Analysis of plasticizers in PVC medical devices: Performance comparison of eight analytical methods

A wide variety of medical devices (MDs) used in hospitals are made of flexible plasticized polyvinylchloride (PVC). Different plasticizers are present in variable amounts in the PVC matrix of the devices and can leach out into the infused solutions and may enter into contact with the patients. The ARMED¹ project aims to assess the migration of these plasticizers from medical devices and therefore the level of exposure in patients. For the first task of the project, eight methods were developed to directly detect and quantify the plasticizers in the PVC matrix of the MDs. We compared the overall performances of the analytical methods using standardized and validated criteria in order to provide the scientific community with the guidance and the technical specifications of each method for the intended application. We have shown that routine rapid screening could be performed directly on the MDs using the FTIR technique, with cost-effective analyses. LC techniques may also be used, but with limits and only with individual quantification of the main plasticizers expected in the PVC matrix. GC techniques, especially GC-MS, are both more specific and more sensitive than other techniques. NMR is a robust and specific technique to precisely discriminate all plasticizers in a MD but is limited by its cost and its low ability to detect and quantify plasticizer contamination, e.g. by DEHP. All these results have been confirmed by a real test, called the " blind test " carried out on 10 MD samples.

Separation of Tic-hydantoin enantiomers, potent sigma-1 agonists, by high performance liquid chromatography and capillary electrophoresis

Stereospecific separations of seven Tic-hydantoin sigma-1 agonists were performed by both HPLC method using derivatized cellulose and amylose chiral stationary phases and capillary electrophoresis (CE) method using neutral and anionic cyclodextrins added in the background electrolyte (BGE). An optimal baseline separation (R(s)>3.3 with analysis times<25min) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. CE was used as an alternative technique to HPLC for the Tic-hydantoin derivatives separation. The enantiomers were fully resolved with highly sulfated beta-cyclodextrins at pH 2.5 (R(s)>1.5 with analysis times <11min). Both methods were validated in terms of linearity, detection and quantification limits. They were used to check the enantiomeric purity of the enantiomers.

Separation of nucleoside phosphoramidate diastereoisomers by high performance liquid chromatography and capillary electrophoresis

Separations of five diastereoisomers of nucleoside phosphoramidate derivatives (pronucleotides) were performed by both HPLC method using derivatized cellulose and amylose chiral stationary phases and CE method using anionic cyclodextrins added in the background electrolyte (BGE). An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using in a normal-phase methodology. Capillary electrophoresis was used as an alternative technique to HPLC for the separation of pronucleotides. The diastereoisomers were fully resolved with sulfated cyclodextrins at both BGE pH (2.5 and 6.2). Limits of detection and limits of quantification, calculated for both methods, are up to 200 times higher in CE separations than in HPLC separations. The analytical HPLC method was then applied in a preliminary study for the pronucleotide 1 quantification in cellular extract.

Chiral resolution of the enantiomers of new selective CB2 receptor agonists by liquid chromatography on amylose stationary phases

Analytical HPLC methods using derivatized amylose chiral stationary phases, Chiralpak AD-H and Chiralpak AS, were developed for the direct enantioseparation of eight substituted 4-oxo-1,4-dihydroquinoline-3-carboxamide derivatives with one stereogenic center. Baseline separation (Rs>1.5) was always achieved on amylose based Chiralpak AD-H column to the difference with Chiralpak AS. Using UV detection, a linear response was observed within a 180-420 micromol L(-1) concentration range (r2>0.991) for three racemic compounds 1, 3 and 4 with best pharmacological potentials; repeatability, limit of detection (LD) and quantification (LQ) were also determined: LD varied, for the solutes, from 0.36 to 2.56 micromol L(-1). Finally, the enantiopurity of these compounds was determined. Additionally, the effect of temperature variations upon isomer separations was investigated.

Determination of pKa values of benzoxa-, benzothia- and benzoselena-zolinone derivatives by capillary electrophoresis

Acidity constants of benzoxa-, benzothia- and benzoselena-zolinone derivatives were determined by capillary electrophoresis, potentiometry and spectrophotometry experiments. These three analytical techniques gave pK(a) results that were in good agreement. A convenient, accurate and precise method for the determination of pK(a) was developed to measure changes in acidity constants induced by heteroatom or 6-benzoyl substituted derivatives. pK(a) values were determined simultaneously for two compounds characterized by different electrophoretic mobility (micro(e)) and pK(a) value and in the presence of an analogous neutral marker.

Enantioseparation of cis and trans nucleosides, aromatic analogues of stavudine, by capillary electrophoresis and high-performance liquid chromatography

Compounds 1-4 are diastereoisomeric thymine derivatives of isochroman aromatic analogues of stavudine, an approved drug. Both capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) techniques were used to separate these species with high resolution and thus permit the determination of enantiomeric excess. Chiral selectivity was developed using anionic (highly sulfated) cyclodextrins as chiral selectors in CE and amylose, cellulose and cyclodextrin chiral stationary phases by HPLC. The HPLC method was found to be more efficient than the CE method and was applied, after validation (repeatability, limit of detection, limit of quantification) to follow and quantify the kinetics of a stereoselective esterification.

Diastereoisomeric resolution of a pronucleotide using solid phase extraction and high performance liquid chromatography: Application to a stereoselective decomposition kinetic in cell extracts

A stereospecific HPLC methodology has been developed for the diastereoisomeric resolution of a mononucleotide prodrug in cell extracts. This method involves the use of solid phase extraction on a C18 cartridge. Diastereoisomers and internal standard resolutions were performed on a cellulose based chiral column (Chiralcel OD-H) used in the normal phase mode. The method was validated in terms of specificity, recovery, linearity (diasteroisomers mixture concentration: 3-60 micromol L(-1)), precision and accuracy and detection limit (1.67 and 1.33 micromol L(-1) for first and second eluted diastereoisomer). This method was applied to the determination of the apparent rate constants of disappearance and half-lives of each stereoisomers. This permits to conclude to the stereoselectivity of the enzymatic activity involved in the decomposition pathway of 2.

Column selection and method development for the separation of nucleoside phosphotriester diastereoisomers, new potential anti-viral drugs. Application to cellular extract analysis

Analytical HPLC methods using derivatized cellulose and amylose chiral stationary phases used in normal and reversed-phase modes were developed for the diastereoisomeric separation of mononucleotide prodrugs (pronucleotides) of 3'-azido-2',3'-dideoxythymidine (AZT). The resolutions were performed with two silica-based celluloses using normal and reversed-phase methodologies: Tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H and Chiracel OD-RH) and Tris-methylbenzoate (Chiralcel OJ and OJ-R). Two amyloses phases, Tris-3,5-dimethylphenylcarbamate (Chiralpak AD) and Tris-(S)-1-phenylethylcarbamate (Chiralpak AS), were used in normal-phase mode. Additionally, we developed separation using two stationary phases with immobilized cyclodextrins in reversed-phase and polar-organic modes. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. Different types and concentration of aliphatic alcohols, acetonitrile or water in the mobile phase were also tested for the different separation modes. An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. The different columns gave complementary results in term of resolution. Limits of detection and quantification were 0.12-0.20 and 0.40-0.67 microm, respectively. This analytical method was applied in a preliminary study for the pronucleotide 2 quantification in cellular extract.

Enantioseparation of four cis and trans diastereomers of 2′,3′-didehydro-2′,3′-dideoxythymidine analogs, by high-performance liquid chromatography and capillary electrophoresis

Compounds 1-4 are the four stereoisomers of a synthetic new potential antiviral agent (d4T analog) containing two chiral centers and a base (uracil). Both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) techniques were used to separate and quantify enantiomers with high resolution. The determination of enantiomeric purity of the compounds was developed using both amylose chiral stationary phase by HPLC and anionic cyclodextrins (highly S-CD) as chiral selectors in CE. The HPLC method was found to be superior in sensitivity to the CE method.

Determination of ionization constants of N-imidazole derivatives, aromatase inhibitors, using capillary electrophoresis and influence of substituents on pKa shifts

Capillary electrophoresis (CE) was used as a method to determine the acidity constants of eight aromatase inhibitors. This method was validated by comparison of results obtained with a traditional method, UV spectroscopy, and additionally with computational calculations. We confirmed here, with our series of compounds, that capillary electrophoresis is an attractive method for pKa measurements which is based on migration time or mobilities of the ionic species over a range of pH values. The precision of pKa measurements of N-imidazole derivatives is useful to observe pKa shifts induced by chemical modifications introduced on adjacent aromatic rings such as heterocycle (benzoxa- or benzothiazolinone) or substituted benzyle. The knowledge of these pKa values is a great interest to predict migration of solutes and qualitative interactions with ionized cyclodextrines as chiral selectors in further enantioseparative CE studies.

Melatonin receptor agents: synthesis, resolution by HPLC on polysaccharides chiral stationary phases, absolute configuration, and pharmacology of the enantiomers of (+/-)-N-[[2[(7-fluoro-1,2,3,4-tetrahydronaphthalen-1-yl)ethyl]acetamide

In order to obtain milligram amounts of the enantiomers of tetrahydronaphthalenic derivative 5 to be tested for binding to the melatonin sites, preparative HPLC employed a mobile phase consisting of n-hexane-alcohol and a silica-based cellulose tris-methylbenzoate (Chiralcel OJ) using isocratic conditions and multiple repetitive injections. The preparative separation was optimized by adjusting the sample size from a scale-up of the analytical method. The enantiomeric elution order was reversed by the change from the carbamate type phase (Chiralcel OD-H) to the benzoate type phase (Chiralcel OJ) in analytical mode. The optical rotation and the circular dichroism spectra of the single enantiomers were determined after separation. The absolute stereochemistry of the two enantiomers of (+/-)-N-[2-(7-fluoro-1,2,3,4-tetrahydronaphthalen-1-yl)ethyl]acetamide 5 was established by X-ray crystallographic analysis. The purity obtained was sufficient for a first screen of their biochemical properties: the (-)-(S) enantiomer shows more affinity for melatonin receptors MT1, MT2 and is responsible of the selectivity towards MT2.

Synthesis of new N-substituted pyrrolidin-2-ones as cyclic analog of gamma-aminobutyric acid

Some new N-substituted pyrrolidin-2-ones, cyclic analogs of baclofen and of 3-(5-methylbenzo[b]furan-2-yl)-gamma-aminobutyric acid, have been prepared starting from corresponding pyrrolidinones and characterized.

Direct separation of the stereoisomers of methoxytetrahydronaphthalene derivatives, new agonist and antagonist ligands for melatonin receptors, by liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the direct separation of the stereoisomers of disubstituted tetralin derivatives with two chiral centers, new agonist and antagonist ligands for melatonin receptors. The separations were made using normal-phase methodology with a mobile phase consisting of n-hexane-alcohol (methanol, ethanol, 1-propanol or 2-propanol) in various proportions, and a silica-based cellulose tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The effects of concentration of various aliphatic alcohols in the mobile phase were studied. A better separation was achieved on cellulose carbamate phase compared with the cellulose ester phase. The effects of structural features of the solutes on the discrimination between the stereoisomers were examined. Baseline separation (Rs>1.5) was easily obtained in many cases.

Isomers of substituted 3-benzo[b]furyl and 3-thienylaminobutyric acids as potent ligands of the GABA-B receptor: synthesis and preparative liquid chromatographic separation

Baclofen (4-amino-3-(4-chlorophenyl)butyric acid) is the only selective agonist for GABA-B receptors. Its R-(-)-enantiomer is about 100 times more active than the S-(+)-enantiomer. In the search for new compounds that bind to GABA-B receptors, it is very important to clarify the structural requirements. The authors report the synthesis and separation of isomers of various 3-heteroaromatic (benzo[b]furan and thiophen) aminobutyric acids. The 4-amino-3-(7-methylbenzo[b]furan-2-yl)butanoic acid is a potent and specific ligand for GABA-B receptors, with an IC50 value of 5.4 microM for the displacement of [3H] GABA.

Chiral resolution of the enantiomers of tetrahydronaphthalenic derivatives, new agonist and antagonist ligands for melatonin receptors, using high-performance liquid chromatography on cellulose chiral stationary phases

Analytical HPLC methods using derivatized cellulose chiral stationary phases were developed for the separation of the enantiomers of methoxy and ethyl tetrahydronaphthalenic derivatives, new agonist and antagonist ligands for melatonin receptors. The resolution were made using normal-phase methodology with a mobile phase consisting of n-hexane-alcohol (methanol, ethanol, 1-propanol or 2-propanol) in various percentage, and a silica-based cellulose tris-3,5-dimethyl-phenylcarbamate (Chiralcel OD-H), or tris-methylbenzoate (Chiralcel OJ). The mobile phase and the chiral stationary phase were varied to achieve the best resolution. The effects of concentration of alcohol, various aliphatic alcohols in the mobile phase were studied. The effects of substitution were analysed. Baseline separation (R(s) > 1.5) was easily obtained in many cases. The resolution results were complementary between the two columns.

GABA(B) receptor antagonism by 7-MBFG, a benzo[b]furan analogue of baclofen, in central and peripheral tissues

(R,S)-4-Amino-3-(7-methylbenzo[b]furan-2-yl)-butanoic acid (7-MBFG), a new benzofuran analogue of the GABA(B) receptor agonist baclofen, has been evaluated for pharmacological activity on GABA(B) receptors in the guinea-pig isolated ileum and rat neocortical slices. 7-MBFG (300 and 500 microM) reversibly antagonized the (R,S)-baclofen induced depression of cholinergic twitch contractions in the guinea-pig ileum and shifted the concentration-response curve for baclofen to the right, in a parallel manner, giving an apparent pA2 value of 3.7+/-0.3. Likewise, 7-MBFG (300 and 500 microM) reversibly blocked the baclofen-induced suppression of spontaneous discharges, in rat neocortical slices maintained in Mg2+ -free Krebs medium, and caused a rightward, parallel shift of the baclofen concentration-response curve, giving an apparent pA2 value of 4.1+/-0.1. The compound 7-MBFG belongs to a novel, new class of antagonist at central and peripheral GABA(B) receptors, in which the antagonist properties reside in the pseudo-aromatic character of their 3-benzo[b]furan-2-yl substituents, and might provide useful leads for further development of GABA(B) receptor ligands.

Actions of thienyl analogs of baclofen at GABA(B) receptors in rat neocortical slices

In rat neocortical slices maintained in Mg2+-free Krebs medium, baclofen and its thienyl analogs, 4-amino-3-(5-chlorothien-2-yl)-butanoic acid (5h), 4-amino-3-(5-methylthien-2-yl)-butanoic acid (5d), 4-amino-3-(5-bromothien-2-yl)-butanoic acid (5f) and 4-amino-3-(thien-3-yl)-butanoic acid (5j) dose-dependently suppressed the spontaneous discharges, antagonised by the GABA(B) receptor antagonist 2-hydroxysaclofen (200 microM). Their relative potencies were baclofen > 5h > 5d > 5f > 5j. These heterocyclic analogs may prove useful as GABA(B) receptor agonists in functional studies.

GABAB receptor antagonism by resolved (R)-saclofen in the guinea-pig ileum

The GABAB receptor antagonist saclofen (3-amino-2-(4-chlorophenyl)propylsulphonic acid) has been resolved by chiral high-performance liquid chromatography. The enantiomer (R)-saclofen, but not (S)-saclofen, reversibly antagonised the (R,S)-baclofen-induced depression of cholinergic twitch contractions in the guinea-pig ileum with an apparent pA2 of 5.3. Also, 2-hydroxy-saclofen was resolved by the same method, its (S)-enantiomer yielding an apparent pA2 of 5.0. This method provides a convenient resolution of these antagonists.

Structure-affinity relationships of baclofen and 3-heteroaromatic analogues

Substituting a furan, a thiophene, a benzo[b]furan, a benzo[b]thiophene, or a quinoline ring for the p-chlorophenyl moiety of baclofen has led to GABAB ligands with different affinities depending on the nature of the heteroaromatic ring, and on the nature and position of its substituent. As steric effects cannot account for all the affinity variations, we have studied the lipophilic and electronic properties of baclofen and selected 3-heteroaromatic analogues, gaining insight into the structural features necessary for GABAB affinity. Centrifugal partition chromatography (CPC) has been used to measure octan-1-ol water distribution coefficients, while ab initio molecular orbital (MO) calculations were performed to study electronic properties.

Thienyl-GABA derivatives as specific baclofen agonists in the rat and cat spinal cord in vivo

The depression of the amplitude of extracellularly recorded monosynaptic excitatory field potentials in the lumbar spinal cord of pentobarbitone anaesthetised rats and cats by three thienyl derivatives of GABA: 4-amino-3-(2-thienyl)-butanoic acid; 4-amino-3-(2-thienyl-5-methyl)-butanoic acid and 4-amino-3-(2-thienyl-5-chloro)-butanoic acid was reversibly blocked by the (-)-baclofen antagonist 3-aminopropyl-diethoxymethyl-phosphinic acid (CGP 35348). These compounds, of which the most potent, the 5-chloro derivative, was weaker than (-)-baclofen, thus activate baclofen receptors in the cat and rat spinal cord.

Differing actions of beta-(2-thienyl)-gamma-aminobutyric acid in central and peripheral preparations

In the guinea-pig isolated ileum, beta-(2-thienyl)-gamma-aminobutyric acid (BTG; 100-500 microM) reversibly and competitively (pA2 = 4.3 +/- 0.1) antagonised the baclofen-induced (5-100 microM) depression of cholinergic twitch contractions, but not that to adenosine or morphine. By contrast, in rat neocortical slice preparations, BTG (100-500 microM) acted as an agonist, abolishing the frequency and amplitude of spontaneous discharges, sensitive to 2-hydroxysaclofen (100-500 microM). BTG exhibits differential actions at GABAB receptors in brain and periphery.

Actions of thienyl analogs of baclofen in the guinea-pig isolated ileum

In guinea-pig isolated ileal preparations, the 5-methylthien-2-yl (5d), 5-bromothien-2-yl (5f) and 5-chlorothien-2-yl (5h) analogs of baclofen depressed twitch responses to field stimulation in a dose-dependent manner. These actions were reversibly and competitively antagonised by 2-hydroxysaclofen but not by naloxone, phentolamine, propranolol or theophylline. The relative potencies (EC50 values) were baclofen (10 microM) greater than 5h (40 microM) greater than 5d (80 microM) greater than 5f (120 microM). These analogs represent a novel class of specific GABAB receptor agonists which, like baclofen, should readily enter the brain.

3-Thienyl- and 3-furylaminobutyric acids. Synthesis and binding GABAB receptor studies

Baclofen (beta-(p-chlorophenyl)-GABA) is a selective agonist for the bicuculline-insensitive GABAB receptor. The search for new compounds that bind to the GABAB receptor is very important to clarify structural requirements. We report herein the synthesis and the binding studies of variously substituted 3-thienyl- and 3-furylaminobutyric acids. 4-Amino-3-(5-methyl-2-thienyl)butyric acid (5d) and 4-amino-3-(5-chloro-2-thienyl)butyric acid (5h) are potent and specific ligands for GABAB receptor. The IC50 values for the displacement of (R)-(-)-[3H]baclofen are 1.34 and 0.61 microM for 5d and 5h, respectively, as compared to 0.33 microM for baclofen.

Baclofen antagonism by 4-amino-3-(5-methoxybenzo[b]furan-2-yl) butanoic acid in the cat spinal cord

When administered microelectrophoretically, 4-amino-3-(5-methoxybenzo[b]furan-2-yl)butanoic acid (MBFG) reversibly reduced the presynaptic depression by (-)-baclofen of the monosynaptic excitation of spinal interneurones by impulses in muscle low-threshold afferent fibres of the cat as well as the postsynaptic depression by (-)-baclofen of the firing of these neurones. MBFG, as an antagonist of (-)-baclofen, may be useful in investigating the structure-activity relationships of central and peripheral baclofen receptors.

Benzofuran analogues of baclofen: a new class of central and peripheral GABAB-receptor antagonists

Two novel beta-(benzo[b]furan) analogues of baclofen (4-amino-3-benzo[b]furan-2-ylbutanoic acid, 9G, and 4-amino-3-(5-methoxybenzo[b]furan-2-yl)butanoic acid, 9H) antagonised the baclofen-induced depression of twitch contractions in the guinea-pig isolated ileum (estimated apparent pA2 3.9 and 4.1 respectively); both 9G and 9H also antagonised in a dose-dependent manner the baclofen-induced reduction of repetitive paroxysmal discharges in rat neo-cortical slice preparations maintained in Mg2+-free Krebs solution. These benzofurans evidently represents a new class of GABAB-receptor antagonist.

[Preparation and schistosomicidal activity of vinylogues of 1,3-dithio-3-thione]

The synthesis of vinylogues of 1,2-dithiol-3-thione is described. The activity in experimental schistosomiasis (schistosomicidal activity and, for the most interesting ones, on the egg-laying) was tested in mice with Schistosoma mansoni in comparison with oltipraz.

Synthesis and pharmacological evaluation of gamma-aminobutyric acid analogues. New ligand for GABAB sites

Baclofen (beta-p-chlorophenyl-GABA) is the only selective agonist for the bicuculline-insensitive GABAB receptor. We report the synthesis of new GABA analogues and baclofen analogues. In vitro, two compounds, 4-amino-3-benzo[b]furan-2-ylbutanoic acid (9g) and 4-amino-3-(5-methoxybenzo[b]furan-2-yl)butanoic acid (9h), showed an affinity for the GABAB receptor. The results obtained with racemic compounds of benzofuran structure, new for this series, and the surprising inactivity of compound 3a (4-amino-3-(4-hydroxyphenyl)butanoic acid) permit the proposal of an hypothesis for the structure-activity relationships with regard to GABAB receptor.