Showing papers by "Artur M. S. Silva published in 2008"
TL;DR: Three azines, two of them doubly labeled with 15N, have been studied by multinuclear magnetic resonance in solution and in the solid state and the spectral parameters obtained by iterative analyses have been compared with DFT/B3LYP calculated values.
Abstract: Three azines, two of them doubly labeled with 15N, have been studied by multinuclear magnetic resonance in solution and in the solid state. The spectral parameters obtained by iterative analyses have been compared with DFT/B3LYP calculated values (absolute shieldings and coupling constants). The agreement is generally good. Some anomalies have been discussed in relation to the structure of these compounds. Copyright © 2008 John Wiley & Sons, Ltd.
109 citations
TL;DR: The hot water soluble green coffee arabinogalactans, representing nearly 7% of total coffee bean arabinosyl, were characterized by (1)H and (13)C NMR and, after partial acid hydrolysis, by ESI-MS/MS.
76 citations
TL;DR: In this paper, a dimer catechin-(4α→8)-cyanidin-3,5-Odiglucoside was identified from a commercial anthocyanin-rich purple corn powder and its structure elucidated by mass spectrometry and 1H and 13C NMR using 1D and 2D techniques.
61 citations
TL;DR: These compounds were also found in the reaction between mv3glc and (+)-catechin mediated by acetaldehyde, which provides evidence for the formation of 8-vinyl catechin and its involvement in theformation of pyranoanthocyanins in aged red wines.
Abstract: Reactions between malvidin-3-glucoside (mv3glc) and 8-vinylcatechin were carried out to synthesize pyranomv3glc-(+)-catechin pigment and to study the formation of intermediates. A rapid decrease of mv3glc content concomitant with the formation of more complex structures such as mv3glc-vinylcatechin [precursor of pyranomv3glc-(+)-catechin pigment] and mv3glc-divinylcatechin was observed. On the other hand, 8-vinylcatechin undergoes acid-catalyzed dimerization in model wine solution, giving rise to 8-vinylcatechin dimers. These compounds were also found in the reaction between mv3glc and (+)-catechin mediated by acetaldehyde, which provides evidence for the formation of 8-vinylcatechin and its involvement in the formation of pyranoanthocyanins in aged red wines.
58 citations
TL;DR: The data reported here demonstrate the success of 2D NMRtechniquest to investigate aerosol WSOC composition, as well as to evaluate aerosol source fingerprints.
Abstract: The potential and the limitations of combining two-dimensional nuclear magnetic resonance (2D NMR) techniques to deliver new qualitative information on the substructures present in water-soluble organic compounds (WSOC) from fine atmospheric aerosols collected during Winter and Spring/Summer seasons are highlighted in this study. The WSOC fractions were extracted from quartz filter samples and further separated into hydrophobic acids and hydrophilic acids fractions by using a XAD-8/XAD-4 isolation procedure. Despite different spectral resolution, it was found that the aliphatic material of both samples includes mostly long-chain (carbons greater than 3 or 4) and branched mono- and dicarboxylic acids, carbonyl, and ester structural types. The presence of such structural fragments could be associated to secondary organic aerosol formation. It has been further demonstrated that spectral signatures typical of anhydrosugars from cellulose and methoxyphenols from lignin can be identified among the carbohydrate ...
56 citations
TL;DR: In this article, a simple synthesis of new amphiphilic chlorin derivatives from protoporphyrin-IX dimethyl ester is reported based on a straightforward methodology, which involves the Diels-Alder reaction of POR with maleic anhydride followed by addition of nucleophilic species to the initially formed cycloadducts, a transformation which is highly regioselective.
40 citations
TL;DR: The N-arylquinolino[2,3,4-at]porphyrins show interesting UV-vis spectra with strong absorption bands in the red region and a new reaction leading to porphyrins bearing fused rings is described.
Abstract: A new reaction leading to porphyrins bearing fused rings is described. Novel N-arylquinolino[2,3,4-at]porphyrins 2 were obtained by thermal oxidative cyclization of beta-arylaminoporphyrins 1. The starting beta-arylaminoporphyrins were prepared by two routes: (i) nucleophilic displacement of the nitro group from 2-nitro-5,10,15,20-tetraphenylporphyrin by anilines and (ii) palladium-catalyzed amination of bromobenzene derivatives with (2-amino-5,10,15,20-tetraphenylporphyrinato)nickel(II). The N-arylquinolino[2,3,4-at]porphyrins show interesting UV-vis spectra with strong absorption bands in the red region.
39 citations
TL;DR: The results of an in vitro tubulin polymerization assay showed that this chromone stabilizes microtubules in a manner similar to paclitaxel, suggesting that the chromone interferes withmicrotubules.
37 citations
TL;DR: The dichloromethane extract from leaves of Juniperus brevifolia, through chromatographic fractionations yield six compounds, which are the first examples of sandaracopimaranes and abieta-8,11,13-triene diterpenoids with a large aliphatic chain on C-18.
33 citations
TL;DR: The study suggests that in ethanol and pH 7 buffer the beta-cyclodextrins embed the highly hydrophobic tetrakis(pentafluorophenyl)-chlorin macrocycle and strongly interact with the chlorin rings in the singlet and triplet manifolds, resulting in a longer lived triplet with spectral properties indistinguishable from that of original difference absorbance spectra.
Abstract: A meso-tetrakis(pentafluorophenyl)-chlorin with the reduced pyrrole ring linked to an isoxazolidine ring (FC) has been conjugated to four β-cyclodextrins (CDFC). The CDFC exhibits excellent water solubility and is a potent photosensitizer towards proliferating NCTC 2544 human keratinocytes. The study by conventional steady state absorption and fluorescence spectroscopies and by time-resolved femto- and nanosecond laser flash spectroscopies suggests that in ethanol and pH 7 buffer the β-cyclodextrins embed the highly hydrophobic tetrakis(pentafluorophenyl)-chlorin macrocycle and strongly interact with the chlorin rings in the singlet and triplet manifolds. In these solvents, femtosecond spectroscopy suggests that the conjugate undergoes a rapid relaxation in the upper excited singlet states induced by photochemical and/or conformation change(s) at a rate of about 5 ps−1 to fluorescent states whose lifetime is ∼8 ns. This interaction is destroyed upon addition of Triton X100 to buffer. Both FC and CDFC strongly fluoresce (ΦF ∼ 0.5) in micelles. Similar behavior is observed at the triplet level. In ethanol and water, the initial transient triplet state absorbance decays within 1–3 μs yielding a longer lived triplet with spectral properties indistinguishable from that of original difference absorbance spectra. The determination of the molar absorbance in the 440–460 nm region (∼35000 M−1 cm−1) leads to an estimate of ∼0.2 for the triplet formation quantum yield of FC in toluene and of FC and CDFC in Triton X100 micelles. Quenching of the CDFC triplets by dioxygen in buffer produces 1O2 in a good yield consistent with the effective photocytotoxicity of the chlorin–cyclodextrins conjugate towards cultured NCTC 2544 human keratinocytes. By contrast, FC which aggregates in buffer produces little if any 1O2.
32 citations
TL;DR: The first report of electrocyclization of β-butadienylporphyrin was given in this article, where the structure of mono-and dibenzoporphyrin nickel complexes, as well as of a Diels-Alder adduct, were determined by single-crystal X-ray diffraction.
TL;DR: It is shown, for the first time that PQ and NaSAL react immediately in aqueous medium and within 2-3 min in the solid state, which provided a new and important mechanism of action of NaSal against the toxicity mediated by PQ.
TL;DR: The results from the scavenging assays were in agreement with those obtained from the cyclic voltammetry, that is, higher scavenging effects corresponded to lower values of oxidation potentials, with significant correlation coefficients.
TL;DR: In this article, a single-source approach using mild temperatures was applied to prepare morphological well-defined and coupled TiO2/metal-sulfide nanocomposites.
Abstract: A single-source approach using mild temperatures was applied to prepare morphological well-defined and coupled TiO2/metal–sulfide nanocomposites. Metal N-alkyldithiocarbamates were used as the precursors to the metal–sulfide nanophases and, in particular, Ag2S nanostructures were investigated in more detail. These were observed as nano-islands at the surface of TiO2 (anatase) particles, which were used as substrates. To explain the formation of these nanocomposite particulates, a tentative mechanism has been proposed which involves the controlled release of sulfide ions from an intermediate coordination compound. Because the growth of the metal sulfide can be controlled at the surface of a photoactive substrate, we anticipate the potential of this synthetic method to chemical design reasonable amounts of semiconductor-sensitized TiO2, such as Ag2S/TiO2 nanocomposites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
TL;DR: The cytotoxic activity was evaluated for the first time for compounds 1-5 against HeLa and Vero cell lines in lag and log phases of growth.
Abstract: The hexane, dichloromethane, acetone and ethanol extracts of the leaves, bark and wood of JUNIPERUS BREVIFOLIA were subjected to screening against human tumour cells lines from the cervix (HeLa) and larynx (Hep-2) in two different stages of the cell cycle. The dichloromethane and the chloroform-soluble portions of the acetone extracts of the leaves were active against both tumour cell lines. Chemical investigation of one of the most active extracts (dichloromethane extract from leaves) by preparative chromatography afforded compounds 1 - 10. Among these, compounds 1 - 3 were isolated for the first time from the JUNIPERUS genus (18-hydroxyferruginol, 6,7-dehydrototarol and 7α-hydroxytotarol) while 4 and 5 are rare as natural products corresponding to ( E)- and ( Z)-isomers of 8α-hydroxy-labda-13(16),14-dien-19-yl-coumarate, respectively. The structures of all compounds were established based on various spectral data. The cytotoxic activity was evaluated for the first time for compounds 1 - 5 against HeLa and Vero cell lines in lag and log phases of growth. Compound 5 was shown to be active and selective to HeLa in the log phase. AB: acetone extract from bark ALIC: chloroform-insoluble portion of the acetone extractfrom leaves ALSC: chloroform-soluble portion of the acetone extract from leaves AW: acetone extract from wood DL: dichloromethane extract from leaves DMSO: dimethyl sulfoxide DW: dichloromethane extract from wood EB: ethanol extract from bark EL: ethanol extract from leaves EW: ethanol extract from wood HB: hexane extract from bark HeLa: human carcinoma of the cervix Hep-2: human carcinoma of the larynx HL: hexane extract from leaves Vero: African green monkey kidney cell line
TL;DR: The microwave assisted solvent-free synthesis of (E)-3-styrylchromones from 3-formylchromones and phenylmalonic acid on sodium acetate support has been developed; the method affords the styryl derivatives in moderate to good yields and with complete diastereoselectivity.
TL;DR: In this paper, a study on the hydroformylation of the methyl esters of the grandiflorenic acids and the trimethylsilyl ether of kaurenol was conducted.
Abstract: Kaurenic and grandiflorenic acids are naturally occurring diterpenes whose biological activity has been described Both acids contain an exocyclic methylenic double bond that allows further functionalization on their structure In an attempt to expand the number of derivatives of these two natural products, we have undertaken a study on the hydroformylation of the methyl esters of the two acids and the trimethylsilyl ether of kaurenol These substrates have been hydroformylated by using unmodified Rh catalysts, as well as Rh/PPh 3 and Rh/ tris -( o - t -butylphenyl)phosphite catalytic systems at 100 °C and 20 bar of CO/H 2 (1:1) For the three substrates, the two Rh catalysts modified with P-donor ligands, produced high conversions and chemo- and regioselectivities in the diastereoisomeric pair of linear aldehydes In all cases, the stereoselectivity observed is strongly dependent of the system used, being the most diastereoselective the least hindered unmodified Rh/CO catalyst A correlation between the higher diastereoselectivity and the faster β-elimination of the metal-alkyl intermediate observed in the unmodified system is discussed
TL;DR: White wine degradation was promoted by a forced aged protocol, and six normally aged white wines from different vintages were analyzed, and possible structures of antioxidant compounds in white wines were proposed.
Abstract: The aim of this study was to obtain new information on antioxidant compounds in white wines For this purpose, white wine degradation was promoted by a forced aged protocol, and six normally aged white wines from different vintages were analyzed Both normal and forced aged wines were sequentially extracted using hexane and ethyl acetate Apolar antioxidants were removed using hexane, and polar antioxidants were extracted with ethyl acetate This last residue was subject to partial re-extraction with hexane and acetone The antioxidant capacity of the wines and of each fraction was evaluated by two free radical methods, ABTS and DPPH Normal aging provides a decrease in the total antioxidant capacity of wines The antioxidant activity of ethyl acetate/acetone extracts was approximately 95% higher than that found for the hexane extracts Concerning the forced aged wines, results showed that the wine submitted to a temperature of 60 °C for 21 days had higher antioxidant activity than that submitted to a tem
TL;DR: The thick uncharged hydrophilic palisade layer and the compact hydrophobic core of Triton X100 micelles are responsible for a much higher microviscosity resulting in a decrease in k 1, as suggested by the increase in the pseudo-first-order rate constant of *Fn formation.
Abstract: In micellar solutions, one-electron reduction of •O2− radical-anions by 3-alkylpolyhydroxyflavones (FnH) with alkyl chains of n = 1, 4, 6, 10 carbons produces phenoxyl radicals (•Fn) identical to those obtained by one-electron oxidation by •Br2− radical-anions or by repair of tryptophan radicals. In cetyltrimethylammonium bromide (CTAB), F1H localizes in the Stern layer, and alkyl chains of other FnH solubilize in the hydrophobic interior, interacting with cetyl tails. This interaction produces more compact micelles with lower intramicellar fluidity, as suggested by the increase in the pseudo-first-order rate constant of •Fn formation (k1) from ∼390 s−1 for n = 1 to 610 s−1 for n = 10, leading to an intramicellar bimolecular rate constant of 1 × 105 M−1 s−1. Additionally, •F1 and •F4 decay by intermicellar bimolecular reaction (2k = 20 and 2 × 105 M−1 s−1, respectively) whereas other •Fn radicals are stable over seconds due to increased localization with regards to the Stern layer. In contrast, the thick ...
TL;DR: The GC–MS analysis of the hexane extract from bark of “cedro-do-mato” (J. brevifolia) allowed to identify three rare compounds for the first time in Juniperus genus: 6,7-dehydroferrugin-12-methyl ether, 11-hydroxy-6,7
TL;DR: In this article, the authors present a review of 13C NMR spectroscopy for the structural elucidation of natural and synthetic compounds and also used in biosynthetic studies.
Abstract: 13C NMR spectroscopy is actually one of the first tools used for the structural elucidation of natural and synthetic compounds and it is also used in biosynthetic studies. The aim of this review is...
TL;DR: In this article, the synthesis of several C60 derivatives containing a 6-(β- d -glycopyranosylamino)pyrimidin-4-one unit and a C60-uridine conjugate is described.
TL;DR: In this article, the decomposition of ethyl diazoacetate by several catalysts in the presence of meso-tetraarylporphyrin complexes with different electronic features was evaluated.
Abstract: The decomposition of ethyl diazoacetate by several catalysts in the presence of meso-tetraarylporphyrin complexes with different electronic features was evaluated. The distribution of the obtained products (chlorins, bacteriochlorins, isobacteriochlorins, and porphyrin derivatives resulting from CH insertion and Buchner ring expansion) is dependent on the catalyst and on the electronic features of the meso-aryl groups.
TL;DR: In this article, the Wittig reaction of chromone-3-carboxaldehyde with benzylic ylides and the Knoevenagel condensation with phenylacetic acids in the presence of potassium tert-butoxide under microwave irradiation were used to obtain (E)-3-styryl chromones.
Abstract: Several (E)- and (Z)-3-styrylchromones were prepared by two different methodologies, the Wittig reaction of chromone-3-carboxaldehyde with benzylic ylides and the Knoevenagel condensation of chromone-3-carboxaldehyde with phenylacetic acids in the presence of potassium tert-butoxide under microwave irradiation. The Knoevenagel reaction followed by a decarboxylation offered an efficient and diastereoselective method for preparing (E)-3-styrylchromones in a shorter reaction time. It was also demonstrated that phenylacetic acid can also be substituted with success by phenylmalonic acid. The stereochemistry of all products was assigned by NMR experiments.
TL;DR: This work demonstrates that valuable structural information about the β-nitroalkenyl substituents linked to meso-tetraarylporphyrins can be achieved using MS/MS, and can be useful for the interpretation of the mass spectra of other nitroalkanyl substituted compounds.
Abstract: β-Nitroalkenyl meso-tetraphenylporphyrins [β-TPPCHC(NO2)R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the [M + H]+ ions are formed. The fragmentation pattern of the resulting [M + H]+ ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of β-nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO2•, HNO2, 2OH•, RNO2, RCNO, RCNO2, RCH2NO2, C6H5• plus NO2• and the formation of the protonated macrocycle, [TPP + H]+ or [ZnTPP + H]+. However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl grou...
TL;DR: The 3-alkyl-3-4-5,7-tetramethoxyflavones were demethylated with boron tribromide.
Abstract: Novel 3-alkyl-3′,4′,5,7-tetrahydroxyflavones have been prepared. The synthetic strategy involves the preparation of 1-(2-hydroxy-4,6-dimethoxyphenyl)alkan-1-ones from the Friedel–Crafts acylation of phloroglucinol followed by methylation. These key compounds were submitted to the three-step Baker–Venkataraman method, giving the 3-alkyl-3′,4′,5,7-tetramethoxyflavones, which were demethylated with boron tribromide.
TL;DR: In this paper, a Diels-Alder re-action of N-substituted 4-quinolone-3-carbaldehyde with ortho- benzoquinodimethanes giving benzo(b)-1,6,6a,12a-tetrahydroacri-dones was described.
Abstract: A novel and efficient route for the synthesis of new ben- zo(b)acridones has been described. It involves the Diels-Alder re- action of N-substituted-4-quinolone-3-carbaldehyde with ortho- benzoquinodimethanes giving benzo(b)-1,6,6a,12a-tetrahydroacri- dones, which are the result of a cycloaddition reaction followed by an in situ deformylation. The oxidation of these tetrahydroacridones in dimethyl sulfoxide using a catalytic amount of iodine gives the new benzo(b)acridone derivatives. It was demonstrated that the cycloaddition reaction is only efficient if an electron-withdrawing N-protecting group is present.
TL;DR: One new prenylated xanthone 5-farnesyltoxyloxanthone B, three known xanthones alpha-mangostin, rubraxanthone and isocowanol as well as (2 E,6 E,10 E)-4beta-hydroxy-3-methyl-5beta-(3,7,11,15-tetramethylhexadeca-2,6,10-tentraenyl)-cyclo
Abstract: One new prenylated xanthone 5-farnesyltoxyloxanthone B ( 4), three known xanthones alpha-mangostin ( 1), rubraxanthone ( 2) and isocowanol ( 3) as well as (2 E,6 E,10 E)-4beta-hydroxy-3-methyl-5beta-(3,7,11,15-tetramethylhexadeca-2,6,10-tetraenyl)-cyclohex-2-en-1-one ( 5) and 3,3',4- O-trimethylellagic acid were isolated from the wood of GARCINIA MERGUENSIS Wight The cytotoxic activities of compounds 1 - 5 were evaluated against the MCF-7, MDA-MB-231, NCI-H-460 and SF-268 cell lines with rubraxanthone 2 and 5 exhibiting the highest activity at 90 and 121 microM, respectively, against MCF-7 cells