Coordinative versatility of a Schiff base containing thiophene: Synthesis, characterization and biological activity of zinc(II) and silver(I) complexes

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interaction of cationic water-soluble meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) with ionic and nonionic micelles: aggregation and binding

The equilibrium of meso-tetrakis(4-N-methylpyridiniumyl)porphyrin (TMPyP) in aqueous solution in the presence of surfactants was studied by optical spectroscopic techniques and SAXS (small angle X-ray scattering). Anionic SDS (sodium dodecyl sulfate), zwitterionic HPS (N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate) and nonionic TRITON X-100 (t-octyl-phenoxypolyethoxyethanol), surfactants were used. TMPyP is characterized by a protonation equilibrium with a pK(a) around 1.0, associated with the diacid-free base transition, and a second pK(a) around 12.0 related with the transition between the free base and the monoanion form. Three independent species were observed for TMPyP at pH 6.0 as a function of SDS concentration: free TMPyP, TMPyP-SDS aggregates and porphyrin monomer bound to micelles. For HPS and TRITON X-100, the equilibrium of TMPyP as a function of pH is quite similar to that obtained in pure aqueous solution: no aggregation was observed, suggesting that electrostatic contribution is the major factor in the interaction between TMPyP and surfactants. SAXS data analysis demonstrated a prolate ellipsoidal shape for SDS micelles; no significant changes in shape and size were observed for SDS-TMPyP co-micelles. Moreover, the ionization coefficient, alpha, decreases with the increase of the porphyrin concentration, suggesting the ""screening"" of the anionic charge of SDS by the cationic porphyrin. These results are consistent with optical absorption, fluorescence and RLS (resonance light scattering) spectroscopies data, allowing to conclude that neutral surfactants present a smaller interaction with the cationic porphyrin as compared with an ionic surfactant. Therefore, the interaction of TMPyP with the ionic and nonionic surfactants is predominantly due to the electrostatic contribution. Copyright (c) 2008 Society of Porphyrins & Phthalocyanines.

A broad study of two new promising antimycobacterial drugs: Ag(I) and Au(I) complexes with 2-(2-thienyl)benzothiazole

Synthesis, characterization, DFT simulation and biological assays of two new metal complexes of 2-(2-thienyl)benzothiazole - BTT are reported. The complexes [Ag(BTT)(2)NO3] - AgBTT2 and [Au(BTT)Cl]center dot 1/2H(2)O - AuBTT were obtained by mixing the ligand with silver (I) nitrate or gold(I) chloride in methanolic solution. Characterization of the complexes were based on elemental (C, H, N and S), thermal (TG-DTA) analysis, C-13 and H-1 NMR, FT-IR and UV-Vis spectroscopic measurements, as well as the X-ray structure determination for AgBTT2. Spectroscopic data predicted by DFT calculations were in agreement with the experimental data for both complexes. The ligand BTT was synthesized by the condensation of 2-thiophenecarboxaldehyde and 2-aminothiophenol in a microwave furnace. AgBTT2 has a monomeric structure. Both complexes show a good activity against Mycobacterium tuberculosis. Free BIT shows low antitubercular activity. (C) 2012 Elsevier Ltd. All rights reserved.

Novel sesquiterpene lactones from Eremanthus seidelii

Two novel sesquiterpene lactones were isolated from crude extract of the Eremanthus seidelii leaves. Reliable structural elucidations to these lactones were established by 1D and 2D NMR spectroscopic techniques and high-resolution electrospray mass spectrometry data. (C) 2012 Elsevier Ltd. All rights reserved.

Meroterpenes isolated from the endophytic fungus Guignardia mangiferae

Two new guignardones and one tricycloalternarene derivatives, named guignardone D, E (2-3) and tricycloalternarene F (4), and the known guignardone A (1) were isolated from Guignardia mangiferae, an endophytic fungus from the leaves of Viguiera arenaria (Asteraceae), after fermentation in Czapek medium. Structures were established on the basis of their spectroscopic data, including H-1 NMR, C-13 NMR, HMQC, HMBC and HRESI-MS. (C) 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.

Design, Synthese und biochemische/biologische Evaluierung bioisosterer Oligopyrrolcarboxamide mit aliphatisch-amidisch verknüpften DNA-Interkalatoren

Die DNA stellt aufgrund der genetischen Krankheitsursache nach wie vor ein überaus attraktives Target für das Design antitumoraktiver Zytostatika dar. Ein wesentlicher Schwerpunkt der heutigen Forschung besteht vor allem in der Entwicklung niedermolekularer, sequenzspezifischer DNA-Liganden zur gezielten Ausschaltung defekter Gene. Im Rahmen dieser Arbeit erfolgte daher in Anlehnung an die antitumoral wirksame Leitsubstanz Netropsin - ein AT-selektiver Minor Groove Binder mit Bispyrrolcarboxamid-Grundstruktur - erstmals der systematische Aufbau einer neuen Serie bioisosterer Hybridmoleküle, bestehend aus einem interkalierenden Strukturelement (Acridon, Naphthalimid, 5-Nitronaphthalimid, Anthrachinon, 11H-Pyrido[2,3-a]carbazol) und Thiophenpyrrol-, Imidazolpyrrol-, Thiazolpyrrol- bzw. Bisimidazolcarboxamid als rinnenbindende Oligoamid-Einheit (sog. Combilexine). Die chromophoren Systeme am N-Terminus wurden hierbei über aliphatische Linker variabler Kettenlänge mit der Carboxamid-Kette verknüpft. Als C-terminale Funktion kam sowohl die N,N-Dimethyl-1,3-diaminopropan- als auch die um ein C-Atom kürzere Dimethylaminoethylamin-Seitenkette zum Einsatz. Unter Verwendung modernster Reagenzien aus der Peptidkupplungschemie ist es gelungen, ein präparativ gut zugängliches, reproduzierbares Verfahren zur Synthese dieser bioisosteren Combilexine zu entwickeln. Anhand biophysikalischer/biochemischer, zellbiologischer und physikochemischer (1H-NMR-spektroskopischer und röntgenstrukturanalytischer) Methoden sowie Molecular Modelling Studien wurden erstmals bezüglich der DNA-Bindung, der Topoisomerase-Hemmung und der Antitumor-Zellzytotoxizität in einem breiten Rahmen vororientierende Struktur-Wirkungsbeziehungen an bioisosteren Liganden erstellt. Wenngleich zwischen den in vitro und in silico ermittelten Befunden keine konkreten Gesetzmäßigkeiten zu erkennen waren, so ließ die Summation der Ergebnisse dennoch darauf schließen, dass es sich bei den Naphthalimidpropion- und Acridonbuttersäure-Derivaten mit C-terminaler Propylendiamin-Funktion um die aussichtsreichsten Kandidaten in Bezug auf die DNA-Affinität bzw. Zytotoxizität handelte.

(Table 1) Concentrations of phthalates in chloroform extracts from waters of the Northwest Indian Ocean and the Red Sea

Chloroform extracts of water-soluble organic matter collected in the water column from the surface to the bottom were studied by C-13 and H-1 NMR chromatographic mass spectrometry, and phthalate concentrations were determined by capillary gas-liquid chromatography. More than 14 compounds were found including diethyl phthalate, ethyl butyl phthalate, dibutyl phthalate, and di-2-ethylhexyl phthalate, phthalates with normal C4-C12 chains, phthalates partially esterified with methanol, and others, at total concentrations up to 0.4 mg/l. Possible reasons for presence of phthalates in oceans, sometimes in high concentrations, are discussed.

Structure of Petunia hybrida Defensin 1, a Novel Plant Defensin with Five Disulfide Bonds

The structure of a novel plant defensin isolated from the flowers of Petunia hybrida has been determined by H-1 NMR spectroscopy. P. hybrida defensin 1 (PhD1) is a basic, cysteine-rich, antifungal protein of 47 residues and is the first example of a new subclass of plant defensins with five disulfide bonds whose structure has been determined. PhD1 has the fold of the cysteine-stabilized alphabeta motif, consisting of an alpha-helix and a triple-stranded antiparallel beta-sheet, except that it contains a fifth disulfide bond from the first loop to the alpha-helix. The additional disulfide bond is accommodated in PhD1 without any alteration of its tertiary structure with respect to other plant defensins. Comparison of its structure with those of classic, four-disulfide defensins has allowed us to identify a previously unrecognized hydrogen bond network that is integral to structure stabilization in the family.

Synthesis in the plakortone series: Plakortone E

A Pd(II)-mediated hydroxycyclisation-carbonylation-lactonisation sequence has operated efficiently with racemic enediol (8) to furnish (four) separable diastereomers of the bicyclic lactone system assigned to the sponge-derived, bioactive plakortone E. All four are cis ring-fused, and one is identical, on the basis of H-1 and C-13 NMR spectroscopic comparisons, with plakortone E, thus confirming its constitution and relative stereochemistry about the bicyclic lactone core. This synthetic approach, when applied to stereoisomer (13), will establish the absolute stereochemistry of plakortone E, likely to be that shown for (14).

The use of simultaneous H-1 & P-31 magic angle spinning nuclear magnetic resonance measurements to characterize energy metabolism during the conversion of muscle to meat

In order to investigate the potential of magic angle spinning nuclear magnetic resonance (MAS NMR) in the elucidation of post-mortem metabolism in muscle biopsies, simultaneous H-1 and (31)p MAS NMR measurements were made continuously on postmortem (20 min to 24 h) muscle longissimus samples from rabbits. The animals had either been or not been given adrenaline (0.5 mg kg(-1) 4 h pre-slaughter) to deplete stores of muscle glycogen. The intracellular pH was calculated from H-1 spectra, and the post-mortem rate of formation of lactate was followed and quantified. Comparison of measurements made on muscle samples from rabbits treated with adrenaline with measurements made on muscle samples from untreated' rabbits revealed significant effects of adrenaline treatment on both pH (pH24 h = 6.42 vs. pH24 It = 5.60) and formation of lactate (16 mmol g(-1) vs. 65 mmol g(-1)). The P-31 NMR spectra were used to follow the rate of degradation of ATP and phosphocreatine. The present study clearly shows that MAS NMR has potential for the study of post-mortem energy metabolism.

Isolation and characterization of novel cyclotides from Viola hederaceae - Solution structure and anti-HIV activity of vhl-1, a leaf-specific expressed cyclotide

Based on a newly established sequencing strategy featured by its efficiency, simplicity, and easy manipulation, the sequences of four novel cyclotides (macrocyclic knotted proteins) isolated from an Australian plant Viola hederaceae were determined. The three-dimensional solution structure of V. hederaceae leaf cyclotide-1 ( vhl-1), a leaf-specific expressed 31-residue cyclotide, has been determined using two-dimensional H-1 NMR spectroscopy. vhl-1 adopts a compact and well defined structure including a distorted triple-stranded β- sheet, a short 310 helical segment and several turns. It is stabilized by three disulfide bonds, which, together with backbone segments, form a cyclic cystine knot motif. The three-disulfide bonds are almost completely buried into the protein core, and the six cysteines contribute only 3.8% to the molecular surface. A pH titration experiment revealed that the folding of vhl-1 shows little pH dependence and allowed the pK(a) of 3.0 for Glu(3) and ∼ 5.0 for Glu(14) to be determined. Met(7) was found to be oxidized in the native form, consistent with the fact that its side chain protrudes into the solvent, occupying 7.5% of the molecular surface. vhl-1 shows anti-HIV activity with an EC50 value of 0.87 μ m.

Disulfide bond mutagenesis and the structure and function of the head-to-tail macrocyclic trypsin inhibitor SFTI-1

SFTI-1 is a novel 14 amino acid peptide comprised of a circular backbone constrained by three proline residues, a hydrogen-bond network, and a single disulfide bond. It is the smallest and most potent known Bowman-Birk trypsin inhibitor and the only one with a cyclic peptidic backbone. The solution structure of [ABA(3,11)]SFTI-1, a disulfide-deficient analogue of SFTI-1, has been determined by H-1 NMR spectroscopy. The lowest energy structures of native SFTI-1 and [ABA(3,11)]SFTI-1 are similar and superimpose with a root-mean-square deviation over the backbone and heavy atoms of 0.26 +/- 0.09 and 1.10 +/- 0.22 Angstrom, respectively. The disulfide bridge in SFTI-1 was found to be a minor determinant for the overall structure, but its removal resulted in a slightly weakened hydrogen-bonding network. To further investigate the role of the disulfide bridge, NMR chemical shifts for the backbone H-alpha protons of two disulfide-deficient linear analogues of SFTI-1, [ABA(3,11)]SFTI-1[6,5] and [ABA(3,11)]SFTI-1[1,14] were measured. These correspond to analogues of the cleavage product of SFTI-1 and a putative biosynthetic precursor, respectively. In contrast with the cyclic peptide, it was found that the disulfide bridge is essential for maintaining the structure of these open-chain analogues. Overall, the hydrogen-bond network appears to be a crucial determinant of the structure of SFTI-1 analogues.

Analysis of lipoproteins using 2D diffusion-edited NMR spectroscopy and multi-way chemometrics

This study represents the first application of multi-way calibration by N-PLS and multi-way curve resolution by PARAFAC to 2D diffusion-edited H-1 NMR spectra. The aim of the analysis was to evaluate the potential for quantification of lipoprotein main- and subtractions in human plasma samples. Multi-way N-PLS calibrations relating the methyl and methylene peaks of lipoprotein lipids to concentrations of the four main lipoprotein fractions as well as 11 subfractions were developed with high correlations (R = 0.75-0.98). Furthermore, a PARAFAC model with four chemically meaningful components was calculated from the 2D diffusion-edited spectra of the methylene peak of lipids. Although the four extracted PARAFAC components represent molecules of sizes that correspond to the four main fractions of lipoproteins, the corresponding concentrations of the four PARAFAC components proved not to be correlated to the reference concentrations of these four fractions in the plasma samples as determined by ultracentrifugation. These results indicate that NMR provides complementary information on the classification of lipoprotein fractions compared to ultracentrifugation. (C) 2004 Elsevier B.V. All rights reserved.

NMR studies of exchange between intra- and extracellular glutathione in human erythrocytes

Glutathione is the main source of intracellular antioxidant protection in the human erythrocyte and its redox status has frequently been used as a measure of oxidative stress. Extracellular glutathione has been shown to enhance intracellular reduced glutathione levels in some cell types. However, there are conflicting reports in the literature and it remains unclear as to whether erythrocytes can utilise extracellular glutathione to enhance the intracellular free glutathione pool. We have resolved this issue using a C-13-NMR approach. The novel use of L-gamma-glutamyl-L-cysteinyl-[2-C-13] glycine allowed the intra- and extracellular glutathione pools to be distinguished unequivocally, enabling the direct and non-invasive observation over time of the glutathione redox status in both compartments. The intracellular glutathione redox status was measured using H-1 spin-echo NMR, while C-13[H-1-decoupled] NMR experiments were used to measure the extracellular status. Extracellular glutathione was not oxidised in the incubations, and did not affect the intracellular glutathione redox status. Extracellular glutathione also did not affect erythrocyte glucose metabolism, as measured from the lactate-to-pyruvate ratio. The results reported here refute the previously attractive hypothesis that, in glucose-starved erythrocytes, extracellular GSH can increase intracellular GSH concentrations by releasing bound glutathione from mixed disulfides with membrane proteins.

Synthesis of polymers and copolymers of lactide through titanium initators

The research described in this thesis explored the synthesis tlnd characteristltion of biocompatible and biodegradable polymers of lactide through non-toxic titanium alkoxide nitiators. The research objectives focused on the preparation of polylactides in both solvent and solventless media, to produce materials with a wide range of molecular weights. The polylactides were fully characterised using gel permeation chromatography and 1H and 13C NMR spectroscopy. NMR spectroscopy was carried out in the study the reaction mechanisms. Kinetic studies of the ring opening polymerisation of lactide with titanium alkoxide initiators were also conducted using NMR spectroscopy. The objectives of this research were also focused on the enhancement of the flexibility of the polymer chains by synthesising random and block copolymers of lactide and ε-caprolactone using Ti(0-i-Pr)4 as an initiator, This work involved extensive characterisalion of the synthesised copolymers using gel permeation chromatography and 1H and 13C NMR spectroscopic analysis. Kinetic studies of the ring opening polymerisation of ε-caplrolactone and of the copolymerisation of lactide and ε-caprolactone with Ti(O-i-Pr)4 as an initiator were also carried out. The last section of this work involved the synthesis of block and star-shaped copolymers of lactide and poly(ethylene glycol) [PEG]. The preparation of lactide/PEG block copolymers was carried out by ring opening polymerisation of L-Iactide using Ti(O-i-Pr)4 as an initiator and hydroxyl-terminated PEG's with different numbers of hydroxyl groups as co-initiators both in solution and solventless media. These all-in-one polymersations yielded the synthesis of both lactide homopolymer and lactide/PEG block copolymer. In order to selectively synthesise copolymers of lactide and PEG, the experiment was carried out in two steps. The first step consisted of the synthesis of a titanium macro-initiator by exchanging the iso-propoxide ligands by PEG with different numbers of hydroxyl groups. The second step involved the ring opening polymerisation of lactide using the titanium macrocatalyst that was prepared as an initiator. The polymerisations were carried out in a solventless media. The synthesis of lactide/PEG copolymers using polyethylene glycol with amino terminal groups was also discussed. Extensive characterisation of the lactide block copolymers and macroinitiators was carried out using techniques such as, gel permeation chromatography (GPC), NMR spectroscopy and differential scanning calorimeter (DeS).