- A Peierls Transition in Long Polymethine Molecular Wires: Evolution of Molecular Geometry and Single-Molecule Conductance
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Molecules capable of mediating charge transport over several nanometers with minimal decay in conductance have fundamental and technological implications. Polymethine cyanine dyes are fascinating molecular wires because up to a critical length, they have no bond-length alternation (BLA) and their electronic structure resembles a one-dimensional free-electron gas. Beyond this threshold, they undergo a symmetry-breaking Peierls transition, which increases the HOMO-LUMO gap. We have investigated cationic cyanines with central polymethine chains of 5-13 carbon atoms (Cy3+-Cy11+). The absorption spectra and crystal structures show that symmetry breaking is sensitive to the polarity of the medium and the size of the counterion. X-ray crystallography reveals that Cy9·PF6 and Cy11·B(C6F5)4 are Peierls distorted, with high BLA at one end of the π-system, away from the partially delocalized positive charge. This pattern of BLA distribution resembles that of solitons in polyacetylene. The single-molecule conductance is essentially independent of molecular length for the polymethine salts of Cy3+-Cy11+ with the large B(C6F5)4- counterion, but with the PF6- counterion, the conductance decreases for the longer molecules, Cy7+-Cy11+, because this smaller anion polarizes the π-system, inducing a symmetry-breaking transition. At higher bias (0.9 V), the conductance of the shorter chains, Cy3+-Cy7+, increases with length (negative attenuation factor, β = -1.6 nm-1), but the conductance still drops in Cy9+ and Cy11+ with the small polarizing PF6- counteranion.
- Xu, Wenjun,Leary, Edmund,Sangtarash, Sara,Jirasek, Michael,González, M. Teresa,Christensen, Kirsten E.,Abellán Vicente, Lydia,Agra?t, Nicolás,Higgins, Simon J.,Nichols, Richard J.,Lambert, Colin J.,Anderson, Harry L.
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supporting information
p. 20472 - 20481
(2021/12/09)
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- Step-Economic Synthesis of Biomimetic β-Ketopolyene Thioesters and Demonstration of Their Usefulness in Enzymatic Biosynthesis Studies
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Studies on the biosynthetic processing of polyene thioester intermediates are complicated by limited access to appropriate substrate surrogates. We present a step-economic synthetic access to biomimetic β-ketopolyene thioesters that is based on an Ir-catalyzed reductive Horner-Wadsworth-Emmons olefination. New β-ketotriene and pentaenethioates of pantetheine and N-acetylcysteamine were exemplarily synthesized via short and concise routes. The usefulness of these compounds was demonstrated in an in vitro assay with the ketoreductase domain MycKRB from mycolactone biosynthesis.
- Hahn, Frank,Ro?, Theresa,Schr?der, Marius,Wunderlich, Johannes
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- Controlling Asymmetric Remote and Cascade 1,3-Dipolar Cycloaddition Reactions by Organocatalysis
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The regio- and stereoselective control of cycloaddition reactions to polyconjugated systems has been demonstrated by applying asymmetric organocatalysis. Reaction of 2,4-dienals with nitrones allows for a highly regio- and stereoselective 1,3-dipolar cycl
- Poulsen, Pernille H.,Vergura, Stefania,Monleón, Alicia,J?rgensen, Danny Kaare Bech,J?rgensen, Karl Anker
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supporting information
p. 6412 - 6415
(2016/06/09)
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- Total synthesis and antibacterial testing of the A54556 cyclic acyldepsipeptides isolated from streptomyces hawaiiensis
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The first total synthesis of all six known A54556 acyldepsipeptide (ADEP) antibiotics from Streptomyces hawaiiensis is reported. This family of compounds has a unique mechanism of antibacterial action, acting as activators of caseinolytic protease (ClpP). Assembly of the 16-membered depsipeptide core was accomplished via a pentafluorophenyl ester-based macrolactamization strategy. Late stage amine deprotection was carried out under neutral conditions by employing a mild hydrogenolysis strategy, which avoids the formation of undesired ring-opened depsipeptide side products encountered during deprotection of acid-labile protecting groups. The free amines were found to be significantly more reactive toward late stage amide bond formation as compared to the corresponding ammonium salts, giving final products in excellent yields. A thorough NMR spectroscopic analysis of these compounds was carried out to formally assign the structures and to aid with the spectroscopic assignment of ADEP analogues. The identity of two of the structures was confirmed by comparison with biologically produced samples from S. hawaiiensis. An X-ray crystallographic analysis of an ADEP analogue reveals a conformation similar to that found in cocrystal structures of ADEPs with ClpP protease. The degree of antibacterial activity of the different compounds was evaluated in vitro using MIC assays employing both Gram-positive and Gram-negative strains and a fluorescence-based biochemical assay.
- Goodreid, Jordan D.,Wong, Keith,Leung, Elisa,McCaw, Shannon E.,Gray-Owen, Scott D.,Lough, Alan,Houry, Walid A.,Batey, Robert A.
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supporting information
p. 2170 - 2181
(2014/12/11)
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- Process for the preparation of 2,4,6-octatriene-1-oic acid and 2,4,6-octatriene-1-ol
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The present invention concerns a process for synthesis of 2,4,6-octatriene-1-oic acid and 2,4,6-octatriene-1-ol, which comprises the following stages: a) reaction between 2,4-trans-hexadienal and triethyl phosphonoacetate to give ethyl 2,4,6-trans-octatrienoate; b) alkaline hydrolysis of ethyl 2,4,6-trans-octatrienoate to give the corresponding alkaline salt; c) acidification of said salt to give 2,4,6-trans-octatrienoic acid, which can be separated or can undergo the following further stages: d) reaction of the 2,4,6-trans-octatrienoic acid with ethyl chloroformiate to give the mixed anhydride formed by 2,4,6-trans-octatrienoic acid and ethyl carbonic acid; e) reduction of said mixed anhydride with sodium borohydride to give 2,4,6-transoctatrienol; and optionally a purification stage of the end product.
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Page/Page column 4
(2010/11/03)
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- Direct conversion of polyconjugated compounds into their corresponding carboxylic acids by Acetobacter aceti
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The conversion of polyconjugated aldehydes or alcohols into their corresponding acids was carried out using Acetobacter aceti. The analytical results were compared with those of the acids chemically obtained using a Horner-Wittig reaction.
- Pini, Elena,Bertacche, Vittorio,Molinari, Francesco,Romano, Diego,Gandolfi, Raffaella
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p. 8638 - 8641
(2008/12/21)
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- Synthesis and spectral properties of amphophilic lipids with linear conjugated polyene and phenylpolyene fluorescent groups
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Lipophilic fluorescent groups with a chain-like linear conformation emitting in the visible range and with high photostability are presently unavailable. These structures would be of great interest as labels for long-chain fatty acids and phospholipids lacking intrinsic fluorescent groups. With this aim in mind, we report the synthesis and the spectroscopic characterization of a series of emitting amphiphilic lipids that may approach that ideal fluorescent tag. Each lipid was constructed by attaching a linear, all-(E) conjugated pentaene, tetraenyne, ω-phenyltetraene, or ω-phenyltrienyne chromophore to a hydrophilic head-group through a polymethylene chain spacer. The key steps of the synthesis were the Pd 0-mediated cross-coupling reaction between bromopolyenes and terminal acetylenic compounds, yielding tetraenynes or ω-phenyltrienynes, and the subsequent triple-bond partial reduction, producing the corresponding pentaenes or ω-phenyltetraenes in good overall yields. This method represents a further successful example of the so-called "acetylenic approach" to the indirect high-yield synthesis of polyene systems. In the case of ω-phenyltrienynes, a higher proportion of the all-(E) isomer was obtained using an alternative method based on the reaction of an ω- phenyldienylphosphonate with an α-acetylenic aldehyde. Some of the resulting compounds exhibit spectral and photochemical properties that warrant their use as emitting lipophilic tags. Thus, the cophenyltetraene and ω-phenyltrienyne members of the series show intense absorption bands in the 320-370 nm range with fluorescence emission centered at 475 nm and quantum yields up to 0.25. These parameters are appropriate for the applications noted above. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Quesada, Ernesto,Delgado, Javier,Hornillos, Valentin,Acuna, A. Ulises,Amat-Guerri, Francisco
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p. 2285 - 2295
(2008/02/06)
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- De novo asymmetric synthesis of anamarine and its analogues
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The enantioselective synthesis of anamarine has been achieved in 21 steps. The route relies on enantio- and regioselective Sharpless dihydroxylation of dienoate ester and zinc borohydride reduction to establish the C-8-C-11 stereochemistry. A diastereosel
- Gao, Dong,O'Doherty, George A.
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p. 9932 - 9939
(2007/10/03)
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- Further Reactions of t-Butyl 3-Oxobutanthioate and t-Butyl 4-Diethylphosphono-3-oxobutanthioate: Carbonyl Coupling Reactions, Amination, Use in The Preparation of 3-Acyltetramic Acids and Application to The Total Synthesis of Fuligorubin A.
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Key words: Acyltetramic acid; Phosphonate; Wadsworth-Emmons; Dieckmann cyclisation; Fuligorubin A. Abstract: The use of t-butyl-3-oxobutanthioate (1) and t-butyl 4-diethylphosphono-3-oxobuthanthioate (2) for the preparation of homologated derivatives suitable for amination in the presence of silver(I) trifluoroacetate to afford the corresponding β-ketoamides is discussed.In particular Wadsworth-Emmons coupling reactions of (2) with various carbonyl compounds gave good yields of E-substituted products.Many of the β-ketoamides were shown to be suitable precursors for 3-acyltetramic acids using a Dieckman cyclisation with tetra-n-butyl ammonium fluoride as the cyclising base.These new reactions were applied to the total synthesis of the polyene 3-acyltetramic acid fuligorubin A.
- Ley, Steven V.,Smith, Stephen C.,Woodward, Peter R.
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p. 1145 - 1174
(2007/10/02)
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- A convenient diastereoselective total synthesis of andrimid
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A convenient diastereoselective synthesis of andrimid was accomplished in a straightforward approach and also several β-substituted cyclic imides were prepared in a facile manner.
- Rama Rao,Singh,Varaprasad
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p. 4393 - 4396
(2007/10/02)
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- USE OF t-BUTYL 4-DIETHYLPHOSPHONO-3-OXOBUTANETHIOATE FOR TETRAMIC ACID SYNTHESIS: TOTAL SYNTHESIS OF THE PLASMODIAL PIGMENT FULIGORUBIN A
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A short, efficient synthesis of the yellow slime mould pigment fuligorubin A (I) has been achieved using coupling of t-butyl 4-diethylphosphono-3-oxobutanethioate with deca-2,4,6,8-tetraenal and subsequent substitution with a glutamic acid derivative followed by Dieckmann cyclisation.
- Ley, Steven V.,Smith, Stephen C.,Woodward, Peter R.
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p. 5829 - 5832
(2007/10/02)
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- Preparation of (E)-1,3,5-Hexatriene and (3E,5E)-1,3,5,7-Octatetraene by the Palladium Catalyzed Elimination of Acetic Acid form Allylic Acetates
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Palladium complex-catalyzed elimination of acetic acid from (2E,4E)-2,4-hexadienyl acetate and (2E,4E,6E)-2,4,6-octatrienyl acetate afforded, respectively, the title conjugated polyenes stereoselectively.
- Yamamoto, Keiji,Suzuki, Shigeaki,Tsuji, Jiro
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p. 2541 - 2542
(2007/10/02)
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