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PubMedDate not supplied

The choice of medium suitable for the reaction of thiol groups with halogen derivatives in the synthesis of some purine and pyrimidine compounds. I. Synthesis of azathioprine.

Investigations were carried out using 6-mercaptopurine and 1-methyl-4-nitro-5-chloroimidazole as model compounds. The reaction kinetics were investigated by the UV spectroscopy at various time intervals. The investigations resulted in elaboration of an efficient synthesis of azathioprine which can be applied on an industrial scale in a yield of 80%.

Azathioprine↗
PubMed1994

Chemical reagents as potential impurities of pharmaceutical products: investigations on their genotoxic activity.

The genotoxic activity of chemical reagents and intermediates as potential impurities of final pharmaceutical products have been investigated by the AFI Mutagenesis Study Group. A number of compounds employed in the synthesis of beta-lactam (12), quinolone (6), antiviral (3), and other drugs (11) were analyzed. The information reported in this article was mainly obtained experimentally in our laboratories. In addition, attempts were made to obtain reference data; however, these were available for only a few compounds. The genetic end-point taken into account was principally gene mutation in bacteria. All chemical reagents used in the synthesis of quinolones and antivirals were negative in the Ames test. As far as reagents employed in beta-lactam synthesis were concerned, genotoxic activity was shown by the alkylating agents bromomethanol acetate and chloromethanol acetate, by carbon disulfide, and by the different dimethylanilines. The other chemicals generically considered as involved in "other syntheses" did not induce gene mutation, except for 2,5-dibromopentyl acetate, which was positive in the Ames test. For this compound, as for the halogenated methanol acetates, genotoxic activity was expected in view of its alerting chemical structure.

Animals↗
PubMed1997

The potential effects of new synthetic drugs against Leishmania amazonensis and Trypanosoma cruzi.

Amidine derivatives, never used before on trypanosomatids, were tested against Leishmania amazonensis and Trypanosoma cruzi. These drugs in doses up to 500 mg/kg inoculated into Swiss mice did not show any toxic effect (Santos, 1993). The in vitro effect of N,N'-diphenyl-4-R- benzamidine was evaluated. L. amazonensis promastigotes, epimastigotes and blood forms of T. cruzi, were assayed with/without the drugs in axenic media, using pentamidine isethionate and benznidazole, as reference drugs. The results were very promising for L. amazonensis, showing that the most active compounds were the metoxy and Br-derivatives, with LD50 of 20 microM and 22 microM, respectively. In general the amidines showed lower activity against T. cruzi than L. amazonensis. The most active compounds against blood trypomastigotes were the same metoxy and Br-derivatives, but in much higher concentrations, e.g. as LD50 of 59 nM and 251 nM, respectively. All amidines had a very low activity against epimastigotes, and the only active compounds were the halogen-derivatives with LD50 = 424 nM for the Br-derivative and LD50 of 474 nM for the C1-derivative.

Animals↗
PubMed2000

Carbon-based quantitation of pyrethrins by supercritical-fluid chromatography.

All six insecticide active ingredients in pyrethrum extract were quantified by supercritical fluid chromatography and carbon calibration. Allethrin is a suitable reference compound for carbon calibration and pyrethrins calibrations. Carbon quantification in SFC is also applied to pyrethroids (phenothrin, permethrin, cypermethrin, fenvalerate and deltamethrin) and alkanes. Halogen substitution on pyrethroids requires halogens on the reference calibration compound. The method was applied to commercial extracts.

Alkanes↗
PubMed2006

Competitive ArC-H and ArC-X (X = Cl, Br) activation in halobenzenes at cationic titanium centers.

The titanium methyl cation [Cp*((tBu3P=N)TiCH3]+ [B(C6F5)4]- reacts rapidly with H2 to give the analogous cationic hydride [Cp*((tBu3P=N)TiH(THF)n]+ [B(C6F5)4]- (n = 0, 1), which can be trapped and isolated as its THF adduct 1 x THF (n = 1). When generated in the presence of chloro or bromobenzene, 1 undergoes C-X activation or ortho-C-H activation, depending on the amount of dihydrogen present in the reaction medium. At approximately 4 atm of H2, C-X activation is preferred, giving the halocations [Cp*((tBu3P= N)TiX]+ [B(C6F5)4]- (2X) and C6H6/biphenyl mixtures. At lower pressures of H2 (>1 atm), the beta-halophenyl cations [Cp*((tBu3P=N)Ti(2-X-C6H4)]+ [B(C6F5)4]- (3X) are the products isolated. In the absence of H2, these compounds are quite thermally stable, but undergo beta-halogen elimination upon moderate heating, to give 2X (approximately 20%) and compounds 4X which are the result of reaction between 2X and benzyne via addition of the benzyne C-C triple bond across the Ti-N bond of the phosphinimide ligand. Thus, three separate bond activation processes are operative in this system: direct C-X activation, ortho-C-H activation, and indirect C-X activation via beta-halogen elimination. Mechanistic studies on all three processes have been done and support a radical pathway for direct C-X cleavage, sigma-bond metathesis of the ortho-C-H bond of eta(1)-coordinated C6H5X, and beta-halogen elimination from base-free compound 3X.

Journal Article↗
PubMed2006

Ultrasonic spectroscopy of pure cyclic compounds.

Ultrasonic studies of the group of halogens of benzene and particularly dependence of acoustic parameters on the structure of organic liquids, demonstrate some interesting regularities in the group of these compounds in gas and liquid states. In this paper results for five cyclic liquids: bromo-, chloro-, fluoro- and jodobenzene are discussed and compared to benzene. Vibrational relaxation was observed in all the compounds. The studies reported here as well as other experimental for great number of compounds support the conclusion that almost all vibrational relaxation processes in liquids can be described using a single relaxation time. It also seems that all vibrational degrees of freedom of the molecule take part in this vibrational process. It seems that differences in transition probabilities between molecules studied could be caused by additional attraction between of molecules having a significant dipole moments.

Journal Article↗
PubMed2006

Iron-mediated reduction rates and pathways of halogenated methanes with nanoscale Pd/Fe: analysis of linear free energy relationship.

The influence of halogen substitution in chlorinated methanes and brominated methanes on their abiotic reductive dehalogenation with nanoscale Pd/Fe bimetallic particles was investigated in this study. The 0.2% and 1.0% Pd/Fe particles, with particle sizes of less than 100nm, were synthesized in the laboratory. Reduction of the halogenated methanes with the Pd/Fe particles followed pseudo-first-order kinetics. The Pd/Fe bimetallic particles demonstrated at least an order of magnitude higher in reactivity compared to the unpalladized Fe particles of similar particle size. Comparing the 0.2% Pd/Fe and the 1.0% Pd/Fe particles, the latter exhibited higher reduction rates of various halogenated methanes. On the other hand, the reduction rates of chlorinated methanes were consistently lower than those of their brominated counterparts. The compounds with higher number of halogen substitutions were more readily reduced than the lightly halogenated ones. Coupled hydrogenolysis-elimination processes were the important mechanism for complete dehalogenation of the chlorinated and brominated methanes. From the kinetic examination of their transformation rates and mechanistic insight into the associated pathways, an attempt to analyze linear free energy relationship between the observed kinetics and the associated thermodynamic constants was performed. The observed reaction rate constants were analyzed for their correlations with one-electron potential (E(1)), two-electron potential (E(2)), bond dissociation energy (BDE) and the lowest unoccupied molecular orbital (LUMO) energy (E(LUMO)). LUMO energy appeared to be the best descriptor for the kinetic prediction, while E(1) and E(2) might be more suitable for mechanistic analysis.

Environmental Pollutants↗
PubMed2003

New beta-adrenergic agonists used illicitly as growth promoters in animal breeding: chemical and pharmacodynamic studies.

Clenbuterol and beta-adrenergic receptor agonist drugs are illegally used as growth promoters in animal production. Pharmacologically active residues in edible tissues led to intoxication outbreaks in several countries. Pressure of official controls pulsed synthesis of new compounds to escape analytical procedures. We report two new compounds named 'A' and 'G4', found in feeding stuffs. Chemical structure was studied through nuclear magnetic resonance-imaging and infrared spectroscopy, and beta(1)- and beta(2)-adrenergic activity was evaluated on isolated guinea-pig atrium and trachea in comparison with clenbuterol. Both compounds share with clenbuterol an halogenated aromatic ring with a primary amino group. Main modifications consisted of substitution of secondary amino group with an alkyl chain in compound A and substitution of the ter-butyl group with a benzene ring in compound G4. In guinea-pig trachea these compounds showed myorelaxant potency lower than clenbuterol (EC(50) was 43.8 nM for clenbuterol, 11700 nM for compound A, 2140 nM for G4). On the contrary, in the guinea-pig atrium (heart-beat rate stimulant effect) the compounds were more potent than clenbuterol (EC(50) was 15.2 nM for clenbuterol, 3.4 nM for compound A, 2.8 nM for G4). These pharmacodynamic properties, and stronger lipophilic properties shown by the two compounds may result in increased cardiovascular risk for consumers of illicitly treated animals.

Adrenergic beta-Agonists↗
PubMed2005

Rejection of trace organic compounds by high-pressure membranes.

High-pressure membranes, encompassing reverse osmosis (RO), nanofiltration (NF), and low-pressure RO, may provide an effective treatment barrier for trace organic compounds including disinfection by-products (DBPs), pesticides, solvents, endocrine disrupting compounds (EDCs) and pharmaceutically active compounds (PhACs). The objective is to develop a mechanistic understanding of the rejection of trace organic compounds by high-pressure membranes, based on an integrated framework of compound properties, membrane properties, and operational conditions. Eight trace organic compounds, four DBPs and four chlorinated (halogenated) solvents, are being emphasized during an initial study, based on considerations of compound properties, occurrence, and health effects (regulations). Four polyamide FilmTec membranes; three reverse osmosis/RO (BW-400, LE-440, XLE-440) and one nanofiltration/NF (NF-90); are being characterized according to pure water permeability (PWP), molecular weight cutoff (MWCO), hydrophobicity (contact angle), and surface charge (zeta potential). It is noteworthy that rejections of compounds of intermediate hydrophobicity by the candidate membranes were observed to be less than salt rejections reported for these membranes, suggesting that transport of these solutes through these membranes is facilitated by solute-membrane interactions. We are continuing with diffusion cell measurements to describe solute-membrane interactions by estimation of diffusion coefficients through membranes pores, either hindered or facilitated.

Diffusion↗
PubMed2001

Global biomonitoring of perfluorinated organics.

The environmental distribution of fluorinated organic compounds (FOCs) has been less well described than the other halogenated hydrocarbons such as chlorinated and brominated compounds. This is despite the fact that FOCs have been used in a wide variety of products and applications for more than 50 years. FOCs are resistant to hydrolysis, photolysis, microbial degradation, or metabolism by vertebrates due to the high energy of carbon-fluorine bond. In particular, perfluorinated (fully fluorinated) compounds (PFCs) have the potential to persist in the environment. But, until recently, the extent and magnitude of environmental distribution of PFCs was unknown. Recent development of an analytical technique for PFCs using high performance liquid chromatography-negative ion electrospray tandem mass spectrometry (HPLC-ESMSMS) permitted the survey of PFCs in livers and blood plasma of wildlife on a global scale.

Animals↗
PubMed2006

Natural and man-made organobromine compounds in marine biota from Central Norway.

Brominated organic pollutants were found in selected samples of mollusk tissue, fish liver, as well as in the eggs and livers of shag from three sites in Central Norway. More than 80 organobromines were identified owing to the defined isotope ratio acquired by GC/ECNI-MS. However, only a few peaks could be assigned to anthropogenic brominated flame retardants (polybrominated diphenyl ethers). Most of the organobromine compounds detected were unknown or halogenated natural products. The known halogenated natural products MHC-1 and TBA were abundant in all samples and usually between equally abundant, and up to 50 fold more concentrated than the major polybrominated diphenyl ether congener BDE 47. The halogenated natural products BC-2 (2-MeO-BDE 68) and BC-3 (6'-MeO-BDE 47), were on level with BDE 100 which was the second most abundant BDE congener in many samples. The previously identified natural polybrominated hexahydroxanthene derivatives (PBHDs) were detected for the first time in bird eggs. Being major contaminants in bird eggs, PBHDs were only present at low levels in bird liver from nestlings originating from the same clutch. Such differences were detected for several other major contaminants. One unknown tetrabromo compound particularly abundant in mussels from Munkholmen was studied by GC/MS and the molecular ion was detected at m/z 446. The abundance of the most important unknown compounds did not correlate with BDEs and they most likely represent halogenated natural products. This study supports that halogenated natural products have to be treated as serious contaminants of marine coastal waters. Our data suggest that their abundance is highest in habitats along the shoreline. Thorough examination of these compounds in environmental samples is an important task.

Animals↗