Chromatographic and spectroscopic studies on the chiral recognition of sulfated β-cyclodextrin as chiral mobile phase additive: Enantiomeric separation of a chiral amine

A fast enantiomeric separation of a chiral aromatic amine was achieved, using ultra high pressure liquid chromatography and highly sulfated beta-cyclodextrin (S-β-CD) as a chiral additive in the mobile phase. The stationary phase consisted of a core–shell support with a particle size of 2.7 μm. Under these conditions the base-line separation was obtained within 2.5 min. The influence of the concentration of the additive, along with the thermodynamics of the separation, was studied. Vibrational circular dichroism (VCD) spectroscopy was applied to assess the absolute configuration of the two enantiomeric analytes, as well as the interaction of these enantiomers with the S-β-CD. The VCD results revealed that S-β-CD undergoes a temperature-induced conformational change. Further, VCD experiments indicate that the interactions of the two enantiomers with the S-β-CD occur through an inclusion of the aromatic part of the analyte, as well as through electrostatic interaction between the protonated amine and the sulfate groups located at the narrow part of the S-β-CD. Molecular mechanics calculations performed according to the VCD results are consistent with experimental data, providing further evidence of these interactions.     

pePC-SAFT: Modeling of polyelectrolyte systems: 1. Vapor–liquid equilibria

A molecular thermodynamic model for polyelectrolyte systems—called pePC-SAFT—is proposed. The effect of charged monomers within the polyelectrolyte chain is explicitly taken into account in the reference term by replacing the hard-chain contribution of the PC-SAFT model by a charged-hard-chain contribution. Moreover, counterion condensation is accounted for to determine the effective number of charges along the polyion as well as of free counterions. The electrostatic contribution of the free counterions is described by a Debye–Hückel term.     

Drug interactions with potential rubber closure extractables: Identification of thiol–disulfide exchange reaction products of captopril and thiurams

Mixtures of thiuram disulfides are frequently used as accelerators in rubber stoppers for injectables and sterilized powders for injection. Rapid reactions of thiuram disulfides between themselves and with thiols yield mixed disulfides due to thiol–disulfide exchange. The possibility of exchange reactions of thiuram disulfides extracted from rubber stoppers and drug products containing pendant thiol groups have not been reported in the analysis of potential stopper extractables. In this paper we report the formation and identification of mixed thiuram disulfides of N,N,N′,N′-dimethylthiuram disulfide (TMTD), N,N,N′,N′-dibutylthiuram disulfide (TBTD), and captopril (a thiol-containing drug). A reversed-phase HPLC method was developed for the determination of TMTD, TBTD, captopril and their disulfides in aqueous vehicles, using a YMC ODS AQ column at 35 °C and mobile phases A and B consisting of acetonitrile:water:trifluoroacetic acid (TFA) (20:80:0.1) and acetonitrile:TFA (100:0.1), respectively. The captopril–TBTD and captopril–TMTD disulfides were identified by MS, with molecular ions at m/z 420.9 and m/z of 337.1, respectively. Possible structures for the fragment ions in the spectra are provided. Mixed captopril–thiuram formation was studied as a function of pH. Captopril–TMTD formation was enhanced at pH 6.0, reaching a maximum of 31.3% in 4.1 h. At pH 4.0 and 2.2, the mixed captopril adduct product was still detected in solution after 20 h. The impact of the formation of mixed disulfide products of thiol-containing drugs with thiurams in the HPLC profile of extractables and leachables studies is discussed.     

On-line analysis of volatile chlorinated hydrocarbons in air by gas chromatography–mass spectrometry: Improvements in preconcentration and injection steps

An analytical system composed of a cryofocusing trap injector device coupled to a gas chromatograph with mass spectrometric detection (CTI-GC–MS) specific for the on-line analysis in air of volatile chlorinated hydrocarbons (VCHCs) (dichloromethane; chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) was developed. The cryofocusing trap injector was the result of appropriate low cost modifications to an original purge-and-trap device to make it suitable for direct air analysis even in the case of only slightly contaminated air samples, such as those from remote zones. The CTI device can rapidly and easily be rearranged into the purge-and-trap allowing water and air analysis with the same apparatus. Air samples, collected in stainless steel canisters, were introduced directly into the CTI-GC–MS system to realize cryo-concentration (at −120 °C), thermal desorption (at 200 °C) and for the subsequent analysis of volatiles. The operating phases and conditions were customised and optimized. Recovery efficiency was optimized in terms of moisture removal, cold trap temperature and sampling mass flow. The injection of entrapped volatiles was realized through a direct transfer with high chromatographic reliability (capillary column–capillary column). These improvements allowed obtaining limits of detection (LODs) at least one order of magnitude lower than current LODs for the investigated substances. The method was successfully employed on real samples: air from urban and rural areas and air from remote zones such as Antarctica.     

(l)- or (d)-Valine tert-butylamide grafted on permethylated β-cyclodextrin derivatives as new mixed binary chiral selectors: Versatile tools for capillary gas chromatographic enantioseparation

This work deals with the synthesis of two mixed binary chiral selectors prepared by grafting (l)- or (d)-valine tert-butylamide on permethylated cyclodextrin macrocycle. The enantioselective properties of the new chiral selectors diluted in OV11 polysiloxane (35% phenyl- and 65% methylsiloxane) were investigated by means of injections of 117 racemic mixtures. The mixed chiral selectors with (l)-valine and, to a lesser extent with (d)-valine, were found to have an improved enantioselectivity toward amino acid derivatives by comparison to permethylated cyclodextrin. The enantioseparation capability of these new chiral selectors has proven to be slightly less efficient than Chirasil-l-Val (Alltech) for amino acid derivatives, but it has been extended to include terpenes, lactones, esters, aliphatic compounds and aryl alcohols.     

Physical properties and structure of fine core–shell particles used as packing materials for chromatography: Relationships between particle characteristics and column performance

The recent development of new brands of packing materials made of fine porous-shell particles, e.g., Halo and Kinetex, has brought great improvements in potential column efficiency, demanding considerable progress in the design of chromatographic instruments. Columns packed with Halo and Kinetex particles provide minimum values of their reduced plate heights of nearly 1.5 and 1.2, respectively. These packing materials have physical properties that set them apart from conventional porous particles. The kinetic performance of 4.6 mm I.D. columns packed with these two new materials is analyzed based on the results of a series of nine independent and complementary experiments: low-temperature nitrogen adsorption (LTNA), scanning electron microscopy (SEM), inverse size-exclusion chromatography (ISEC), Coulter counter particle size distributions, pycnometry, height equivalent to a theoretical plate (HETP), peak parking method (PP), total pore blocking method (TPB), and local electrochemical detection across the column exit section (LED). The results of this work establish links between the physical properties of these superficially porous particles and the excellent kinetic performance of columns packed with them. It clarifies the fundamental origin of the difference in the chromatographic performances of the Halo and the Kinetex columns.     

Application of ultra-high-pressure liquid chromatography–tandem mass spectrometry to the determination of multi-class pesticides in environmental and wastewater samples: Study of matrix effects

An ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple quadrupole mass analyzer was used. This analyzer (minimum dwell time, 5 ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2 g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1 μg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7 pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples.     

Determination of the local electron number density in laser-induced plasmas by Stark-broadened profiles of spectral lines: Comparative results from Hα, Fe I and Si II lines

Measurements of the local electron density in laser-induced plasma have been carried out from the Stark-broadened profiles of three reference lines (H_α, Fe I and Si II). The plasma has been generated from a Fe–Si sample in air using a Nd:YAG laser. Compatible values of the local electron density have been obtained from the three lines. The experiment is based on the use of an imaging spectrometer, the capability for spatial resolution of a charge-coupled device and the application of a spatial deconvolution procedure to the spectra. Distributions of the emission coefficient have been obtained, showing that the three lines are emitted from different regions of the plasma. The implications in the apparent electron density values obtained in spatially-integrated measurements are discussed: similar values are obtained for the H_α and Si II lines, while the Fe I line leads to a 25% lower value.     

Stille cross-coupling reaction of polyfluorovinylstannanes: Stereospecific synthesis of polyfluoro-alkenes and -α,β-unsaturated ketones

The palladium/copper (I) iodide cocatalyzed coupling reaction of (Z)-α-fluoro-β-trifluoromethylvinylstannanes 1 with aryl iodides 2 and acid chloride 4 has been explored affording substituted (E)-α-fluoro-β-trifluoromethylalkenes 3 and (E)-α-fluoro-β-trifluoromethyl-α,β-unsaturated ketones 5, respectively. The effect of cocatalyst, solvent as well as reaction temperature has been investigated in more detail. The geometric isomers were easily ascertained on the basis of their coupling constant () across the double bond and the retention of the configuration of the products for this conversion was found.     

Chemometric approach to open validation protocols: Prediction of validation parameters in multi-residue ultra-high performance liquid chromatography–tandem mass spectrometry methods

The recent technological advancements of liquid chromatography–tandem mass spectrometry allow the simultaneous determination of tens, or even hundreds, of target analytes. In such cases, the traditional approach to quantitative method validation presents three major drawbacks: (i) it is extremely laborious, repetitive and rigid; (ii) it does not allow to introduce new target analytes without starting the validation from its very beginning and (iii) it is performed on spiked blank matrices, whose very nature is significantly modified by the addition of a large number of spiking substances, especially at high concentration. In the present study, several predictive chemometric models were developed from closed sets of analytes in order to estimate validation parameters on molecules of the same class, but not included in the original training set. Retention time, matrix effect, recovery, detection and quantification limits were predicted with partial least squares regression method. In particular, iterative stepwise elimination, iterative predictors weighting and genetic algorithms approaches were utilized and compared to achieve effective variables selection. These procedures were applied to data reported in our previously validated ultra-high performance liquid chromatography–tandem mass spectrometry multi-residue method for the determination of pharmaceutical and illicit drugs in oral fluid samples in accordance with national and international guidelines. Then, the partial least squares model was successfully tested on naloxone and lormetazepam, in order to introduce these new compounds in the oral fluid validated method, which adopts reverse-phase chromatography. Retention time, matrix effect, recovery, limit of detection and limit of quantification parameters for naloxone and lormetazepam were predicted by the model and then positively compared with their corresponding experimental values. The whole study represents a proof-of-concept of chemometrics potential to reduce the routine workload during multi-residue methods validation and suggests a rational alternative to ever-expanding procedures progressively drifting apart from real sample analysis.     

The Soave,Twu and Boston–Mathias alpha functions in cubic equations of state: Part I. Theoretical analysis of their variations according to temperature

A theoretical analysis of the strengths and weaknesses of the Soave, Twu and Boston–Mathias attractive terms was performed with the Redlich–Kwong EoS. Special attention was paid to the variations of the alpha functions and their first and second derivatives with respect to temperature. Contrary to the Soave function, abnormal behaviors of the derived Twu and Boston–Mathias functions were evidenced in the temperature range commonly covered by industrial applications. The unsuccessful variations of the derived alpha functions observed with these two last models strengthen the interest of the Soave equation for the modeling of derived thermodynamic properties. The accuracy of pure component data modeling by means of the cubic equation of state is discussed in a second part.     

Two-dimensional liquid chromatography–ion trap mass spectrometry for the simultaneous determination of ketorolac enantiomers and paracetamol in human plasma: Application to a pharmacokinetic study

A bioanalytical method was developed for the simultaneous determination of paracetamol and ketorolac enantiomers in human plasma using two-dimensional liquid chromatography–mass spectrometry. Separation was first achieved in a reversed-phase C18 column by using a gradient solvent system consisting of 0.1% aqueous formic acid and acetonitrile (ACN). The effluent between 8.9 and 9.9 min, corresponding to phenacetin and racemic ketorolac peaks, was transferred to a polysaccharide-based chiral column (ChiralPak AD-RH) by using a six-port switching valve. Ketorolac enantiomers were subsequently separated on the chiral column using an isocratic mobile phase composed of ACN/0.1% formic acid 50:50 (v/v). The total run-time was less than 18 min. This innovative strategy prolongs the lifetime of chiral columns by avoiding damages due to the sample matrix. The detection was carried out with an ion trap mass spectrometer equipped with an electrospray ionisation source. The tested ranges were 0.05–20 μg/ml for paracetamol and 0.005–2 μg/ml for each ketorolac enantiomer. This method was fully validated and showed good performances in terms of trueness (80–110%) and precision (6.7–13.2%). The mean extraction recoveries were 60%, 72% and 76% for paracetamol, R-ketorolac and S-ketorolac, respectively. Finally, this procedure was successfully applied to a pharmacokinetic study.     

IgG adsorption on a new protein A adsorbent based on macroporous hydrophilic polymers: II. Pressure–flow curves and optimization for capture

Pressure–flow curves are obtained for a new protein A adsorbent matrix based on macroporous hydrophilic polymer beads with average diameter of 57 μm and a narrow particle size distribution. Experimental data are obtained in a 1 cm diameter laboratory column and in preparative scale columns with diameters of 20, 30, and 45 cm. The results are consistent with a model that assumes a linear relationship between bed compression and relative flow velocity. Surprisingly, the packing compressibility is essentially independent of column diameter for the preparative columns. As a result, after accounting for the variation in extraparticle porosity caused by compression, the column pressure drop is accurately predictable using the Carman–Kozeny equation. A model is also developed to predict productivity for IgG capture as a function of operating conditions based on dynamic binding capacity data presented in Part I of this work. For typical conditions, the model predicts maximum productivity at low residence times, between 1 and 1.5 min, when the dynamic binding capacity is at about 70–80% of the maximum. Combining the two models for column pressure and for dynamic binding capacity allows the design of preparative scale columns that maximize productivity while meeting specified pressure constraints.     

Elemental fluorine: Part 22. Fluorination of 3β-acetoxy-5α-androstan-17-one using fluorine and Selectfluor

Reactions of 3β-acetoxy-5α-androstan-17-one with elemental fluorine and Selectfluor^® are reported and give contrasting results. Fluorine gives a mixture of mono-fluorinated steroids in which fluorine atoms are attached to tertiary carbon sites whereas Selectfluor^® gives fluoro-steroid systems arising from electrophilic aliphatic substitution of the most sterically accessible secondary saturated positions. The identities of the fluoro-steroid products were determined by NMR analysis and X-ray crystallography.     

Qualitative detection of diuretics and acidic metabolites of other doping agents in human urine by high-performance liquid chromatography–tandem mass spectrometry: Comparison between liquid–liquid extraction and direct injection

Direct injection of urine has gained interest in the field of analytical toxicology, including doping control analysis. However, implementation of a direct urinalysis method for the LC–MS/MS detection of 34 diuretics and 9 other doping agents yielded several analytical problems, which were not observed using a traditional liquid–liquid extraction. Therefore a comparative study was made between liquid–liquid extraction and direct injection. Comparison of validation results showed that the liquid–liquid extraction at pH 7 allows to analyze samples without major drawbacks regarding matrix effects. Hence, good sensitivity was observed and detection limits ranged between 1 and 250 ng/mL for all compounds. In the direct injection approach shifted retention times were observed for several acidic and basic compounds due to unwanted matrix effects. This shift was reduced by a 25-fold dilution of the urine samples. Besides the improved retention time stability the diluted samples also exhibited lower ion suppression than the undiluted ones. After 25-fold dilution, detection limits ranged between 10 and 250 ng/mL for all compounds. Since these detection limits are at or below the minimum required performance level, imposed by the World Anti-Doping Agency, the method could be applied to routine anti-doping analysis. Samples, previously declared positive, were reanalysed using both the liquid–liquid extraction and direct injection. With both techniques all 26 samples were found to be positive, showing the applicability of direct injection for the analysis of diuretics.     

Reactions of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone: A convenient route to trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides

A new series of six 3-aryl-5-hydroxy-5-trifluoromethyl-4,5-dihydro-1H-1-picolinoylpyrazole hydrochlorides were synthesised in one-step in high yields by the reaction of β-methoxyvinyl trifluoromethyl ketones with 2-pyridinecarboxamidrazone in the presence of hydrochloric acid. The hydrochloride salts were easily converted to the respective new series of free trifluoromethylated 4,5-dihydro-1H-1-picolinoylpyrazoles using triethylamine in anhydrous diethyl ether. X-ray structure and NMR data from the pyrazole hydrochlorides are reported.     

Sodium dithionite initiated addition of CF2Br2 to β-pinene and reactions of the adduct: Synthesis and the reactivity of new 1,1-difluorodienes

Sodium dithionite effectively promotes the addition of dibromodifluoromethane to the exocyclic double bond of β-pinene. The reaction proceeded in a MeCN/H₂O system to give almost quantitatively an adduct, 1-(2-bromo-2,2-difluoroethyl)-4-(2-bromoisopropyl)-cyclohexene, as the sole product. On treatment of the adduct with 2,2,6,6-tetramethylpiperidine elimination of HBr only from the (CH₃)₂CHBr group occurred to give a mixture of regioisomeric dienes, while treatment with 50% KOH under phase transfer catalysis conditions or with K₂CO₃ in DMF resulted in total dehydrobromination to give trienes possessing an exocyclic CHCF₂ group. Surprisingly, the main course of the reactions of the adduct with DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) and also with t-BuOK in THF was elimination of HBr only from the CH₂CF₂Br group to afford 1-(2,2-difluorovinyl)-4-(2-bromoisopropyl)cyclohexene as the main product. Catalytic hydrogenation of the adduct followed by treatment with DBU afforded a conjugated diene, 1-(2,2-difluorovinyl)-4-isopropylcyclohexene. Compounds bearing the CHCF₂ group are new 1,1-difluorodienes which readily reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to give cycloadducts, derivatives of triazolo[1,2-α]cinnoline.     

Dynamic resolution of α-halo chiral esters for the synthesis of 3-substituted piperazin-2-ones

Dynamic resolution of α-halo esters derived from five chiral alcohols has been investigated in nucleophilic substitution with ethylenediamine nucleophiles. Stereoselective substitution of α-halo esters and following spontaneous cyclization provide a practical protocol for asymmetric syntheses of 3-substituted piperazin-2-ones up to 94:6 er.     

Structure-based study of antiamyloidogenic cyclic d,l-α-peptides

Protein misfolding and aggregation are the hallmarks of many devastating diseases. We have previously shown that cyclic d,l-α-peptide CP-2 reacts and stabilizes less toxic forms of amyloid β (Aβ), and protects the cells from Aβ-induced toxicity. Here, we performed extensive structure-based studies on CP-2 to elucidate the contribution of each residue to the total antiamyloidogenic activity and determine the interactions that are involved between CP-2 and Aβ. We showed that the hydrophobicity of CP-2 analogs correlates with their antiamyloidogenic potency, however, aromatic interactions are even more important for this activity. The antiamyloidogenic activity of CP-2 analogs also correlates with their ability to self-assemble, as shown by the critical micelle concentration measurements. The cell survival studies performed on rat pheochromocytoma PC-12 cells suggest that incorporation of an additional aromatic residue to the CP-2's sequence increases its protective effect against Aβ42-induced toxicity.     

Sodium dithionite initiated addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to β-pinene: Synthesis of CF3-substituted terpenoids

Sodium dithionite effectively promotes the addition of 1-bromo-1-chloro-2,2,2-trifluoroethane to the exocyclic double bond of β-pinene. The reaction proceeded in an MeCN/H₂O system to give almost quantitatively a 1:1 mixture of diastereoisomers of 4-(2-bromoisopropyl)-1-(2-chloro-3,3,3-trifluoropropyl)-cyclohexene (1). Dehydrobromination of 1 with pyridine gave a mixture of regioisomeric dienes 2 and 3, while treatment with DBU at elevated temperature resulted in total dehydrohalogenation to give trienes 4 and 5. Reduction of 1 with Bu₃SnH gave 1-(2-chloro-3,3,3-trifluoropropyl)-4-(isopropyl)cyclohexene (6) which on dehydrochlorination with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded conjugated diene, 4-isopropyl-1-(trans-3,3,3-trifluoropropenyl)-cyclohexene (7), with 50% overall yield. All the transformations proceeded with the retention of configuration at the carbon atom C-4 and the final compound 7 exhibited high optical activity.