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See detailEnantioselective Determination of Oxprenolol in Human Plasma Using Dialysis Coupled on-Line to Reversed-Phase Chiral Liquid Chromatography
Ceccato, Attilio ULg; Toussaint, B.; Chiap, Patrice ULg et al

in Journal of Pharmaceutical & Biomedical Analysis (1997), 15(9-10), 1365-74

A fully automated method for the determination of the enantiomers of oxprenolol in human plasma was developed, involving dialysis through a cellulose acetate membrane, clean-up and enrichment of the ... [more ▼]

A fully automated method for the determination of the enantiomers of oxprenolol in human plasma was developed, involving dialysis through a cellulose acetate membrane, clean-up and enrichment of the dialysate on a short precolumn and subsequent chiral liquid chromatographic (LC) analysis. All sample handling operations were executed automatically by a sample processor equipped with a robotic arm (ASTED system). The trace enrichment column (TEC) was packed with octadecylsilica. After conditioning of the TEC with the LC mobile phase and pH 3.0 acetate buffer. After the enrichment step, the analyte was transferred by the LC mobile phase to the analytical column by means of a switching valve. The influence of different parameters of the dialysis process on the recovery of oxprenolol was first investigated using achiral LC conditions. The volume as well as the aspirating and dispensing flow rates of the acceptor solution were the main parameters studied. Oxprenolol was separated on a C18 stationary phase used for the enantioseparation of oxprenolol was a Chiralcel OD-R column which contained cellulose tris (3,5-dimethylphenylcarbamate) coated on silica as chiral selector. The corresponding mobile phase consisted of a mixture of pH 6.0 phosphate buffer containing NaClO4 at 0.45 M concentration and acetonitrile (70:30 v/v). UV detection was performed at 273 nm. The method developed was validated. Recoveries for each enantiomer of oxprenolol were about 80%. The method was found to be linear in the 50-2500 ng ml-1 concentration range (r2 = 0.999 for both enantiomers) and good results with respect to intra- and inter-day reproducibility as well as accuracy were obtained. [less ▲]

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See detailEnantioselective synhteses of n.c.a. L-2-[18F]fluoro-4-chlorophenylalanine and of L-(a-methyl)-2-[18F]fluoro-4-chlorophenylalanine.
Al-Darwich, M. J.; Plenevaux, Alain ULg; Lemaire, Christian ULg et al

in Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine (1994), 35

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See detailEnantioselective Syntheses and Absolute Configuration of the Ladybird Defence Alkaloids (+)-Calvine and (+)-2-Epicalvine
Laurent, Pascal ULg; Braekman, Jean-Claude; Daloze, Désiré

in European Journal of Organic Chemistry (2000), 11

Enantiomerically pure (+)-calvine (1a) and (+)-2-epicalvine (Ib), two piperidine alkaloids isolated from ladybird beetles of the genus Calvia (Coccinellidae), were synthesized by two different strategies ... [more ▼]

Enantiomerically pure (+)-calvine (1a) and (+)-2-epicalvine (Ib), two piperidine alkaloids isolated from ladybird beetles of the genus Calvia (Coccinellidae), were synthesized by two different strategies starting from (-)-2,3,6,7,8,8a-hexahydro-3-phenyl-5H-[1,3]oxazolo[3,2-a]pyridine-5-carbonitrile (2). The key steps of these syntheses are the stereocontrolled formation of an asymmetric centre a to the nitrogen atom of 2 and the subsequent introduction of the methoxycarbonylmethyl substituent at the u'-position. Comparison of the optical rotations of the synthetic benzoates (12a) and (12b) with those of the corresponding benzoates derived from the natural compounds has revealed the absolute configuration of (+)-calvine to be (2S,6S) and that of (+)-2-epicalvine to be (2R,6S). [less ▲]

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See detailEnantioselective syntheses of n.c.a. L-(a-methyl)-[b-11C]-4-chlorophenylalanine and L-(a-[11C]methyl-tryptophan.
Plenevaux, Alain ULg; Al-Darwich, M. J.; Lemaire, Christian ULg et al

in Journal of Labelled Compounds & Radiopharmaceuticals (1994), 35

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See detailENANTIOSELECTIVE SYNTHESES OF NCA (S)-L-[BETA-C-11]-4-CHLOROPHENYLALANINE AND (S)-L-(ALPHA-METHYL)-[BETA-C-11]-4-CHLOROPHENYLALANINE
Plenevaux, Alain ULg; Al-Darwich, M. J.; Lemaire, Christian ULg et al

in Applied Radiation & Isotopes (1994), 45(3), 361-369

The radiolabeling of (S)-L-4-chlorophenylalanine and (S)-L-(alpha-methyl)-4-chlorophenylalanine were realized with carbon-11 at position beta through a radiochemical synthesis relying on the highly ... [more ▼]

The radiolabeling of (S)-L-4-chlorophenylalanine and (S)-L-(alpha-methyl)-4-chlorophenylalanine were realized with carbon-11 at position beta through a radiochemical synthesis relying on the highly enantioselective reaction between 4-chloro[alpha-C-11]benzyl bromide and the lithium enolate of (S)-1-(t-butyloxycarbonyl)-2-(t-butyl)-3-methyl-1,3-imidazolidine-4-one for (S)-L-[beta-C-11]-4-chlorophenylalanine and of (2S,5S)-1-(t-butyloxycarbonyl)-2-(t-butyl)-3,5-dimethyl-1,3-imidazolidin e-4-one for (S)-L-(alpha-methyl)-[beta-C-11]-4-chlorophenylalanine. Quantities of about 25-35 mCi were obtained at the end of synthesis, ready for injection, after hydrolysis and HPLC purification with a radiochemical yield of 19% corrected to EOB within 45 min. The enantiomeric excesses were shown to be greater than or equal to 97% for both molecules without chiral separation. The radiochemical and the chemical purities of the final compounds were greater than or equal to 98% and the specific activity at the end of synthesis ranged between 250-800 mCi/mu mol. [less ▲]

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See detailEnantioselective syntheses of no-carrier-added (nca) (S)-4-chloro-2 F-18 fluorophenylalanine and (S)-(alpha-methyl)-4-chloro-2 F-18 fluorophenylalanine
Al-Darwich, M. J.; Plenevaux, Alain ULg; Lemaire, Christian ULg et al

in Journal of Fluorine Chemistry (1996), 80(2), 117-124

(S)-4-Chloro-2-fluorophenylalanine and (S)-( a-methyl)-4-chloro-2-fluorophenylalanine were synthesized and labeled with no carrier added (n.c.a.) fluorine-18 through a radiochemical synthesis relying on ... [more ▼]

(S)-4-Chloro-2-fluorophenylalanine and (S)-( a-methyl)-4-chloro-2-fluorophenylalanine were synthesized and labeled with no carrier added (n.c.a.) fluorine-18 through a radiochemical synthesis relying on the highly enantioselective reaction between 4-chloro-2-[18F] fluorobenzyl iodide and the lithium enolate of (2s) -1-( tert-butyloxycarbonyl) -2-( tert-butyl)-3-methyl- 1,3-imidazolidine-4-one for (S) -4-chloro-2- [18F] fluorophenylalanine and (2S,5S)-1-( tert-butyloxycarbonyl) -2-( tert-butyl) -3,5-dimethyl- 1,3-imidazolidine-4-one for (S) -( a-methyl) -4-chloro-2- [18F] fluorophenylalanine. Quantities of about 20-25 mCi were obtained at the end of synthesis, ready for injection after hydrolysis and high performance liquid chromatography (HPLC) purification, with a radiochemical yield of 17%-20% corrected to the end of bombardment after a total synthesis time of 90-105 min from [18F] fluoride. The enantiomeric excesses were shown to be 97% or more for both molecules without chiral separation and the radiochemical and chemical purities were 98% or better. [less ▲]

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See detailEnantioselective synthesis of 2-[18F]fluoro-L-Tyrosine by catalytic phase-transfer alkylation.
Lemaire, Christian ULg; Gillet, S.; Ooi, T. et al

in Journal of Labelled Compounds & Radiopharmaceuticals (2001), 44

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See detailEnantioselective synthesis of 6-[fluorine-18]-fluoro-L-dopa from no-carrier-added fluorine-18-fluoride.
Lemaire, Christian ULg; Damhaut, Philippe; Plenevaux, Alain ULg et al

in Journal of Nuclear Medicine : Official Publication, Society of Nuclear Medicine (1994), 35(12), 1996-2002

METHODS: A trimethylammonium veratraldehyde triflate was synthesized and used as a precursor for the asymmetric synthesis of 6-[18F]fluoro-L-dopa. RESULTS: Its nucleophilic fluorination with 18F-fluoride ... [more ▼]

METHODS: A trimethylammonium veratraldehyde triflate was synthesized and used as a precursor for the asymmetric synthesis of 6-[18F]fluoro-L-dopa. RESULTS: Its nucleophilic fluorination with 18F-fluoride produced by the 18O(p,n)18F nuclear reaction on enriched 18O-water led to the corresponding no-carrier-added [18F]fluoroveratraldehyde (45 +/- 5% EOB). Diiodosilane was used to prepare the corresponding [18F]fluorobenzyl iodide (36.5 +/- 5.3% EOB). Akylation of (S)-1-tert-boc-2-tert-butyl-3-methyl-4-imidazolidinone with this electrophilic agent, hydrolysis and purification by preparative high-pressure liquid chromatography made 6-[18F]fluoro-L-dopa ready for human injection, in a 23% +/- 6% decay-corrected radiochemical yield. The enantiomeric purity and the specific activity were above 96% and 1 Ci/mumole respectively. CONCLUSION: Through this procedure, starting from 250 mCi of 18F-fluoride, multimillicurie amounts (32 +/- 8.5 mCi) of no-carrier-added 6-[18F]fluoro-L-dopa are now available at the end of synthesis (90 min) with a good radiochemical purity (more than 98%). [less ▲]

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See detailENANTIOSELECTIVE SYNTHESIS OF NCA (S)-L-([ALPHA-C-11]METHYL)-TRYPTOPHAN
Plenevaux, Alain ULg; Lemaire, Christian ULg; Delfiore, Guy et al

in Applied Radiation & Isotopes (1994), 45(6), 651-653

N.c.a. (S)-L-([alpha-C-11]methyl)-tryptophan was prepared by treatment at -78-degrees-C of (2S,3aR,8aS)-1,2-bis(-methoxycarbonyl)-1,2,3,3a,8,8a-hexahydropyrrolo[2, 3-b]-indole with lithium ... [more ▼]

N.c.a. (S)-L-([alpha-C-11]methyl)-tryptophan was prepared by treatment at -78-degrees-C of (2S,3aR,8aS)-1,2-bis(-methoxycarbonyl)-1,2,3,3a,8,8a-hexahydropyrrolo[2, 3-b]-indole with lithium diisopropylamide and [C-11]CH3I. After hydrolysis with HI and HPLC purification, the title compound was isolated with a radiochemical yield of 36% (EOB corrected) within 22 min; e.e. was shown > 97% (n = 20); specific activity was ranging between 0.8 and 1.2 Ci (30-45 GBq)/mu mol EOB. [less ▲]

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See detailEnantioselective synthesis of thioesters as substrates for high-through put screening assays of Penicillin Binding Proteins
Simon, Justine ULg; Zervosen, Astrid ULg; Bouillez, André ULg et al

Poster (2013, June 19)

Excessive utilization of beta-lactam antibiotics like penicillin has created drug-resistant strains in bacteria. One of the main mechanisms of resistance is the production of drug resistant Penicillin ... [more ▼]

Excessive utilization of beta-lactam antibiotics like penicillin has created drug-resistant strains in bacteria. One of the main mechanisms of resistance is the production of drug resistant Penicillin Binding Proteins (PBPs) and the over expression of these proteins. The transglycosidase and transpeptidase activities of PBPs catalyze the last two steps of peptidoglycan biosynthesis, which is unique to bacteria, and lies outside the cytoplasmic membrane. PBPs are interesting targets and efforts are still done to find new inhibitors. <br />A thioesterase activity has been described for various PBPs. For example, the thioester S2d is a substrate of PBP R39 of Actinomadura and of PBP2x of Streptococcus pneumoniae. The utilization of thioesters allows a rapid screening of active compounds in high-through put screening assays. Furthermore detailed kinetic studies using thioesters as reporter substrates are also possible. <br />Here we will present the enantioselective synthesis of the thioesters and their application as substrates in high through put screening assays. [less ▲]

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See detailEnantioseparation of Acidic Drugs by Capillary Electrophoresis Using Dual Systems with Mixtures of Charged and Neutral Cyclodextrins
Fillet, Marianne ULg; Fotsing, Lucas ULg; Schomburg, G. et al

in Biomedical Chromatography : BMC (1998), 12(3, May-Jun), 131-2

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See detailEnantioseparation of aminoglutethimide with cyclodextrins in capillary electrophoresis and studies of selector-selectand interactions using NMR spectroscopy and electrospray ionization mass spectrometry.
Chankvetadze, Bezhan; Fillet, Marianne ULg; Burjanadze, N. et al

in Enantiomer (2000), 5(3-4), 313-22

The enantiomers of aminoglutethimide [2-(p-aminophenyl)-2-ethylglutarimide, AGT] can be resolved in CE using all of three most commonly used native cyclodextrins (CD): alpha-, beta-, and gamma-CDs. The ... [more ▼]

The enantiomers of aminoglutethimide [2-(p-aminophenyl)-2-ethylglutarimide, AGT] can be resolved in CE using all of three most commonly used native cyclodextrins (CD): alpha-, beta-, and gamma-CDs. The migration order of the enantiomers was opposite using beta-CD compared to alpha- and gamma-CDs as chiral selectors. In order to examine some underlying mechanisms of the chiral recognition the interaction of AGT with the chiral selectors was studied with one- and two-dimensional NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The Job's and Scott's plots constructed based on the complexation-induced chemical shifts (CICS) observed in NMR spectra provided some preliminary information on the stoichiometry of the intermolecular complexes but did not seem to be absolutely reliable perhaps because the self-association of the analyte molecules and the formation of multiple type selectand-selector complexes. Therefore, an attempt was made to characterize the complexes using ESI-MS. This technique provided information on the stoichiometry and relative affinity constants of selector-selectand complexes. The information on the structure of complexes in the solution was obtained using one-dimensional rotating frame nuclear Overhauser enhancement (1D-ROESY) NMR spectroscopic studies. Significant differences were observed between the structures of the AGT complexes with beta- and gamma-CD. [less ▲]

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See detailEnantioseparation of nonsteroidal anti-inflammatory drugs by capillary electrophoresis using mixtures of anionic and uncharged beta-cyclodextrins as chiral additives.
Fillet, Marianne ULg; Hubert, Philippe ULg; Crommen, Jacques ULg

in Electrophoresis (1997), 18(6), 1013-8

Nine nonsteroidal anti-inflammatory drugs (NSAIDs) were enantioseparated by capillary electrophoresis using an anionic cyclodextrin derivative (sulfobutyl ether beta-cyclodextrin or carboxymethyl-beta ... [more ▼]

Nine nonsteroidal anti-inflammatory drugs (NSAIDs) were enantioseparated by capillary electrophoresis using an anionic cyclodextrin derivative (sulfobutyl ether beta-cyclodextrin or carboxymethyl-beta-cyclodextrin) in combination with a neutral cyclodextrin as chiral additives to a pH 3 phosphoric acid-triethanolamine buffer. In the presence of a negatively charged cyclodextrin, the analytes were given an appropriate mobility but relatively low enantioselectivities were generally obtained when such a cyclodextrin was the only selector added to the buffer. The addition of an uncharged cyclodextrin, such as the native beta-cyclodextrin or one of its derivatives (dimethyl-, trimethyl- and hydroxypropyl-beta-cyclodextrin), to this kind of buffer containing an anionic cyclodextrin, was found to give rise to considerable improvement in chiral resolution for all compounds studied. Resolution and analysis time were optimized by varying the nature and concentration of the two cyclodextrins. The best compromise was usually achieved by the simultaneous addition of sulfobutyl ether beta-cyclodextrin and trimethyl-beta-cyclodextrin. Under optimum conditions, the enantiomers of all NSAIDs examined could be completely separated (most often with resolution values higher than 5) in short analysis times (generally lower than 15 min). [less ▲]

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