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.

Diastereoselectivity and site dependency in the photochemistry of ketoprofen in the bovine serum albumin matrix.

The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumin matrix was studied by steady-state photolysis with the use of lambda(irr) > 320 nm and transient absorption spectroscopy with lambda(exc) = 355 nm, at 1/1 and 2/1 KP/BSA molar ratios. R(-)-KP was found to be more labile than S(+). Triplet ketoprofen species were evidenced with lifetimes of 400 ns for S(+) and 600 ns for R(-)-KP. Further longer-lived transients with lifetimes of 2.6 and 6.0 mus for S(+) and R(-), respectively, were detected. On the basis of the binding constants of the drug enantiomers to the two main binding sites of the protein, obtained from circular dichroism experiments, the individual disappearance quantum yields of the 1:1 and 2:1 diastereomeric KP:BSA complexes could be estimated. The photoreactivity in the BSA matrix was rationalized on the basis of diastereoselective photodecarboxylation in the two main protein sites.

Enzymatic procedures in the preparation of regioprotected D-fructose derivatives.

A combination of different lipases from Pseudomonas cepacia, Candida antarctica B, Candida rugosa and Mucor miehei, aided the regioesterification of the free fructose allowing the synthesis of 1,6-di-O-acetyl-D-fructofuranose, 1,4,6-tri-O-acetyl-D-fructofuranose, 1,6-di-O-acetyl-4-O-benzoyl-D-fructofuranose and 1,6-di-O-benzoyl-D-fructofuranose. Using C. antarctica B and C. rugosa lipases the alcoholysis of fructose peracetate (alpha, beta-form) has furnished 1,2,3,4-tetra-O-acetyl-alpha-D-fructofuranose and 2,3,4,6-tetra-O-acetyl-beta-D-fructofuranose. 1,4,6-Tri-O-acetyl-D-fructofuranose was successfully employed to produce a rare ketohexose, namely D-psicose.

Binding of a chiral drug to a protein: an investigation of the 2-(3-benzoylphenyl)propionic acid/bovine serum albumin system by circular dichroism and fluorescence.

A combined approach using global analysis of circular dichroism multiwavelength data and time resolved fluorescence was applied to investigate the interaction of R-(-)- and S-(+)-ketoprofen with bovine serum albumin in buffer solution at neutral pH. A characterization of the most stable drug : protein adducts of 1 : 1 and 2 : 1 stoichiometry, as individual chemical species, was obtained. The stability constants and the absolute circular dichroism spectra of the diastereomeric complexes were determined. The spectra of the 1 : 1 conjugates are opposite in sign, those of the 2 : 1 complexes are both negative, but different in shape from each other (peaks at 358 and 342 nm for S-(+)- and R-(-)-ketoprofen, respectively). A tryptophan residue was shown to be involved in the binding of the drug, in the primary site for the R-(-) and in the secondary site for the S-(+) enantiomer, thereby showing that chiral recognition by the protein causes the site of highest affinity being not the same for both optical antipodes.

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

The molecular interaction of quercetin-3-O-palmitate (QP) with dimyristoylphosphatidylcholine (DMPC) has been studied. Film balance measurements of the average molecular area vs QP molar fraction in DMPC/QP mixed monolayers showed that relevant positive deviations from ideality, i.e., a less dense monolayer packing, occurred for a temperature of 10 degrees C, below the critical melting transition temperature of DMPC monolayers T c m approximately equal 20 degrees C), while ideal behavior was observed at 37 degrees C, above this phase transition temperature. The positive deviation observed at low temperatures in the average molecular area increased with the surface pressure. Scanning probe microscopy measurements performed on mixed monolayers transferred on mica showed that the deviations from ideality were connected to the formation of nanometric-scale QP-rich domains. However, the formation of aggregates was observed only for relatively high-QP molar fractions X QP > or = 0.25 at 10 degrees C, while it was not observed at 37 degrees C, i.e., when the ideal mixing was found at the air/water interface. The observed effects are explained in terms of a temperature- and surface pressure-dependent phase-separation process based on the predominance at low temperature and low molecular mobility of QP-QP and DMPC-DMPC aggregation forces, prompting the formation of QP-rich domains embedded in a DMPC-rich matrix. High temperature prompts the QP/DMPC ideal mixing.

Chloroperoxidase from Caldariomyces fumago is active in the presence of an ionic liquid as co-solvent.

Chloroperoxidase from Caldariomyces fumago catalyses the oxidation of 1,2-dihydronaphthalene to (1R,2R)-(+)-dihydroxytetrahydronaphthalene in homogenous citrate buffer/ionic liquid mixtures, using t-butyl hydroperoxide as O2 donor. It tolerates up to 30 (v/v) 1,3-dimethylimidazolium methylsulfate or 1-butyl-3-methylimidazolium methylsulfate. The enzyme activity in these ionic liquid co-solvent systems is retained for 24 h, but it falls to 3 h using non-ionic organic solvents such as t-BuOH or acetone.

'In vitro' antioxidant and photoprotective properties and interaction with model membranes of three new quercetin esters.

Quercetin is well known to possess the strongest protective effect against UV light-induced lipoperoxidation. However, the absolute water insolubility of quercetin is a key step that may limit its bioavailability and, thus, its 'in vivo' employment as a photoprotective agent. The aim of the present paper was to evaluate 'in vitro' the antioxidant and photoprotective properties and the interaction with model membranes of three new semisynthetic quercetin derivatives, quercetin-3-O-acetate (Q-ac), quercetin-3-O-propionate (Q-pr) and quercetin-3-O-palmitate (Q-pal), obtained by esterification of the C-3 OH function with an aliphatic side-chain of different length. The antioxidant activity of quercetin and of its three esters was assessed in two 'in vitro' experimental models: (a) the bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical; (b) UV radiation-induced peroxidation in multilamellar vesicles (MLVs). Differential scanning calorimetry on dimyristoylphosphatidylcholine MLVs and unilamellar vesicles was employed to investigate the interaction of the drugs tested with model membranes. Finally, the stability following UV light exposure and the lipophilicity and water solubility of quercetin and its three esters were examined. The findings obtained demonstrated that the esterification with an opportune aliphatic side chain of the OH function located at the C-3 position allows the production of new quercetin derivatives, which may be good candidates as photoprotective agents. In particular, one could speculate that the esterification with a short side-chain (such as in Q-ac and Q-prop) provides the suitable chemico-physical features not only to maintain the antioxidant and photoprotective effectiveness of the parent drug, but also to be able to migrate through the aqueous environment and to interact with and cross phospholipid membranes.

Improvement of (+)-catechin inhibitory activity on human PMN respiratory burst by (+)-3-O-propionyl and (-)-3-O-valeryl substitution.

Catechins and their derivatives are abundant flavanols in the plant kingdom. Usually, catechin activity correlates with chemical structure. We hypothesized that by adding hydrophobic groups to the native catechin, we could ameliorate penetration of the cell and make the derivatives more active than native molecule in inhibiting polymorphonuclear leucocyte (PMN) oxidative burst. This study was designed to compare the antioxidant activity of native catechin with that of (+)-3-propionylcatechin and (-)-3-Ovalerylcatechin esters by two cell-free colorimetric methods and by their effects on whole blood leucocytes as well as on isolated PMN chemiluminescence activity. The results showed that the colorimetric methods did not detect differences between catechins. On the contrary, cellular chemiluminescence studies showed that light emission by resting, as well as by phorbol myristate acetate (PMA)-stimulated PMNs and whole blood leucocytes was inhibited by catechin esters more intensively than native catechin. The compartmental chemiluminescence evaluation showed that the extracellular activity was similar with all catechins, while the intracellular activity was higher with esters. PMN pre-incubation, with catechins at various times before stimulation with PMA, enhanced the inhibitory activity of all compounds. Since the esterification with propionic or valeric acid increased the lipophilicity of (+)-catechin, we hypothesized that native and esterified catechins have different intracellular availability and therefore differ in effectiveness. An ancillary result obtained is that a single approach, chemical or cellular, is not sufficient to evaluate overall antioxidant activity in biological sytems. The results indicate that modified catechins may be very intriguing as possible future leucocyte modulating drugs, with possible applications in vascular and inflammatory diseases.

Effective enzymatic resolution of rac-1-(3-trifluoromethylphenyl)propan-2-ol, precursor of fenfluramine.

Lipases from Candida antarctica and from Mucor miehei efficiently catalyze the enantioselective esterification of rac-1-(3-trifluoromethylphenyl)propan-2-ol. The obtained enantioforms are suitable to prepare both enantiomers of fenfluramine.

Antimicrobial and anti-lipase activity of quercetin and its C2-C16 3-O-acyl-esters.

Neither quercetin (Q), nor 3-O-acylquercetines, up to 100 microg/mL, had any significant activity on selected gram-positive strains (Staphylococcus aureus, Bacillus subtilis, Listeria ivanovi, Listeria monocytogenes, Listeria serligeri), gram-negative strains (Escherichia coli, Shigella flexneri, Shigella sonnei, Salmonella enteritidis, Salmonella tiphymurium) and yeasts (Candida albicans and Candida glabrata). In addition, we confirmed the known anti-HIV activity of Q (80% inhibition at 40 microM), which might depend on the free hydroxyl in the C-3 position, as suggested by the lack of activity of the 3-O-acylquercetines. Finally, we described an interesting inhibitory activity on Candida rugosa lipase by Q (IC(16)=10(-4) M) and its esters (3-O-acylquercetines) which, in vivo, could play an important role against lipase producing microorganisms. In particular, 3-O-acyl-quercetines, being more active (IC(16)=10(-4)-10(-6) M) and more lipophilic, could be more effective than Q when applied to the skin or mucosae, and deserve to be studied further.