Academic literature on the topic 'Bis-a-amino acids'
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Journal articles on the topic "Bis-a-amino acids"
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Adamczyk, Maciej, and Rajarathnam E. Reddy. "A stereoselective synthesis of bis-β-amino acids." Tetrahedron: Asymmetry 9, no. 22 (November 1998): 3919–21. http://dx.doi.org/10.1016/s0957-4166(98)00429-7.
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Adamczyk, Maciej, and Rajarathnam E. Reddy. "ChemInform Abstract: A Stereoselective Synthesis of Bis-β-amino Acids." ChemInform 30, no. 17 (June 16, 2010): no. http://dx.doi.org/10.1002/chin.199917208.
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Villemin, Didier, Bernard Moreau, and Nathalie Bar. "MCR under Microwave Irradiation: Synthesis in Water of New 2-Amino-bis(2-phosphonoacetic) Acids." Organics 2, no. 2 (May 11, 2021): 98–106. http://dx.doi.org/10.3390/org2020009.
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Novel 2-amino bis(2-phosphonoacetic) acids were prepared by microwave irradiation of a mixture of amine, glyoxylic acid and phosphorous acid. The reaction takes place with various amines including primary and secondary amines and polyamines, but this reaction is more sensitive to steric hindrance of amine than the similar Kabachnik–Fields reaction. Amino acids can be also transformed into the expected bis(2-phosphonoacetic) acids, with the exception of tryptophan, which gives a β-carboline product.
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Kulsi, Goutam, Abhijit Ghorai, Basudeb Achari, and Partha Chattopadhyay. "Design and synthesis of conformationally homogeneous pseudo cyclic peptides through amino acid insertion: investigations on their self assembly." RSC Advances 5, no. 79 (2015): 64675–81. http://dx.doi.org/10.1039/c5ra11850f.
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Macrocyclic C2 symmetric peptides have been synthesized that contain bis furanoid triazole amino acids linked to a d-α-amino acid or a β-amino acid in each half. Only the former undergoes parallel homo-stacking in solution.
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Tagle, Luis H., Claudio A. Terraza, Alain Tundidor-Camba, and Pablo A. Ortiz. "Silicon-containing oligomeric poly(imido-amides) with amino moieties. Synthesis, characterization and thermal studies." RSC Adv. 4, no. 57 (2014): 30197–210. http://dx.doi.org/10.1039/c4ra04291c.
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Silicon-containing oligomeric poly(imido-amides) (PIAs) were synthesized from dicarboxylic imido-acids containing a Si atom, which were obtained from dianhydrides, amino acids and p-aminobenzoic acid, were polymerized with the diamine bis(4-aminophenyl)diphenylsilane.
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Lindahl, Fredrik, Huy N. Hoang, David P. Fairlie, and Matthew A. Cooper. "Facile synthesis of mono- and bis-methylated Fmoc-Dap, -Dab and -Orn amino acids." Chemical Communications 51, no. 21 (2015): 4496–98. http://dx.doi.org/10.1039/c4cc09780g.
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Kuprat, Marcus, Axel Schulz, Max Thomas, and Alexander Villinger. "Synthesis and characterization of a stable non-cyclic bis(amino)arsenium cation." Canadian Journal of Chemistry 96, no. 6 (June 2018): 502–12. http://dx.doi.org/10.1139/cjc-2017-0420.
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The reaction of Li[Mes*NH] (1, Mes* = 2,4,6-tri-tert-butylphenyl) with aminoarsane Mes*N(H)AsCl2 (2, Mes* = 2,4,6-t-Bu3C6H2) at −80 °C resulted in the formation of bisamino(chloro)arsane (Mes*NH)2AsCl (3Cl) by elimination of LiCl. 3Cl reacted with the Lewis acids such as AlCl3, GaCl3, and Ag[X] (X = AsF6−, OTf−, BF4−; OTf = trifluoromethanesulfonate = OSO2CF3−) upon chloride ion abstraction to give salts bearing the cation [(Mes*NH)2As]+ (3[X]; X = AsF6−, OTf−, BF4−, ECl4; E = Al, Ga). 3+ represents the first NH-functionalized acyclic bis(amino)arsenium cation. The formation of the salts bearing 3+ could also be observed in the reaction of cyclo-1,3-diarsa-2,4-diazane [ClAs(μ-NMes*)]2 (4) with Lewis acids (AlCl3, GaCl3) in the presence of proton sources in solution. All presented salts 3[X] were stable at room temperature and fully characterized.
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Sarmiento-Sánchez, Juan I., Adrián Ochoa-Terán, and Ignacio A. Rivero. "Synthesis and Antioxidant Evaluation of Enantiomerically Pure Bis-(1,2,3-triazolylmethyl)amino Esters from Modifiedα-Amino Acids." Scientific World Journal 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/264762.
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The efforts for synthesis of enantiomerically pure bis-(1,2,3-triazolylmethyl)amino esters6are reported in good yields from anin situgeneratedα-azidomethyl ketone. Optimum experimental conditions were established for preparation ofα-halomethyl ketones10andα-N,N-dipropargylamino esters11, all derived fromα-amino acids. The starting materials reacted under conventional click chemistry conditions, revealing a specific reactivity of bromomethyl ketones over chloromethyl ketones. The antioxidant activity of compounds6was assayed by DPPH method. The compound6cwith an IC50of 75.57 ± 1.74 μg mL−1was the most active. Technically, this methodology allows the preparation of a combinatorial library of analogues with different structural characteristics depending on the nature of the modifiedα-amino acids employed in the synthesis.
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Miličević, Ante, and Nenad Raos. "Theoretical analysis of apical bonding in copper(II) chelates withN-substituted amino acids." Journal of Applied Crystallography 43, no. 1 (December 9, 2009): 42–47. http://dx.doi.org/10.1107/s0021889809047748.
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The interdependence between the side of apical coordination of H2O and steric crowding at the apical positions was investigated on a set of 34 copper(II) bis-complexes withN- andN,N-substituted amino acids. As a measure of steric crowding, overlapping volumesV* were used, calculated using a modified overlapping spheres method. Steric crowding around the apically bonded ligand was the same for this set of complexes as for the copper(II) bis-complexes with naturally occurring amino acids, with the optimal occupied volume values between 1 and 1.5 Å3. The interdependence between the length of the apical bond and distortion of the coordination polyhedron was also studied. The apical bond length showed sigmoidal dependence on the magnitude of distortion.
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Chen, Jingtang, Thomas Pili, and Wolfgang Beck. "Metallkomplexe mit biologisch wichtigen Liganden, L [1] Palladium(II)-, Platin(II)- und Kupfer(II)-Komplexe von α-Aminosäure-N-Glykosiden und von Fructose-Aminosäuren (Amadori-Verbindungen) / Metal Complexes of Biologically Important Ligands, L [1] Palladium(II), Platinum(II) and Copper(II) Complexes of α-Amino Acid-N-Glycosides and of Fructose-Amino Acids (Amadori-Compounds)." Zeitschrift für Naturforschung B 44, no. 4 (April 1, 1989): 459–64. http://dx.doi.org/10.1515/znb-1989-0414.
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Various N-glycosides derived from glucose and α-amino acids and the isomeric Amadori compounds form bis(chelate) complexes of copper(II), palladium (II) and platinum (II). The IR spectra indicate that the ligands are coordinated through the amino group and a carboxylate oxygen atom.
Dissertations / Theses on the topic "Bis-a-amino acids"
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Swift, Jonathan Paul. "The allenyl bis-amino acids : a novel mimic for the disulphide bond." Thesis, University of Bath, 1999. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760730.
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Ranzenigo, Anna. "Synthesis of hydroxylated indolizidines and diamino suberic acid derivatives: use of tartaric acid and other approaches." Doctoral thesis, 2022. http://hdl.handle.net/2158/1286510.
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Tartaric acid enantiomers are very versatile and useful chiral pool compounds. Part of this research project was devoted to the study of these molecules as starting materials for the synthesis of biologically active natural products and analogs such as iminosugars and bis-a-amino acids. Bis-a-amino acids are a class of structurally interesting compounds. Among them, diaminosuberic acid is an appealing stable mimic of cystine. Object of this work was to synthetize different derivatives of diamino suberic acid using various strategies, including the tartaric acid approach, in order to get new interesting polyfunctionalized small molecules and to assess a stereoselective synthetic approach to the challenging structure of the aglycone of ascaulitoxin. Iminosugars are another class highly studied compounds. Lentiginosine is a natural iminosugar whose synthesis can be achieved by 1,3-dipolar cycloaddition of an enantiopure dialkoxypyrroline N-oxide, in turn derived from tartaric acid. The highly versatility of cyclic nitrones as precursors of azaheterocycles motivated the labeling a dialkoxypyrroline N-oxide with deuterium and its application to the synthesis of 8a-d-lentiginosine. It was also interesting to modify the parent structure of DHA, to try to control the half-life of the system and then insert an amino group useful to couple in an easy way DHA with biologically active products including amino acids. The last two projects presented, in addition to the synthetic challenge, some kinetic studies that were carried out using different techniques.
Book chapters on the topic "Bis-a-amino acids"
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"Peptide Natural Products II: Nonribosomal Peptides." In Natural Product Biosynthesis, 150–91. The Royal Society of Chemistry, 2022. http://dx.doi.org/10.1039/bk9781839165641-00150.
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Peptide natural products assembled by nonribosomal peptide synthetase (NRPS) machinery activate proteinogenic and nonproteinogenic amino acids, install them as thioesters tethered to phosphopantetheinyl prosthetic groups on peptidyl carrier protein domains, and carry out chain elongations by amide bond formations. The growing peptidyl chain, as a series of elongating peptidyl thioesters, is released when it reaches the most downstream NRPS assembly-line module, typically by either hydrolysis, macrolactonization/macrolactamization, reductive elimination, or Dieckmann condensation. A series of dedicated tailoring enzymes act both on assembly lines or as post-assembly-line tailoring catalysts to morph the peptide backbone and side chains into compact, hydrolysis-resistant linear and cyclic end products. NRPS assembly lines build the aminoadipyl-cysteinyl-d-valine tripeptide, which is then bis-cyclized to the 4,5-fused ring system of lactam antibiotics, as well as the heptapeptide scaffold of vancomycin-type glycopeptide antibiotics. Additional nonribosomal peptide biosynthesis products analyzed include didemnin, kutzneride, tyrocidine, polymyxin, ADEPs, daptomycin, enterobactin, yersiniabactin, echinocandin, and obafluorin. Hybrid nonribosomal peptide-polyketide assembly lines lead to rapamycin, bleomycin, and colibactin.
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Benkoski, Léa, and Tristan H. Lambert. "Construction of Multiple Stereocenters." In Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0039.
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Erick M. Carreira at ETH Zürich reported (Science 2013, 340, 1065) the enantioselective α-allylation of aldehyde 1 with alcohol 2 to produce 3 using a dual catalytic system involving a chiral iridium complex and amine 5. This stereodivergent method allows access to all of the possible stereoisomers of 3. In a conceptually related process, John F. Hartwig at the University of California, Berkeley reported (J. Am. Chem. Soc. 2013, 135, 2068) the highly stereoselective allylic alkylation of azlactone 6 with allylic carbonate 7 catalyzed by a combination of Ir(cod)Cl₂, ligand 9, and racemic silver phosphate 10. An enantioselective three-component Mannich-type reaction of tert-butyl diazoacetate, aniline, and imine 11 to produce α,β-bis(arylamino) acid derivative 13 under dual catalysis with Rh₂(OAc)₄ and acid 12 was developed (Synthesis 2013, 45, 452) by Wenhao Hu at the Shanghai Engineering Research Center of Molecular Therapeutics and New Drug Development. Keiji Maruoka at Kyoto University reported (Chem. Commun. 2013, 49, 1118) a one-pot cross double-Mannich reaction of acetylaldehyde 14, and imines 16 and 17 using axially chiral amino sulfonamide 15 to obtain densely functionalized 1,3-diamine 18 as a single stereoisomer. Jeffrey S. Johnson at the University of North Carolina at Chapel Hill reported (Org. Lett. 2013, 15, 2446) the asymmetric synthesis of enantioenriched anti-α-hydroxy-β-amino acid derivative 21 from 19 by treatment with oxone followed by catalytic hydrogenation using Ru(II) complex 20. Naoya Kumagai and Masakatsu Shibasaki at the Institute of Microbial Chemistry found (Org. Lett. 2013, 15, 2632) that a silver complex of bisphosphine 24 effected a syn-selective and highly enantioselective Mannich-type reaction of aldimine 22 and α-sulfanyl lactone 23 to furnish the stereodiad 25 with very high ee. The enantioselective homocrotylation of octanal 26 with cyclopropylcarbinylboronate 27 to produce alcohol 28 with high ee was disclosed (J. Am. Chem. Soc. 2013, 135, 82) by Isaac J. Krauss at Brandeis University with computational studies provided by Kendall N. Houk at UCLA. Benjamin List at the Max-Planck-Institut für Kohlenforschung reported (J. Am. Chem. Soc. 2013, 135, 6677) the enantioselective epoxidation of cyclohexenone 29 utilizing cinchona alkaloid- derived catalyst 30.
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Taber, Douglass F. "Synthesis of C-N Natural Products: (-)-α-Kainic Acid (Helmchen), (+)-Tylophorine (Opatz), (-)-Lycoperine A (Rychnovsky), Fluvirucidine A2 (Suh), Complanidine A (Sarpong)." In Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0058.
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Günter Helmchen of the Ruprecht-Karls-Universität Heidelberg set (Organic Lett. 2010, 12, 1108) the absolute configuration of 3 by Ir*-mediated coupling of 1 with 2. Diastereoselective Pauson-Khand cyclization then led to (-)-α-kainic acid 5. Till Opatz, now at the Johannes Gutenberg-Universität Mainz, showed (Organic Lett. 2010, 12, 2140) that the product from the Dibal reduction of 6 could be condensed with the amine 7 without epimerization. Kim cyclization then directly delivered the pentacyclic alkaloid (+)-tylophorine 9. The interesting dimeric alkaloid lycoperine A 13 was recently isolated from the Japanese club moss Lycopodium hamiltonii. Scott D. Rychnovsky of the University of California, Irvine, prepared (Organic Lett. 2010, 12, 72) 12 by double alkylation of the bis-nitrile 11 with the enantiomerically pure allylic bromide 10. Although the projected reductive decyanation of 12 failed, hydrolysis followed by diastereoselective reductive amination successfully gave 13. Retrosynthetic analysis of fluvirucinine A2 16 could lead to an acyclic amino acid, which could be cyclized to the macrolactam. Young-Ger Suh of Seoul National University took (Organic Lett. 2010, 12, 2040) a different approach, building up the 14-membered ring system by two four-carbon ring expansions, beginning with an enantiomerically pure piperidine precursor. The second of these enolate-based aza-Claisen ring expansions is illustrated in the conversion of 14 to 15. Richmond Sarpong of the University of California, Berkeley, faced (J. Am. Chem. Soc. 2010, 132, 5926) a different sort of challenge in the synthesis of the dimeric Lycopodium alkaloid complanadine A 19. Even with established access to monomers such as 17 and its precursors, it was not clear how the 5-position of the pyridine ring could be selectively activated for bond formation. The solution to this dilemma was found in the work of Hartwig. Following that precedent, Ir-catalyzed activation of 17 converted it cleanly into the borinate 18, which could then be coupled with a pyridone triflate to complete the synthesis of 19.
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Taber, Douglass F. "Enantioselective Construction of Arrays of Stereogenic Centers: The Breit Synthesis of (+)-Bourgeanic Acid." In Organic Synthesis. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199965724.003.0044.
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Kyungsoo Oh of Indiana University Purdue University Indianapolis devised (Organic Lett. 2009, 11, 5682) a new ligand that with Cu delivered predominantly one diastereomer of the Henry adduct 3, and with Zn delivered the other. Liu-Zhu Gong of the University of Science and Technology of China reported (Angew. Chem. Int. Ed. 2009, 48, 6503) the Darzens condensation of the diazoacetamide 5 with a variety of aldehydes to give the corresponding epoxy amides with high diastereo- and enantiocontrol. Michael J. Krische of the University of Texas, Austin, applied (Organic Lett. 2009, 11, 3108, 3112) his asymmetric allylation to a variety of primary diols including 7, leading to the homologated product 9. M. Christina White of the University of Illinois showed (J. Am. Chem Soc. 2009, 131, 11707) that Pd-mediated oxidative amination of carbamate 10 delivered the protected 1,3-amino alcohol 11 with high diastereocontrol. James P. Morken of Boston College devised (J. Am. Chem Soc. 2009, 131, 9134) a Pt catalyst for the asymmetric bis-boration of dienes. The allyl borane prepared from 12 added with high stereocontrol to benzaldehyde, to give, after oxidation, the diol 13. Carlos F. Barba III of Scripps/La Jolla optimized (Angew. Chem. Int. Ed. 2009, 48, 9848) an organocatalyst for the enantioselective conjugate addition of an alkoxy aldehyde 15 to a nitroalkene. Do Hyun Ryu of Sungkyunkwan University found (Chem. Commun. 2009, 5460) that an organocatalyst could also mediate the dipolar cycloaddition of a diazo ester 18 to an unsaturated aldehyde, giving 19 with high diastereo- and enantiocontrol. Francesco Fini and Luca Bernardi of the University of Bologna developed (J. Am. Chem Soc. 2009, 131, 9614) an organocatalyst that effected enantioselective dipolar cycloaddition of the nitrone derived from 20 to the unsaturated ester 21. Kevin Burgess of Texas A&M optimized (J. Am. Chem Soc. 2009, 131, 13236) an Ir catalyst for the enantioselective hydrogenation of trisubstituted alkenes such as 23. In the course of a synthesis of (+)-faranal, Varinder K. Aggarwal of the University of Bristol described (Angew. Chem. Int. Ed. 2009, 48, 6317) a one-pot procedure for the conversion of the allyl borane 25 into 27.
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Taber, Douglass F. "Organic Functional Group Interconversion." In Organic Synthesis. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190646165.003.0003.
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Alois Fürstner of the Max-Planck-Institut Mülheim devised (Angew. Chem. Int. Ed. 2013, 52, 14050) a Ru catalyst for the trans- selective hydroboration of an alkyne 1 to 2. Qingbin Liu of Hebei Normal University and Chanjuan Xi of Tsinghua University coupled (Org. Lett. 2013, 15, 5174) the alkenyl zirconocene derived from 3 with an acyl azide to give the amide 4. Chulbom Lee of Seoul National University used (Angew. Chem. Int. Ed. 2013, 52, 10023) a Rh catalyst to convert a terminal alkyne 5 to the ester 6. Laura L. Anderson of the University of Illinois, Chicago devised (Org. Lett. 2013, 15, 4830) a protocol for the conversion of a terminal alkyne 7 to the α-amino aldehyde 9. Dewen Dong of the Changchun Institute of Applied Chemistry developed (J. Org. Chem. 2013, 78, 11956) conditions for the monohydrolysis of a bis nitrile 10 to the monoamide 11. Aiwen Lei of Wuhan University optimized (Chem. Commun. 2013, 49, 7923) a Ni catalyst for the conversion of the alkene 12 to the enamide 13. Kazushi Mashima of Osaka University optimized (Adv. Synth. Catal. 2013, 355, 3391) a boronic ester catalyst for the conversion of an amide 14 to the ester 15. Jean- François Paquin of the Université Laval prepared (Eur. J. Org. Chem. 2013, 4325) the amide 17 by coupling an amine with the activated intermediate from reaction of an acid 16 with Xtal- Fluor E. Steven Fletcher of the University of Maryland School of Pharmacy designed (Tetrahedron Lett. 2013, 54, 4624) the azodicarbonyl dimorpholide 18 as a reagent for the Mitsunobu coupling of 19 with 20. The reduced form of 18 was readily separated by extraction into water and reoxidized. Jens Deutsch of the Universität Rostock found (Chem. Eur. J. 2013, 19, 17702) simple ligands for the Ru-mediated borrowed hydrogen conversion of an alcohol 22 to the amine 23. Ronald T. Raines of the University of Wisconsin devised (J. Am. Chem. Soc. 2013, 135, 14936) a phosphinoester for the efficient conversion in water of an azide 24 to the diazo 25.
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Taber, Douglass F. "Reactions of Alkenes." In Organic Synthesis. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190200794.003.0030.
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Fung-E Hong of the National Chung Hsing University devised (Adv. Synth. Catal. 2011, 353, 1491) a protocol for the oxidative cleavage of an alkene 1 (or an alkyne) to the carboxylic acid 2. Patrick H. Dussault of the University of Nebraska found (Synthesis 2011, 3475) that Na triacetoxyborohydride reduced the methoxy hydroperoxide from the ozonolysis of 3 to the aldehyde 4. Reductive amination of 4 can be effected in the same pot with the same reagent. Philippe Renaud of the University of Bern used (J. Am. Chem. Soc. 2011, 133, 5913) air to promote the free radical reduction to 6 of the intermediate from the hydroboration of 5. Robert H. Grubbs of Caltech showed (Org. Lett. 2011, 13, 6429) that the phosphonium tetrafluoroborate 8 prepared by hydrophosphonation of 7 could be used directly in a subsequent Wittig reaction. Dominique Agustin of the Université de Toulouse epoxidized (Adv. Synth. Catal. 2011, 353, 2910) the alkene 9 to 10 without solvent other than the commercial aqueous t-butyl hydroperoxide. Justin M. Notestein of Northwestern University effected (J. Am. Chem. Soc. 2011, 133, 18684) cis dihydroxylation of 9 to 11 using 30% aqueous hydrogen peroxide. Chi-Ming Che of the University of Hong Kong devised (Chem. Commun. 2011, 47, 10963) a protocol for the anti-Markownikov oxidation of an alkene 12 to the aldehyde 13. Aziridines such as 14 are readily prepared from alkenes. Jeremy B. Morgan of the University of North Carolina Wilmington uncovered (Org. Lett. 2011, 13, 5444) a catalyst that rearranged 14 to the protected amino alcohol 15. A monosubstituted alkene 16 is particularly reactive both with free radicals and with coordinately unsaturated metal centers. A variety of transformations of monosubstituted alkenes have been reported. Nobuharu Iwasawa of the Tokyo Institute of Technology employed (J. Am. Chem. Soc. 2011, 133, 12980) a Pd pincer complex to catalyze the oxidative monoborylation of 16 to give 17. The 1,1-bis boryl derivatives could also be prepared. Professor Renaud effected (J. Am. Chem. Soc. 2011, 133, 13890) radical addition to 16 leading to the terminal azide 18.
Conference papers on the topic "Bis-a-amino acids"
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Simijonović, Dušica, Marko Antonijević, Edina Avdović, Zorica Petrović, and Zoran Marković. "INHIBITORY EFFECT OF COUMARIN BENZOYLHYDRAZONES ON MCL-1 PROTEIN." In 1st INTERNATIONAL Conference on Chemo and BioInformatics. Institute for Information Technologies, University of Kragujevac, 2021. http://dx.doi.org/10.46793/iccbi21.442s.
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The protein that controls cell differentiation in acute myeloid leukemia is MCL-1. High-level of this protein causes the carcinogenesis. In this paper inhibitory effect of two coumarin benzoylhydrazones,(E)-2-hydroxy-N’-(1-(2-oxo-2H-chromen-3-yl)ethylidene)benzohydrazide (A) and (E)-4-hydroxy-N’-(1-(2-oxo-2H-chromen-3-yl)ethylidene)benzohydrazide (B) against MCL-1 protein was investigated. For this purpose, a molecular docking simulations were used. The obtained results showed that compound A showed better activity than compound B. Also, the docking simulations against MCL-1 protein were performed for melphalan or (2S)-2-amino- 3-{4-[bis(2-chloroethyl)amino]phenyl}propanoic acid and two 4-chlorocoumarin benzoylhydrazone derivatives, N′-[(E)-(4-chloro-2-oxo-2H-chromen-3-yl)- methylidene]benzohydrazide (4a) and N′-[(E)-(4-chloro-2-oxo-2H-chromen-3-yl)- methylidene]-4-hydroxybenzohydrazide (4b). In this study, melphalan as a chemotherapy drug commonly used in treating multiple myeloma and compounds 4a and 4b as structurally similar compounds with A and B were used as reference compounds. It was shown that these reference compounds exhibited similar activity as compound B. In addition, the potential toxicology of compounds A and B, as well as reference compounds was determined by the ProTox-II webserver. The results revealed that compounds A and B are 3 to 5 times lower toxic than reference compounds.
Reports on the topic "Bis-a-amino acids"
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Rouseff, Russell L., and Michael Naim. Characterization of Unidentified Potent Flavor Changes during Processing and Storage of Orange and Grapefruit Juices. United States Department of Agriculture, September 2002. http://dx.doi.org/10.32747/2002.7585191.bard.
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Citrus juice flavor quality traditionally diminishes after thermal processing and continuously during storage. Our prior studies found that four of the five most potent off-aromas formed during orange juice storage had not been identified. The primary emphasis of this project was to characterize and identify those potent flavor degrading aroma volatiles so that methods to control them could be developed and final flavor quality improved. Our original objectives included: 1 Isolate and characterize the most important unidentified aroma impact compounds formed or lost during pasteurization and storage. 2. Determination of thiamine and carotenoid thermal decomposition and Strecker degradation pathways in model solutions as possible precursors for the unidentified off-flavors. 3. Evaluate the effectiveness of an "electronic nose" to differentiate the headspace aromas of from untreated and heat pasteurized orange and grapefruit juices. 4. Use model systems of citrus juices to investigate the three possible precursor pathways (from 2) for flavor impact compounds formed or lost during pasteurization or storage. RESULTS - The components responsible for citrus storage off flavors and their putative precursors have now been identified. Certain carotenoids (b-carotene) can thermally degrade to produce b-ionone and b-damascenone which are floral and tobacco smelling respectively. Our GC-O and sensory experiments indicated that b-damascenone is a potential storage off-flavor in orange juice. Thiamine (Vitamin B1) degradation produces 2-methyl-3-furan thiol, MFT, and its dimer bis(2- methyl-3-furyl) disulfide which both produce meaty, savory aromas. GC-O and sensory studies indicated that MFT is another storage off-flavor. Methional (potato aroma) is another off flavor produced primarily from the reaction of the native amino acid, methionine, and oxidized ascorbic acid (vitamin C). This is a newly discovered pathway for the production of methional and is more dominant in juices than the classic Maillard reaction. These newly identified off flavors diminish the flavor quality of citrus juices as they distort the flavor balance and introduce non-typical aromas to the juice flavor profile. In addition, we have demonstrated that some of the poor flavor quality citrus juice found in the market place is not only from the production of these and other off flavors but also due to the absence of desirable flavor components including several potent aldehydes and a few esters. The absence of these compounds appears to be due to incomplete flavor volatile restoration after the making of juice concentrates. We are the first to demonstrate that not all flavor volatiles are removed along with water in the production of juice concentrate. In the case of grapefruit juice we have documented which flavor volatiles are completely removed, which are partially removed and which actually increase because of the thermal process. Since more that half of all citrus juices is made into concentrate, this information will allow producers to more accurately restore the original flavor components and produce a juice with a more natural flavor. IMPLICATIONS - We have shown that the aroma of citrus juices is controlled by only 1-2% of the total volatiles. The vast majority of other volatiles have little to no direct aroma activity. The critical volatiles have now been identified. The ability to produce high quality citrus juices requires that manufacturers know which chemical components control aroma and flavor. In addition to identifying the critical flavor components (both positive and negative), we have also identified several precursors. The behavior of these key aroma compounds and their precursors during common manufacturing and storage conditions has been documented so manufacturers in Israel and the US can alter production practices to minimize the negative ones and maximize the positive ones.