiral allylsilanes were accessed through organosilane based alkyne-alkene reductive coupling of readily available propargyl silanes. The chemodivergent reactivity of the generated allylsilanes was controlled with ease to deliver a broad range of novel carbocycles through the intramolecular allylation, [3 + 2] annulations, and a Sakurai-like homodimerization.
