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Fernando Pina - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic stability of Flavylium salts as a valuable tool to design the synthesis of a type proanthocyanidin analogues
Journal of Organic Chemistry, 2018Co-Authors: Fernando Pina, Jorge A Parola, Alfonso Alejoarmijo, Joaquin Altarejos, Sofia SalidoAbstract:: A convenient method to synthesize A-type proanthocyanidin analogues from Flavylium salts and π-nucleophiles has been developed. It was found that the thermodynamic stability of the starting Flavylium salt, assessed by the measurement of the apparent acidity constant ( K'a), was the key parameter to design effective one-pot reactions between Flavylium salts and nucleophiles such as phloroglucinol and (+)-catechin. When Flavylium salts have a p K'a value of 1.7 or lower, the synthesis of the corresponding 2,8-dioxabyciclo[3.3.1]nonane derivative was properly achieved.
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Electronic and charge transfer properties of bio-inspired Flavylium ions for applications in TiO 2 -based dye-sensitized solar cells
Photochem. Photobiol. Sci., 2017Co-Authors: Giuseppe Calogero, Stefano Caramori, L. Casarin, A. Jorge Parola, João Avó, Ilaria Citro, García Marco, Carlo Alberto Bignozzi, Fernando PinaAbstract:We present a complete study on four synthetic environmentally friendly Flavylium salts employed as sensitizers for dye-sensitized solar cells (DSSCs).
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synthesis and multistate characterization of bis Flavylium dications symmetric resorcinol and phloroglucinol type derivatives as stochastic systems
RSC Advances, 2016Co-Authors: Nuno Basílio, Tony Garnier, Mathieu Danel, Stefan Chassaing, Fernando PinaAbstract:Two symmetric bis-Flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown to be fully stochastic and behave like a single compound suggesting that the two Flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid–base reaction between Flavylium cation and quinoidal base were calculated using a stopped flow technique. It was further demonstrated that the equilibrium between AH+–AH+ and indistinguishable Flavylium-quinoidal base isomers AH+–A (A–AH+) can be calculated by subtracting 0.3 pH units from the observed acid–base constant. On the other hand, the equilibrium between both Flavylium-quinoidal base isomers and the bis-quinoidal base A–A is obtained by adding 0.3 pH units. Moreover, both systems do not have a cis–trans isomerization barrier and the rate constants of interconversion between Flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagram. It was also proved that the rate constant to form both isomers AH+–Ct from the bis-Flavylium upon a pH jump from 1 to less acidic solutions is twice that of the observed value and the formation of the bis-trans-chalcone from both isomers AH+–Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.
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Synthesis and multistate characterization of bis-Flavylium dications – symmetric resorcinol- and phloroglucinol-type derivatives as stochastic systems
RSC Advances, 2016Co-Authors: Nuno Basílio, Tony Garnier, Mathieu Danel, Stefan Chassaing, Fernando PinaAbstract:Two symmetric bis-Flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown to be fully stochastic and behave like a single compound suggesting that the two Flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid–base reaction between Flavylium cation and quinoidal base were calculated using a stopped flow technique. It was further demonstrated that the equilibrium between AH+–AH+ and indistinguishable Flavylium-quinoidal base isomers AH+–A (A–AH+) can be calculated by subtracting 0.3 pH units from the observed acid–base constant. On the other hand, the equilibrium between both Flavylium-quinoidal base isomers and the bis-quinoidal base A–A is obtained by adding 0.3 pH units. Moreover, both systems do not have a cis–trans isomerization barrier and the rate constants of interconversion between Flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagram. It was also proved that the rate constant to form both isomers AH+–Ct from the bis-Flavylium upon a pH jump from 1 to less acidic solutions is twice that of the observed value and the formation of the bis-trans-chalcone from both isomers AH+–Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.
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spatiotemporal control over the co conformational switching in ph responsive Flavylium based multistate pseudorotaxanes
Faraday Discussions, 2015Co-Authors: Fernando Pina, Nuno Basílio, Ana Diniz, Hugo Cruz, Jorge A ParolaAbstract:A multistate molecular dyad containing Flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The Flavylium cation is only stable at acidic pH values. Above pH ≈ 5 the hydration of the Flavylium leads to the formation of the hemiketal followed by ring-opening tautomerization to give the cis-chalcone. Finally, this last species isomerizes to give the trans-chalcone. For the present system only the Flavylium cation and the trans-chalcone species could be detected as being thermodynamically stable. The hemiketal and the cis-chalcone are kinetic intermediates with negligible concentrations at the equilibrium. All stable species of the network were found to form 1 : 1 and 2 : 1 host : guest complexes with cucurbit[7]uril (CB7) with association constants in the ranges 105–108 M−1 and 103–104 M−1, respectively. The 1 : 1 complexes were particularly interesting to devise pH responsive bistable pseudorotaxanes: at basic pH values (≈12) the Flavylium cation interconverts into the deprotonated trans-chalcone in a few minutes and under these conditions the CB7 wheel was found to be located around the viologen unit. A decrease in pH to values around 1 regenerates the Flavylium cation in seconds and the macrocycle is translocated to the middle of the axle. On the other hand, if the pH is decreased to 6, the deprotonated trans-chalcone is neutralized to give a metastable species that evolves to the thermodynamically stable Flavylium cation in ca. 20 hours. By taking advantage of the pH-dependent kinetics of the trans-chalcone/Flavylium interconversion, spatiotemporal control of the molecular organization in pseudorotaxane systems can be achieved.
Jorge A Parola - One of the best experts on this subject based on the ideXlab platform.
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thermodynamic stability of Flavylium salts as a valuable tool to design the synthesis of a type proanthocyanidin analogues
Journal of Organic Chemistry, 2018Co-Authors: Fernando Pina, Jorge A Parola, Alfonso Alejoarmijo, Joaquin Altarejos, Sofia SalidoAbstract:: A convenient method to synthesize A-type proanthocyanidin analogues from Flavylium salts and π-nucleophiles has been developed. It was found that the thermodynamic stability of the starting Flavylium salt, assessed by the measurement of the apparent acidity constant ( K'a), was the key parameter to design effective one-pot reactions between Flavylium salts and nucleophiles such as phloroglucinol and (+)-catechin. When Flavylium salts have a p K'a value of 1.7 or lower, the synthesis of the corresponding 2,8-dioxabyciclo[3.3.1]nonane derivative was properly achieved.
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ph tunable fluorescence and photochromism of a Flavylium based mcm 41 pigment
ACS omega, 2017Co-Authors: Sandra Gago, Cesar A T Laia, Marcia Pessego, Jorge A ParolaAbstract:Incorporation of Flavylium-derived chalcones in the cetyltrimethylammonium bromide-templated synthesis of mesoporous silica particles with no subsequent removal of the micellar phase leads to high luminescence (0.3 < ϕf < 0.5) and strong color-contrast photochromic pigments finely tunable over a large pH range (1 < pH < 11).
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spatiotemporal control over the co conformational switching in ph responsive Flavylium based multistate pseudorotaxanes
Faraday Discussions, 2015Co-Authors: Fernando Pina, Nuno Basílio, Ana Diniz, Hugo Cruz, Jorge A ParolaAbstract:A multistate molecular dyad containing Flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The Flavylium cation is only stable at acidic pH values. Above pH ≈ 5 the hydration of the Flavylium leads to the formation of the hemiketal followed by ring-opening tautomerization to give the cis-chalcone. Finally, this last species isomerizes to give the trans-chalcone. For the present system only the Flavylium cation and the trans-chalcone species could be detected as being thermodynamically stable. The hemiketal and the cis-chalcone are kinetic intermediates with negligible concentrations at the equilibrium. All stable species of the network were found to form 1 : 1 and 2 : 1 host : guest complexes with cucurbit[7]uril (CB7) with association constants in the ranges 105–108 M−1 and 103–104 M−1, respectively. The 1 : 1 complexes were particularly interesting to devise pH responsive bistable pseudorotaxanes: at basic pH values (≈12) the Flavylium cation interconverts into the deprotonated trans-chalcone in a few minutes and under these conditions the CB7 wheel was found to be located around the viologen unit. A decrease in pH to values around 1 regenerates the Flavylium cation in seconds and the macrocycle is translocated to the middle of the axle. On the other hand, if the pH is decreased to 6, the deprotonated trans-chalcone is neutralized to give a metastable species that evolves to the thermodynamically stable Flavylium cation in ca. 20 hours. By taking advantage of the pH-dependent kinetics of the trans-chalcone/Flavylium interconversion, spatiotemporal control of the molecular organization in pseudorotaxane systems can be achieved.
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Flavylium supported poly n isopropylacrylamide a class of multistimuli responsive polymer
Macromolecules, 2013Co-Authors: Noemi Jordao, Raquel Gavara, Jorge A ParolaAbstract:A new multistimuli responsive polymer was prepared by means of the free-radical copolymerization of N-isopropylacrylamide and a vinyl Flavylium derivative. The polymer shows response to temperature (conferred by the N-isopropylacrylamide units) and pH and light stimuli (conferred by the Flavylium moieties). The polymer follows the typical pH dependent network of chemical reactions of Flavylium compounds in water that was studied by means of UV–vis spectroscopy and stationary fluorescence emission. Regarding the temperature response, the presence of the Flavylium cation in the polymeric chains reduces the LCST, and it is possible to take advantage of this effect to photo-collapse partially the polymer by irradiating the system in defined ranges of pH and temperature.
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kinetic and thermodynamic study of 2 hydroxy 8 methoxyFlavylium reaction network interconverting Flavylium cation and flavanone
RSC Advances, 2013Co-Authors: Vesselin Petrov, Jorge A Parola, Ana M Diniz, Luis Cunhasilva, Fernando PinaAbstract:2′-HydroxyFlavylium and 2′-hydroxyflavanone derivatives can be interconverted by a precise sequence of pH jumps, through the respective intermediate (mono) ionized trans-chalcones. In acidic and neutral media, the well known network of chemical reactions involving Flavylium cation, quinoidal base, hemiketal, and cis and trans chalcones is established. In the pH range 8 < pH < 10, the chalcone (Ct) deprotonates and evolves to the formation of a flavanone (F). At higher pH values, the di-ionized trans-chalcone is the stable species, formed from the Flavylium cation. Acidification of the di-ionized trans-chalcone gives the Flavylium cation or the flavanone, via the mono-ionized trans-chalcone, respectively at pH < 1 and pH ≈ 9. In contrast with the chalcones, the flavanone once formed is stable even in acidic media. However, under strongly basic conditions, it leads back to the di-ionized trans-chalcone, the most stable species at more basic pH values, and the reactions leading to Ct−, F, Ct2−, Ct−, constitute a one direction cycle for interconversion of these species.
Yongjun Chen - One of the best experts on this subject based on the ideXlab platform.
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tfa mediated tandem friedel crafts alkylation cyclization hydrogen transfer process for the synthesis of Flavylium compounds
Journal of Organic Chemistry, 2007Co-Authors: Yanchao Wu, Dong Wang, Yongjun ChenAbstract:The tandem reaction of phenols and chalcones in refluxing TFA gave the Flavylium species of 2-hydroxy-2-phenyl-2H-chromenes in moderate to good isolated yields. The reaction was proposed to involve a tandem transformation of Friedel−Crafts alkylation, dehydrative cyclization, intermolecular hydrogen transfer, and hydration. As a multifunctional catalyst, TFA mediated the processes efficiently and cleanly.
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TFA-mediated tandem Friedel-Crafts alkylation/cyclization/hydrogen transfer process for the synthesis of Flavylium compounds.
Journal of Organic Chemistry, 2007Co-Authors: Yanchao Wu, Dong Wang, Yongjun ChenAbstract:The tandem reaction of phenols and chalcones in refluxing TFA gave the Flavylium species of 2-hydroxy-2-phenyl-2H-chromenes in moderate to good isolated yields. The reaction was proposed to involve a tandem transformation of Friedel−Crafts alkylation, dehydrative cyclization, intermolecular hydrogen transfer, and hydration. As a multifunctional catalyst, TFA mediated the processes efficiently and cleanly.
Nuno Basílio - One of the best experts on this subject based on the ideXlab platform.
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binding of Flavylium ions to sulfonatocalix 4 arene and implication in the photorelease of biologically relevant guests in water
Journal of Organic Chemistry, 2019Co-Authors: Miguel A Romero, Pedro Mateus, Beatriz Matos, Angel Acuna, Luis Garciario, Jesus F Arteaga, Uwe Pischel, Nuno BasílioAbstract:: The formation of host-guest complexes between seven Flavylium cations and water-soluble p-sulfonatocalix[4]arene (SC4) was investigated by UV/vis absorption, fluorescence, and NMR spectroscopies. The results show the cationic guests form complexes with affinities in the submillimolar range. A representative chalcone/Flavylium photoswitch was investigated in more detail regarding its pH- and light-triggered interconversion between the two forms. The dramatic affinity differentiation of the SC4 binding of the two switchable species (40 M-1 for the trans-chalcone versus 3.5 × 104 M-1 for the Flavylium cation) enables the pH-gated photocontrol of the complexation process. These responsive properties were explored to demonstrate the competitive and selective release of biologically relevant guests from their supramolecular complexes with p-sulfonatocalix[4]arene (SC4), following the principle of AND logic. The guest release can be reverted by the thermally activated reaction of the Flavylium ion back to the trans-chalcone.
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synthesis and multistate characterization of bis Flavylium dications symmetric resorcinol and phloroglucinol type derivatives as stochastic systems
RSC Advances, 2016Co-Authors: Nuno Basílio, Tony Garnier, Mathieu Danel, Stefan Chassaing, Fernando PinaAbstract:Two symmetric bis-Flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown to be fully stochastic and behave like a single compound suggesting that the two Flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid–base reaction between Flavylium cation and quinoidal base were calculated using a stopped flow technique. It was further demonstrated that the equilibrium between AH+–AH+ and indistinguishable Flavylium-quinoidal base isomers AH+–A (A–AH+) can be calculated by subtracting 0.3 pH units from the observed acid–base constant. On the other hand, the equilibrium between both Flavylium-quinoidal base isomers and the bis-quinoidal base A–A is obtained by adding 0.3 pH units. Moreover, both systems do not have a cis–trans isomerization barrier and the rate constants of interconversion between Flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagram. It was also proved that the rate constant to form both isomers AH+–Ct from the bis-Flavylium upon a pH jump from 1 to less acidic solutions is twice that of the observed value and the formation of the bis-trans-chalcone from both isomers AH+–Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.
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Synthesis and multistate characterization of bis-Flavylium dications – symmetric resorcinol- and phloroglucinol-type derivatives as stochastic systems
RSC Advances, 2016Co-Authors: Nuno Basílio, Tony Garnier, Mathieu Danel, Stefan Chassaing, Fernando PinaAbstract:Two symmetric bis-Flavylium dications were readily synthesized and further evaluated for their multistate profile. Both systems were shown to be fully stochastic and behave like a single compound suggesting that the two Flavylium moieties do not communicate via the bridge linking them. Global pKa values of ca. 4 regarding the acid–base reaction between Flavylium cation and quinoidal base were calculated using a stopped flow technique. It was further demonstrated that the equilibrium between AH+–AH+ and indistinguishable Flavylium-quinoidal base isomers AH+–A (A–AH+) can be calculated by subtracting 0.3 pH units from the observed acid–base constant. On the other hand, the equilibrium between both Flavylium-quinoidal base isomers and the bis-quinoidal base A–A is obtained by adding 0.3 pH units. Moreover, both systems do not have a cis–trans isomerization barrier and the rate constants of interconversion between Flavylium cation and quinoidal base as a function of pH are fitted with a mono-exponential and follow a bell-shaped curve. The systems proved also to be photochromic and from the fitting of the bell-shaped curve, flash photolysis measurements and quantum yields, it is possible to calculate all rate and equilibrium constants and construct a global energy-level diagram. It was also proved that the rate constant to form both isomers AH+–Ct from the bis-Flavylium upon a pH jump from 1 to less acidic solutions is twice that of the observed value and the formation of the bis-trans-chalcone from both isomers AH+–Ct is equal to the observed rate constant. An energy-level diagram of all the multistate species was constructed from the equilibrium constants.
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spatiotemporal control over the co conformational switching in ph responsive Flavylium based multistate pseudorotaxanes
Faraday Discussions, 2015Co-Authors: Fernando Pina, Nuno Basílio, Ana Diniz, Hugo Cruz, Jorge A ParolaAbstract:A multistate molecular dyad containing Flavylium and viologen units was synthesized and the pH dependent thermodynamics of the network completely characterized by a variety of spectroscopic techniques such as NMR, UV-vis and stopped-flow. The Flavylium cation is only stable at acidic pH values. Above pH ≈ 5 the hydration of the Flavylium leads to the formation of the hemiketal followed by ring-opening tautomerization to give the cis-chalcone. Finally, this last species isomerizes to give the trans-chalcone. For the present system only the Flavylium cation and the trans-chalcone species could be detected as being thermodynamically stable. The hemiketal and the cis-chalcone are kinetic intermediates with negligible concentrations at the equilibrium. All stable species of the network were found to form 1 : 1 and 2 : 1 host : guest complexes with cucurbit[7]uril (CB7) with association constants in the ranges 105–108 M−1 and 103–104 M−1, respectively. The 1 : 1 complexes were particularly interesting to devise pH responsive bistable pseudorotaxanes: at basic pH values (≈12) the Flavylium cation interconverts into the deprotonated trans-chalcone in a few minutes and under these conditions the CB7 wheel was found to be located around the viologen unit. A decrease in pH to values around 1 regenerates the Flavylium cation in seconds and the macrocycle is translocated to the middle of the axle. On the other hand, if the pH is decreased to 6, the deprotonated trans-chalcone is neutralized to give a metastable species that evolves to the thermodynamically stable Flavylium cation in ca. 20 hours. By taking advantage of the pH-dependent kinetics of the trans-chalcone/Flavylium interconversion, spatiotemporal control of the molecular organization in pseudorotaxane systems can be achieved.
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host guest complexes of Flavylium cations and cucurbit 7 uril the influence of Flavylium substituents on the structure and stability of the complex
ChemPlusChem, 2015Co-Authors: Nuno Basílio, Vesselin Petrov, Fernando PinaAbstract:: The host-guest complexes formed from six differently substituted Flavylium cations and cucurbit[7]uril (CB7) have been characterized by UV/Vis absorption, fluorescence emission and 1 H NMR spectroscopy. It was observed that all Flavylium cations form 1:1 inclusion complexes with association constants that depend on the nature and position of the substituents. The results indicate that CB7 displays higher affinity for more hydrophobic Flavylium compounds and for those bearing amino substituents. 1 H NMR spectroscopy was used to elucidate the structure of the complexes. While for 7-hydroxyFlavylium and 4-methyl-7-hydroxyFlavylium the phenyl group (ring B) is included within the host's cavity leaving the benzopyrilium group (rings A and C) outside, in 4',7-dihydroxyFlavylium and 3',4',7-trihydroxyFlavylium the macrocycle shuttles between rings A and B. For compounds with amino substituents it was found that CB7 is attracted towards these groups regardless of their position in ring A or B. In addition, it was observed that the dimethylamino group tends to be positioned near the carbonyl-decorated portal while the diethylamino motif prefers the hydrophobic cavity of CB7.
Raymond Brouillard - One of the best experts on this subject based on the ideXlab platform.
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aged red wine pigments as a source of inspiration for organic synthesis the cases of the color stable pyranoFlavylium and Flavylium 4 8 flavan chromophores
Tetrahedron, 2015Co-Authors: Stefan Chassaing, Geraldine Isorezmahler, Marie Kuenystotz, Raymond BrouillardAbstract:Abstract Two Flavylium-based chromophores peculiar to aged red wine pigments are investigated from a synthetic viewpoint. The condensation between easy-to-prepare 5-hydroxy-4-methylFlavylium salts and aldehydes, giving birth to color-stable pyranoFlavylium pigments, further proves efficient and wide in scope. A set of some twenty structurally-related Flavylium-based pigments has been prepared and structure:color relationships are discussed. Furthermore, the synthesis of the Flavylium-(4→8)-flavan chromophore is achieved via a novel three-step sequence. The elaborated sequence starts with an iodine–magnesium exchange from an 8-iodinated flavan, thus generating a magnesiated species that then smoothly reacts with a flavone to furnish an adduct, that finally leads to the expected chromophore via dehydration.
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Aged red wine pigments as a source of inspiration for organic synthesis—the cases of the color-stable pyranoFlavylium and Flavylium-(4→8)-flavan chromophores
Tetrahedron, 2015Co-Authors: Stefan Chassaing, Géraldine Isorez-mahler, Marie Kueny-stotz, Raymond BrouillardAbstract:Abstract Two Flavylium-based chromophores peculiar to aged red wine pigments are investigated from a synthetic viewpoint. The condensation between easy-to-prepare 5-hydroxy-4-methylFlavylium salts and aldehydes, giving birth to color-stable pyranoFlavylium pigments, further proves efficient and wide in scope. A set of some twenty structurally-related Flavylium-based pigments has been prepared and structure:color relationships are discussed. Furthermore, the synthesis of the Flavylium-(4→8)-flavan chromophore is achieved via a novel three-step sequence. The elaborated sequence starts with an iodine–magnesium exchange from an 8-iodinated flavan, thus generating a magnesiated species that then smoothly reacts with a flavone to furnish an adduct, that finally leads to the expected chromophore via dehydration.
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Flavylium salts as in vitro precursors of potent ligands to brain gaba a receptors
Bioorganic & Medicinal Chemistry Letters, 2008Co-Authors: Marie Kuenystotz, Raymond Brouillard, Stefan Chassaing, Mogens Brondsted Nielsen, Maurice GoeldnerAbstract:The synthesis of a series of derivatized Flavylium cations was undertaken and the affinity to the benzodiazepine binding site of the GABA-A receptor evaluated. The observed high affinity for some derivatives (sub-μM range) was explained by an in vitro transformation of the Flavylium cations into the corresponding trans-retrochalcones, components which are proposed to be the active species in this series.
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synthetic dyes simple and original ways to 4 substituted Flavylium salts and their corresponding vitisin derivatives
Canadian Journal of Chemistry, 2001Co-Authors: Christine Roehristoeckel, Emmanuel Gonzalez, Andre Fougerousse, Raymond BrouillardAbstract:Flavylium salts substituted at the 4-position have been prepared according to a Grignard reaction of some flavones with appropriate alkyl- and aryl-magnesium bromides. Among these compounds, 4-methyl Flavylium salts were gently reacted with aromatic aldehydes, affording new anthocyanidin pigments, some of which are of the vitisin family. These are the first examples of chemically synthesized vitisidins (aglycones of vitisins). Compared to the more common Flavylium salts, they demonstrate a large bathochromic shift (from about 100200 nm), thus providing blue-violet and green colours, so difficult to obtain with anthocyanidins in general.Key words: 4-substituted Flavylium chlorides, vitisin aglycones, blue-violet and green anthocyanidin pigments.
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3 β d glycopyranosyloxy Flavylium ions synthesis and investigation of their properties in aqueous solution hydrogen bonding as a mean of colour variation
Helvetica Chimica Acta, 1997Co-Authors: Hakima El Hajji, Olivier Dangles, Paulo Figueiredo, Raymond BrouillardAbstract:This work describes a straightforward synthesis of two 3’-(,fl-~-glycopyranosyloxy)Flavylium ions thought to be good models of natural anthocyanins (pigments). For both pigments and for the non-glycosylated Flavylium ion taken as a reference, H,O addition and proton-transfer reactions as well as formation of molecular complexes with chlorogenic acid and caffeine (copigmentation) are quantitatively investigated in mildly acidic aqueous solution. A remarkable affinity of caffeine for the trans-chalcone form of the pigments is demonstrated. Moreover, the differences in the Flavylium pK, values are interpreted in terms of possible intramolecular H-bonding between the glycosyl residue and the chromophore. The discussion is then extended to a series of malonylated anthocyanins recently reported for their unusual pigmentation properties. A possible role for the malonyl group (frequently encountered in the structure of naturally occurring anthocyanins) in plant colour expression is outlined for the first time.