EVALUATION OF THE ANTIOXIDANT ACTIVITY OF THE FLAVONOIDS ISOLATED FROM HELIOTROPIUM SINUATUM RESIN USING ORACFL, DPPH AND ESR METHODOLOGIES

Indexación: Web of Science; Scielo.The antioxidant capacity has been determined for a number of flavonoid compounds from Heliotropium sinuatum, a plant that grows in arid areas in the north of Chile. The methodologies used were: ORAC(FL) (oxygen radical absorbance capacity - fluorescein), DPPH (2,2-diphenyl-2-picrylhydrazyl) bleaching and electron spin resonance (ESR). These compounds were studied in homogeneous and heterogeneous media. The results showed that the 7-o-methyleriodictiol and 3-o-methylisorhamnetin are those with the highest antioxidant capacity.http://ref.scielo.org/m82cz

Thermodynamic and geometric study of diasteroisomeric complexes formed by racemic flavanones and three cyclodextrins through NMR

Artículo de publicación ISIThe main purpose of this work was to study the chiral recognition thermodynamics of inclusion complexes formed by flavanones and b-cyclodextrins, and its relation with the inclusion geometries, through NMR experiments. By using the racemic mixtures of (±)-flavanone (FL) and (±)-20-hydroxyflavanone (20OHFL), diasteroisomeric complexes were formed employing b-cyclodextrin (bCD), (2- hydroxypropil)-b-cyclodextrin (HPbCD) and heptakis-(2, 6-O-dimethyl)-b-cyclodextrin (DMbCD). 1H NMR experiments of the complexes showed enantiodifferentiation for FL/bCD, FL/HPbCD, FL/DMbCD, 20OHFL/HPbCD and 20OHFL/DMbCDcomplexes, so they were able to be studied by obtaining the stoichiometry (1:1 for each complex), association constants (Ka), Ka ratios, and thermodynamics (DH, DS and DG). The results show that Ka values decrease with increasing temperature and that Ka ratio values removed from 1 not always reflect better enantiodiscrimination by NMR. Thermodynamics (DH and DG) show an exothermic and spontaneous formation of the complexes. Since the results were established for each couple of diasteroisomeric complexes separately, comparison of thermodynamics between them was possible, concluding that one half of the couples of diasteroisomeric complexes present chiral recognition due to enthalpic phenomena and the other half due to entropic phenomena. Additionally, ROESY experiments were performed to estimate the inclusion geometry of the complexes, which are in good agreement with the thermodynamic and Ka results

Cyrhetrenylaniline and new organometallic phenylimines derived from 4- and 5-nitrothiophene: Synthesis, characterization, X-Ray structures, electrochemistry and in vitro anti-T. brucei activity

A novel series of cyrhetrenyl (3a-4a) and ferrocenyl (3b-4b) Schiff bases were synthesized through a condensation reaction, between the known 4-ferrocenylaniline (2b) or the unreported 4-cyhretrenylaniline (2a) with 4- or 5-nitrothiophenecarboxaldehyde. The structure of 2a and the new Schiff bases have been elucidated using conventional spectroscopic techniques (FT-IR, 1H and 13C NMR), mass spectrometry, and single-crystal X-ray diffraction analysis of compounds 2a, 4a and 3b. Cyclic voltammetry of organometallic phenylimines derived from 5-nitrothiophene showed NO2 group reduction potentials (E1/2z 0.575 V) that were more anodic than those registered for their 4-nitro analogues (E1/2z 0.981 V). All organometallic imines were tested against the bloodstream form of Trypanosoma brucei. Evaluation indicated that the most active complexes are the 5-nitrothiophene derivatives, 4a, which were remarkably more active than nifurtimox. In addition, complex 4b resulted in less toxicity to host L6 cells than nifurtimox. The results revealed that the electronic effects of cyrhetrene and ferrocene are not an influential factor in E1/2 and anti-Trypanosoma brucei activity for these new imines, which is probably due to the non-coplanarity of the [(h5-C5H4)-C6H4-N=CH-(C4H2S)] system

Insight into the Bioreductive Mode of Action of Antitrypanosomal 5-Nitrofuryl Containing Thiosemicarbazones

In order to get insight into the trypanocidal mechanism of action of a series of 5-nitrofuryl containing thiosemicarbazones some studies related to their bioreduction were performed. Electron spin resonance spectra of radicals generated in T. cruzi by compounds´ bioreduction were analyzed. Three different patterns of ESR signals were observed for the different assayed compounds. These results were in agreement with the changes in the T. cruzi-oxygen uptake promoted by these compounds. On the other hand, free-radical scavenger properties, measured as oxygen radical absorbance capacity (ORAC), did not seem to correlate with the trypanocidal activity.This research was partially supported by TWAS (research grant RG/CHE/LA 04-205), FONDECYT 1030949 and 1061072 grants, CONICYT AT-4040020 grant, PBCT/ CONICYT Anillo ACT 29, U. de Chile DID graduate grant PG-65. L.O. thanks RTPD and CSIC (Uruguay) for a scholarship

NMR as a tool for simultaneous study of diasteroisomeric inclusion complexes, part 2: Complexes formed by racemic mixture of 4′- hydroxyflavanone and two cyclodextrins

Complexes formed by (±)-4′-hydroxyflavanone (OHFL) and the cyclodextrins β-cyclodextrin and (2-hydroxypropyl)-β-CD were obtained using the racemic mixture of the OHFL. These complexes were able to be studied due to their enantiodifferentiation by 1H-NMR spectroscopy. Stoichiometry, association constants and thermodynamic parameters were obtained from these NMR data, and inclusion geometries were proposed from ROESY spectra. The results show a 1:1 stoichiometry, K a values decrease with increasing temperature, a spontaneous and exothermic complexes formation, and that ROESY spectra cannot differentiate between enantiomers, and therefore the estimated inclusion geometries were proposed for the mixture of diasteroisomeric complexes. © 2011 Springer Science+Business Media B.V

NMR as a tool for simultaneous study of diastereoisomeric inclusion complexes formed by racemic mixture of 4′-hydroxyflavanone and heptakis-(2,6-O-dimethyl)-β-cyclodextrin

The complexes formed by (±)-4′-hydroxyflavanone (OHFL) and heptakis-(2,6-O-dimethyl)-β-cyclodextrin (DM-β-CD) were obtained using the racemic mixture of OHFL. These complexes were able to be studied due to their enantiodifferentiation by 1H-NMR spectroscopy. Stoichiometry, association constants and thermodynamic parameters were obtained from these NMR data, and inclusion geometries were proposed from ROESY and docking experiments. The results show that diastereoisomeric complexes can be studied even when they are formed by enantiomeric mixtures. © 2010 Springer Science+Business Media B.V