Academic literature on the topic 'Alkyne protecting groups'
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Journal articles on the topic "Alkyne protecting groups"
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Breckle, Gregor, Kurt Polborn, and Thomas Lindel. "Synthesis of the Pyrrole-Imidazole Alkaloid Sventrin from the Marine Sponge Agelas sventres." Zeitschrift für Naturforschung B 58, no. 5 (2003): 451–56. http://dx.doi.org/10.1515/znb-2003-0516.
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The marine pyrrole-imidazole alkaloid sventrin (1) and the hitherto unknown dehydrooroidin (3) have been synthesized stereoselectively via alkyne intermediates. The pathways start from a 2-azido-4-alkynylimidazole which can be chemo- and stereoselectively reduced to the corresponding amino alkene using NaAlH2(OCH2CH2OMe)2 (Red-Al) or, alternatively, to the amino alkyne. Selective removal of simultaneously present Boc or trityl protecting groups was possible employing either p-TsOH or acetic resp. formic acid.
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Valverde, Ibai E., Agnès F. Delmas, and Vincent Aucagne. "Click à la carte: robust semi-orthogonal alkyne protecting groups for multiple successive azide/alkyne cycloadditions." Tetrahedron 65, no. 36 (2009): 7597–602. http://dx.doi.org/10.1016/j.tet.2009.06.093.
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Saneyoshi, Hisao, Kazuhiko Kondo, Koichi Iketani, and Akira Ono. "Alkyne-linked reduction-activated protecting groups for diverse functionalization on the backbone of oligonucleotides." Bioorganic & Medicinal Chemistry 25, no. 13 (2017): 3350–56. http://dx.doi.org/10.1016/j.bmc.2017.04.020.
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Wintergerst, Pascal, Kamil Witas, Djawed Nauroozi, et al. "Minimizing Side Product Formation in Alkyne Functionalization of Ruthenium Complexes by Introduction of Protecting Groups." Zeitschrift für anorganische und allgemeine Chemie 646, no. 13 (2020): 842–48. http://dx.doi.org/10.1002/zaac.202000042.
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Sydnes, Leiv K., Ole H. Kvernenes, and Stig Valdersnes. "From 3,3,4,4-tetraethoxybutyne to carbohydrate mimics." Pure and Applied Chemistry 77, no. 1 (2005): 119–30. http://dx.doi.org/10.1351/pac200577010119.
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3,3,4,4-Tetraethoxy-1-butyne, available in high yield in four simple steps from ethyl vinyl ether, is a highly functionalized alkyne, which appears to be a versatile starting material for the synthesis of a range of alkylated, more-or-less deoxygenated carbohydrate mimics. However, many of the reactions used to achieve extension and subsequent structural modification of the carbon chain as well as removal of the protecting groups turn out to be rather sensitive to the substituents’ steric and electronic influence. As a result, the reactivity pattern that emerges is somewhat complex.
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Carvalho, M. Fernanda N. N., Rudolf Herrmann, and Gabriele Wagner. "Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds." Beilstein Journal of Organic Chemistry 13 (June 26, 2017): 1230–38. http://dx.doi.org/10.3762/bjoc.13.122.
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Compounds containing two alkyne groups in close vicinity at the rigid skeleton of camphorsulfonamide show unique reactivities when treated with electrophiles or catalytic amounts of platinum(II). The formed product structures depend not only on the reagents used but also on the substituents attached to the triple bonds. Cycloisomerisations with perfect atom economy lead to polycyclic heterocycles that resemble to some extent the AB ring system of paclitaxel. Herein, we present practical synthetic methods for the selective synthesis of precursor dialkynes bearing different substituents (alkyl, aryl) at the triple bonds, based on ketals or an imine as protecting groups. We show for isomeric dialkynes that the reaction cascade induced by Pt(II) includes ring annulation, sulphur reduction, and ring enlargement. One isomeric dialkyne additionally allows for the isolation of a pentacyclic compound lacking the ring enlargement step, which we have proposed as a potential intermediate in the catalytic cycle.
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Hu, Zhifang, Lifen Peng, Renhua Qiu, and Akihiro Orita. "Recent Progress of Protecting Groups for Terminal Alkynes." Chinese Journal of Organic Chemistry 40, no. 10 (2020): 3112. http://dx.doi.org/10.6023/cjoc202005094.
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Ficker, Mario, Søren W. Svenningsen, Thomas Larribeau, and Jørn B. Christensen. "Inexpensive and rapid hydrogenation catalyst from CuSO4/CoCl2 — Chemoselective reduction of alkenes and alkynes in the presence of benzyl protecting groups." Tetrahedron Letters 59, no. 12 (2018): 1125–29. http://dx.doi.org/10.1016/j.tetlet.2018.02.026.
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Oliveira, Juliana M., Dayvson J. Palmeira, João V. Comasseto, and Paulo H. Menezes. "Influence of different protecting groups on the regioselectivity of the hydrotelluration reaction of hydroxy alkynes." Journal of the Brazilian Chemical Society 21, no. 2 (2010): 362–66. http://dx.doi.org/10.1590/s0103-50532010000200024.
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Wünsch, Matthias, David Schröder, Tanja Fröhr, et al. "Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics." Beilstein Journal of Organic Chemistry 13 (November 15, 2017): 2428–41. http://dx.doi.org/10.3762/bjoc.13.240.
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The amide moiety of peptides can be replaced for example by a triazole moiety, which is considered to be bioisosteric. Therefore, the carbonyl moiety of an amino acid has to be replaced by an alkyne in order to provide a precursor of such peptidomimetics. As most amino acids have a chiral center at Cα, such amide bond surrogates need a chiral moiety. Here the asymmetric synthesis of a set of 24N-sulfinyl propargylamines is presented. The condensation of various aldehydes with Ellman’s chiral sulfinamide provides chiralN-sulfinylimines, which were reacted with (trimethylsilyl)ethynyllithium to afford diastereomerically pureN-sulfinyl propargylamines. Diverse functional groups present in the propargylic position resemble the side chain present at the Cαof amino acids. Whereas propargylamines with (cyclo)alkyl substituents can be prepared in a direct manner, residues with polar functional groups require suitable protective groups. The presence of particular functional groups in the side chain in some cases leads to remarkable side reactions of the alkyne moiety. Thus, electron-withdrawing substituents in the Cα-position facilitate a base induced rearrangement to α,β-unsaturated imines, while azide-substituted propargylamines form triazoles under surprisingly mild conditions. A panel of propargylamines bearing fluoro or chloro substituents, polar functional groups, or basic and acidic functional groups is accessible for the use as precursors of peptidomimetics.
Dissertations / Theses on the topic "Alkyne protecting groups"
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Valverde, Ibai. "La multi-ligation triazole : développement de nouveaux outils pour la synthèse de mimes de protéines par cycloadditions successives." Thesis, Orléans, 2010. http://www.theses.fr/2010ORLE2010.
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Ce travail est consacré au développement d’une nouvelle méthode de synthèse d’analogues bioactifs de protéinesen utilisant des réactions successives de cycloaddition entre les alcynes terminaux et les azotures (CuAAC).Pour pouvoir effectuer des cycloadditions itératives, nous avons étudié la stabilité et les conditions de coupure dedifférents groupements masquants des alcynes terminaux. Cette étude a été valorisée par le développement d’unestratégie originale pour réaliser un triple cycloaddition successive une même molécule basée sur la protectiontemporaire de la fonction alcyne.La méthode a été appliquée à la synthèse d'un analogue de la stéfine A humaine, un inhibiteur naturel deprotéases à cystéine d’intérêt thérapeutique. Pour cela, nous avons mis au point des conditions de CuAACsuccessive compatibles avec des peptides déprotégés de façon beaucoup à obtenir in fine un analogue bis-triazolede la stéfine A. Les études par dichroïsme circulaire et d’inhibition de diverses protéases à cystéines confirmentque notre analogue synthétique conserve la structure et l’activité biologique de la protéine native.La stratégie de ligation triazole successive a été étendue par la mise au point de conditions pour réaliser desligations sur phase solide. La méthodologie développée permet la synthèse de protéines de façon plus rapide etplus simple que par des procédés classiques de ligation successive en solution. Dans l’optique de la synthèse destructures glycopeptidiques capables d’induire une réponse immunitaire contre MUC1 tumorale, nous avons réaliséla synthèse d’analogues peptidiques de MUC1 par ligation successive sur phase solide de 160 acides aminés<br>The aim of this work was the development of a novel method for the synthesis of triazolo-proteins by multiplesuccessive copper-catalyzed azide-alkyne cycloadditions (CuAAC).In order to achieve several successive cycloadditions, we have studied the stability and cleavage conditions ofseveral alkyne protective groups. This study leaded us to the development of an original strategy in order toachieve three successive cycloadditions on a same scaffold by temporal protection of alkyne functionalities.The method has been applied to the synthesis of an analogue of human stefin A, a natural inhibitor of severaltherapeutically relevant cysteine proteases. Therefore, we have developed CuAAC conditions compatible withunprotected peptide ligation. The strategy allowed us to obtain a bis-triazolo analogue of human stefin A. Circulardichroism and enzymology assays on several cysteine cathepsins revealed that the synthetic analogue hasretained the folding and full biological activity of the native protein.In order to expand the possibilities of this strategy, we have developed reaction conditions allowing us to performsuccessive triazole ligation on solid phase. This methodology avoids the need for a time-consuming and laborintensivepurification step before and after each ligation. With the aim of exploring the use of analogues of thetumor-associated form of the glycoprotein MUC1 to induce a specific immune response, we have synthesized atriazolo-analogue of MUC1 of 160 aminoacids using solid phase peptide ligation
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Yang, Gang. "SYNTHESIS OF A POLYMER/ N-ALKYL UREA PEPTOID CONJUGATE." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1380613053.
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Henklein, Petra. "N alpha -Arensulfonyl-Aminosäurechloride." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2000. http://dx.doi.org/10.18452/14600.
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Obwohl die methodische Entwicklung der Peptidsynthese gewöhnlich eine automatisierte Herstellung erlaubt, sind für die Herstellung einer Reihe von Peptiden auch gegenwärtig Grenzen gesetzt. Einerseits kann eine im Verlauf der Kettenverlängerung auftretende Bildung intra- und /oder intermolekularer Wasserstoffbrücken zu einer begrenzten Solvatation und damit Zugänglichkeit der zu acylierenden Aminokomponente am Syntheseharz führen, andererseits kommt es beim Einbau sterisch anspruchsvoller Aminosäuren zu ungenügenden Acylierungsausbeuten. Urethangeschützte Aminosäurefluoride haben sich für den Einbau von alpha, alpha-Dialkylaminosäuren als geeignet erwiesen. Die reaktiveren urethangeschützten Aminosäurechloride sind zwar herstellbar, besitzen aber in Gegenwart einer Hilfsbase, die zum Abfangen der während ihrer Reaktion gebildeten HCl notwendig ist, eine zu geringe Stabilität (Oxazolonbildung, Abspaltung der Schutzgruppen). Erst die Verwendung von N(alpha)-Schutzgruppen, die keinen reaktionsfähigen Carbonylkohlenstoff enthalten, wie Arensulfonyl- Schutzgruppen, ermöglichen die volle Ausschöpfung der hohen Reaktivität der Aminosäurechloride. Mit Hilfe dieser Schutzgruppen gelang ein erster Vergleich der Reaktivität der Aminosäurechloride und -fluoride. Bei den durchgeführten Reaktionen wurde keine Stereomutation beobachtet. Unter Verwendung von Arensulfonylschutzgruppen war es erstmals möglich, zwei aufeinanderfolgende N-Alkyl-alpha, alpha-dialkylaminosäuren in Peptide einzubauen. Weiterhin konnten wir zeigen, daß derart geschützte Aminosäuren sich für in situ Aktivierungen mit Thionylchlorid eignen. Als Fänger für überschüssiges Aktivierungsreagenz wurden tertiäre Alkohole bzw. Amine eingesetzt. Arensulfonyl-geschützte Aminosäurechloride haben wir darüber hinaus erfolgreich in der Festphasenpeptidsynthese verwendet. In Kombination von Arensylfonyl-Schutz mit der Standard-Fmoc-Strategie gelang die Synthese eines biologisch aktiven Analogen des CRF, eines 41-mer Peptides mit einer eingefügten Tetrapeptidsequenz -Ala-MeAib-MeAib-Aib-.<br>Despite its wide field of application automatic peptide synthesis is still limited in certain cases. One of the limiting factors is the possibility of intra- or intermolecular hydrogen bond formation during the elongation of the peptide chain. This causes decreased solvation and thus reduced accessibility to the resin-bound amino component. Another limitation is the incorporation of sterically hindered amino acids that usually give rise to insufficient yields of acylation. Urethane protected amino acid fluorides have been shown suitable for the incorporation of alpha,alpha-dialkyl amino acids. Though the more reactive urethane protected amino acid chlorides can be readily synthesized, they do not possess the necessary stability in the presence of an auxiliary base that must be used for trapping of the hydrochloric acid formed during the reaction. Formation of oxazolons and deprotection of formerly protected functional groups would occur. Only the advent of protecting groups for the amino acid N-alpha that do not have a reactive carbonyl function - like arene sulfonyl groups - allowed to take full advantage of the high reactivity of the amino acid chlorides. These protecting groups enabled us to compare the reactivities of amino acid chlorides and fluorides for the first time. We didn't observe any stereo mutation in our experiments. The use of arene sulfonyl protecting groups permitted the consecutive incorporation of two N-alkyl-alpha,alpha-dialkyl amino acids into a peptide for the first time. Furthermore we could show, that amino acids protected in this way, are suitable for in situ activation with thionyl chloride. Tertiary alcohols and amines were used as scavenger for excessive activating reagent. Arene sulfonyl protected amino acids were also successfully used in solid phase peptide synthesis. By combining this protecting concept with the standard Fmoc approach we were able to synthesize a biologically active analogue of CRF, a peptide containing 41 residues into which we inserted the tetrapeptide Ala-MeAib-MeAib-Aib.
Book chapters on the topic "Alkyne protecting groups"
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Taber, Douglass F. "Functional Group Protection: The Pohl Synthesis of β-1,4-Mannuronate Oligomers." In Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0015.
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D. Srinivasa Reddy of the National Chemical Laboratory converted (Org. Lett. 2015, 17, 2090) the selenide 1 to the alkene 2 under ozonolysis conditions. Takamitsu Hosoya of the Tokyo Medical and Dental University found (Chem. Commun. 2015, 51, 8745) that even highly strained alkynes such as 4 can be generated from a sulfinyl vinyl triflate 3. An alkyne can be protected as the dicobalt hexacarbonyl complex. Joe B. Gilroy and Mark S. Workentin of the University of Western Ontario found (Chem. Commun. 2015, 51, 6647) that following click chemistry on a non-protected distal alkyne, deprotection of 5 to 6 could be effected by exposure to TMNO. Stefan Bräse of the Karlsruhe Institute of Technology and Irina A. Balova of Saint Petersburg State University showed (J. Org. Chem. 2015, 80, 5546) that the bend of the Co complex of 7 enabled ring-closing metathesis, leading after deprotection to 8. Morten Meldal of the University of Copenhagen devised (Eur. J. Org. Chem. 2015, 1433) 9, the base-labile protected form of the aldehyde 10. Nicholas Gathergood of Dublin City University and Stephen J. Connon of the University of Dublin developed (Eur. J. Org. Chem. 2015, 188) an imidazolium catalyst for the exchange deprotection of 11 to 13, with the inexpensive aldehyde 12 as the acceptor. Peter J. Lindsay-Scott of Eli Lilly demonstrated (Org. Lett. 2015, 17, 476) that on exposure to KF, the isoxazole 14 unraveled to the nitrile 15. Masato Kitamura of Nagoya University observed (Tetrahedron 2015, 71, 6559) that the allyl ester of 16 could be removed to give 17, with the other alkene not affected. Benzyl ethers are among the most common of alcohol protecting groups. Yongxiang Liu and Maosheng Cheng of Shenyang Pharmaceutical University showed (Adv. Synth. Catal. 2015, 357, 1029) that 18 could be converted to 19 simply by exposure to benzyl alcohol in the presence of a gold catalyst. Reko Leino of Åbo Akademi University developed (Synthesis 2015, 47, 1749) an iron catalyst for the reductive benzylation of 20 to 21. Related results (not illustrated) were reported (Org. Lett. 2015, 17, 1778) by Chae S. Yi of Marquette University.
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Taber, Douglass F. "Oxidation of Organic Functional Groups." In Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0008.
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Cancheng Guo of Hunan University devised (J. Org. Chem. 2014, 79, 2709) conditions for the oxidative cleavage of an alkyne 1 to the esters 2 and 3. Hirokazu Arimoto of Tohoku University found (Chem. Commun. 2014, 50, 2758) that IBX oxidized a primary alcohol 4 to the acid 5 one carbon shorter. David Milstein of the Weizmann Institute of Science uncovered (J. Am. Chem. Soc. 2014, 136, 2998) conditions for the direct oxidation of the cyclic amine 6 to the lactam 7, with concomitant evolution of H₂. Cyclic ene sulfonamides such as 9 are versatile synthetic intermediates. Henri Doucet of the Université de Rennes reported (Adv. Synth. Catal. 2014, 356, 119) the regioselective conversion of 8 to 9. In this case, the oxidizing agent was the organo-PdBr intermediate. There have been many reports of the functionalization of the oxygenated carbons of cyclic ethers, as exemplified by the conversion of 10 to 11, observed (J. Org. Chem. 2014, 79, 3847) by Jianlin Han of Nanjing University. If these methods were regioselective with an acyclic benzyl ether, this could be a new method for the removal of that common protecting group. Jianliang Xiao of the University of Liverpool described (J. Am. Chem. Soc. 2014, 136, 8350) a selective benzylic ether oxidation that converted 12 to 13. Baris Temelli of Hacettepe University effected (Synthesis 2014, 46, 1407) the conversion of a primary nitro compound 14 into the corresponding nitrile 15. Jean- Michel Vatèle of Université Lyon 1 oxidized (Synlett 2014, 25, 1275) the primary alcohol 16 to the nitrile 17. Many methods have been put forward for the oxidation of primary alcohols to aldehydes and secondary alcohols to ketones. Piperidinium oxy radicals such as TEMPO are widely used to catalyze this transformation. Yoshikazu Kimura of Iharanikkei Chemical Industry Co. Ltd. established (Synlett 2014, 25, 596) a manufacturing process for crystalline NaOCl•5H₂O that served as the bulk oxidant for the conversion of 18 to 19. Neither a ketone nor an aldehyde was chlorinated under the reaction conditions. Yoshiharu Iwabuchi of Tohoku University showed (Angew. Chem. Int. Ed. 2014, 53, 3236) that with his piperidinium oxy radical AZADO and Cu catalysis, air could be the bulk oxidant for the otherwise difficult conversion of the amino alcohol 20 to the amino ketone 21.
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"7.3 Alkyl Esters." In Protecting Groups, edited by Philip J. Kocieński. Georg Thieme Verlag, 2005. http://dx.doi.org/10.1055/b-0035-108290.
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"4.3 Alkyl Ethers (I)." In Protecting Groups, edited by Philip J. Kocieński. Georg Thieme Verlag, 2005. http://dx.doi.org/10.1055/b-0035-108263.
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"4.3 Alkyl Ethers (II)." In Protecting Groups, edited by Philip J. Kocieński. Georg Thieme Verlag, 2005. http://dx.doi.org/10.1055/b-0035-108264.
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"8.6 N-Alkyl Derivatives." In Protecting Groups, edited by Philip J. Kocieński. Georg Thieme Verlag, 2005. http://dx.doi.org/10.1055/b-0035-108300.
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Taber, Douglass F. "Reduction and Oxidation." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0007.
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Craig M. Williams of the University of Queensland and John Tsanaktsidis of CSIRO Victoria decarboxylated (Org. Lett. 2011, 13, 1944) the acid 1 to the hydrocarbon 2 by coupling the crude acid chloride, formed in CHCl3, with 3 while irradiating with a tungsten bulb. In a related development, David C. Harrowven of the University of Southampton showed (Chem. Commun. 2011, 46, 6335, not illustrated) that tin residues can be removed from a reaction mixture by passage through silica gel containing 10% K2CO3. Sangho Koo of Myong Ji University selectively removed (Org. Lett. 2011, 13, 2682) the allylic oxygen of 5, leaving the other protected alcohol. Donald Poirier of Laval University reduced (Synlett 2011, 2025) the nitrile of 7 to a methyl group. Kiyotomi Kaneda of Osaka University prepared (Chem. Eur. J. 2010, 16, 11818; Angew. Chem. Int. Ed. 2011, 50, 2986) supported Au nanoparticles that deoxygenated an epoxide 9 to the alkene 10. Epoxides of cyclic alkenes also worked well. Shahrokh Saba of Fordham University aminated (Tetrahedron Lett. 2011, 52, 129) the ketone 11 by heating it with an amine 12 in the presence of ammonium formate. Shuangfeng Yin and Li-Biao Han of Hunan University devised (J. Am. Chem. Soc. 2011, 133, 17037) catalyst systems that reduced the alkyne 14 selectively to either the Z or the E product. Professor Kaneda uncovered (Chem. Lett. 2011, 40, 405) a reliable Pd catalyst for the hydrogenation (not illustrated) of an alkyne to the Z alkene. David R. Spring of the University of Cambridge established (Synlett 2011, 1917) biphasic reaction conditions for the conversion of 16 to the azide 18 that were compatible with the base-sensitive Fmoc protecting group. Noritaka Mizuno of the University of Tokyo developed (J. Org. Chem. 2011, 76, 4606) a Ru catalyst for the transformation of an alkyl azide 19 to the nitrile 20. Chi-Ming Che of the University of Hong Kong (Synlett 2011, 1174) and Philip Wai Hong Chan of Nanyang Technological University (J. Org. Chem. 2011, 76, 4894) independently oxidized an aldehyde 21 to the amide 22.
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Taber, Douglass F. "The Funk Synthesis of (-)-Nakadomarin A." In Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0101.
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The Z alkene of nakadomarin A 3 suggested to Raymond L. Funk an approach (Org. Lett. 2010, 12, 4912) based on ring-closing alkyne metathesis. The efficient assembly of 3 he reported illustrates the power of convergent design in target-directed synthesis. A practical limit on applications of alkyne metathesis is the requirement for internal alkynes, necessitating methyl capping of a terminal alkyne. In an alternative approach, Professor Funk took advantage of the long-known ( J. Chem. Soc. 1954 , 3201) equilibration of a terminal alkyne 4 to the internal alkyne 5. Homologation of 5 with the phosphonate 6, followed by condensation with the ketone 7, then delivered the furan 8. The assembly of the other half of 1 began with the commercial alcohol derived by reduction of D -pyroglutamic acid. Protection gave 9, which on hydride addition and dehydration was converted to 10. One-carbon homologation with the Vilsmeier-Haack reagent proceeded with the expected regiocontrol. This set the stage for the triply convergent assembly of 14 , first reductive amination of the aldehyde 11 with 12 , then acylation of the resulting secondary amine with 13. The nucleophilic 14 was condensed with the aldehyde 8 to give an enone (not illustrated). Exposure of the enone to InCl 3 initiated an elegant cascade cyclization, first of the enamide in a conjugate sense to the enone, then Friedel-Crafts addition of the resulting N-stabilized carbocation to the furan, to deliver 15. The pendant silyloxymethyl group exerted the hoped-for diastereocontrol, allowing the direct construction of the central tetracycle of 3. Hydrolysis and decarboxylation completed the assembly of the diyne 1. Initially, it was found that exposure of 1 to a molybdenum catalyst delivered 2 in only modest yield. As an alternative, they employed the technically more challenging tungsten-based Schrock catalyst. Later, they found that the recently developed Fürstner Mo protocol also worked well. The amide 2 could readily be carried on to the triene 18. With the first-generation Grubbs catalyst G1, kinetic ring-closing metathesis of 18, to complete the assembly of (-)-nakadomarin 3, could be effected without jeopardizing the existing Z alkene.
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"Protection for the Alkyne CH." In Greene's Protective Groups in Organic Synthesis. John Wiley & Sons, Inc., 2014. http://dx.doi.org/10.1002/9781118905074.ch08.
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Chessum, N., S. Couty, and K. Jones. "Selective Hydrogenation in the Presence of Oxygen or Nitrogen Protective Groups." In Alkanes. Georg Thieme Verlag KG, 2009. http://dx.doi.org/10.1055/sos-sd-048-00199.
Full textConference papers on the topic "Alkyne protecting groups"
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Van Reempts, J., B. Van Deuren, M. Borqers, and F. De Clerck. "R 68 070, A COMBINED TXA2-SYNTHETASE/TXA2-PROSTAGLANDIN ENDOPEROXIDE RECEPTOR INHIBITOR. REDUCES CEREBRAL INFARCT SIZE AFTER PHOTOCHEMICALLY INITIATED THROMBOSIS IN SPONTANEOUSLY HYPERTENSIVE RATS." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643470.
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The effects of R 68 070, an oxime-alkane carboxylic acid derivative combining specific thromboxane A2 (TXA2) synthetase inhibition with TXA2/prostaglandin endoperoxide receptor blockade in one molecule, were investigated in a model of photochemically induced stroke in spontaneously hypertensive rats.Each experimental group was compared with an untreated control group. All animals were anesthetized with halothane in N20/02 and artificially ventilated. After incision of the scalp and stereotaxic positioning of a fibre optic light source, halothane was discontinued. When physiological variables reached normal values, a focal cortical infarction was produced by injection of 10 mg.kg-1 rose bengal and 20 min irradiation of the brain through the intact skull. Four hours later the brains were perfusion fixed and damaged areas measured on consecutive histologic sections. Infarct size was calculated by numerical integration.R 68 070 (40 mg.kg-1 p.o.,-3 h) significantly reduced the cerebral infarct size to 2.32 mm3 compared with 5.78 mm3 in controls (median values; n = 5; p < 0.05). At 2.5 mg.kg-1 the lesion was reduced from 11.75 mm3 in the control group to 7.82 mm3 in the treated group (n = 5; p = 0.095). Serum TXB2 levels were reduced by > 80 %.Production of damage in this model is based upon photodynamic generation of singlet molecular oxygen, resulting in peroxidative endothelial cell injury and subsequent platelet thrombus formation. Protection with R 68 070 can be explained by the anti-thrombotic effect of the compound. The relative contribution to this protective effect of synthetase and receptor blockade by R 68 070 are being investigated.
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Suciu, Claudiu Valentin. "Thermal Effects on Nano-Energy Absorption Systems (Nano-EAS)." In 2008 Second International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2008. http://dx.doi.org/10.1115/micronano2008-70039.
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Development of intelligent and ecological energy absorption systems (EAS) is important to various fields such as automotive (vehicle suspensions, bumpers, engine mounts), construction (protections against seismic and wind-induced vibrations), and defense (parachuted objects, armors). Usual EAS use composites, shape-memory alloys and foams. Recently, liquid adsorption/desorption in/from nanoporous solids was employed to develop high-performance nano-EAS. Energy loss is based on the well-known capillary phenomenon: external work must be done to spread a non-wetting liquid on a solid surface. Nano-EAS provide considerably higher dissipated energies, about 1–10J/g at deformability of 30–70%, compared with the energy absorption of Ti-Ni alloys, about 0.01–0.05J/g at deformability of 5–8%. For water against hydrophobic nanoporous silica gel (artificial sand), the nano-EAS become ecological; they can be also made intelligent by thermo-electrical control. Relative to thermal effects, Qiao et al. have investigated, for nanoporous silica gel with insufficient coverage of the alkyl-based hydrophobic coating, the problem of hysteresis recovery by increasing the temperature in the range 20∼80°C. Energy loss capacity reduced severely after the first loading-unloading cycle, so, the hysteresis was found as irreversible. Shape of the first hysteresis, the accessible specific pore volume and the desorption pressure were almost unaffected by the temperature change. At temperature augmentation the second hysteresis was partially recovered and when the temperature exceeded 50°C the system became almost fully reusable. Water inflow was found as governed by Laplace-Washburn equation but the outflow process was perceived as thermally aided. On the other hand, Eroshenko et al. have contradictorily obtained for nanoporous silica gel with full coverage of the alkyl-based hydrophobic coating, a stable hysteresis at repeated working cycles. Adsorption pressure decreased and desorption pressure increased at temperature augmentation, this producing a reduction of the hysteresis area and damping. However, the accessible specific pore volume was found as thermally unaffected. Oppositely, both the in- and out-flows were found as governed by Laplace-Washburn equation. In this work, for nanoporous silica gels with partial and full coverage of the alkyl and fluorocarbon based hydrophobic coatings, the thermal effects on the hysteresis and damping performances are studied. Test rig used is a compression-decompression chamber introduced inside of an incubator that allows temperature adjustment in the range of −10∼50°C. Results reveal that, depending on the hydrophobic coating coverage, findings reported by Qiao et al. and Eroshenko et al. are in fact not contradictory but complementary. However, as expected, the accessible specific pore volume was found to decrease at temperature reduction. In order to explain all these apparently opposite experimental findings, a model based on the water cluster size distribution versus temperature, the pore size distribution of silica gel and the ability of water molecules to form hydrogen bonds with the uncovered hydroxyl groups on the solid surface is proposed.