Determination of artemisinin and artemisinic acid by capillary and packed supercritical fluid chromatography

Artemisinin (an antimalarial compound) and its bioprecursor artemisinic acid, present in the plant Atemisia annua L., were analyzed by supercritical fluid chromatography (SFS) using capillary and packed columns, coupled respectively with a flame ionization detector (FID) and an evaporative light scattering detector (ELSD). Both methods were optimized and validated with columns of different polarity in order to separate artemisinin and artemisinic acid. Analytical results were comparable, but the paced SFC-ELSD method was faster. Indeed, artemisinin and artemisinic acid were separated with an aminopropyl silica column in less than 8 minutes instead of about 25 minutes by capillary SFS. Contrary to conventional gas and liquid chromatography coupled to an UV-visible detector, SFS methods determined both compounds directly, without degradation and/or derivatization in the concentration range expected in the plant material. Results obtained on plant extracts by capillary SFS-FID and packed SFS-ELSD were confirmed by GC-MS.     

One-electron oxidation of the guanine moiety of 2'-deoxyguanosine: influence of 8-oxo-7,8-dihydro-2'-deoxyguanosine

The influence of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) on riboflavin and UVA-mediated one-electron oxidation of an aqueous aerated solution of 2'-deoxyguanosine (dGuo) has been studied. Using labeled experiments, we have demonstrated that, despite not being able to detect significant amounts of 8-oxodGuo upon one-electron oxidation of dGuo, 8-oxodGuo is indeed produced but is further rapidly degraded to oxidized nucleosides. Evidence is provided showing that an efficient electron transfer reaction from 8-oxodGuo to the guanine radical cation or rather its deprotonated form occurs, giving rise to the specific decomposition of 8-oxodGuo together with the restitution of dGuo. It could be concluded that 8-oxodGuo efficiently protects dGuo from decomposition by the one-electron oxidation reaction.     

INTERACTIONS AND PHOTOREACTIVITY OF 8-ALKOXYPSORALENS WITH THYMINE. A MODEL APPROACH

Abstract— To investigate the interactions and the photoreactions in solution between thymine and psoralen, model compounds have been synthesized in which a thymine molecule is linked to a psoralen ring by a polymethylene bridge. Two series of compounds have been studied and compared as models for the two major drugs 5-MOP and 8-MOP. We report here the results obtained in the 8-alkoxypso-ralen series. In water, intramolecular ring-ring stacking interactions were evidenced using UV and ¹H NMR spectroscopies. In organic solvents such as ethanol, these interactions disappear completely. The photoreactivity of the models was examined in relation to their ground state interaction properties. in water and in ethanol. Slow photolysis of the pyrone ring of psoralen occurs whatever the length of the linking chain (3 to 12 methylenes). No intramolecular thymine-psoralen photoaddition nor psoralen photodimerization were observed. These results are discussed with regards to the behavior of the 5-alkoxy models which lead selectively to the 3,4 psoralen-thymine photoadduct.     

α-Diimines as nitrogen ligands for ruthenium-catalyzed allylation reactions and related (pentamethylcyclopentadienyl) ruthenium complexes

The new Cp*Ru(II) (Cp*: pentamethylcyclopentadienyl) complexes Cp*(dab-R)RuCl, [Cp*(dab-R)(MeCN)Ru][PF₆] (dab-R: RNCH-CHNR; R: iso-propyl, mesityl), and [Cp*(cod)(MeCN)Ru][PF₆], are synthesized in high yields by reacting the corresponding α-diimine or 1,5-cyclooctadiene with [Cp*RuCl]₄ and [Cp*(MeCN)₃Ru][PF₆], respectively. The α-diimine ligands are strongly bonded to the ruthenium centre as shown by the subsequent formation of the alkynyl derivatives Cp*(dab-R)RuCCR′ (R′ = tert-butyl or phenyl) and of the cationic derivatives [Cp*(dab-R)(L)Ru][PF₆] (L = CO, PMe₃). The neutral and cationic α-diimine or 1,5-cyclooctadiene ruthenium complexes are compared as catalyst precursors for the ruthenium-catalyzed allylation of diethyl-sodiomalonate and diethylamine with cinnamyl acetate or ethyl cinnamyl carbonate.     

THE THYMIDINE-PSORALEN PHOTOADDITION. A MODEL APPROACH

Abstract— In order to investigate the photoreactions between the thymidine and the psoralen chromophores and to devise a synthetic route to prepare thymidine-5-methoxypsoralen adducts, we have prepared and studied a compound in which thymidine is linked to a 5-methoxypsoralen derivative by a diester chain. Irradiation at 365 nm carried out at usual concentrations (10–³ M ) leads exclusively to one diastereoisomer of an intramolecular 3,4 cis-anti [2+2] adduct. No photodimerization is observed in these conditions. These results are compared to those obtained for models studied previously in which the thymine and the psoralen rings are linked by polymethylenic chains of varying length.     

Analysis of selected withanolides in plant extract by capillary electrochromatography and microemulsion electrokinetic chromatography

Microemulsion electrokinetic chromatography (MEEKC) coupled with a diode-array detector was developed for the simultaneous analysis of natural steroidal compounds, withanolides including withaferin A, withacnistin and iochromolide. Optimal resolution was obtained with a microemulsion consisting of 70 mM octane, 800 mM 1-butanol, 100 mM sodium dodecyl sulfate (SDS), and 10 mM phosphate-borate buffer (pH 7) using a fused-silica capillary at 25 kV and 40 degrees C. Since this technique is not compatible with mass spectrometry detection, a capillary electrochromatographic method was developed to separate the investigated withanolides. The effects of mobile phase composition and pH were systematically investigated. Complete separation was obtained with a capillary electrochromatography (CEC) Hypersil C18 bonded silica column (packed length, 25 cmx100 microm ID and 375 microm OD), packed with 3 microm particles. The mobile phase consisted of formic acid-ammonia, pH 8 / acetonitrile (40/60 v/v); the voltage was set at 25 kV and the temperature at 20 degrees C. Under these conditions, resolution of these closely related compounds, including the critical pair withacnistin and iochromolide, was achieved in less than 5 min. The separations by MEEKC and CEC were compared with that obtained by reversed-phase liquid chromatography and showed similar retention order, indicating the analogy of the retention mechanism of these techniques. To further improve specificity and sensitivity, the developed CEC method was interfaced with electrospray ionization mass spectrometry using a Teflon connection between the CEC column and a void fused-silica capillary. Finally, the described methods were applied to the qualitative analysis of withanolides in Iochroma gesnerioides plant extract.     

Photophysical properties of ruthenium(II) polyazaaromatic compounds: a theoretical insight

Quantum-chemical methods are applied to study the nature of the excited states relevant in the photophysical processes (absorption and emission) of a series of polyazaaromatic-ligand-based ruthenium(II) complexes. The electronic and optical properties of the free polyazaaromatic ligands and their corresponding ruthenium(II) complexes are determined on the basis of correlated Hartree-Fock semiempirical approaches. While the emission of complexes containing small-size ligands, such as 1,10-phenanthroline or 2,2'-bipyridine, arises from a manifold of metal-to-ligand charge-transfer triplet states ((3)MLCTs), an additional ligand-centered triplet state ((3)L) is identified in the triplet manifold of complexes containing a pi-extended ligand such as dipyrido[3,2-a:2',3'-c]phenazine, tetrapyrido[3,2-a:2',3'-c:3',2'-h:2',3'-j]phenazine, and 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene. Recent experimental data are interpreted in light of these theoretical results; namely, the origin for the abnormal solvent- and temperature-dependent emission measured in pi-extended Ru complexes is revisited.     

Use of the Gaussian Distribution Function as a Tool to Estimate Continuous Heterogeneity in Adsorbing Systems

In environmental engineering, adsorption and desorption are phenomena commonly referred to as responsible for pollution dispersion, retention, or retardation in soils, aquifers, and hydrologic systems. They are also used to remove organic pollutants from water or odorous compounds in gas deodorization. Most often, the characterization of the aqueous adsorption systems that are of engineering interest involves a narrow adsorbate concentration range and low values of the adsorbate concentration. The practice is to use the Freundlich equation that best fits most data and is considered sufficient to design adsorption contactors. However, no physical or chemical meaning can be associated with the values taken by the parameters. The present paper gives a new way of analyzing adsorption data, using an extension of the Freundlich equation and the Gaussian distribution function that makes it possible to associate parameter values of this extension with the adsorbate–adsorbent normal interaction energy, its heterogeneity, and to some extent the adsorbate–adsorbate lateral interaction energy.     

Tandem cheletropic additions of sulfur dioxide to [2.2.2]hericene. The ‘barrelene effect’

At 20°, [2.2.2]hericene ( = 2,3,5,6,7,8-hexamethylidenebicyclo[2.2.2]octane; 1 ) adds 2 equiv. of SO₂ to give successively mono-sulfolene 13 and the bis-sulfolene 14 (for thermodynamic and kinetic data, see Tables 1 and 2). Under forcing conditions (high concentration, long reaction time), no trace of tris-sulfolene 15 could be detected. The inertia of bis-sulfolene 14 is attributed to the ‘barrelene effect’ which destabilizes the tris-sulfolene 15 .     

Riboflavin and UV-Light Based Pathogen Reduction: Extent and Consequence of DNA Damage at the Molecular Level

We are developing a technology based on the combined application of riboflavin (RB) and light for inactivating pathogens in blood products while retaining the biological functions of the treated cells and proteins. Virus and bacteria reduction measured by tissue culture infectivity or colony formation with UV light alone and in combination with RB yield equivalent results. The effects of RB as a sensitizing agent on DNA in white cells, bacteria and viruses in combination with UV light exposure have been evaluated. UV-mediated DNA degradation in Jurkat T cells and leukocytes in plasma as measured by the FlowTACS assay was significantly increased in the presence of RB. Agarose gel electrophoretic analysis of DNA in Escherichia coli and leukocytes in plasma demonstrated enhanced DNA degradation in the presence of RB. UV light in combination with RB prevented the reactivation of lambda phage compared with samples irradiated in the absence of RB. UV-mediated oxidative damage in calf thymus DNA was also enhanced in the presence of RB. These observations clearly demonstrate that the presence of RB and UV light selectively enhances damage to the guanine bases in DNA. These data also suggest that the type and extent of damage to DNA for virus in the presence of RB and light make it less likely to be repaired by normal repair pathways available in host cells.