Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: CAS:25150-61-2 (pyrrolidine)
 5,499 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A series of 16 tricyclic thrombin inhibitors was prepared by using the 1,3-dipolar cycloaddition of azomethine ylides derived from 3- or 4-hydroxyproline and 4-bromobenzaldehyde, with N-(4-fluorobenzyl)maleimide as the key step. The terminal pyrrolidine ring of the inhibitors was systematically substituted to explore the potential bioisosteric behavior of C-F, C-OH, and C-OMe residues pointing into the environment of the catalytic center of a serine protease. X-ray crystal structure analyses revealed a distinct puckering preference of this ring. Substitution by F, HO, and MeO has a strong effect on the basicity of the adjacent pyrrolidine nitrogen center which originates from two sigma-inductive pathways between this center and the electronegative O and F atoms. gem-Difluorination decreases the pKa value of this tertiary amine center to <2, making the conjugated ammonium ion a moderately strong acid. Unexpectedly, F substitution next to the nitrogen center reduced the lipophilicity of the ligands, as revealed by measurements of the logarithmic partition coefficient log D. The biological assays showed that all compounds are thrombin inhibitors with activities between Ki=0.08 and 2.17 microM. Bioisosteric behavior of F, HO, and MeO substituents was observed. Their electronegative F and O atoms undergo energetically similar polar interactions with positively polarized centers, such as the N atom of His 57 which is hydrogen bonded to the catalytic Ser 195. However, for energetically similar polar interactions of C-F, C-OH, and C-OMe to occur, sufficient space is necessary for the accommodation of the Me group of the C-OMe residue, and a H-bond acceptor must be present to prevent unfavorable desolvation of the C-OH residue.
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PMID:A fluorine scan at the catalytic center of thrombin: C--F, C--OH, and C--OMe bioisosterism and fluorine effects on pKa and log D values. 1689 1

A new method based on cloud point extraction (CPE) separation and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICPMS) detection has been proposed for the speciation of inorganic selenium in environmental waters. When the temperature of the system is higher than the cloud point temperature (CPT) of the selected surfactant Triton X-114, the complex of Se(IV) with ammonium pyrrolidine dithiocarbamate (APDC) seems to be extracted into the surfactant-rich phase, whereas the Se(VI) remains in aqueous solutions. Thus, an in situ separation of Se(IV) and Se(VI) could be realized. The concentrated analyte was introduced into the ETV-ICP mass spectrometer for determination of Se((IV) after dilution with 200 microL methanol. Se(VI) was reduced to Se(IV) prior to determining total selenium, and its assay was based on subtracting Se(IV) from total selenium. The main factors affecting the CPE and the vaporization behavior of the analyte were investigated in detail. Under the optimized experimental conditions, the limit of detection (LOD) for Se(IV) was 8.0 ng/L with an enhancement factor of 39 when 10 mL of sample solution was preconcentrated to 0.2 mL. The relative standard deviation (RSD) was found to be 3.9% (C(Se(IV)) = 1.0 microg/L, n = 7). The proposed method was applied to the speciation of inorganic selenium in different environmental water samples with the recovery for the spiked samples in the range of 82-102%.
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PMID:Cloud point extraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic selenium in environmental water samples. 1694 41

A previously reported enantioselective LC-MS assay for the determination of (R)- and (S)-methadone [Met] and (R)- and (S)-2-ethylidene-1,5-dimethyl-3,3-diphenyl-pyrrolidine [EDDP] (the primary metabolite of Met) has been adapted for use in the simultaneous determination of the plasma concentrations of Met, EDDP, buprenorphine (Bu) and norbuprenorphine (norBu). All of the target compounds were separated within 15 min using an alpha1-acid glycoprotein chiral stationary phase, a mobile phase composed of acetonitrile: ammonium acetate buffer [10 mM, pH 7.0] in a ratio of 18:82 (v/v), a flow rate of 0.9 ml/min at 25 degrees C. Deuterium labeled compounds were used as internal standards [d4-Bu, d3-norBu, (R,S)-d3-Met and (R,S)-d3-EDDP] and linear relationships between peak height ratios and drug concentrations were obtained for Bu and norBu in the range 0.2-12 ng/ml with correlation coefficients greater than 0.999. The relative standard deviations (%R.S.D.) for the intra- and inter-day precision of the method were <4.5% and for accuracy was <4.0%. The method was validated and used to analyze plasma samples obtained from opioid dependent methadone-maintained adults enrolled in a research study.
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PMID:Simultaneous determination of buprenorphine, norbuprenorphine and the enantiomers of methadone and its metabolite (EDDP) in human plasma by liquid chromatography/mass spectrometry. 1714 82

An enrichment method for trace amounts of Ag(I) and Pb(II) has been established prior to their flame atomic absorption spectrometric determinations. The preconcentration/separation procedure is based on chelate formation of Ag(I) and Pb(II) with ammonium pyrrolidine dithiocarbamate (APDC) and on retention of the chelates on cellulose nitrate membrane filter. The influences of some analytical parameters including pH and amounts of reagent, etc. on the recoveries of analytes were investigated. The effects of interferic ions on the quantitative recoveries of analytes were also examined. The detection limits (k=3, N=11) were 4.6 microg L(-1) for silver(I) and 15.3 microg L(-1) for lead(II). The relative standard deviations (R.S.D.) of the determinations for analyte ions were below 3%. The method was applied to environmental samples for the determination of analyte ions with satisfactory results (recoveries>95%).
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PMID:Separation/preconcentration of silver(I) and lead(II) in environmental samples on cellulose nitrate membrane filter prior to their flame atomic absorption spectrometric determinations. 1719 41

A solid phase extraction procedure has been established for chromium speciation in natural water samples. The procedure is based on the solid phase extraction of the Cr(VI)-ammonium pyrrolidine dithiocarbamate (APDC) chelate on multiwalled carbon nanotubes (MWNTs). After oxidation of Cr(III) to Cr(VI) by using hydrogen peroxide, the presented method was applied to the determination of the total chromium. The level of Cr(III) is calculated by difference of total chromium and Cr(VI) levels. The procedure was optimized for some analytical parameters including pH, eluent type, flow rates of sample and eluent, matrix effects, etc. The detection limit based on 3 sigma criterion was 0.90 microg L(-1) for Cr(VI). The adsorption capacity of multiwalled carbon nanotubes was 9.50 mg g(-1) Cr (VI). The presented method was applied for the speciation of chromium in natural water sample with satisfactory results (recoveries>95%, R.S.D.'s<9%).
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PMID:Multiwalled carbon nanotubes for speciation of chromium in environmental samples. 1725 92

A simple method is described for preconcentration and separation of trace metals such as Ag, Co, Cr, Cu, Fe, Mn, Ni and Pb simultaneously from seawater using a cloud point extraction (CPE) procedure. Triton X-114 nonionic surfactant and ammonium pyrrolidine dithiocarbamate (APDC) have been used as an extraction medium and a chelating extractant, respectively. The amounts of Triton X-114 and APDC and the pH value necessary for extraction were carefully optimized. The preconcentration factor of about 200 is achieved for all the studied metals. Electrothermal atomic absorption spectrometry (ETAAS) with an Ir coated graphite tube as permanent chemical modifier has been used for determination. The limits of detection of Ag, Co, Cr, Cu, Fe, Mn, Ni and Pb were 0.003, 0.008, 0.003, 0.006, 0.015, 0.002, 0.009 and 0.01 ng ml-1, respectively. Certified reference materials such as CASS-4 and NASS-5 (seawater) and NIST-1640 (natural water) have been used for validation of the new method. The relative standard deviation (%) obtained for all the metals are in the range 0.8 - 3.6% for natural water and 11-25% for seawater materials, except for Co in NASS-5 for which it was 50%.
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PMID:Cloud point extraction of trace metals from seawater and determination by electrothermal atomic absorption spectrometry with iridium permanent modifier. 1737 81

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 microL methanol (disperser solvent) containing 34 microL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25+/-1 microL). Then a 20 microL of sedimented phase containing enriched analyte was determined by GF AAS. Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-20 ng L(-1) with detection limit of 0.6 ng L(-1). The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L(-1) of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L(-1) are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid-liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).
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PMID:Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry: ultra trace determination of cadmium in water samples. 1738 79

To establish the method for the determination of 7 trace impurity elements including Co, Ni, Cu, Mo, Cd, Pb and Bi in high-purity aluminium by inductively coupled plasma-mass spectrometry (ICP-MS), the impurity elements were extracted from the aluminium matrix in the form of chelates with ammonium pyrrolidine dithiocarbamate (APDC) into methyl isobutylketone (MIBK). The instrument parameters, and conditions of separation and interference of matrix were discussed in detail. The optimal detection conditions were determined. The detection limits range from 0. 011 to 0. 052 microg x L(-1) depending on the elements, recoveries of samples are in the range of 92. 2%-103. 0%, and the precision is RSD<2. 3%. This method is accurate, quick and convenient. It is used in the determination of impurity elements in high-purity aluminium with satisfactory results.
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PMID:[Determination of impurity elements in high-purity aluminium using inductively coupled plasma-mass spectrometry after matrix extraction and separation]. 1739 Jun 77

A two-step, direct asymmetric synthesis of the trifluoroacetate ammonium salt of boroproline is reported. (-)-Sparteine-mediated lithiation of N-Boc-pyrrolidine afforded N-Boc-aminoboronic acid in good yield and enantioselectivity as determined by HPLC (pinanediol ester). Deprotection using TFA yielded the ammonium salt; full characterization data are presented, and the structure in aqueous solution and the occurrence of a B-N species are discussed.
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PMID:A (-)-sparteine-directed highly enantioselective synthesis of boroproline. Solid- and solution-state structure and properties. 1762 10

In this work, a methodology for the determination of total mercury in human hair is presented. This methodology is an improvement of a previous technique which has been reported by Chen et al. in 2002. This previous work was based on an acid digestion, C, cartridge clean-up, a 2,3-dimercaptopropane-1-sulfonate complexing agent, solid phase extraction and a graphite furnace atomic absorption spectrophotometric determination. In the present study, the complexing agent has been replaced by the ammonium pyrrolidine dithiocarbamate followed by a liquid-liquid extraction and the clean-up has been avoided in order to obtain a less expensive and less time consuming methodology.
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PMID:Improvements on a total mercury determination absorption spectrophotometry detection method in human hair using graphite-furnace atomic. 1771 37


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