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PubMed2003

Radiolysis of kaempferol in water/methanol mixtures. Evaluation of antioxidant activity of kaempferol and products formed.

Oxidative reaction between hydroxymethyl radical ((*)CH(2)OH) and kaempferol, in methanol and methanol/water mixtures, was studied by gamma-radiolysis using a (60)Co source. Radiolysis was performed with concentrations and doses ranging from 5 x 10(-)(5) M to 5 x 10(-)(3) M and from 0.5 kGy to 14 kGy, respectively. Kaempferol degradation was followed by HPLC. Results showed that (*)CH(2)OH reacts with kaempferol at the 3-OH group and produces two depsides (K1 and K2) and other products including K3. K1, K2, and K3 were identified by NMR, LC-MS, and HRMS. The kaempferol degradation pathway leading to the K1, K2, and K3 formation is proposed. It was observed that the more water concentration in the irradiation medium increases, the more K2 concentration increases. Comprehension of food preservation is not clear because many phenomena occurring during irradiation are not established. Radiolysis of kaempferol in water/methanol mixtures helps to elucidate the phenomenon and it is possible that during the treatment of nutriments by gamma-irradiation, a series of products such as depside K2 could be formed. Antioxidant properties of kaempferol radiolysis products were evaluated according to their capacity to decrease the EPR DPPH (1,1-diphenyl-2-picrylhydrazil) signal and to inhibit superoxide radicals formed by the enzyme reaction "xanthine + xanthine oxidase".

Antioxidants↗
PubMed2000

Radical-capturing reaction of 5,7,3',4'-tetramethylquercetin with the AIBN radical initiator.

In order to clarify the mechanism for the radical-capturing reaction which is initiated at the C3-hydroxyl group of flavonols, 5,7,3',4'-tetramethylquercetin (TMQ) was reacted with the 2,2'-azobis-isobutyronitrile (AIBN) radical initiator in benzene. Six products, one depside and its two hydrolytic products, one nitrile adduct, and two others, were isolated from the reaction mixture, and their structures were determined by instrumental analyses. The quantitative change to the four main products against the reaction time was measured by an HPLC method. The radical-capturing reaction pathway for TMQ with AIBN is proposed from these products and their quantitative changes. The pathway dividing into two clearly reveals that one subpath formed the depside and its hydrolytic products, while the other formed the nitrile adduct. The reactivity of each two sub-path was nearly the same, different from the case of TMQ and the 2,2'-azobis-2,4-dimethylvaleronitrile (AMVN) radical initiator.

Benzene↗
PubMed2001

Pharmaceutically relevant metabolites from lichens.

Lichen metabolites exert a wide variety of biological actions including antibiotic, antimycobacterial, antiviral, antiinflammatory, analgesic, antipyretic, antiproliferative and cytotoxic effects. Even though these manifold activities of lichen metabolites have now been recognized, their therapeutic potential has not yet been fully explored and thus remains pharmaceutically unexploited. In this mini-review, particular attention is paid to the most common classes of small-molecule constituents of lichens, from both the chemical viewpoint and with regard to possible therapeutic implications. In particular, aliphatic acids, pulvinic acid derivatives, depsides and depsidones, dibenzofuans, anthraquinones, naphthoquinones as well as epidithiopiperazinediones are described. An improved access to these lichen substances in drug discovery high-throughput screening programs will provide impetus for identifying novel lead-compounds with therapeutic potential and poses new challenges for medicinal chemistry.

4-Butyrolactone↗
PubMed2004

Anti-proliferative lichen compounds with inhibitory activity on 12(S)-HETE production in human platelets.

Several lichen compounds, i.e. lobaric acid (1), a beta-orcinol depsidone from Stereocaulon alpinum L., (+)-protolichesterinic acid (2), an aliphatic alpha-methylene-gamma-lactone from Cetraria islandica Laur. (Parmeliaceae), (+)-usnic acid (3), a dibenzofuran from Cladonia arbuscula (Wallr.) Rabenh. (Cladoniaceae), parietin (4), an anthraquinone from Xanthoria elegans (Link) Th. Fr. (Calaplacaceae) and baeomycesic acid (5), a beta-orcinol depside isolated from Thamnolia vermicularis (Sw.) Schaer. var. subuliformis (Ehrh.) Schaer. were tested for inhibitory activity on platelet-type 12(S)-lipoxygenase using a cell-based in vitro system in human platelets. Lobaric acid (1) and (+)-protolichesterinic acid (2) proved to be pronounced inhibitors of platelet-type 12(S)-lipoxygenase, whereas baeomycesic acid (5) showed only weak activity (inhibitory activity at a concentration of 100 microg/ml: (1) 93.4+/-6.62%, (2) 98,5+/-1.19%, 5 14.7+/-2.76%). Usnic acid (3) and parietin (4) were not active at this concentration. 1 and 2 showed a clear dose-response relationship in the range of 3.33-100 microg/ml. According to the calculated IC50 values the highest inhibitory activity was observed for the depsidone 1 (IC50 = 28.5 microM) followed by 2 (IC50 = 77.0 microM). The activity of 1 was comparable to that of the flavone baicalein, which is known as a selective 12(S)-lipoxygenase inhibitor (IC50 = 24.6 microM).

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed2004

Cytotoxic and apoptotic effects on hepatocytes of secondary metabolites obtained from lichens.

There are a large number of species of Antarctic lichens, and several studies describing the secondary metabolites present in these lichens, as well as the advances in understanding the chemistry of these metabolites, have been reported. In addition, some derivatives displaying interesting antibacterial effects have been described. The cytotoxic and apoptotic effects of 15 secondary metabolites (depsides, depsidones and usnic acid) obtained from Continental (Chilean) and Antarctic lichens were evaluated in primary cultures of rat hepatocytes. Intracellular lactate dehydrogenase release, caspase 3 activation and DNA fragmentation were measured. In this study, we have evaluated a set of markers associated with pivotal steps in the execution phase of apoptosis, in order to detect compounds with apoptotic effects on hepatocytes before significant necrosis takes place. Flow cytometric analysis of DNA fragmentation revealed an increase in apoptotic nuclei with sub-diploid DNA content after the exposure of hepatocytes to sub-cytotoxic concentrations of the compounds. Among these, salazinic acid, stictic acid and psoromic acid displayed significant apoptotic activities.

Animals↗
PubMed2003

Design and development of integrase inhibitors as anti-HIV agents.

A review is presented on different categories of compounds that have been studied for the inhibition of the HIV-1 integrase to develop anti-HIV agents. These compounds are: oligonucleotides (double-stranded, triplex, and G-quartet), curcumin analogues, polyhydroxylated aromatic compounds, diketo acids, caffeoyl- and galloyl - based compounds, hydrazides and amides, tetracyclines, and depsides and depsidones. For all these compounds, the important structural features essential for the inhibition of the integrase are pointed out.

Amides↗
PubMed1999

Lichen biodeterioration of the Convento de la Peregrina, Sahagún, Spain.

Lichen encrustations from Diploschistes scruposus involved in the biodeterioration of the 13th Century Convento de la Peregrina in Sahagún Spain, have been analyzed using Raman spectroscopy. The vibrational spectra are characteristic of calcium oxalate monohydrate, beta-carotene, chlorophyll, and para-depside phenolic acids such as atranorin, lecanoric acid, and diploschistesic acid. The destructive colonization of the monumental stonework is highlighted and evidence presented for deleterious lichen invasion of the wall paintings inside the Convent.

Architecture↗
PubMed1992

Green tea composition, consumption, and polyphenol chemistry.

Tea is grown in about 30 countries but is consumed worldwide, although at greatly varying levels. It is the most widely consumed beverage aside from water with a per capita worldwide consumption of approximately 0.12 liter per year. Tea is manufactured in three basic forms. Green tea is prepared in such a way as to preclude the oxidation of green leaf polyphenols. During black tea production oxidation is promoted so that most of these substances are oxidized. Oolong tea is a partially oxidized product. Of the approximately 2.5 million metric tons of dried tea manufactured, only 20% is green tea and less than 2% is oolong tea. Green tea is consumed primarily in China, Japan, and a few countries in North Africa and the Middle East. Fresh tea leaf is unusually rich in the flavanol group of polyphenols known as catechins which may constitute up to 30% of the dry leaf weight. Other polyphenols include flavanols and their glycosides, and depsides such as chlorogenic acid, coumarylquinic acid, and one unique to tea, theogallin (3-galloylquinic acid). Caffeine is present at an average level of 3% along with very small amounts of the other common methylxanthines, theobromine and theophylline. The amino acid theanine (5-N-ethylglutamine) is also unique to tea. Tea accumulates aluminum and manganese. In addition to the normal complement of plant cell enzymes, tea leaf contains an active polyphenol oxidase which catalyzes the aerobic oxidation of the catechins when the leaf cell structure is disrupted during black tea manufacture. The various quinones produced by the enzymatic oxidations undergo condensation reactions which result in a series of compounds, including bisflavanols, theaflavins, epitheaflavic acids, and thearubigens, which impart the characteristic taste and color properties of black tea. Most of these compounds readily form complexes with caffeine. There is no tannic acid in tea. Thearubigens constitute the largest mass of the extractable matter in black tea but their composition is not well known. Proanthocyanidins make up part of the complex. Tea peroxidase may be involved in their generation. The catechin quinones also initiate the formation of many of the hundreds of volatile compounds found in the black tea aroma fraction. Green tea composition is very similar to that of the fresh leaf except for a few enzymatically catalyzed changes which occur extremely rapidly following plucking. New volatile substances are produced during the drying stage. Oolong tea is intermediate in composition between green and black teas.

Agriculture↗
PubMed2004

Reactivity of flavonoids with 1-hydroxyethyl radical: a gamma-radiolysis study.

We have investigated the reactivity between 11 flavonoids and 1-hydroxyethyl radical (HER). HER was recently implicated in many liver injuries induced by ethanol intoxication. In this study, HER was generated by radiolysis; due to its reaction rate, HER is well known to be responsible for solute degradation in irradiated ethanol. Flavonoid ethanol solutions were irradiated with gamma-rays and the flavonoid degradation was followed by HLPC. We observed the degradation of flavonols while all other flavonoids (flavones, flavanones, dihydroflavonols, catechins) were not degraded after irradiation. The major radiolysis products were identified by NMR and LC-MS and we concluded that flavonols were essentially transformed into depsides. We proposed a reactivity mechanism between flavonols and HER. In a first step, H-transfer occurred from the 3-OH group to HER. Afterwards, C-ring opening occurred due to the presence of the 2,3-double bond in flavonols. Finally, we calculated the reaction constants in order to evaluate the antioxidant activity of flavonols against HER and to compare it with reference compounds.

Catechin↗
PubMed2005

Evaluation of selected South African medicinal plants for inhibitory properties against human immunodeficiency virus type 1 reverse transcriptase and integrase.

Seventeen aqueous and methanol extracts from nine South African medicinal plants, ethnobotanically selected, were screened for inhibitory properties against HIV-1 reverse transcriptase (RT). Isolated compounds were additionally evaluated on HIV-1 integrase (IN). The strongest inhibition against the RNA-dependent-DNA polymerase (RDDP) activity of RT was observed with the methanol extract of the stem-bark of Peltophorum africanum Sond. (Fabaceae) (IC(50) 3.5 microg/ml), while the methanol extract of the roots of Combretum molle R.Br. ex G. Don (Combretaceae) was the most inhibitory on the ribonuclease H (RNase H) activity (IC(50) 9.7 microg/ml). The known compounds bergenin and catechin, and a red coloured gallotannin composed of meta-depside chains of gallic and protocatechuic acids esterified to a 1-O-isobutyroly-beta-D-glucopyranose core, were isolated from the methanol extract of the roots and stem-bark of Peltophorum africanum. The gallotannin inhibited the RDDP and RNase H functions of RT with IC(50) values of 6.0 and 5.0 microM, respectively, and abolished the 3'-end processing activity of IN at 100 microM. Catechin showed no effect on RT but had a moderate activity on HIV-1 IN. Bergenin was inactive on both enzymes. The aqueous and methanol extracts were non-toxic in a HeLaP4 cell line at a concentration of 400 microg/ml.

Anti-HIV Agents↗
PubMed2004

Secretion, purification, and characterization of a recombinant Aspergillus oryzae tannase in Pichia pastoris.

Tannase (tannin acyl hydrolase) is an industrially important enzyme produced by a large number of fungi, which hydrolyzes the ester and depside bonds of gallotannins and gallic acid esters. In the present work, a tannase from Aspergillus oryzae has been cloned and expressed in Pichia pastoris. The catalytic activity of the recombinant enzyme was assayed. A secretory form of enzyme was made with the aid of Saccharomyces cerevisiae alpha-factor, and a simple procedure purification protocol yielded tannase in pure form. The productivity of secreted tannase achieved 7000 IU/L by fed-batch culture. Recombinant tannase had a molecular mass of 90 kDa, which consisted of two kinds of subunits linked by a disulfide bond(s). Our study is the first report on the heterologous expression of tannase suggesting that the P. pastoris system represents an attractive means of generating large quantities of tannase for both research and industrial purpose.

Aspergillus oryzae↗
PubMed2004

Molecular phylogeny of the Pertusariaceae supports secondary chemistry as an important systematic character set in lichen-forming ascomycetes.

The Pertusariaceae is a diverse, cosmopolitan group of crustose lichen-forming fungi. It is particularly rich in secondary metabolites, containing a variety of compounds from different substance classes, such as xanthones, depsides, depsidones, and depsones. Morphology and chemistry-based studies have provided conflicting views of relationships among taxa, and phylogenetic relationships among genera in the Pertusariaceae are still unsettled. To evaluate these relationships, we generated a phylogeny based on nucleotide sequences of the nuclear large subunit (nu LSU) and the mitochondrial small subunit (mt SSU) rRNA genes. For a subset of taxa, we additionally sequenced the mitochondrial large subunit (mt LSU) rDNA. We studied a total of 49 taxa from the family Pertusariaceae and the enigmatic genus Loxosporopsis including four Agyrialean taxa used as outgroups. The alignments were analyzed using a Bayesian approach with Markov Chain Monte Carlo tree sampling (B/MCMC), and maximum parsimony methods. In the resulting phylogenetic estimates the genus Pertusaria in its current circumscription is polyphyletic comprising three major clades: the Pertusaria s.str.-group, the Variolaria-group and the Varicellaria-group. Loxosporopsis is closely related to Pertusaria s.str. We re-analyzed morphological, anatomical, and chemical features in the light of the molecular study and found novel character combinations to describe monophyletic entities. The taxonomic significance of particular secondary chemical constituents in the Pertusariaceae is corroborated.

Ascomycota↗
PubMed2001

Genetic approaches to harvesting lichen products.

Lichens are symbiotic associations between fungi, green algae and/or cyanobacteria. They have a varied chemistry and produce many polyketide-derived compounds, including some, such as depsides and depsidones, that are rarely reported elsewhere. Although lichens have been appreciated in traditional medicines, their value has largely been ignored by the modern pharmaceutical industry because difficulties in establishing axenic cultures and conditions for rapid growth preclude their routine use in most conventional screening processes. Recently, molecular genetic techniques using PCR, genomic library construction and heterologous expression have provided an alternative approach to begin exploring the diversity of polyketide biosynthetic pathways in lichens. The techniques can be expanded to cover other pathway types and be integrated with conventional culture collection-based screening to provide a comprehensive search for novel chemical entities in these organisms.

Amino Acid Sequence↗
PubMed2001

Variation of free phenolic acids in medicinal plants belonging to the Lamiaceae family.

Ten species belonging to the family Lamiaceae and representing the most popular medicinal plants used in Polish phytotherapy were examined for the content of free phenolic acids (PhAs). Two depsides, rosmarinic and chlorogenic acids, as well as eight simple PhAs, protocatechuic, gentisic, p-hydroxybenzoic, caffeic, vanillic, syringic, p-coumaric and ferulic acids, in different qualitative and quantitative proportions depending on the plant examined were determined by the rapid, selective and accurate method combining solid-phase extraction and high-performance liquid chromatography.

Chromatography, High Pressure Liquid↗
PubMed2002

Flavonoid oxidation by the radical generator AIBN: a unified mechanism for quercetin radical scavenging.

Four oxidized flavonoid derivatives generated from reacting quercetin (a pentahydroxylated flavone) with the peroxyl radical generator 2,2'-azobis-isobutyronitrile (AIBN) were isolated by chromatographic methods and identified by NMR and MS analyses. Compounds included 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2); 1,3,11a-trihydroxy-9-(3,5,7-trihydroxy-4H-1-benzopyran-4-on-2-yl)-5a-(3,4-dihydroxyphenyl)-5,6,11-hexahydro-5,6,11-trioxanaphthacene-12-one (3); 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (4); and methyl 3,4-dihydroxyphenylglyoxylate (5). Product ratios under different hydrogen ion concentrations and external nucleophiles revealed that two of the products, namely the substituted benzofuranone (2) and the depside (4), are generated from a common carbocation intermediate. Indirect evidence for the operation of a cyclic concerted mechanism in the formation of the dimeric product (3) is provided. The identification of these products supports the model that the principal site of scavenging reactive oxygen species (ROS) in quercetin is the o-dihydroxyl substituent in the B-ring, as well as the C-ring olefinic linkage.

Flavonoids↗
PubMed1966

The esterase and depsidase activities of tannase.

The esterase and depsidase activities of tannase have been examined by kinetic methods. Although the esterase/depsidase ratio of tannase may be varied by cultural methods and isolation procedures, evidence has been obtained to show that tannase, esterase and depsidase are enzymes with low specificities capable of hydrolysing both esters and depsides of gallic acid.

Chemical Phenomena↗
PubMed1966

The leaf tannin of willow-herb [Chamaenerion angustifolium (L.) Scop.].

1. The leaf tannin of willow-herb [Chamaenerion angustifolium (L.) Scop.] has been isolated and separated into two fractions of differing solubility. 2. The tannin contains a penta-O-galloyl-beta-d-glucose core to which further galloyl groups are depsidically bound. 3. The unfractionated tannin contains an average of 10.5 galloyl groups/glucose molecule; the soluble fraction has on average 7.6 galloyl groups/glucose molecule and the less soluble fraction has 12.4. 4. The tannin is a mixture of molecules ranging at least from hepta- to trideca-galloyl-beta-d-glucose. 5. The tannin forms complexes with proteins and the fact that it is a hydrolysable gallotannin has a bearing on the release of nitrogen from the protein of the dead leaf.

Chemical Phenomena↗
PubMed1969

The pH-dependence of the binding of competitive inhibitors to pepsin.

1. The pH-dependence of the binding to pepsin of four dipeptide competitive inhibitors is reported. Values of K(i) obtained from equilibrium-dialysis experiments agree closely with those from kinetic measurements. 2. The binding of uncharged N-acyl-dipeptide amides to pepsin is essentially independent of pH from 0.2 to 5.8. Values of K(i) for the corresponding N-acyl-dipeptide acids rise rapidly above pH3.5, and depend on the ionization of a group of apparent pK(a) 3.6. 3. The data indicate that pepsin does not undergo any gross conformation change (at least none that affects binding) over the whole pH range of its catalytic activity. The pH-dependence of the dipeptide acid inhibitors indicates that the acid anions do not bind to pepsin, presumably because of electrostatic repulsion between the inhibitor anion and a negative centre at or near the active site of the enzyme. 4. The binding of all four stereoisomers of N-acetylphenylalanylphenylalanine, of the depside analogues of the l-l- and d-l-compounds and of N-acetylglycyl-l-phenylalanine and N-acetyl-l-phenylalanylglycine was studied at pH2.2. 5. These results throw further light on the binding specificity of pepsin and on the charge nature of the active site of this enzyme.

Amides↗