Temperature and pressure dependence of quercetin-3-O-palmitate interaction with a model phospholipid membrane: film balance and scanning probe microscopy study

Regioselective Synthesis of Quercetin and Myricetin Derivatives

A regioselective method for the synthesis of esters of quercetin and myricetin at the hydroxy group in the position 3 was developed. As acids participating in the esterification reaction, 2-hydroxybenzoic (salicylic), 4-hydroxybenzoic, 2,6-dihydroxybenzoic, 3,4-dihydroxybenzoic (procatechuic), 3,4,5-trihydroxybenzoic (gallic) acids were used. A new series of quercetin and myricetin esters were obtained.

Synthesis of regioselectively acylated quercetin analogues with improved antiplatelet activity

The aim of the present study was to report on a complete synthetic approach, namely benzylation-hydrolysis-acylation‑hydrogenation, to the synthesis of regioselectively acylated quercetin analogues using low‑cost rutin as a starting material. Three quercetin analogues, quercetin‑3‑O‑propionate (Q‑pr), quercetin‑3‑O‑butyrate (Q‑bu) and quercetin‑3‑O‑valerate (Q‑va), containing 3‑, 4‑ and 5‑carbon aliphatic acyl chains, respectively, were synthesized and characterized with 1H nuclear magnetic resonance (NMR), 13C NMR and mass spectrometry. Compared with quercetin, all three analogues exhibited improved lipophilicity. The lipophilicity of the analogue increased with increasing acyl chain length. Q‑va exhibited the highest lipophilicity among the three analogues, but a lower water solubility compared with quercetin. By contrast, Q‑pr and Q‑bu exhibited 8.2‑ and 4.7‑fold higher water solubility compared with quercetin, respectively. The in vitro and in vivo studies demonstrated that Q‑pr and Q‑bu were more effective whereas Q‑va was less effective in inhibiting platelet aggregation compared with quercetin. These results indicated that the water solubility and the lipophilicity of the analogues must be improved in order to achieve higher antiplatelet activity, and an optimal acyl chain length is crucial for the synthesized quercetin analogues to be more effective.

Enhanced stability and intracellular accumulation of quercetin by protection of the chemically or metabolically susceptible hydroxyl groups with a pivaloxymethyl (POM) promoiety

In order to increase stability of quercetin, its metabolically and chemically susceptible hydroxyl groups 7-OH and 3-OH respectively were transiently blocked with a pivaloxymethyl (POM) promoiety to provide two novel quercetin conjugates [7-O-POM-Q, 3-O-POM-Q]. In the absence of stabilizer (ascorbic acid), the synthesized conjugates showed significantly increased stability in cell culture media [t(½) = 4 h, 52 h] compared with quercetin (t(½) < 30 min) and quercetin prodrug 1 (t(½) = 0.8 h). In addition, the quercetin conjugate 2 underwent efficient cellular uptake and intracellular levels of its hydrolysis product, quercetin, were maintained up to 12 h. Stability and intracellular accumulation of were demonstrated by its stabilizer-independent cytostatic effect and induction of apoptotic cell death. Even though was more stable than, it failed to penetrate cell membranes. However, the remarkable stability of warrants further investigation of quercetin conjugates with various promoieties at the 3-OH position.

Monolayers of mixture of alkylaminomethyl rutin and lecithin at the air/water interface

A compound of flavonol-based biosurfactant, as C(8)-substituted alkylaminomethyl rutin (DAMR) for a potential pharmaceutical or agrochemical use, was prepared experimentally. The surface behavior of DAMR and its mixture with lecithin from soybean (SL) had been studied. DAMR, regarded as a pseudo-amphoteric character, exhibits both liquid-condensed (LC) and liquid-expanded (LE) phases while SL is in the form of the LE phase only. The phase parameters of DAMR (including A(limt), pi(coll)) are observed to strongly depend on both the subphase temperature and the pH, which regulate the degree of ionization. In addition, the observed positive deviation calculated from excess Gibbs free energies of the DAMR-SL system suggests a repulsive interaction between DAMR and SL at all X(DAMR) values. Also the interaction parameter is found to increase linearly with surface pressure, regardless of composition. Notably, the relationship of logarithmic activity coefficient vs. X(DAMR)(2) reveals that the molecular interaction of DAMR-SL can be adequately simulated using a simple regular mixture model. Importantly, lower C(S)(-1) values of this mixture than those with pure DAMR and SL denote weak elasticity of mixed monolayers with values of X(DAMR) of 0.2-0.8, indicating that the direct addition of DAMR may exert a somewhat adverse influence on SL membranes.

Comparison of the extended isotropic periodic sum and particle mesh Ewald methods for simulations of lipid bilayers and monolayers

3D-IPS/DFFT is an extension of the three-dimensional isotropic periodic sum (3D-IPS) for evaluation of electrostatic and Lennard-Jones interactions in heterogeneous systems; it utilizes a discrete fast Fourier transform (DFFT) for efficient calculation of the IPS potential with a large local region radius. The method is demonstrated to be highly accurate for simple bulk fluids, liquid/liquid and liquid/vapor interfaces, and lipid bilayers and monolayers. Values for r(C) (the cutoff distance for direct evaluation of pairs) and R(C) (the local region radius) equal to 10 A and twice the longest edge of the periodic cell, respectively, provide excellent efficiency and accuracy. Dimyristoylphosphatidylcholine (DMPC) monolayers simulated with the CHARMM (Chemistry at HARvard Molecular Mechanics) C27r lipid parameter set and 3D-IPS/DFFT yield surface tensions approximately 8 dyn/cm higher than those simulated using particle mesh Ewald (PME), and with experiment. In contrast, surface tensions for DMPC bilayers are 16 dyn/cm/leaflet with both 3D-IPS/DFFT (r(C) = 10 and 12 A) and PME (r(C) = 12 A). This indicates that PME (r(C) = 12 A) may be used for simulations of bilayers, but not monolayers, and that the large bilayer surface tension arising from C27r is incorrect.

In vitro evaluation of quercetin-3-O-acyl esters as topical prodrugs

Quercetin-3-O-acyl esters (I-VI) were synthesized and their usefulness as quercetin topical prodrugs was evaluated. Quercetin esters were assayed to determine their water stability and solubility, their susceptibility to undergoing enzymatic hydrolysis and their permeation through excised human skin. Quercetin ethyl (I) and hexyl (IV) esters proved poorly stable in aqueous media and they were not assayed further. Among the derivatives tested, quercetin propyl (II) and butyl (III) esters were more water-soluble than the parent drug. Esters II, III and V were readily hydrolyzed by human plasma and esters II and III penetrated excised human skin better than quercetin from aqueous saturated solutions. On the basis of the results obtained, esters II and III could be regarded as promising quercetin topical prodrugs.

Hydroxytyrosol lipophilic analogues: Enzymatic synthesis, radical scavenging activity and DNA oxidative damage protection

The olive oil phenol hydroxytyrosol (3), as well its metabolite homovanillic alcohol (4), were subjected to chemoselective lipase-catalysed acylations, affording with good yield 10 derivatives (5-14) bearing C(2), C(3), C(4), C(10) and C(18) acyl chains at C-1. Hydroxytyrosol (3) and its lipophilic derivatives showed very good DPPH. radical scavenging activity. Compounds 3, 4 and their lipophilic analogues 5-14 were subjected to the atypical Comet test on whole blood cells: 3 and its analogues 5 and 6, with little hydrophobic character (logP<or=1.20), showed a good protective effect against H(2)O(2) induced oxidative DNA damage. The homovanillic alcohol 4 and its analogues 10-14 resulted scarcely effective both as radical scavengers and antioxidant agents.

Viscoelastic properties of insoluble amphiphiles at the air/water interface

The effects of the presence of a molecular monolayer on the dilatational properties of the air/water interface have been investigated. Two water insoluble amphiphiles, dipalmitoyl phosphatidyl choline and quercetin 3-O-palmitate, were spread onto a pendant drop and the dynamic surface pressure was measured by means of drop shape analysis. The surface dilatational elasticity and viscosity of the spread monolayers were also determined by the oscillating drop technique. Constraints on the range of measuring conditions were investigated and we demonstrated that the pressure-area isotherms derived from oscillatory dynamic measurements display phase behaviour similar to that found in equilibrium measurements, albeit at reduced resolution. Both the amphiphiles formed purely elastic films that were characterised by a dilatational modulus that depended on the surface concentration and obeyed a power scaling law. The exponent of the relationship could be related to the thermodynamic conditions prevailing at the interface. The phospholipid monolayer scaling exponent was 2.8 in a temperature range of 20-26 degrees C indicates a favourable solvency of molecules in the bidimensional matrix. A very high scaling exponent (11.8 at 7 degrees C) for quercetin palmitate was interpreted assuming that molecules self-organise in fibre-like structures. This interface structure and the phase behaviour was found consistent with observations of the surface film obtained by Brewster angle microscopy. The structured quercetin 3-O-palmitate monolayers are disrupted by temperature increase or by adding a 0.2 molar fraction of the immiscible dipalmitoyl phosphatidyl choline.