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A simple analytical high-performance liquid chromatography (HPLC) method was applied for the enantiomeric excess determination of esomeprazole ((S)-OME), the enantiopure active ingredient contained in drug products, in the presence of its potential organic impurities A-E. The enantioselective separation was accomplished on the immobilized-type Chiralpak ID-3 chiral stationary phase (CSP) under reversed-phase conditions. The results were evaluated and compared with those obtained by the official enantioselective method of European Pharmacopoeia used as the reference for checking the enantiomeric excess of (S)-OME. It has been established that the use of the Chiralpak ID-3 CSP allows the determination of the enantiomeric purity of (S)-OME without any interference coming from its chiral and achiral related substances. The analytical procedure of the drug regulatory agencies based on the AGP CSP suffered instead from poor specificity due to overlap of the peaks pertinent to the achiral impurity A and the chiral impurity (R)-OME (impurity F).

(R,R)-oxaliplatin is an anticancer enantiopure active pharmaceutical ingredient. Little attention has been devoted to the analysis of its enantiomeric composition. The enantioselective HPLC method reported in the current Pharmacopoeias shows clear disadvantages with regard to the low resolution and long elution times. In this work, it has been proven the applicability of a last generation polysaccharide-based chiral stationary phase (CSP), i.e. the Chiralpak IC-3, in the enantioseparation of oxaliplatin. Experimental results demonstrated the benefits arising from the development of enantioselective hydrophilic interaction liquid chromatography (HILIC) based strategies. A baseline separation with resolution factor of 5.8 was achieved using a 100 mm × 4.6 mm I.D. IC-3 column set at the temperature of 40 °C and a mobile phase consisting of acetonitrile–water 100:5 mixture. At a flow rate of 1 mL min−1 the separation was completed within 8 min. The optimized method was proven to be sensitive with LOD and LOQ of the enantiomeric impurity of 0.07 and 0.21 μg mL−1, respectively.

Introduction In developed countries the phenomenon of pharmaceutical counterfeiting is steadily increasing through the illegal and the Internet market. Medicines for the treatment of erectile dysfunctions containing phosphodiesterase type 5 inhibitors (PDE5) are especially prone to falsification. Aims To obtain evidence of the health risks for patients taking these products and to provide useful information to general practitioners and specialists in sexual medicine. Methods First the samples were visually inspected and then analyzed to get information about their identity and quality. Main Outcome Measures A survey on the PDE5 medicines analyzed by the Italian official medicines control laboratory between 2005 and 2011 was performed. All the analyzed medicines were gathered from the Italian illegal market (seizures by police forces) or were bought from illegal online pharmacies. Results The study revealed that 24% of the analyzed samples were counterfeit and 54% were illegal medicines. In 12% of the cases an intermediate classification ( illegal/counterfeit ) was assigned. Only 7% of the samples were original. Moreover, the examination of the packaging evidenced potential risks: outer and immediate packaging missing; inconsistency between the carton box and the blister as regards the expiry date and/or the batch number; expiry date or manufacturer's name or country missing. Conclusions In 19% of the samples a potential health risk for patients was identified due to either the presence in the sample of more than one undeclared PDE5(s) or an amount of the active ingredient higher than that declared (up to 190% of the maximum dose) or to the presence of potentially dangerous excipients of non‐pharmaceutical origin or quality (e.g., gypsum or non‐purified talc). Gaudiano MC, Manna L, Rodomonte AL, Bartolomei M, Bertocchi P, Gallinella B, Antoniella E, Muleri N, Civitelli G, Alimonti S, Romanini L, Rufini L, and Valvo L. A survey on illegal and counterfeit medicines for the treatment of erectile dysfunctions in Italy. J Sex Med 2012;9:2130–2137.

A set of ten C5-chiral 4,5-dihydro-(1H)-pyrazole derivatives was synthesized and analyzed by high-performance liquid chromatography (HPLC) on the polysaccharide-based Chiralcel OJ-H chiral stationary phase (CSP). The enantioseparations were carried out using pure ethanol as eluent. Different structural elements of the investigated compounds were recognized for obtaining a very high enantioselectivity. In order to clarify some aspects of the chiral discrimination process, the thermodynamic parameters associated to the enantiorecognition and the enantiomer elution order were established.

Analytical and semipreparative high-performance liquid chromatography (HPLC) enantioseparation of the proton-pump inhibitor omeprazole (OME) and its potential organic chiral impurities were accomplished on the immobilised-type Chiralpak IA chiral stationary phase (CSP) under both polar organic and normal-phase conditions. The (S)-enantiomers were isolated with a purity of >99% ee and their absolute configuration was empirically assigned by circular dichroism (CD) spectroscopy. A chemo- and enantioselective HPLC method was validated to control the enantiomeric purity of the (S)-enantiomer of OME (ESO), an active ingredient contained in drug products, in the presence of chiral and achiral related substances. The precision, linearity and accuracy of the determination of the (R)-impurity as well as the recovery of ESO from a pharmaceutical preparation were determined. The proposed method uses the mixture methyl tert-butylether (M t BE)–ethyl acetate (EA)–ethanol (EtOH)–diethylamine (DEA) 60:40:5:0.1 (v/v/v/v) as a mobile phase. In these conditions, linearity over the concentration range 0.5–25 μg/ml for (R)-enantiomer was obtained. The limits of detection and quantification were 99 and 333 ng/ml, respectively. The intra and inter-day assay precision was less than 2% (RSD%).

Novel 1-(4-arylthiazol-2-yl)-2-(3-methylcyclohexylidene)hydrazine derivatives have been investigated for their ability to inhibit selectively the activity of the human B isoform of monoamine oxidase. These compounds were obtained as racemates and (R)-enantiomers by a stereoconservative synthetic pattern in high yield and enantiomeric excess. The (S)-enantiomers of the most active derivatives have been separated by enantioselective HPLC. All compounds showed selective activity against hMAO-B with IC(50) ranging between 21.90 and 0.018 microM.

A simple high-performance liquid chromatography (HPLC) method with ultraviolet diode array (UV-DAD) and electrospray ionisation mass spectrometry (ESI-MS) detection has been developed for the determination of vardenafil, sildenafil, tadalafil, testosterone, procaine, lidocaine, prilocaine, and benzocaine in cosmetic creams sold as promising remedies for male erectile dysfunction and female genitals stimulation. The presence of these substances in commercial cosmetic samples is prohibited. Aliquots (1 g) of the cosmetic creams under investigation were diluted 1:100 in methanol, subjected to ultrasonic treatment, added with benzoic acid as internal standard, and analyzed by HPLC–DAD and HPLC–ESI-MS after a further 1:1000 dilution. The compounds were separated by reversed phase chromatography with water (0.02% trifluoroacetic acid) and acetonitrile gradient elution and detected by UV-DAD at 228, 255 and 290 nm and by ESI-MS positive ionisation mode. Benzoic acid was used as internal standard. Linearity was studied with UV-DAD detection from 2.5–7.8 to 250 μg/g range, depending on the different compounds and with ESI-MS in the 3.3–8.9 to 250 ng/g range. Good determination coefficients ( r 2 ≥ 0.99) were found in both UV-DAD and ESI-MS. Limits of quantifications ranged between 2.5 and 7.8 μg/g for HPLC–UV-DAD assay and between 3.3 and 8.9 ng/g for HPLC–ESI-MS assay depending on different analyzed substances. At three concentrations spanning the linear dynamic ranges of both UV-DAD and ESI-MS assay, mean recoveries were always higher than 90% for the different analytes and intra-assay and inter-assay precision always better than 15% and 12%. This method was successfully applied to the analysis of substances under investigations present in cosmetic creams, freely sold on the Internet web-sites.

High-performance liquid chromatography (HPLC) enantioseparation of terazosin (TER) was accomplished on the immobilised-type Chiralpak IC chiral stationary phase (CSP) under both polar organic and reversed-phase modes. A simple analytical method was validated using a mixture of methanol–water–DEA 95:5:0.1 (v/v/v) as a mobile phase. Under reversed-phase conditions good linearities were obtained over the concentration range 8.76–26.28 μg mL −1 for both enantiomers. The limits of detection and quantification were 10 and 30 ng mL −1 , respectively. The intra- and inter-day assay precision was less than 1.66% (RSD%). The optimised conditions also allowed to resolve chiral and achiral impurities from the enantiomers of TER. The proposed HPLC method supports pharmacological studies on the biological effects of the both forms of TER and analytical investigations of potential drug formulations based on a single enantiomer. At the semipreparative scale, 5.3 mg of racemic sample were resolved with elution times less than 12 min using a mobile phase consisting of methanol–DEA 100:0.1 (v/v) and both enantiomers were isolated with a purity of ≥99% enantiomeric excess (ee). The absolute configuration of TER enantiomers was assigned by comparison of the measured specific rotations with those reported in the literature.

A reversed-phase high-performance liquid chromatography (HPLC) method was developed for evaluating the chiral discrimination ability of Chiralpak IA chiral stationary phase (CSP) towards flavanone. The effect of the nature and pH buffer as well as nature of alcohol modifier on enantioselectivity was investigated. Comparative study of enantioseparation in reversed-phase and polar organic conditions indicated a significative improvement in resolution when aqueous-based eluents were used. The developed reversed-phase chromatographic method was able to separate the enantiomers of flavanone from its isomeric form, the 2'-hydroxychalcone. The stereochemical stability of flavanone was studied by classical off-column HPLC kinetic procedures in aqueous and non-aqueous media. It was clearly demonstrated that the 2'-hydroxychalcone was involved as intermediate in the on-column and off-column enantiomerization process of flavanone.

Pyrrolylethanoneamines 1-12, 18-23 and related amino alcohols 13-15, 24-27 were synthesized and tested against monoamine oxidases A and B (MAO-A and MAO-B) enzymes. In general, aminoketones 1-12, 18-23 were found to be potent and selective MAO-A inhibitors. In particular, 18 was more potent and selective against the MAO-A isoenzyme than reference drugs. Interestingly, amino alcohol 25 selectively inhibited MAO-B enzyme and could be a lead compound for designing more potent and selective MAO-B inhibitors.

The enantiomeric separation of a series of imidazole analogues of Fluoxetine and Miconazole endowed with potent antifungal activity was performed using cellulose tris(4-methylbenzoate) (Chiralcel OJ) and cellulose tris(3,5-dimethylphenylcarbamate) (Chiralcel OD) as chiral stationary phases. Binary mixtures of n-hexane and alcohol as well as pure alcohols (ethanol or 2-propanol) were used as eluents. The enantiomer elution order was monitored by chiroptical detectors based on on-line optical rotation and circular dichroism measurements. For some of the compounds studied very high enantioseparation factor values (alpha > 7) on Chiralcel OJ CSP were observed. In order to study the chiroptical characteristics of the two most biologically active compounds, chromatographic resolutions were carried out on a semipreparative scale. Assignment of the absolute configuration was empirically established by comparing the CD spectra of the separated enantiomers with those obtained from the enantiomers of Miconazole.

A simple and efficient strategy to convert the racemic mixture of 8-chloro-2-(2,6-difluorophenylmethyl)-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-one 1,1-dioxide, a new anti-HIV-1 agent targeted to reverse transcriptase, into the more active (S)-enantiomer is described. The method utilizes repetition of the following two steps: 1) semipreparative enantioseparation by HPLC on chiral stationary phase; 2) base-induced racemization of the less active (R)-enantiomer.

A chiral high performance liquid chromatography method was developed for the resolution of the enantiomers of two new β-aminoalcohols, isamoltane and enciprazine. The separation of the enantiomers was accomplished, without any derivatization, on a chiral column containing 3,5-dimethylphenylcarbamate of cellulose (Chiralcel OD) as chiral selector. The effects of diethylamine, organic modifiers (ethanol and 2-propanol) and temperature were studied. The α and Rs values of isamoltane and enciprazine ranged, respectively, from 1.25 to 2.03 and from 0.80 to 5.16. The optimized conditions were used for a semipreparative chromatographic separation to determine the elution order of the enantiomers.

Coupled achiral-chiral high-performance liquid chromatography (HPLC) with an achiral amino-based column coupled with a chiral amylose-based column has been used for qualitative and quantitative determination of the potential chiral and achiral impurities of Voriconazole (UK-109,496), a new antifungal agent with two stereogenic centres. The effect of the organic mobile-phase modifier, ethanol, was studied. The assay response was linearly dependent on concentration over the range 1.2–40.4 μg for Voriconazole and 2.5–104.0 ng for the impurities. The limit of detection was 2.5 ng for each analyte.

High-performance liquid chromatography was employed for the determination of the optical purity of diphosphine and diphosphine oxide ligands of transition metals used in stereoselective reactions. The separation of the enantiomers was accomplished, without any derivatization, on chiral columns containing, as chiral selectors, urea derivatives [Supelcosil LC-(R)-Phenyl Urea and (R)-Naphthyl Urea] and cellulose carbamate derivative (Chiralcel OG). The use of these three columns is complementary. The mobile phases were optimised to obtain enantiomeric resolution. The α and Rs values ranged from 1.12 to 1.83 and from 0.62 to 4.97 on Supelcosil LC-(R)-Phenyl and (R)-Naphthyl Urea based columns, whereas α and Rs values were between 1.11 and 1.38 and 0.24 and 2.00 on a cellulose carbamate based column. Poor α and Rs values were obtained with columns containing tetrahydronaphthyl [(R,R)-Whelk-01] and cellulose derivatives (Chiralcel OJ) as chiral selectors. The method is capable of determining a minimum limit of 2.5 ng of each enantiomer of compound 1.

High-performance liquid chromatography (HPLC) was employed for the separation and determination of becliconazole, an imidazole derivative with antifungal activity containing a stereogenic centre, and its impurities. Chiral columns, containing carbamate of cellulose and amylose, were used. The effects of the organic modifiers, ethanol and 2-propanol, in the mobile phase, were studied. The HPLC method gave good performances from qualitative and quantitative standpoints, allowing the enantiomeric ratio of becliconazole and its impurities to be determined. The assay showed linearity over the range 400–4000 ng ml −1 for the impurities and 400–4000 μg ml −1 for becliconazole.

Four commercially available immobilized amylose-derived CSPs (Chiralpak IA-3, Chiralpak ID-3, Chiralpak IE-3 and Chiralpak IF-3) were used in the HPLC analysis of the chiral sulfoxides albendazole (ABZ-SO) and fenbendazole (FBZ-SO) and their in vivo sulfide precursor (ABZ and FBZ) and sulfone metabolite (ABZ-SO2 and FBZ-SO2) under organic–aqueous mode. U-shape retention maps, established by varying the water content in the acetonitrile- and ethanol–water mobile phases, were indicative of two retention mechanisms operating on the same CSP. The dual retention behavior of polysaccharide-based CSPs was exploited to design greener enantioselective and chemoselective separations in a short time frame. The enantiomers of ABZ-SO and FBZ-SO were baseline resolved with water-rich mobile phases (with the main component usually being 50–65% water in acetonitrile) on the IF-3 CSP and ethanol–water 100:5 mixture on the IA-3 and IE-3 CSPs. A simultaneous separation of ABZ (or FBZ), enantiomers of the corresponding sulfoxide and sulfone was achieved on the IA-3 using ethanol–water 100:60 (acetonitrile–water 100:100 for FBZ) as a mobile phase.

In the present study, the chromatographic behavior of two immobilized polysaccharide-derived chiral stationary phases (CSPs), the Chiralpak ID-3 and Chiralpak IE-3, under aqueous mobile phases conditions is presented. Four proton pump inhibitors (PPIs) (omeprazole, lansoprazole, pentaprazole and rabeprazole) were selected as test compounds. The effect of the concentration of water in the mobile phase was investigated with respect to its contribution to enantioselectivity and retention. Under acetonitrile-water mobile phase conditions, retention behavior evidenced an interesting pattern. At lower water content, the retention factors decreased with increasing water and at higher water content a reversed trend was observed. These findings support the hypothesis that two retention mechanisms operated successively on the same CSP: the HILIC (with water-poor eluents) and RPLC (with water-rich eluents) modes. The retention factors were minimum in the intermediate region, corresponding to a water concentration of about 20%. Interestingly, the baseline separation of all PPIs investigated was optimized under organic-aqueous mobile phases containing a high water content (from about 50 to 65%). Thus, the dual retention behavior of the PPIs on the Chiralpak ID-3 and Chiralpak IE-3 made it possible to reach greener and harmless enantioselective conditions in a short analysis time.

High-performance liquid chromatography (HPLC) was employed for the determination of dexfenfluramine together with the impurities l -fenfluramine (enantiomeric impurity), ortho -( d,l )-fenfluramine and para -( d,l )-fenfluramine in bulk powder and pharmaceutical formulations. The separation of the enantiomers was accomplished, without any derivatization, on a chiral column containing cellulose carbamate (Chiralcel OF) coupled with an achiral column. The effect of diethylamine and 2-propanol, added to the mobile phase was studied. The HPLC method gave good performances, allowing determination of the enantiomeric purity of dexfenfluramine together with the related impurities ortho - and para -( d,l )-fenfluramine. The method is capable of determining a minimum limit of 0.5% of l -isomer in commercial samples containing dexfenfluramine.

High-performance liquid chromatography (HPLC) was employed for the separation and determination of impurities[5-benzoyl-2-acetylthiophene (BAT), 5-benzoyl-2-ethylthiophene (BET) and ( RS )-5-benzoyl- α -methyl-3-thiopheneacetic acid (3-isomer of tiaprofenic acid) contained in bulk racemic tiaprofenic acid and pharmaceutical formulations. Chiral columns containing the 3,5-dimethylphenylcarbamate of cellulose and amylose were used. The effect of the orgaaic modifier, 2-propanol, in the mobile phase was studied. The HPLC method gave good performances from qualitative and a quantitative standpoints, allowing the enatiomeric ratios of taiprofenic acid and its 3-isomer to be determined together with the related impurities BAT and BET.

The best of both: SIRT1/2 inhibitors were developed by combining chemical features of selisistat (SIRT1-selective inhibitor; blue) and carprofen (anti-inflammatory drug; red). The most potent compound (shown) increased acetyl-p53 and acetyl-α-tubulin levels, and induced slight apoptosis at 50 μM in U937 cells, differently from selisistat and carprofen.

In this work, we report on the difference in performance of the two 3 μm particle-based Chiralpak IA-3 and Chiralpak AD-3 chiral stationary phases (CSPs) in the direct resolution of four racemic cinnamyl 2-aminoanilides, endowed with histone deacetylase inhibitory activity. The 3 μm CSPs were explored to determine if they could provide an effective resolution of enantiomers in presence of alcoholic eluents such as pure methanol, ethanol and 2-propanol. Temperature variable enantioselective HPLC and subsequent van’t Hoff analysis were performed. In most of cases the van’t Hoff plots were found to show a non-linear behaviour. The knowledge of the enantiomeric elution order associated with the data coming from enantioselective HPLC permitted to advance some hypothesis about the groups involved in chiral recognition mechanism.

An accurate and reproducible high-performance liquid chromatographic (HPLC) method has been developed and validated for the direct separation of individual enantiomers of lansoprazole, a potent proton pump inhibitor belonging to the family of the substituted benzimidazoles. The enantiomers were resolved on a Chiralpak IA by using a mobile phase consisting of methyl-tert-butyl ether (MtBE)-ethyl acetate (EA)-ethanol (EtOH)-diethylamine (DEA) in the ratio 60:40:5:0.1 (v/v/v/v). Baseline separation of the enantiomers of lansoprazole was obtained with a resolution factor of 8.14. The standard curves for the two enantiomers were linear (r(2)>0.999) in the concentration range of 10-80microg/ml with a working concentration of about 60microg/ml for each enantiomer. Apparent recovery was 100.8% with a relative standard deviation less than 2%. The limit of quantization for each enantiomer of lansoprazole was 0.22microg/ml. The intra-day precisions were in the range of 0.21-0.36 and 0.59-0.66 while the inter-day precisions were in the range of 0.55-1.24 and 0.66-1.19% in terms of retention times and area response RSD% for (R)-(+)- and (S)-(-)-lansoprazole, respectively. The method was also able to resolve impurities from the enantiomers of lansoprazole.

First baseline HPLC enantioseparation of kavain is described. Complete enantiodiscrimination was achieved on the immobilised-type Chiralpak IA chiral stationary phase (CSP) using pure methanol and simple methanol-water and ethanol-water mixtures as eluents. A water-dependent enantioselectivity was clearly demonstrated. Performance of the Chiralpak IA CSP in polar organic and RP conditions was compared with that of five coated polysaccharide-derived CSPs used in normal-phase mode.

The assignment of the absolute configuration of novel anti-inflammatory pyrrole derivatives has been accomplished by a combined strategy based on independent physical methods. The key step of our stereochemical characterization approach is the production at mg-scale of enantiomerically pure forms by HPLC on Chiralpak IA stationary phase.

The chiral resolving ability of the amylose-based Chiralpak IA chiral stationary phase towards omeprazole and other proton pump inhibitors under reversed-phase conditions was investigated. Organic modifier-buffer demonstrated to be a valid alternative elution mode with respect to conventional polar organic and normal-phases. No evidence of deterioration of performance of the enantioselective column after several multimodal cycles of elution was observed. Mobile phase composition was systematically changed in order to modulate the enantiomer elution order of set of compounds studied. A very simple method based on on-line detection of optical rotational sign during enantioselective HPLC was developed to assign the absolute configuration and enantiomeric elution order.

Objectives We evaluated whether the effectiveness of albendazole against encapsulated larvae increases when 2-hydroxypropyl-beta-cyclodextrin (HP-betaCD) is added to improve bioavailability. Methods Mice were infected with Trichinella spiralis and treated with albendazole alone, albendazole plus HP-betaCD or not at all (controls) (Experiment I). Both immediately after treatment [76 days post-infection (p.i.)] and later (139 days p.i.) larvae were recovered, and the mean count was expressed in proportion to the larva count for controls. To evaluate the infectivity of the recovered larvae, the larvae recovered at 76 days p.i. and 139 days p.i. were used to infect another three groups (Experiments II and III, respectively). Results At 76 days p.i., the percentage of larvae recovered was 77.4% for mice treated with albendazole alone and 61.2% for those treated with albendazole plus HP-betaCD; at 139 days p.i., these percentages were 67.4% and 40.9%, respectively (Experiment I). In Experiments II and III, the percentage of larvae collected from the albendazole group and the combined-treatment group was 55.2% and 27.6%, and 53.1% and 26.6%, respectively. The ABZSO active metabolite was analysed to determine the bioavailability of albendazole. For the combined-treatment group, the area under the plasma concentration-time curve between 0 and 6 h was higher than that for the albendazole group. Conclusions These data suggest that HP-betaCD increases the bioavailability and consequently the effectiveness of albendazole against encapsulated Trichinella larvae.

To determine whether the addition of a pre-S/S human vaccine increases the antiviral activity of lamivudine, four woodchucks were treated with a daily dose of 100 mg/kg lamivudine and four 50 microg doses of CHO-derived pre-S/S human vaccine. WHV DNA titres decreased up to two logarithms in three woodchucks. At week 4, in three of the animals, the sequence analysis showed a predominant strain containing a nucleotide change from A to T at position 1696 of domain B of the WHV DNA polymerase. Vaccination did not further suppress WHV DNA, despite anti-HBs production in three animals. The woodchuck remains a useful model for characterising the biology and kinetics of the emergence of drug-resistant variants and could be used for pre-clinical studies of combinations of new antiviral drugs.

Direct HPLC separation of stereoisomers of three novel 5-methyl-2-(alkylthio)-6-(2,6-difluorophenylalkyl)-3,4-dihydropyrimidin-4(3H)-ones endowed with antiviral and potential antiproliferative and morphological differentiation activity against melanoma cells was performed by using the new immobilised amylose-based Chiralpak IA chiral stationary phase. Stereoselective conditions were achieved using normal phase eluents containing “non-standard” solvents such as ethyl acetate, methyl tert-butyl ether, or dichloromethane. In order to study the chiroptical properties of single stereoisomers, mg-scale separations were performed on analytical and semipreparative size Chiralpak IA columns in combination with ethyl acetate-based eluents.

A newly developed procedure to reverse the enantiomer elution order of compounds resolved on chiral stationary phases (CSPs) for HPLC is presented. The optimized analytical protocol is based on the effect of temperature on enantioselectivity and does not involve any changing in mobile phase composition or type of CSP. In essence, the approach entails variable temperature chromatography at two temperatures. The enantiomer separation is performed at a low column temperature, with stopping the flow prior to elution of the less retained enantiomer. Then, the column temperature is changed with the peaks trapped inside the column, followed by elution with the same mobile phase in reverse direction. Under these conditions, the more pronounced loss in free energy of binding for the more strongly bound enantiomer results in an inversion of the elution order. This procedure may be applied to each enantiomer pair that is separated by chiral HPLC under an appreciable enthalpy-control.

The HPLC enantiomer separation of a novel series of C5-chiral 1-acetyl-3-(4-hydroxy- and 2,4-dihydroxyphenyl)-5-phenyl-4,5-dihydro-(1H)-pyrazole derivatives, with inhibitory activity against monoamine oxidases (MAO) type A and B, was accomplished using polysaccharide-based chiral stationary phases (CSPs: Chiralpak AD, Chiralcel OD, and Chiralcel OJ). Pure alcohols, such as ethanol and 2-propanol, and typical normal-phase binary mixtures, such as n-hexane and alcohol modifier, were used as mobile phases. Single enantiomers of several analytes examinated were isolated on a semipreparative scale, and their chiroptical properties were measured. The assignment of the absolute configuration was established for one compound by single-crystal X-ray diffraction method and for the other three by CD spectroscopy. The inhibitory activity against MAO of racemic samples and single enantiomers were evaluated in vitro. Chirality 16:625–636, 2004. © 2004 Wiley-Liss, Inc.

Optically active synthetic and semisynthetic polymers were utilized as chiral stationary phases (CSPs) for the direct chromatographic enantioseparation of a series of 8-chloro-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-one and thione 1,1-dioxide. Evaluation of stereochemical integrity of chiral analytes was assessed by enantioselective temperature and flow-dependent HPLC. A stopped-flow high-performance liquid chromatography (sfHPLC) procedure was developed for the determination of the rate constants and free energy barriers of enantiomerization of enantiomers of 8-chloro-2-(3-methyl-but-2-enyl)-2,3-dihydro-3-methyl-1,2,5-benzothiadiazepin-4(5H)-thione 1,1-dioxide (compound 2) in the presence of Chiraspher and Chiralcel OD CSPs. In order to study the chiroptical properties of the individual enantiomers of analytes investigated, semipreparative chromatographic resolutions were performed. The assignment of the absolute configuration was empirically established by comparing the CD spectra of the separated enantiomers with those obtained from structural analogues.

A stereospecific high-performance liquid chromatography method for the determination of trans-(-)-paroxetine and its enantiomer in bulk raw material and pharmaceutical formulations was developed and validated. The enantiomeric separation was achieved, without any derivatization, on a carbamate derivative-based column (Chiralpak AD). The effect of the organic modifiers, 2-propanol and ethanol, in the mobile phases was optimised to obtain enantiomeric separation. Limits of detection and quantitation of 2 and 6 ng, respectively, were obtained for both of the enantiomers. The linearity was established in the range of 5-41 microg for trans-(-)-paroxetine and in the range of 10-160 ng for trans-(+)-paroxetine. The accuracy of the method was 102.3% (mean value) for trans-(-)-paroxetine and 99.9% (mean value) for trans-(+)-paroxetine. For the precision (repeatability), a relative standard deviation value of 1.5% (mean value) for trans-(-)-paroxetine and of 2.1% (mean value) for trans-(+)-paroxetine was found. The method is capable of determining a minimum limit of 0.2% of trans-(+)-isomer in commercial samples.

A study of a multiple high-performance liquid chromatographic procedure for the separation of 30 different corticosteroids is described. Normal- and reversed-phase general methods operating in a wide polarity range have been developed for the rapid screening of multicomponent mixtures. The complementary application of both normal- and reversed-phase methods could permit clarification of uncertainty deriving from analyses performed by only one method.

A study of an HPLC method for the analysis of related substances in triamcinolone acetonide is described. Several systems of solvents and samples of different lots and preparative origins were examined and a rapid-scanning diode array UV detector (DAD) was particularly useful. With the proposed technique it was possible to identify 9 alpha-bromo desonide as a principal impurity, which was present in all examined samples of triamcinolone acetonide. This identification was rendered possible by the investigation of the second derivative of the UV spectra and by means of study of the mass spectrum. Furthermore, it was possible, primarily on the basis of the spectrophotometric data, to formulate reliable hypotheses on the possible identification of 9 beta, 11 beta-epoxide of the desonide which was present at very low levels and to exclude the presence of 11-deoxy-9(11)-unsaturated desonide. The presence of the above-mentioned related substances was explained considering the scheme of synthesis described in the literature. The spectrophotometric characteristics of the studied compounds and the limits of applicability of the present procedure are discussed.

A method for the analysis and identification of the principal related substances in 9 alpha-fluoroprednisolone acetate is described. This compound has been chosen as a model for the investigation of related substances which can be originated in the general procedure for introducing a fluorine substituent at position 9 of a corticosteroid molecule. HPLC procedures, both in reversed and in normal phase were used; a rapid scanning UV detector which allows direct spectrophotometric data to be obtained on chromatographic peaks, proved to be a tool of great importance. Thus, after reversed-phase chromatographic separation and observation of the UV spectra and their respective second derivatives, it was possible to characterize some of the principal effective and potential related substances such as 9 alpha-fluorohydrocortisone acetate, 9 alpha-bromoprednisolone acetate, 9 beta, 11 beta-epoxyprednisolone acetate and 9(11)-dehydroprednisolone acetate, emerging as chromatographic peaks. Identification of 9 alpha-bromoprednisolone acetate and of 9 alpha-fluorohydrocortisone acetate which proved to be the most significant impurities, was confirmed by means of an exhaustive study of the mass spectra of these substances conveniently isolated by normal-phase HPLC. The chromatographic, spectrophotometric and mass-spectrometric characteristics of the studied compounds are reported.

Some HPLC procedures with isocratic or gradient elution are reported for the identification and determination of most of the characteristic components of cortical extracts. The proposed solvent systems were: A) for normal phase chromatography, mixtures of chloroform-methanol-water on silica columns. B) For reversed phase chromatography, mixtures of methanol-water or acetonitrile-water or tetrahydrofuran-water on octadecyl silica columns of different brands. With these systems it was possible to identify and determine, in addition to the principal corticosteroids, some minor components of the cortical extracts as the 20β-dihydroderivatives of compounds F, E, A, B, the 17-ketosteroids adrenosterone, 11β-hydroxyandrostendione and androstendione and finally, progesterone and 17-OH progesterone. In reversed phase chromatography it was also possible, by monitoring the effluent at 205 nm, to reveal the 5α- and 5β-tetrahydroderivatives of the main corticosteroids and to separate them from most of the steroidal components of the adrenal extracts; in these conditions it was also possible to reveal some characteristic, unknown components of the cortical extracts. Some results of quantitative analysis of cortical extracts are also reported, comparing different analytical procedures.

A liquid chromatographic procedure is described for the analysis of the principal natural corticosteroids in extracts of adrenal glands. Microparticulate silicic acid columns and gradients of methanol in chloroform are used: conditions are described for the quantitative analysis of the single principal steroidal components of adrenal extracts for pharmaceutical use and of adrenal extracts of rats. It the last case, the use of a 5-μm silica column with the appropriate gradient allows the determination of corticosterone and of 18-hydroxydeoxycorticosterone, which were identified by means of mass spectromety on their eluates. A single analysis can be performed on the extract of 15 mg of rat adrenal tissue. For the last type of analysis, isocratic conditions on a 10-μm LiChrosorb Diol column are also described. The application of the gradient elution procedure to the analysis of steroidal compounds in human plasma is also described.

A rapid, simple and specific high performance liquid chromatographic procedure for assaying alpha- and beta-carotene is described. The method also enables the simultaneous determination of retinol and dl-alpha-tocopherol in human serum. The same chromatographic procedure can be used to assay the major carotenoids in human serum, provided analyses are replicated and the effluent is monitored at 450 nm. The conditions described also enable determination of licopene, cryptoxanthine and lutein with zeaxanthine. An aliquot of 0.5 ml serum is deproteinized with ethanol (0.5 ml) and extracted with petroleum ether (0.75 ml). The petroleum ether extract is evaporated until dry and then redissolved immediately with 0.5 ml of an eluent mixture consisting of methanol-hexane (85:15, v/v). Aliquots of 50 microl are then injected onto a 250 x 4.6 mm column packed with Spherisorb ODS-2. Owing to its good reproducibility, the procedure can be used for assays with external standards. Clinical applications are described for cases of hypercarotinemia associated with endocrine dysfunctions such as hypothyroidism and diabetes.