Effect of Methyl, Hydroxyl, and Chloro Substituents in Position 3 of 3′,4′,7‐Trihydroxyflavylium: Stability, Kinetics, and Thermodynamics

Abstract

The effect of methyl, hydroxyl, and chloride substituents in position 3 of the 3',4',7-trihydroxyflavylium core structure was studied. The stability, relative energy of each of chemical species (thermodynamics), and their rates of interconversion (kinetics) are very dependent on these substituents. By comparing the mole fraction distribution at equilibrium of the three multistate systems with the parent 3',4',7-trihydroxyflavylium, introduction of a methyl substituent in position 3 increases the mole fraction of hemiketal at the expense of the trans-chalcone and increases the hydration rate very significantly; a hydroxyl substituent in position 3 gives rise to a degradation process, as observed in anthocyanidins. In the case of 3-chloro-3',4',7-trihydroxyflavylium, a dramatic increase of the flavylium cation acidity was observed and a photochromic system can be operated upon irradiation of the respective trans-chalcone in 1 m HCl. According to the photochromic response of 3,3',4',7-tetrahydroxyflavylium and 3',4',7-trihydroxyflavylium, some requirements for a good photochromic performance are discussed.

Thermodynamic Stability of Flavylium Salts as a Valuable Tool To Design the Synthesis of A-Type Proanthocyanidin Analogues

“…With this idea in mind, our research groups have recently described the synthesis of several flavylium salts and studied their thermodynamic and kinetic properties . The analysis of the data obtained in this study allowed us to propose that the overall thermodynamic stability of flavylium salts, as measured by the apparent acidity constant K ′ a (Scheme ), is related to the electronic density of the flavylium cation . On this basis, we envisioned that electronic density of flavylium salts could be estimated by the experimental measurement of K ′ a , and therefore, their applicability to the synthesis of 2,8-dioxabicyclo[3.3.1]­nonanes could be predicted.…”

“…With this idea in mind, our research groups have recently described the synthesis of several flavylium salts and studied their thermodynamic and kinetic properties . The analysis of the data obtained in this study allowed us to propose that the overall thermodynamic stability of flavylium salts, as measured by the apparent acidity constant K ′ a (Scheme ), is related to the electronic density of the flavylium cation .…”

“… a Reaction conditions: (i) H 2 SO 4 , HOAc; (ii) HCl (g), EtOH; (iii) HCl (g), MeOH. b See the Experimental Section. c In water d In MeOH/H 2 O 1:1 (v/v) e In MeOH/H 2 O 3:1 (v/v) …”

Synthesis and Evaluation of Antimicrobial and Antibiofilm Properties of A-Type Procyanidin Analogues against Resistant Bacteria in Food

“…10 In order to broaden the knowledge about structural features that could influence the antimicrobial and antibiofilm activities of A-type procyanidins against foodborne pathogens, we have now designed a set of analogues to the Atype procyanidin A-2, the structurally simplified version of cinnamtannin B-1 (Figures 1 and 2), and we have tested their antimicrobial and antibiofilm activities against a selection of resistant bacteria previously isolated from organic foods. We therefore describe here the synthesis of the procyanidin analogues following a procedure based on flavylium chemistry, 11 their antimicrobial and antibiofilm activities against 12 Gram-positive and Gram-negative resistant bacteria previously isolated from organic foods, and the resulting structure−activity relationships.…”

3‐Deoxyanthocyanidin Colorant: Nature, Health, Synthesis, and Food Applications

“…When the pH is raised, two simultaneous pathways are involved: (1) AH + can be easily deprotonated to form A, which is responsible for the color; (2) and hydration to give the colorless hemiketal species B that is in tautomeric equilibrium with Cc , which can also be converted to Ct via cis‐trans isomerization, usually the most thermodynamically stable species at moderate acidic or neutral pH. Depending on the nature of the substituents, the pH‐dependent equilibrium significantly varies and other forms may also be involved, and the final color of the solution relies on the overall dissociation ( k a ), hydration ( k h ), tautomerization ( k t ), and isomerization ( k i ) equilibrium of the system (Alejo‐Armijo et al., ). Substitution such as the hydroxylation, methylation, glycosylation, and acylation have a large influence on their color and stability.…”