Application of evaporative light scattering detection to the characterization of combinatorial and parallel synthesis libraries for pharmaceutical drug discovery

Modulation of kanamycin B and kanamycin A biosynthesis in Streptomyces kanamyceticus via metabolic engineering

Both kanamycin A and kanamycin B, antibiotic components produced by Streptomyces kanamyceticus, have medical value. Two different pathways for kanamycin biosynthesis have been reported by two research groups. In this study, to obtain an optimal kanamycin A-producing strain and a kanamycin B-high-yield strain, we first examined the native kanamycin biosynthetic pathway in vivo. Based on the proposed parallel biosynthetic pathway, kanN disruption should lead to kanamycin A accumulation; however, the kanN-disruption strain produced neither kanamycin A nor kanamycin B. We then tested the function of kanJ and kanK. The main metabolite of the kanJ-disruption strain was identified as kanamycin B. These results clarified that kanamycin biosynthesis does not proceed through the parallel pathway and that synthesis of kanamycin A from kanamycin B is catalyzed by KanJ and KanK in S. kanamyceticus. As expected, the kanamycin B yield of the kanJ-disruption strain was 3268±255 μg/mL, 12-fold higher than that of the original strain. To improve the purity of kanamycin A and reduce the yield of kanamycin B in the fermentation broth, four different kanJ- and kanK-overexpressing strains were constructed through either homologous recombination or site-specific integration. The overexpressing strain containing three copies of kanJ and kanK in its genome exhibited the lowest kanamycin B yield (128±20 μg/mL), which was 54% lower than that of the original strain. Our experimental results demonstrate that kanamycin A is derived from KanJ-and-KanK-catalyzed conversion of kanamycin B in S. kanamyceticus. Moreover, based on the clarified biosynthetic pathway, we obtained a kanamycin B-high-yield strain and an optimized kanamycin A-producing strain with minimal byproduct.

Statistical Optimization of Evaporative Light Scattering Detection for Molten Sucrose Octaacetate and Comparison With Ultraviolet Diode Array Detection Validation Parameters Using Tandem HPLC Ultraviolet Diode Array Detection/Evaporative Light Scattering Detection-Specific Stability-Indicating Method

A sucrose octaacetate (SOA) gradient HPLC evaporative light scattering detection (ELSD) and low-wavelength UV-diode array detection (UV-DAD)-specific stability-indicating method development and validation comparison is reported. A central composite response surface design and multicriteria optimization was used to maximize molten SOA area-under-the-curve response and signal-to-noise ratio. The ELSD data were also analyzed using multivariate principal component analysis, analysis of variance, and standard least squares effects modeling. The method suitability and validation parameters of both methods were compared. To the authors' knowledge, this is the first report that validates an ELSD method using a molten analyte. SOA exhibited a low molar absorptivity of 439 absorption units/cm/M in water at 210 nm requiring low-wavelength UV-DAD detection. The low-wavelength UV-DAD method provided substantially better intraday and interday precision, intraday and interday goodness-of-fit, detection limit, and quantitation limit than ELSD. ELSD exhibited a 60-fold greater area-under-the-curve response, better resolution, and 58% more theoretical plates. On balance, the UV-DAD method was chosen for SOA chemical kinetic studies. This study illustrates that ELSD may not always be the best alternative to gradient HPLC low-wavelength UV detection.

Antihyperlipidemic effect of Cyclocarya paliurus (Batal.) Iljinskaja extract and inhibition of apolipoprotein B48 overproduction in hyperlipidemic mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cyclocarya paliurus (CP) Batal., the sole species in its genus, is a native plant to China. As a traditional Chinese folk medicine, the tree leaves have been widely used for the treatment of metabolic disorders, including hyperlipidemia, obesity, diabetes and hypertension.

AIM OF THE STUDY

The study aimed to evaluate the antihyperlipidemic effect of CP ethanol extract, as well as its inhibitory activity on apolipoproteinB48 (apoB48), in normal and hyperlipidemic mice.

MATERIALS AND METHODS

The antihyperlipidemic effect of CP was evaluated in hyperlipidemic mice induced by high-fat diet for 4 weeks. CP ethanol extract (0.37, 0.75 and 1.5g/kg/day) was orally administrated once daily. Lipids and antioxidant profiles, including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), together with the indices of hepatic and renal functions were examined. RT-qPCR and western blotting were used to analysis the expression levels of tumor necrosis factor (TNF-α), total- and triglyceride-rich apoB48 (TRL-apoB48), as well as the phosphorylation of the mitogen-activatein kinase (MAPK).

RESULTS

CP as well as simvastatin remarkably lowered the levels of TC, TG, LDL-C and MDA, and at the same time, elevated the HDL-C, SOD and GSH-Px in high-fat diet mice. It also decreased the serum concentration of total- and TRL-apoB48 in the fasting state. CP inhibited TNF-α expression and phosphorylation level of MAPK. Furthermore, the HE staining of liver and kidney, together with hepatic and renal function analysis showed hepato- and renoprotective activities of CP.

CONCLUSIONS

These results suggested that CP possesses beneficial potentials for use in treating hyperlipidemia and the underlying lipid-lowering mechanism might associate with a down-regulation of the intestinal-associated lipoprotein apoB48, which may provide evidence about its practical application for treating hyperlipidemia and its complications.

Automated high-throughput system to fractionate plant natural products for drug discovery

The development of an automated, high-throughput fractionation procedure to prepare and analyze natural product libraries for drug discovery screening is described. Natural products obtained from plant materials worldwide were extracted and first prefractionated on polyamide solid-phase extraction cartridges to remove polyphenols, followed by high-throughput automated fractionation, drying, weighing, and reformatting for screening and storage. The analysis of fractions with UPLC coupled with MS, PDA, and ELSD detectors provides information that facilitates characterization of compounds in active fractions. Screening of a portion of fractions yielded multiple assay-specific hits in several high-throughput cellular screening assays. This procedure modernizes the traditional natural product fractionation paradigm by seamlessly integrating automation, informatics, and multimodal analytical interrogation capabilities.

Metabolite quantitation: detector technology and MIST implications

HPLC detector technology has advanced dramatically over the past 20 years, with a range of highly sensitive and specific detectors becoming available. What is still missing from the bioanalyst’s armoury, however, is a highly sensitive detector that gives an equimolar response independent of the compound. This would allow for quantification of compounds without the requirement for a synthetic standard or a radiolabeled analogue. In particular, such a detector applied to metabolism studies would establish the relative significance of the various metabolic routes. The recently issued US FDA guidelines on metabolites in safety testing (MIST) focus on the relative quantitation of human metabolites being obtained as soon as feasible in the drug-development process. In this article, current detector technology is reviewed with respect to its potential for quantitation without authentic standards or a radiolabel and put in the context of the MIST guidelines. The potential for future developments are explored.

Improving the universal response of evaporative light scattering detection by mobile phase compensation

Mobile phase compensation, first reported for the charged aerosol detector (CAD), was used as a suitable method to overcome problems related to the mobile phase-dependent response of the evaporative light scattering detector (ELSD). Mobile phase compensation was effectively performed both in the flow injection- and in gradient modes. Without compensation, the response factors of the ELSD for six sulfonamide drugs differed by a factor of two when varying the mobile phase composition between 10 and 90% acetonitrile. This change could be effectively eliminated using the technique of mobile phase compensation, where a secondary pump with a reversed gradient was used to provide the detector with a constant composition of the mobile phase. For identical experimental conditions, the ELSD showed a nearly constant, albeit somewhat reduced, response with compensation. This indicates that under such conditions, the ELSD behaved as a concentration-sensitive detector. The analysis of sulfonamides drugs at 0.05% level using gradient UPLC-ELSD separation with mobile phase compensation is demonstrated.

Development of a novel liquid chromatography--evaporative light scattering detection method for bacitracins and applications to quality control of pharmaceuticals

A novel liquid chromatography method for the direct determination of bacitracin main components (Bc-A, -B1, -B2 and -B3), a basic, cyclic polypeptide antibiotic, was developed and validated, based on ion pairs formation with trifluoroacetic acid (TFA) and evaporative light scattering detection (ELSD). The selected analytical column was the Waters Nova-pak C8 (3.9 x 150 mm), for which the optimum (using modified Simplex algorithm) mobile phase was H2O-ACN (73:27, v/v) containing 0.80 microL mL(-1) of TFA, at a flow rate of 1.0 mL min(-1). Optimized ELSD parameters were: nebulizing gas (nitrogen) pressure=3.5 bar, evaporation temperature=50 degrees C, detector gain=12. Retention time of Bc-B1, -B2, -B3, -A and -F (oxidative degradation product of Bc-A) was 5.3, 5.8, 7.7, 8.7, 15.9 min, respectively, while zinc ions and related peptides were eluted at 1.3-1.9 min. A logarithmic calibration curve was obtained for each component (r>0.998), while the concentration range of total bacitracin was 30-235 microg mL(-1). Detection limits for the individual components were in the range 1.0-1.6 microg mL(-1). The proposed method was applied for the direct determination of Bc components and related peptides in raw materials and pharmaceutical formulations (tablets, powder and aerosol) without tedious pretreatment (for tablets, a liquid-liquid extraction of magnesium with oxine was required). In the case of matrix interference, synthetic standards containing the same amounts of excipients or the standard addition technique were used. Recovery from spiked commercial formulations was ranged from 96.7% to 101.5% (in respect of total Bc).

Development and validation of a novel LC non-derivatization method for the determination of amikacin in pharmaceuticals based on evaporative light scattering detection

A novel method for the direct determination of the aminoglycoside antibiotic amikacin and its precursor component kanamycin was developed and validated, based on reversed phase LC with evaporative light scattering detector (ELSD). ELSD response to amikacin was found to be enhanced by: (a) use of ion-pairing acidic reagents of increased molecular mass, (b) increase of mobile phase volatility and (c) decrease of peak width and asymmetry (obtained by controlling the mobile phase acidity and/or ratio of organic solvent to water). Utilizing a Thermo Hypersil BetaBasic C(18) column, the selected optimized mobile phase was water-methanol (60:40, v/v), containing 3.0 mll(-1) nonafluoropentanoic acid (18.2mM) (isocratic elution with flow rate of 1.0 mlmin(-1)). ELSD experimental parameters were: nitrogen pressure 3.5 bar, evaporation temperature 50 degrees C, and gain 11. Amikacin was eluted at 8.6 min and kanamycin at 10.4 min with a resolution of 1.5. Logarithmic calibration curves were obtained from 7 to 77 microgml(-1) (r>0.9995) for amikacin and 8 to 105 microgml(-1) (r>0.998) for kanamycin, with a LOD equal to 2.2 and 2.5 microgml(-1), respectively. In amikacin sulfate pharmaceutical raw materials, the simultaneous determination of sulfate (t(R)=2.3 min, LOD=1.8 microgml(-1), range 5-40 microgml(-1), %R.S.D.=1.1, r>0.9997), kanamycin and amikacin was feasible. No significant difference was found between the results of the developed LC-ELSD method and those of reference methods, while the mean recovery of kanamycin from spiked samples (0.5%, w/w) was 97.3% (%R.S.D.<or=2.0, n=6). Further, the developed method was applied for the determination of amikacin in pharmaceutical formulations (injection solutions) without any interference from the matrix (recovery from spiked samples ranged from 95.6 to 103.8%).

HPLC determinations of enantiomeric ratios

Evaporative light-scattering detection (ELSD) is widely applied in the HPLC analysis of organic compounds lacking a UV chromophore. However, this detection method is generally unsuitable for determination of enantiomeric ratios (er). The er calculated from a UV trace and an ELS trace of the same compound differs significantly. Because of the nonlinear concentration response of the ELS detector, a compound with an er of 95:5 appears to be enantiomerically pure by ELS detection. It is possible to obtain a calibration curve and to calculate a correction factor, but this procedure is time consuming and therefore not very practical for routine analyses. In contrast, a charged aerosol detector allows a very accurate determination of the enantiomeric ratios. Like the ELS detection, the CA detection is independent of the chromophore properties of the substrate. Therefore, we recommend the use of CA instead of ELS detection for determination of the enantiomeric ratios of non-UV active compounds.

Synthesis of a Library of Complex Macrodiolides Employing Cyclodimerization of Hydroxy Esters

The synthesis of complex macrodiolides involving microwave-accelerated transesterification of chiral, nonracemic, hydroxy esters is described. Methodology development studies indicate that both microwave power and reaction temperature play an important role in the efficiency of cyclodimerizations. Hydroxy ester monomer pairs were evaluated using an analytical rehearsal leading to the preparation of a 127-member library of highly diverse and stereochemically well-defined macrodiolides. Preliminary assays identified a novel macrodiolide antagonist of the kappa opioid receptor.

Development and validation of a novel HPLC/ELSD method for the direct determination of tobramycin in pharmaceuticals, plasma, and urine

A novel method for the direct determination of the aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with evaporative light scattering detector (ELSD). Using a Waters ODS-2 C18 Spherisorb column with an evaporation temperature of 45 degrees C and nitrogen pressure of 3.5 bar, the selected mobile phase consisted of water/acetonitrile 55:45 containing 1.5 mL L(-1) HFBA (11.6 mM) in an isocratic mode at a rate of 1.0 mL min(-1). Tobramycin's retention time was 4.3 min with an asymmetry factor of 1.7. A logarithmic calibration curve was obtained from 1 to 38 microg mL(-1) (r > 0.9998). LOD was 0.3 microg mL(-1); within-day %RSD was 1.0 (n = 3, 4.7 microg mL(-1)) and between-day %RSD was 1.1 (3 days within a week). The developed method was applied to the determination of tobramycin in a pharmaceutical crude substance and formulations (eye drops and ointments). Dilution experiments revealed the absence of interference from excipients (no constant and proportional errors); recovery from spiked samples was 99-103% with %RSD < 2.2 (n = 3x3). The developed HPLC/ELSD method was also found to be applicable in the determination of tobramycin in human plasma (0.6-12.5 microg mL(-1)) and urine (1.5-12.5 microg mL(-1)) after solid-phase extraction using carboxylate cartridges followed by solvent evaporation (x2 preconcentration). A mean recovery of 86% for plasma and 91% for urine was obtained.

Gradient elution of organic acids on a β-cyclodextrin column in the polar organic mode and its application to drug discovery

A high performance liquid chromatographic method was developed that separated organic acids using the polar organic mode. The separation was obtained using a beta-cyclodextrin stationary phase with a mobile phase that was composed of acetonitrile/methanol/triethylamine (TEA)/acetic acid. The compounds were eluted under gradient conditions and the elution order depended on the number, type and position of the hydrogen bonding functional groups present in the molecule. Adjusting the acid to base ratio resulted in the biggest change in selectivity. In addition, increasing the methanol concentration decreased the retention times of the analytes, which had little effect on the selectivity. Using a certain set of conditions one could separate a large number of organic acids, which allowed these acids to be detected by UV and mass spectrometry. These conditions were used to evaluate the purity of potential pharmaceutical drug candidates that showed activity towards a kinase target vascular endothieal growth factor (Vegf). Each compound contained a carboxylic acid group that was critical to the activity. The method was able to give purity estimates of these samples, which were difficult to determine by other HPLC methods.

Development and validation of a novel LC/ELSD method for the quantitation of gentamicin sulfate components in pharmaceuticals

The equivalent response of evaporative light scattering detector (ELSD) for compounds of similar structure is exploited to develop an LC/ELSD method for the simultaneous quantitation of the four main components of gentamicin sulfate, using as external standard the one main component kanamycin. A C18 column was used along with a mobile phase consisting of H2O (containing 35.4 microg/ml of trichloroacetic acid and 0.89 microl/ml of trifluoroacetic acid)-methanol-acetonitrile (990:5:5, v/v/v), in an isocratic mode at 1.1 ml/min. Parameters of ELSD were 50 degrees C for evaporation temperature and 3.0 bar for pressure of carrier gas (N2). A logarithmic calibration curve was obtained for sulfate (tR = 1.9 min) from 4.2 to 150 microg/ml (r > 0.994) with a precision of 0.18%R.S.D. Kanamycin and the four gentamicin components (C(1a), C2, C(2a) and C1) were eluted at 3.2, 4.6, 5.9, 7.1 and 8.7 min, respectively, with good resolution (Rs > 1.5). Logarithmic calibration curve was obtained for each component (r > 0.99) with statistically equal slopes varying from 2.457 to 2.558. The mass range of total gentamycin was 35-240 microg/ml. The proposed method was applied for the determination of gentamicin components and sulfate in raw materials and pharmaceutical formulations (injection, drops and cream) without any pretreatment except cream, for which liquid-liquid extraction was required. Recovery from standard addition experiments in commercial formulations was 99-100% regarding total gentamicin and 89-108% regarding individual components, with a precision (%RSD, n = 4) 0.7-5.8%.

Screening of natural products extracts for the presence of phosphodiesterase inhibitors using liquid chromatography coupled online to parallel biochemical detection and chemical characterization

The ability to rapidly identify active compounds in a complex mixture (e.g., natural products extract) is still one of the major problems in natural products screening programs. An elegant way to overcome this problem is to separate the complex mixture by gradient liquid chromatography followed by online biochemical detection parallel with chemical characterization, referred to as high-resolution screening (HRS). To find and identify phosphodiesterase (PDE) inhibitors in natural products extracts using the HRS technology, the authors developed a continuous-flow PDE enzymatic assay. The suitability of the continuous-flow PDE enzymatic assay for natural products screening was demonstrated. After optimization of the continuous-flow PDE assay, the limit of detection for 3-isobutyl-1-methyl-xanthine (IBMX) was 1 muM, with a dynamic range from 1 to 100 muM IBMX. The applicability of the HRS technology for the detection of PDE inhibitors in natural products extracts was demonstrated by the analysis of a plant extract spiked with 2 naturally occurring PDE inhibitors. The plant extract was analyzed with 2 assay lines in parallel, enabling background fluorescence correction of the sample. The simultaneous quantification of the active compounds using evaporative light-scattering detection allowed the estimation of the IC(50) value of the active compounds directly in the crude extract.

Simultaneous separation and quantitation of four antiepileptic drugs—a study with potential for use in patient drug level monitoring

The purpose of this study was to illustrate the applicability of high-performance liquid chromatography (HPLC) coupled with evaporative light scattering detector (ELSD) in simultaneously separating and quantitating four commonly used antiepileptic drugs (AEDs). A mixture of the four AEDs were separated using a C8 column using volatile mobile phases and were detected using ELSD. Optimal instrumental conditions were obtained by assessing the effect of various critical experimental parameters such as evaporator tube temperature, carrier gas flow rate, photomultiplier gain on separation efficiency, accuracy, reproducibility and sensitivity of measurement on all four AEDs. A novel, rapid, accurate, sensitive, reproducible and robust HPLC-ELSD method for simultaneous separation and quantitation of four commonly used AEDs was developed. The physical basis of the results obtained as a consequence of varying several critical experimental parameters has been explained. This study illustrates the potential for use of HPLC-ELSD in drug level monitoring of patients undergoing mono- or polytherapy for epilepsy.

Quality control in combinatorial chemistry: determination of the quantity, purity, and quantitative purity of compounds in combinatorial libraries

The quality of combinatorial libraries determines the success of biological screening in drug discovery programs. In this paper, we evaluate and compare various methods for measuring identity, purity, and quantity (yield) of combinatorial libraries. Determination of quantitative purity reveals the true library quality and often indicates potential quality problems before full-scale library production. The relative purity can be determined for every member in a large library in a high-throughput mode, but must be cautiously interpreted. In particular, many impurities are not observable by relative purity measurements using detectors such as UV(214), UV(254), and evaporative light-scattering detection. These "invisible" impurities may constitute a significant portion of the sample weight. We found that TFA, plastic extracts, inorganic compounds, and resin washout are among these impurities. With compelling evidence, we reach a conclusion that purification is the only way to remove "invisible" impurities and improve the quantitative purity of any compound even though some compounds may have a high relative purity before purification.

Ammonium hydrogencarbonate, an excellent buffer for the analysis of basic drugs by liquid chromatography-mass spectrometry at high pH

Ammonium hydrogencarbonate buffer has been found to be especially useful for high-pH HPLC analysis of samples from both combinatorial and medicinal chemistry sources. Satisfactory results were obtained by the standard diode array, evaporative light-scattering, and MS detection by using this buffer at a concentration of 10 mM. From a practical standpoint, ammonium hydrogencarbonate is an ideal buffer for chromatographers since it provides excellent chromatographic behaviour and reproducible separation. In addition to this, its volatility makes it an essential tool for rapid LC-MS product identification. Ammonium hydrogencarbonate was tested for a number of drug-like compounds analysed as mixtures, and data obtained were compared to those from the classical and MS-friendly buffers widely used by chromatographers: trifluoroacetic and formic acids. The results of this study revealed the suitability of this buffer for routine HPLC application in research laboratories.

The automation of a commercial Fourier transform mass spectrometer to provide a quick and robust method for determining exact mass for the synthetic chemist

Automation of a commercially available Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer for the routine analysis of the synthetic products from high-speed chemistry is described. The automation includes software written by the instrument manufacturer and in-house developed software; allowing electronic submission of samples from the chemist and e-mailing of results back to the chemist. The use of samples of relatively high concentration (ca 1 mg x mL(-1)) is possible due to the protocol that has been developed, which includes dilution by the autosampler during sample injection. Though high concentrations are used for speed and convenience the amount of sample consumed is still small ca 15 microg per injection. The results from this method have been shown to be both accurate (average error +/- 0.91 ppm) and precise (-0.70 ppm to 2.26 ppm). The system is capable of analysing up to 800 samples per 24 hours. As high speed chemistry becomes more highly utilised within discovery the number of samples requiring accurate mass analysis will rise, and the method we have described will prevent high resolution mass spectrometry becoming the bottleneck in new chemical entity production. The accuracy and precision demonstrated by this method allows high confidence levels in assigned molecular formulae for expected compounds and reduces the number of possible formulae to consider when working with a compound that is not the desired product of a given reaction.

Determination of relative UV response factors for HPLC by use of a chemiluminescent nitrogen-specific detector

Ultraviolet (UV) absorbance is the most widely used detection method for high-performance liquid chromatography (HPLC) separations. In pharmaceutical analysis, purity determinations often include quantitation of related impurities based on relative HPLC peak areas obtained at a specific wavelength. In order for this quantitation to accurately reflect weight percentages of impurities, the relative UV response factors (absorptivities) at the given wavelength must be known. In this work, we present a convenient method for determining relative UV response factors on-line, without isolation or purification of impurities, without standards, and without requiring known analyte concentrations. The procedure described makes use of a chemiluminescent nitrogen-specific HPLC detector (CLND) in conjunction with a UV detector. The CLND response is directly proportional to the number of moles of nitrogen in each eluting peak, and can, therefore, be used to determine relative amounts of each nitrogen-containing impurity present in the sample, provided the molecular formulas are known (e.g. from exact mass LC-MS). It is a simple matter, then, to determine the relative UV response factors from the UV area ratios obtained for the same sample. The feasibility and accuracy of this method is demonstrated for gradient HPLC separations of commercially available compounds of widely varying structures. Finally, the method's utility in obtaining accurate mass balance is demonstrated by application to photodegradation of nifedipine.

High-throughput determination of identity, purity, and quantity of combinatorial library members using LC/MS/UV/ELSD

We have used a high-throughput LC/MS/UV/ELSD method to rapidly determine the absolute quantity and purity of 42 organic compounds from seven lead discovery libraries. A general calibration curve generated from a different set of 42 compounds with seven different scaffolds was used in this analysis. We have also studied 33 organic compounds with different molecular weight (MW) by LC/MS/UV/ELSD to investigate the effect of MW on ELSD response and the accuracy for purity and quantity measurement using UV(214) and ELSD. A general ELSD calibration curve from these compounds was also generated to quantify 42 library compounds. Purity measurement by ELSD underestimates the amounts of impurities due to a reduced ELSD response from smaller molecular weight impurities often produced in library synthesis. Absolute quantity determination by ELSD is more accurate (RSD 28%) than that by UV(214) (48%) using a calibration curve generated from the same set of compounds with diverse MWs. Error assessment for the measurement of absolute quantity of a class of commercial compounds and a class of representing reference compounds from seven diverse lead discovery libraries shows that structurally related compounds should be used to generate calibration curves to sustain smaller deviation.

Techniques for analysis and purification in high-throughput chemistry

The success of combinatorial chemistry, and the increased emphasis on single well-characterised compounds of high purity, has had a significant impact on analytical and purification technologies. The requirement for ever-increasing throughput has led to the automation and parallelisation of these techniques. Advances have also been made in developing faster methods to augment throughput further.

Mass spectrometry innovations in drug discovery and development

This review highlights the many roles mass spectrometry plays in the discovery and development of new therapeutics by both the pharmaceutical and the biotechnology industries. Innovations in mass spectrometer source design, improvements to mass accuracy, and implementation of computer-controlled automation have accelerated the purification and characterization of compounds derived from combinatorial libraries, as well as the throughput of pharmacokinetics studies. The use of accelerator mass spectrometry, chemical reaction interface-mass spectrometry and continuous flow-isotope ratio mass spectrometry are promising alternatives for conducting mass balance studies in man. To meet the technical challenges of proteomics, discovery groups in biotechnology companies have led the way to development of instruments with greater sensitivity and mass accuracy (e.g., MALDI-TOF, ESI-Q-TOF, Ion Trap), the miniaturization of separation techniques and ion sources (e.g., capillary HPLC and nanospray), and the utilization of bioinformatics. Affinity-based methods coupled to mass spectrometry are allowing rapid and selective identification of both synthetic and biological molecules. With decreasing instrument cost and size and increasing reliability, mass spectrometers are penetrating both the manufacturing and the quality control arenas. The next generation of technologies to simplify the investigation of the complex fate of novel pharmaceutical entities in vitro and in vivo will be chip-based approaches coupled with mass spectrometry.

Optical detection methods for combinatorial libraries

The main interests in the development of new combinatorial assays are the reduction of time for screening and an increase in the number of samples measured in parallel. The variety of detection methods is increasing, but the optimal one has not yet been determined. In the past two years, the first parallel detection methods for non-labelled compounds have been developed.

Solid phase synthesis and biological evaluation of enantiomerically pure wasp toxin analogues PhTX-343 and PhTX-12

PhTX-343 and PhTX-12, analogues of the natural polyamine wasp toxin PhTX-433, were synthesised in 40-60% yields as pure enantiomers using solid phase synthesis techniques. Capillary electrophoresis procedures were developed for chiral separation and determination of enantiomeric purity (ee) of the enantiomers of PhTX-343 and PhTX-12. The methods were optimised with respect to chiral selector, buffer pH, and temperature around the capillary. Thus, rac-PhTX-343 was resolved using a separation buffer containing 30 mM heptakis-(2, 6-di-O-methyl)-beta-cyclodextrin in 50 mM 6-aminocarproic acid (pH 4. 0) at 15 degrees C. rac-PhTX-12 was not resolvable in this system, but could be resolved using a separation buffer containing 10% w/v of dextrin 10, a linear maltodextrin, in 50 mM 6-aminocaproic acid (pH 4.0) at 15 degrees C. Using these methods, the optical purity of the synthetic enantiomers was determined to be ee > 99%. The enantiomers were also characterised by chiroptical methods. The antagonist potency of the enantiomers was tested on nicotinic acetylcholine receptors (human muscle-type nAChR) expressed in TE671 cells, ionotropic glutamate receptors in Xenopus laevis oocytes (expressing recombinant GluR1flop receptors), and locust muscle ionotropic glutamate receptors sensitive to quisqualate (qGluR). The potencies of each pair of enantiomers were similar (eudismic ratio close to 1).