- Femtosecond ultraviolet-visible absorption study of all-trans→13-cis9-cis photoisomerization of retinal
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The all-trans→13-cis9-cis photoisomerization reaction of retinal in aerated nonpolar solvents has been studied by femtosecond time-resolved ultraviolet-visible (UV-VIS) absorption spectroscopy. The excited-state absorption spectra in the wavelength region 400-800 nm indicate that there is no all-trans→13-cis9-cis isomerization reaction pathway that is complete in the electronic excited singlet manifold of S1, S2, and S3. The ground-state bleaching recovery of all-trans retinal monitored in the near UV (ultraviolet) wavelength region 310-390 nm shows that a perpendicular excited singlet state (p*) takes part in the all-trans→13-cis9-cis isomerization reaction. The lifetime of p* is about 7 ps, and the precursor of p* is most probably the S2 state. The isomerization quantum yield derived from the femtosecond UV absorption data agrees well with those determined by the HPLC analysis of the photoproduct. The temperature dependence of the isomerization quantum yield indicates the existence of a potential-energy barrier as high as (1.2±0.6)×103cm-1 on the reaction pathway from the S2 state to the p* state.
- Yamaguchi, Shoichi,Hamaguchi, Hiro-O
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- The Crystal Structure of 13-cis-Retinal. The Molecular Structures of its 6-s-cis and 6-s-trans Conformers
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The crystal and molecular structure of 13-cis-retinal, C20H28O, has been determined by single-crystal X-ray diffraction techniques using counter methods.The structure was refined by full-matrix least-squares procedures using 2762 unique and significant (at the 2? level) reflections to a final weighted R index of 0.062.Triclinic crystals form in the space group P1/ with unit-cell dimensions of a=12.494(6), b=18.279(8), c=7.992(5) Angstroem, α=100.26(4), β=90.26(5), γ=94.35(4) deg, with V=1790(2) Angstroem3, Z=4, Dc=1.055 Mg m-3, Mr=284.4, F(000)=624.The crystal structure discloses the presence of two conformers.In the 6-s-trans conformer, the double bond in the cyclohexene ring lies nearly in the plane of the polyene chain of the molecule, while in the 6-s-cis conformer, the ring is rotated 110 deg from this orientation.Although the greater extent of the conjugated system in the 6-s-trans conformer indicates that it has more resonance stabilization than the 6-s-cis conformer, its intramolecular contacts and distortions show that it also has a higher steric energy.For the two conformers to coexist in the crystal, these two energy differences must nearly balance.
- Simmons, Charles J.,Liu, Robert S. H.,Denny, Marlene,Seff, Karl
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- A porous coordination network catalyzes an olefin isomerization reaction in the pore
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(Figure Presented) All-trans retinal efficiently diffused into the pore of a porous coordination network consisting of ZnI2 and an electron-deficient triazine-cored ligand. Enclathrated retinal was isomerized into the 13-cis form and easily replaced with all-trans retinal in solution, thus revealing the catalysis of retinal isomerization by the porous network.
- Ohara, Kazuaki,Kawano, Masaki,Inokuma, Yasuhide,Fujita, Makoto
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Read Online
- Catalytic synthesis of 9-cis-retinoids: Mechanistic insights
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The regioselective Z-isomerization of thermodynamically stable all-trans retinoids remains challenging, and ultimately limits the availability of much needed therapeutics for the treatment of human diseases. We present here a novel, straightforward approach for the catalytic Z-isomerization of retinoids using conventional heat treatment or microwave irradiation. A screen of 20 transition metal-based catalysts identified an optimal approach for the regioselective production of Z-retinoids. The most effective catalytic system was comprised of a palladium complex with labile ligands. Several mechanistic studies, including isotopic H/D exchange and state-of-the-art quantum chemical calculations using coupled cluster methods indicate that the isomerization is initiated by catalyst dimerization followed by the formation of a cyclic, six-membered chloropalladate catalyst-substrate adduct, which eventually opens to produce the desired Z-isomer. The synthetic development described here, combined with thorough mechanistic analysis of the underlying chemistry, highlights the use of readily available transition metal-based catalysts in straightforward formats for gram-scale drug synthesis.
- Kahremany, Shirin,Kubas, Adam,Tochtrop, Gregory P.,Palczewski, Krzysztof
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supporting information
p. 10581 - 10595
(2019/07/22)
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- Z -isomerization of retinoids through combination of monochromatic photoisomerization and metal catalysis
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Catalytic Z-isomerization of retinoids to their thermodynamically less stable Z-isomer remains a challenge. In this report, we present a photochemical approach for the catalytic Z-isomerization of retinoids using monochromatic wavelength UV irradiation treatment. We have developed a straightforward approach for the synthesis of Z-retinoids in high yield, overcoming common obstacles normally associated with their synthesis. Calculations based on density functional theory (DFT) have allowed us to correlate the experimentally observed Z-isomer distribution of retinoids with the energies of chemically important intermediates, which include ground- and excited-state potential energy surfaces. We also demonstrate the application of the current method by synthesizing gram-scale quantities of 9-cis-retinyl acetate 9Z-a. Operational simplicity and gram-scale ability make this chemistry a very practical solution to the problem of Z-isomer retinoid synthesis.
- Kahremany, Shirin,Sander, Christopher Lane,Tochtrop, Gregory P.,Kubas, Adam,Palczewski, Krzysztof
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supporting information
p. 8125 - 8139
(2019/09/19)
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- Efficient, low-cost synthesis of retinal (Vitamin A aldehyde)
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Inexpensive retinyl acetate has been subjected to transesterification followed by allylic oxidation to give retinal in 98% yield as a 92:8 mixture of all-trans/13-cis isomers after chromatographic separation. More convenient methods of isolating the all-trans isomer have also been employed. Georg Thieme Verlag Stuttgart ? New York.
- Hruszkewycz, Damian P.,Cavanaugh, Kathryn R.,Takamura, Kathryn T.,Wayman, Lora M.,Curley Jr., Robert W.
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experimental part
p. 2205 - 2207
(2011/09/14)
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- Cyclopropyl and isopropyl derivatives of 11- cis and 9- cis retinals at C-9 and C-13: Subtle steric differences with major effects on ligand efficacy in rhodopsin
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Retinal is the natural ligand (chromophore) of the vertebrate rod visual pigment. It occurs in either the 11-cis (rhodopsin) or the 9-cis (isorhodopsin) configuration. In its evolution to a G protein coupled photoreceptor, rhodopsin has acquired exceptional photochemical properties. Illumination isomerizes the chromophore to the all-trans isomer, which acts as a full agonist. This process is extremely efficient, and there is abundant evidence that the C-9 and C-13 methyl groups of retinal play a pivotal role in this process. To examine the steric limits of the C-9 and C-13 methyl binding pocket of the binding site, we have prepared C-9 and C-13 cyclopropyl and isopropyl derivatives of its native ligands and of α-retinal at C-9. Most isopropyl analogues show very poor binding, except for 9-cis-13-isopropylretinal. Most cyclopropyl derivatives exhibit intermediate binding activity, except for 9-cis-13-cyclopropylretinal, which presents good binding activity. In general, the binding site shows preference for the 9-cis analogues over the 11-cis analogues. In fact, 13-isopropyl-9-cis-retinal acts as a superagonist after illumination. Another surprising finding was that 9-cyclopropylisorhodopsin is more like native rhodopsin with respect to spectral and photochemical properties, whereas 9-cyclopropylrhodopsin behaves more like native isorhodopsin in these aspects.
- DeGrip, Willem J.,Bovee-Geurts, Petra H. M.,Wang, Yajie,Verhoeven, Michiel A.,Lugtenburg, Johan
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body text
p. 383 - 390
(2011/05/30)
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- Preparation of 3-bromomethyl-3-butenal diethylacetal and its conversion into isoprenoid aldehydes derivatives
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The cyclopropanation of ethyl 3,3-diethoxypropionate with alkoxytitanacyclopropane reagents followed by the cleavage of the three-membered carbocycle in the formed cyclopropyl mesylate provided in a good yield 3-bromomethyl-3-butenal diethylacetal. The la
- Mineeva,Kulinkovich
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experimental part
p. 1623 - 1632
(2010/04/27)
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- Complex thermal behavior of 11-cis-retinal, the ligand of the visual pigments
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Upon heating to 80 °C, 11-cis-retinal yields a mixture of all-trans-retinal and 13-cis-retinal. This isomerization has been studied by means of density functional theory methods, and the computational results suggest a close competition between two mechanisms of very different nature. A classical internal rotation around the C11-C12 cis double bond, via a diradical transition state, accounts for the formation of the all-trans isomer. An intricate sequence of pericyclic reactions, namely a reversible [1,7]-H sigmatropic shift and a reversible 6-π-oxa-electrocyclic reaction, is responsible for the formation of 13-cis-retinal. Experiments using 11-cis-retinal labeled with deuterium at C19 confirmed the mechanistic proposal and also revealed an unprecedented outcome on the product composition of isotopologues.
- Lopez, Carlos Silva,Alvarez, Rosana,Dominguez, Marta,Faza, Olalla Nieto,De Lera, Angel R.
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experimental part
p. 1007 - 1013
(2009/07/04)
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- New syntheses of retinal and its acyclic analog γ-retinal by an extended aldol reaction with a C6 building block that incorporates a C5 unit after decarboxylation. A formal route to lycopene and β-carotene
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Since the C15 β-end-group aldehyde 10 ((β-ionylidene) acetaldehyde), an excellent intermediate in the syntheses of retinoids, can be synthesized in many ways from β-ionone, and since the corresponding acyclic C15 ψ-end-group aldehyde 5 can easily be synthesized from citral (1) (Scheme 3), we applied the C15 + C5 route to the syntheses of γ-retinal ((all-E)-8) (Scheme 3) and retinal ((all-E)-13) (Scheme 4), and therefore, by coupling (2 x C20 → C 40), to the preparation of lycopene (14) and β-carotene (15) (Scheme 5). Our new syntheses of retinal ((all-E)-13) and γ-retinal ((all-E)-8 use an extended aldol reaction with a C6 building block that incorporates a C5 unit after decarboxylation.
- Valla, Alain,Valla, Benoist,Le Guillou, Regis,Cartier, Dominique,Dufosse, Laurent,Labia, Roger
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p. 512 - 520
(2008/02/07)
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- Selective isomerization of retinal upon two-photon excitation
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The products of photo-isomerization when excited directly up to the two-photon-allowed 1Ag- excited state of alltrans and five cis isomers of retinal were determined. The composition of the isomers at the photo-stationary state was drastically changed as compared to one-photon excitation. The production of the 13-cis isomer was selectively increased, and the production of the dicis isomers was observed in the case of a direct excitation upon the 31Ag- state, although they were hard to be produced by one-photon excitation in n-hexane solution. These results clearly evidenced that there exist isomerization pathways via two-photon-allowed excited states.
- Sashima, Tokutake,Hashimoto, Hideki,Koshihara, Shin-ya
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p. 380 - 385
(2007/10/03)
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- Vinyltin acetals in terpenic and nor-terpenic synthesis
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Vinyltin acetals obtained by stannylmetallation of homopropargyl acetals with Bu3SnMgMe/CuCN (E configuration) or by titanation of the corresponding alkyltin acetals (Z configuration) have been proved to be efficient storable precursors for the stereoselective synthesis of terpenoids, under mild experimental conditions.Due to the presence of a nucleophilic centre (Csp2-Sn bond) and of a protected electrophilic centre, they are also useful intermediates for an iterative synthesis of retinal and nor-retinoids. - Keywords: vinyltin; acetal; vinyllithium; monoterpenoid; retinal; nor-retinoid
- Launay, Valerie,Beaudet, Isabelle,Quintard, Jean-Paul
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p. 937 - 946
(2007/10/03)
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- Pyrylium salts in polyene natural product synthesis: organometallic additions to 4-methylpyrylium tetrafluoroborate
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The synthetic utility of organometallic additions to pyrylium salts as a procedure for the stereocontrolled preparation of 2Z,4E-dienals, and the use of these compounds in polyene natural product synthesis, is summarised.The extension of this methodology to 4-methylpyrylium tetrafluoroborate to give a new route to 3-methyl-2Z,4E-dienals via a six-carbon organometallic homologation procedure is then described.Finally, the utilisation of this methodology to provide a concise synthetic approach to 13Z-retinal, retinal and a range of retinal analogues is then elaborated.
- Taylor, Richard J. K.,Hemming, Karl,Medeiros, Edna Faria De
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p. 2385 - 2392
(2007/10/02)
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- Retinal isomer composition in some bacteriorhodopsin mutants under light and dark adaptation conditions
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The isomeric composition of retinal was measured in a number of bacteriorhodopsin (bR) mutants (D85N), D212N, R82A, Y185F, and D115N) under various conditions, using a rapid retinal extraction technique followed by HPLC analysis. Besides the 13-cis and the all-trans retinal isomers observed in wild type (wt) bR under physiological conditions, the 11-cis and 9-cis retinal isomers were observed in variable but minor amounts in the bR mutants. In addition, the values of the equilibrium constant at two temperatures and the enthalpy change for the all-trans to 13-cis isomerization process in the dark-adapted state of D212N, D85N, deionized blue bR, and wt bR were determined. We find that perturbation of the retinal cavity (pocket) by residue replacement changes the relative thermal stability of the different retinal isomers, allowing for thermal-and/or photoisomerization of the retinal chromophore along C9-C10 and C11-C12 bonds to moderately compete with the isomerization around the C13-C14 bond. The bR mutants expressed in Halobacterium salinarium studied in the present work showed normal 13-cis to all-trans light adaptation, in contrast with abnormal all-trans to 13-cis light adaptation observed for D212E, D212A, and D212N expressed in Escherichia coli, suggesting an influence of the purple membrane lattice and/or the lipids on the stability of the different retinal isomers within the protein.
- Song,Yang,El-Sayed,Lanyi
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p. 10052 - 10055
(2007/10/02)
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- A new approach to retinoids via organometallic addition to pyrylium salts
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A new, concise approach to retinoid synthesis is described based on organometallic addition to pyrylium salts, the use of 4-methylpyrylium tetrafluoroborate giving 13Z-retinal which is readily isomerised to retinal itself; the corresponding unsubstituted and 4-cyclohexyl pyrylium salts are transformed into 13-H and 13-cyclohexyl retinal analogues.
- Hemming,De Medeiros,Taylor
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p. 2623 - 2624
(2007/10/02)
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- Palladium-catalysed vinylation of tertiary allylic alcohols: A new protocol for the synthesis of isoprenoid aldehydes.
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Heck vinylation of tertiary allylic alcohols with iodo-acetal Ic, followed by an acid catalysed acetal hydrolysis-dehydration reaction, furnished isoprenoid aldehydes regioselectively in high yields.
- Bienayme,Yezeguelian
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p. 3389 - 3396
(2007/10/02)
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- Low-valent titanium reductive elimination: a direct and highly stereoselective synthesis of vitamin A aldehyde and all-trans retinoic acid orthothioester
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It is shown that low-valent titanium reductive elimination can be carried out in the presence of a thioacetal or an orthothioester group.The application to the synthesis of vitamin A aldehyde and all-trans retinoic acid orthothioester is described.Keywords - Ti(0) reductive elimination / vitamin A aldehyde / all-trans retinoic acid
- Solladie, G.,Berl, V.
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p. 568 - 574
(2007/10/02)
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- Polyvinylogation Reagents: 1-Lithio-4-trimethylsiloxy-penta-1,3-diene and 1-Lithio-4-ethoxy-2-methyl-buta-1,3-diene
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Title products, lithiodienol ethers 6a and 7a, synthetic equivalents of 4-lithio pent-3-ene-2-one and 4-lithio-senecialdehyde were obtained by bromine-lithium exchange.They are choice reagents for the transformations 1 -> 2 and 1 -> 3, respectively.
- Duhamel, Lucette,Ancel, Jean-Erick
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p. 9237 - 9250
(2007/10/02)
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- A new prenylation method using the lithium enolate of prenal. Reaction with polyunsaturated aldehydes. A short access to retinal
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The enolate of prenal 1 prepared from the corresponding silyl enol ether 2 or enol acetate 3 led to a γ-regiospecific reaction with polyunsaturated aldehydes 4 yielding dihydropyrans 5 leading after hydrolysis to polyenals 7. This process allows the introduction of the isoprenyl skeleton. A synthesis of retinal, from β-ionylidenacetaldehyde is reported.
- Duhamel, Lucette,Guillemont, Jerome,Poirier, Jean-Marie,Chabardes, Pierre
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p. 4499 - 4500
(2007/10/02)
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- Photoisomerization of Hindered Poly-cis Isomers of Retinal. Regioselectivity And One -Photon-Multiple-Bond Isomerization.
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Direct irradiation of five dicis (7,9, 7,11, 7,13, 9,11 and 9,13) and one tricis (7,9,11) isomers of retinal led to regioselective isomerization at the 13,14 bond as well as multiple-bond isomerization.
- Ganapathy, Srinivasan,Liu, Robert S. H.
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p. 6957 - 6960
(2007/10/02)
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- Dependence of the Triplet Potential of Retinal Homologues on the Chain Length: Resonance Raman Spectroscopy and Analysis of Triplet-Sensitized Isomerization
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The Raman spectra of triplet species produced from the all-trans, 7-cis and 9-cis isomers of β-ionylideneacetaldehyde (C15 aldehyde) and of β-ionylidenecrotonaldehyde (C17 aldehyde) were recorded.Each isomer of C15 aldehyde showed its own triplet Raman spectrum, while all the isomers of C17 aldehyde showed an identical triplet spectrum.The results were compared with those of isomeric retinal (C20 aldehyde) and retinylideneacetaldehyde (C22 aldehyde) obtained previously.Triplet-sensitized isomerization as well as direct photoisomerization of the all-trans isomer and the complete set of mono-cis isomers of C15, C17, C20, and C22 aldehydes were analyzed by HPLC.Mutual isomerization among the all-trans was seen for C17, C20, and C22 aldehydes.The quantum yield of triplet-sensitized isomerization for each isomer of the above aldehydes was determined. all the results are discussed in terms of triplet potentials with minima at cis and trans positions, the relative stability being dependent on the length of the polyene chain; the cis minima are as stable as the trans minimum for C15 aldehyde, while the cis minima are far less stable than the trans minimum for C17, C20, and C22 aldehydes.
- Mukai, Yumiko,Hashimoto, Hideki,Koyama, Yasushi
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p. 4042 - 4051
(2007/10/02)
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- β-Lactoglobulin Directed Photoisomerization of Retinal and Related Compounds
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The 11-cis enriched photostationary state mixture of retinal trapped in BLG, a water soluble protein, is similar to that of retinal in heptanol.The results, along with those of the lower homologs, are consistend with a model involving specific protein interaction with the cyclohexenyl portion of the substrate and remote protonation of the aldehyde carbonyl group.
- Li, Xiao-yuan,Asato, Alfred E.,Liu, R. S. H.
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p. 4841 - 4844
(2007/10/02)
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- Photoisomerization of 7-cis-Retinal. The Concentration Effect
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A triplet quantum chain process is believed to be responsible for the concentration dependent quantum yield of isomerization of 7-cis-retinal.
- Ganapathy, S.,Trehan, A.,Liu, R. S. H.
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p. 199 - 200
(2007/10/02)
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- Synthesis of New Aromatic Retinoid Analogues by Low-Valent Titanium Induced Reductive Elimination
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The low-valent titanium reductive elimination reaction, already applied to the stereospecific synthesis of vitamin A and 13-cis-retinol, was used to prepare several retinoic acid analogues in the all-trans configuration or in the 13-cis configuration.This highly stereospecific trans-diene formation allowed an improved synthesis of the title compounds without any purification of the intermediates before the final stage.
- Solladie, Guy,Girardin, Andre,Lang, Gerard
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p. 2620 - 2628
(2007/10/02)
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- Sensitized photoisomerization of all-trans- and 11-cis-retinal
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The photoisomerization of all-trans-retinal (all-trans) and 11-cis-retinal (11-cis) sensitized by a range of sensitizers (porphyrins, Zn-porphyrins, naphthacene and a Zn-phthalocyanine) with varying triplet energies above and below the vertical triplet energy of all-trans-retinal (E(T) = 149 kJ/mol) has been investigated by continuous illumination and HPLC analysis of the products. The composition of the photostationary states, the relative isomerization quantum yields of all-trans and 11-cis, and the primary product ratios are reported. One photon-one bond isomerizations are dominant. With Zn-TPP as sensitizer it is shown that 11-cis and possibly all-trans undergoes one photon-two bond isomerizations as well. The quantum yields of photoisomerization of 11-cis sensitized by biphenyl (E(T) = 275 kJ/mol) and anthracene (E(T) = 178 kJ/mol) were found to be identical. Absolute measurements allowed evaluation of the overall triplet isomerization quantum yield of 11-cis, Φ(iso)(T)(11-cis→) = 1.0 ± 0.2, from which the corresponding quantity for all-trans, Φ(iso)(T)(trans-→) = 0.15 ± 0.05, was obtained. The overall photoisomerization quantum yield of 11-cis with direct excitation at 254 nm was determined as Φ(iso)(d)(11-cis→) = 0.42 ± 0.05 assuming all-trans and 13-cis to be the primary products. Quenching rate constants of several of the sensitizer triplet states by retinal were measured by laser flash photolysis. Possible mechanisms that could account for the experimental results are discussed, and it is concluded that the photoisomerizations most likely involve the retinal triplet states as intermediates. Within this model the observed sensitizer triplet energy dependence of the primary product ratios suggests that the triplet states of the different retinal isomers are different mixtures of triplet excited species, and that the composition of these mixtures depends on the starting isomers as well as on the sensitizer triplet energy for energies below the vertical triplet energy of all-trans-retinal. In the light of a review of the existing literature on the direct and the sensitized photoisomerization of retinals these conclusions suggest substantial corrections to the accepted picture of retinal photochemistry.
- Jensen,Wilbrandt,Bensasson
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p. 7877 - 7888
(2007/10/02)
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- High-Resolution Carbon-13 NMR of Retial Derivatives in the Solid State
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13C NMR spectra of a large number of crystalline retinal derivatives have been obtained by using cross-polarization and magic-angle sample spinning.Most derivatives yield spectra with narrow lines (width around 20 Hz) which can be assigned via their 13C-1H dipolar coupling, their chemical shift tensors, comparison with solution spectra, or specific labeling.Measurement of the rotational sideband intensities in the spectra permit calculation of the chemical shielding tensors, and these data have allowed us to analyze variations in isotropic shifts of these compounds in more detail.We show that the tensors exhibit an odd/even effect which results from the steric crowding on one side of the polyene chain, that ?-electron pertubations affect primarily the in-plane elements of the tensor, and, conversely, that strong steric interactions due to cis-trans isomerization affect the out-of-plane element.Finally, we observe a downfield shift at the C-5 position on isomerization about the 6-7 bond, and thus deduce from the observed shifts that retinal derivatives are 25-30percent 6-s-trans in solution.
- Harbison, G. S.,Mulder, P. P. J.,Pardoen, H.,Lugtenburg, J.,Herzfeld, J.,Griffin, R. G.
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p. 4809 - 4816
(2007/10/02)
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- A MODEL STUDY OF REGENERATION PROCESS IN RHODOPSIN VISUAL CYCLE
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The regeneration process in rhodopsin was studied by an estimation of isomer population at photoequilibrium for the model compounds of N-retinylidene phosphatidylethanolamine.We suggested that the preferential formation of 11-cis isomer may be induced by the through-bond effect of oxygen atom of imine moiety of a Schiff base.
- Sakurai, Minoru,Shirota, Osamu,Inoue, Yoshio,Chujo, Riichiro
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p. 167 - 170
(2007/10/02)
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- Studies on the Catalyzed Interconversions of Vitamin A Derivatives
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The kinetics of the I2-catalyzed isomerization of the retinal isomers were studied.The all-trans isomer formed 13-cis-retinal rapidly with a rate constant 1.9E-4 s-1.The reverse reaction occurred with a rate constant of 4.5E-4 s-1.The 11-cis isomer was first converted to all-trans-retinal with a rate constant of 3.1E-4 s-1, although the 13-cis isomer was also rapidly formed.The 9-cis isomer was isomerized to the 9-cis, 13-cis isomer before the other isomers were generated and the 13-cis isomer was converted to its all-trans congener prior to the formation of the other isomers.Similar results appear to occur when other methods of catalysis are used.This isomerization about the C13-C14 double bond appears to be kinetically favored event, eliminating the possibility that 11-cis might be a kinetic product formed from the all-trans isomer.At equilibrium, only 0.1percent of 11-cis-retinal is found.Equilibration of all-trans-retinol palmitate also generated very little of the 11-cis-isomer (/= 0.2percent) 11-cis-retinol palmitate at equilibrium.The implications of these results for an 11-cis-retinal regeneration mechanism in the eye are discussed.
- Rando, Robert R.,Chang, Andrew
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p. 2879 - 2882
(2007/10/02)
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- Silica Gel Mediated Photoisomerization of Retinal Isomers and Comparisons with Other Forms of Environmental Pertubation
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The electronic spectra and photoreactivity of slurries of retinal isomers, prepared by adsorbing the isomers onto wet silica gel and suspending the support in cyclohexane, have been investigated.Adsorption of 9-cis-, 11-cis-, 13-cis-, and all-trans-retinal is accompanied by an ca. 3000-cm-1 red shift of their lowest energy absorption band maxima relative to their band positions in homogeneous cyclohexane solution.Irradiation of the slurries at 514.5 nm, a wavelength inefficiently absorbed in the absence of silica gel, leads to reasonably efficient photoisomerization of each of these isomers.Prolonged photolysis yields a mixture of the four isomers that is photostationary with respect to relative concentrations and richest in 11-cis-retinal, which constitutes ca. 35percent of this mixture.Although small quantities of other isomers are present, the photostationary composition of the heterogeneous photolysate can be predicted with reasonable accuracy from the relative absorptivities and primary photoprocesses of the four principal isomers comprising the photolysate.Comparisons with primary photoprocesses reported for retinal isomers in polar and nonpolar solvents reveal that adsorption onto silica gel can result in novel patterns of photoisomerization.Complementary comparisons are made with the electronic spectra and photoreactivity of adducts formed in hydrocarbon solution from retinal isomers and a lanthanide β-diketonate complex.The excited-state properties of these various retinal-based systems highlight the impotance of environment in controlling photoreactivity.Steric and electronic factors that may contribute to the observed features of silica gel mediated photoisomerization are discussed in this context.
- Zawadzki, Mary E.,Ellis, Arthur B.
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p. 3156 - 3161
(2007/10/02)
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- A SHORT PATH SYNTHESIS OF RETINALS. SYNTHESIS OF 13C- OR 2H-LABELED RETINALS
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Trimethylsilylated acetaldehyde t-butylimine 4 was found to be an effective two carbon-homologenation reagent in the synthesis of retinals and its congeners.A short path synthesis of retinals (1 and 2) by using 4 and its application to the synthesis of 13C-labeled retinal 12 and octadeuterium retinal 27 is described.KEYWORDS - retinal; retinoid; vitamin A aldehyde; visual pigment; α,β-unsaturated aldehyde synthesis; silylated imine
- Akita, Hiroyuki
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p. 1796 - 1799
(2007/10/02)
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- Thermal Sigmatropic Rearrangements of Vinylallenes Leading to 11-cis-Retinoids and the Novel Properties of 9-cis,11-cis,13-cis-Retinal and 11-cis,13-cis-Retinal
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The thermally induced sigmatropic hydrogen shift of vinylallene 5 provided a route to highly hindered 11-cis-retinoids.The coupling ot the hetero cuprate 14 with the propargyl benzoate 13b gave the vinylallene 5, which upon heating (69 deg C, 2 h) gave three geometrically isomeric retinoids: 11-sis (8), 11-cis,13-cis (9), and 9-cis,11-cis,13-cis (11).The fourth possible geometric isomer, 9-cis,11-cis (10), was unstable to the conditions of thermolysis and underwent further electrocyclizations to the tricyclic compound 22.The thermal rearramgement of 9,10-allene 5, though highly specific for the formation of 11-cis-retinoids, exhibits no selectivity in the formation of Δ9 and Δ13 double bonds.The highly hindered 11-cis,13-cis- and 9-cis,11-cis,13-cis-retinals, 9b and 11b, exhibit extraordinary electronic absorption spectra in that they exhibit their main maxima (302 nm) actually to the blue of the corresponding alcohols.The retinals 9b and 11b were thermally unstable and underwent clean isomerization to 13-cis-retinal and 9-cis,13-cis-retinal, respectively.
- Knudsen, Christopher G.,Chandraratna, Roshantha A. S.,Walkeapaeae, Leslie P.,Chauhan, Yeshpal S.,Carey, Stephen C.,et al.
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p. 1626 - 1631
(2007/10/02)
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- Transient Phenomena in the Pulse Radiolysis of Retinyl Polyenes. 1. Radical Anions
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The spectra and kinetics of formation and decay of radical anions of a number of retinyl polyenes have been studied in methanol and 2-propanol at room temperature, using pulse radiolysis and kinetic spectrophotometry.The bimolecular rate constants for the attachment of solvated electrons, e-MeOH, to the retinyl polyenes are in the diffusion-controlled limit (8.6 x 109-1.6 x 1010 M-1 s-1).The radical anions of retinol and retinol acetate have their spectral maxima at 370-390 nm, and undergo decay very slowly with second-order kinetics.On the other hand, the radical anions of retinal, retinal n-butylamine Schiff base, and retinoic acid/ester have spectral maxima at 430-510 nm, and decay by first-order kinetics in methanol with rate constants in the range 1 x 104-1 x 106 s-1.The decay rates of radical anions of retinal and retinoic acid/ester become considerably longer on going from methanol to less acidic alcohol, 2-propanol, suggesting that protonation by solvent is the major mode of their decay in protic media.In the case of retinal Schiff base, an additional slow process with bimolecular rate constant 9.0 x 107 M-1 s-1 im methanol is observed for the formation of radical anion and is ascribed to the electron-transfer reaction from the methanol radical, .CH2OH.
- Raghavan, N.V.,Das, P.K.,Bobrowski, K.
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p. 4569 - 4573
(2007/10/02)
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- Models for Visual Pigments. The Effect of the Imidazolyl Group on the Absorption Maxima of the Retinal Schiff Base
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The title effect has been investigated with the imidazolyl group either externally added or intramolecularly combined.N-Retinylidenebutylamine was protonated with imidazole derivatives under neutral conditions and was absorbed at longer wavelengths compared with carboxylic acids.The absorption peak with the imidazolyl group intramolecularly combined was highly affected by the structure, protonated Nα-retinylidene-L-histidine octadecylamide having an absorption maximum at 494 nm caused by the inductive effect and the polar imidazolyl group.
- Nanasawa, Masato,Kamogawa, Hiroyoshi
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p. 1101 - 1104
(2007/10/02)
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- PHOTOISOMERIZATION OF THE C18 KETONE IN THE VITAMIN A SERIES. SOLVENT EFFECT ON PHOTOISOMERIZATION OF COMPOUNDS RELATED TO RETINAL
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The directions of photoisomerization of polyenals and polyenones are believed to be controlled by the relative ordering of n,?* and ?,?* states.
- Ramamurthy, V.,Denny, M.,Liu, R. S. H.
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p. 2463 - 2466
(2007/10/02)
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