High-performance liquid chromatography of uroporphyrinogen and coproporphyrinogen isomers with amperometric detection.

A reversed-phase h.p.l.c. system, with an ODS-Hypersil column with acetonitrile or methanol in ammonium acetate buffer as mobile phase, is described for the separation of uro-and copro-porphyrinogen isomers. The porphyrinogens are detected amperometrically with sensitivity comparable with that of the fluorescent detection of porphyrins. The effects of pH, buffer concentration and organic modifiers on retention and resolution were studied. The method is suitable for both analytical and preparative separation of porphyrinogens.     

Isolation and characterization of three positional isomers of diglucosylcyclomaltoheptaose

Three positional isomers of diglucosylcyclomaltoheptaose [(G)2-beta-cyclodextrin], 6(1),6(4)-di-O-(a-D-glucopyranosyl)-cyclomaltoheptaose (1), 6(1),6(3)-di-O-(a-D-glucopyranosyl)-cyclomaltoheptaose (2), and 6(1),6(2)-di-O-(a-D-glucopyranosyl)-cyclomaltoheptaose (3) were isolated by h.p.l.c. on a reversed-phase column from the mother liquors of a large-scale preparation of beta CD with Bacillus ohbensis cyclomaltodextrin glucanotransferase (EC 2.4.1.19) and were characterized by h.p.l.c. analysis of partial hydrolyzates and by 13C-n.m.r. spectroscopy. Their molecular weights were confirmed by f.a.b.-m.s. Their characteristic chromatographic behavior on four h.p.l.c. columns of different separation modes was found to be very useful for their identification. It is particularly noteworthy that the first application of a graphitized carbon column to CDs enabled a fine separation of all three positional isomers.     

Separation and characterization of pentacarboxylic porphyrinogen isomers by high-performance liquid chromatography with electrochemical detection.

A reversed-phase h.p.l.c. system is described for the separation of all five naturally occurring pentacarboxylic porphyrinogen isomers. The compounds are detected electrochemically with high sensitivity. The peaks are positively identified by h.p.l.c. analysis of the pentacarboxylic porphyrinogens from reduction of pentacarboxylic porphyrins prepared by partial decarboxylation of hexa- and hepta-carboxylic porphyrin III of known structures. The resolution of pentacarboxylic porphyrinogens is superior to that of the porphyrins and the method is applicable to the small-scale preparative isolation of pure isomers.     

Simulated moving bed chromatography with supercritical fluids for the resolution of bi-naphthol enantiomers and phytol isomers

The combination of the simulated moving bed (SMB) technique with supercritical fluid chromatography (SFC) leads to a process with unique features. Besides the known advantages of the SMB process, the use of supercritical carbon dioxide as the mobile phase offers the advantages of reduction in organic solvents and an easy eluent/solute separation. Because of the low viscosity and high diffusion coefficients of supercritical fluids, a high efficiency is possible. The steps of process development for SMB SFC are presented using the separations of the bi-naphthol enantiomers and phytol isomers as examples. The development of a packed column SFC method at an analytical scale is shown for the separation of the bi-naphthol enantiomers on a chiral stationary phase and CO(2) with a modifier as the mobile phase. The influence of the modifier, modifier content, and column configuration on productivity of the SMB SFC process was investigated by simulation. The first set of experiments was performed in the SMB separation of phytol isomers at low concentration to test the feasibility of the SMB SFC high purity separation of the binary mixtures. In the second set of experiments, the productivity of the process was increased by increasing the feed concentration up to 54 grams feed per liter stationary phase (SP) and hour (g(feed)/l(SP) h).     

Determination of intracellular nitrate.

A sensitive procedure has been developed for the determination of intracellular nitrate. The method includes: (i) preparation of cell lysates in 2 M-H3PO4 after separation of cells from the outer medium by rapid centrifugation through a layer of silicone oil, and (ii) subsequent nitrate analysis by ion-exchange h.p.l.c. with, as mobile phase, a solution containing 50 mM-H3PO4 and 2% (v/v) tetrahydrofuran, adjusted to pH 1.9 with NaOH. The determination of nitrate is subjected to interference by chloride and sulphate when present in the samples at high concentrations. Nitrite also interferes, but it is easily eliminated by treatment of the samples with sulphamic acid. The method has been successfully applied to the study of nitrate transport in the unicellular cyanobacterium Anacystis nidulans.     

Quantification of tipranavir in human plasma by high-performance liquid chromatography with UV detection

A simple method for the quantification of tipranavir, a new non-peptidic protease-inhibitor, was developed. An internal standard, prazepam, was added to 100 microl of plasma before a liquid-liquid extraction by 3 ml of tert-butyl methyl ether. The extracts were evaporated to dryness and reconstituted with 100 microl of mobile phase before being injected in the chromatographic system. The separation was made on a C8 column using sodium acetate buffer (pH 5):methanol:acetonitrile (35:30:35, v/v/v) as mobile phase. The detection was performed at a wavelength of 260 nm. The method was linear and has been validated over a concentration range of 2-80 mg/l. The mean precision and accuracy of the method were respectively, 10.5 and -9.1%. The mean recovery was 70.8%.     

High-performance liquid chromatography of pyridylamino derivatives of unsaturated disaccharides produced from chondroitin sulfate isomers by chondroitinases

A sensitive method was developed for the separation and quantitation of four unsaturated disaccharides (delta Di-0S, delta Di-4S, delta Di-6S, and delta Di-diS) by high performance liquid chromatography. The unsaturated disaccharides were coupled with a fluorescent compound, 2-aminopyridine. Complete separation of the resulting pyridylamino derivatives was achieved on a column of muBondapak-C18 with 8 mM KH2PO4-Na2HPO4 (pH 6.0)/methanol (30/l, by volume) as a mobile phase. There was a linear relationship between the fluorescence emission (peak height), and the amount of each authentic disaccharide used for the coupling reaction. This method was applied to analyze commercially available chondroitin sulfates A and C, dermatan sulfate, and urinary glycosaminoglycans obtained from patients with mucopolysaccharidosis after digestion with chondroitinases. The data indicated that the present method is useful for the separation and quantitation of nmol-pmol levels of the unsaturated disaccharides produced from chondroitin sulfate isomers by chondroitinases and can be used for their structural characterization.     

2-Propanol in the mobile phase reduces the time of analysis of CLA isomers by silver ion-HPLC

Individual isomers of octadecadienoic acid (C18:2) with conjugated double bonds (conjugated linoleic acids; CLA) exert different biological activities. Their distribution in food and tissues differs. Therefore, the separation of the various positional and geometric isomers is important. The time of analysis using silver ion-high performance liquid chromatography can extend up to 90 min. The aim of this study was to reduce this time. The time of analysis reduced from ca. 90 min onto 45 to 35 min, respectively, by the addition of 0.05% or 0.1% (v/v) 2-propanol to the mobile phase [acetonitrile (0.1%; v/v) and diethyl ether (0.5%; v/v) in n-hexane]. There was no effect on resolution of the 17 individual CLA isomers of the CLA mixture. Regarding the lowest coefficient of variation and an adequate baseline separation the use of 0.05% 2-propanol in the mobile phase is recommended, without any disadvantages and adverse effects on the service life of columns. In conclusion, adding 0.05% or 0.1% 2-propanol to the mobile phase shortens the time of analysis of CLA isomers, saves solvents and reduces costs.     

Effect of temperature on the reversal in the retention order of the enantiomers of mosapride on Chiral-AGP

The retention order of the enantiomers of mosapride could be controlled by column temperature and mobile phase pH. In the presented paper, temperature studies have been used to study the thermodynamics of the reversal in retention order. A linear relationship was obtained plotting the logarithm of the capacity factor versus the inverted column temperature. However, at higher mobile phase pHs, the logarithm of the separation factor versus the inverted column temperature showed a non-linear behaviour and at the highest mobile phase pH used (pH=7.4), an optimum in the separation factor was observed. The plots showed that the thermodynamics for the two enantiomers of mosapride differ in the studied mobile phase pH interval. Thermodynamic values, enthalpy and entropy were calculated and showed that at a low mobile phase pH, the enantiomeric resolution was caused by differences in enthalpy between the two enantiomers. However, at a higher mobile phase pH, the chiral discrimination was a result of entropy effects. High correlation was obtained between experimental and predicted separation factors at different mobile phase pHs.     

Formation of native insulin from the scrambled molecule by protein disulphide-isomerase.

The formation of native insulin either from scrambled insulin or from the separated A chain and B chain S-sulphonates by protein disulphide-isomerase was demonstrated with yields of 20-30% as measured by h.p.l.c. analysis, receptor binding and stimulation of lipogenesis. The h.p.l.c. profile of the reaction products shows that, among all the possible isomers containing both chains, the native hormone is by far the predominating product and consequently the most stable under certain conditions.     

Simultaneous determination of mycophenolic acid and its phenolic glucuronide in human plasma using an isocratic high-performance liquid chromatography procedure

Simultaneous determination of mycophenolic acid (MPA) and mycophenolic acid glucuronide (MPAG) in plasma was accomplished by isocratic HPLC with UV detection. After protein precipitation and phase separation with saturated sodium dihydrogenphosphate, chromatographic separation was achieved on a monolithic column "Chromolith Performance RP-18e", with acetonitrile/0.01 M phosphate buffer, pH 3, (25:75, v/v), as the mobile phase; flow rate 3.3 ml/min and measurement at 214 nm. Linearity was verified up to 40 mg/l for MPA and up to 400 mg/l for MPAG. Detection limits based on the analysis of 50 microl plasma were 0.05 and 0.5 mg/l for MPA and MPAG, respectively. Accuracy was 99.6-104% for MPA and 95.6-105% for MPAG and total imprecision (CV) was <7% for both compounds. Analytical recovery was >95% for MPA and MPAG. The method is simple, rapid, accurate and suitable for routine determination of MPA and MPAG in plasma.     

Separation and quantification of ropinirole and some impurities using capillary liquid chromatography

Ropinirole, 4-[2-(dipropylamino)ethyl]-1,3-dihydro-2H-indol-2-one, is a potent anti-Parkinson’s disease drug developed by SmithKline Beecham Pharmaceuticals. Capillary liquid chromatography (CLC) was used for the separation and quantification of ropinirole and its five related impurities, potentially formed during its synthesis. A simultaneous optimization of three mobile phase parameters, i.e., pH, buffer concentration and acetonitrile content was performed employing an experimental design approach which proved a powerful tool in method development. The retention factors of the investigated substances in different mobile phases were determined. Baseline resolution of the six substances on a C₁₈ reversed stationary phase was attained using a mobile phase with an optimized composition [acetonitrile–8.7 mM 2-(N-morpholino)ethanesulfonic acid adjusted to pH 6.0 (55:45, v/v)]. It was shown that CLC, operated in the isocratic mode under the mobile phase flow-rate of 4 μl/min, can determine the level of these impurities, down to a level of 0.06% of the main component within 25 min.     

Conversion of biosynthetic human proinsulin to partially cleaved intermediates by collagenase proteinases adsorbed to isolated rat adipocytes.

Studies of the biological activity of proinsulin have resulted in widely varying conclusions. Relative to insulin, the biological activity of proinsulin has been reported from less than 1% to almost 20%. Many of the assays in vitro for the biological potency of proinsulin have utilized isolated rat adipocytes. To examine further the interaction of proinsulin with rat adipocytes, we prepared specifically-labelled proinsulin isomers that were iodinated on tyrosine residues corresponding to the A14, A19, B16 or B26 residue of insulin. These were incubated with rat adipocytes and their metabolism was examined by trichloroacetic acid precipitation, by Sephadex G-50 chromatography, and by h.p.l.c. chromatography. By trichloroacetic acid-precipitation assay, there was little or no proinsulin degradation. By G-50 chromatography and subsequent h.p.l.c. analysis, however, we found that the labelled proinsulin isomers were converted rapidly and almost completely to materials which eluted differently on h.p.l.c. from intact proinsulin. This conversion was due primarily to proteolytic activity which adsorbed to the fat cells from the crude collagenase used to isolate the cells. Two primary conversion intermediates were found: one with a cleavage at residues 23-24 of proinsulin (the B-chain region of insulin), and one at residues 55-56 in the connecting peptide region. These intermediates had receptor binding properties equivalent to or less than intact proinsulin. These findings show that isolated fat cells can degrade proinsulin to intermediates due to their contamination with proteolytic activity from the collagenase used in their preparation. Thus the previously reported range in biological activities of proinsulin in fat cells may have arisen from such protease contamination. Finally, the present findings demonstrate that a sensitive assay for degradation of hormones is required to examine biological activities in isolated cells.     

Chiral separation of tryptophan enantiomers by liquid chromatography with BSA-silica stationary phase

The separation of tryptophan enantiomers was carried out with medium-pressure liquid chromatography using BSA (bovine serum albumin)-bonded silica as a chiral stationary phase. The influence of various experimental factors such as pH and ionic strength of mobile phase, separation temperature, and the presence of organic additives on the resolution was studied. In order to expand this system to preparative scale, the loadability of sample and the stability of stationary phase for repeated use were also examined. The separation of tryptophan enantiomers was successful with this system. The data indicated that a higher separation factor (α) was obtained at a higher pH and lower temperature and ionic strength in mobile phase. Addition of organic additives (acetonitrile and 2-propanol) in mobile phase contributed to reduce the retention time of L-tryptophan. About 30% of the separation factor was reduced after 80 days of repeated use.     

Microbial reductions of the sesquiterpene quadrone

One hundred microorganisms have been screened for their abilities to selectively modify the structure of the sesquiterpene lactone known as quadrone. The only products obtained were those formed when the 4-ketone functional group was reduced to the stereoisometric 4-quadronols. Quadrone alcohol isomers of (S) or (R) absolute configurations were identified by proton and carbon n.m.r., and high performance liquid chromatography (h.p.l.c.) was used to separate and quantitate these compounds in extracts of fermentations. Microorganisms were categorized according to their abilities to achieve Re- or Si-face carbonyl reduction to yield (S)- or (R)-alcohol isomers by h.p.l.c. Three groups of microorganisms were identified: those yielding only the (R)-alcohol isomer; those yielding only the (S)-alcohol isomer; and those providing mixtures of the two alcohol isomers. With quadrone as substrate, Mucor and Curvularia spp. may contain either Re- or Si-face reductases. The selection of microorganisms for their abilities to achieve enantiospecific reductions of ketones to alcohol products is discussed.     

Stereoselective HPLC separation of alvimopan on cellulose‐based immobilized polysaccharide as a chiral stationary phase

Chiral separation by normal phase high performance liquid chromatography is one of the most powerful technique to quantify the chiral purity of the compounds. In this study, a novel, simple, and specific analytical method was proposed to ascertain the chiral purity of alvimopan (ALV). The normal phase HPLC method was developed based on cellulose tris (3,5‐dichlorophenylcarbamate) stationary phase. The separation of ALV isomers achieved by using column CHIRALPAK IC (250 × 4.6 mm, 5 μm), mobile phase n‐hexane: isopropyl alcohol: ethanol: diethylamine (650:200:150:5 v/v), column oven temperature 30°C, flow rate 1.0 mL min^?1, injection volume was 10 μL, chromatographic response monitored at 273 nm. The developed method was validated as per the ICH guidelines and found precise, accurate, and linear. The advantage of the method is a good separation of ALV isomers within 35 minutes of the analysis time. Therefore, this method is suitable for routine determination of chiral purity of ALV active pharmaceutical ingredient.     

Electrochromatographic enantioseparation of amino acids using polybutylmethacrylate-based chiral monolithic column by capillary electrochromatography

This article describes the development of a polybutylmethacrylate‐based monolithic capillary column as a chiral stationary phase. The chiral monolithic column was prepared by polymerization of butyl methacrylate (BMA), ethylene dimethacrylate (EDMA), and N‐methacryloyl‐l ‐glutamic acid (MAGA) in the presence of porogens. The porogen mixture included N,N‐dimethyl formamide and phosphate buffer. MAGA was used as a chiral selector. The effect of MAGA content was investigated on electrochromatographic enantioseparation of d,l ‐histidine, d,l ‐tyrosine, d,l ‐phenyl alanine, and d,l ‐glutamic acid. The effect of acetonitrile (ACN) content in mobile phase on electro‐osmotic flow was also investigated. It was demonstrated that the poly(BMA‐EDMA‐MAGA) monolithic chiral column can be used for the electrochromatographic enantioseparation of amino acids by capillary electrochromatography (CEC). The mobile phase was ACN/10 mM phosphate buffer (45:55%) adjusted to pH 2.7. It was observed that l ‐enantiomers of the amino acids migrated before d ‐enantiomers. The separation mechanism of electrochromatographic enantioseparation of amino acids in CEC is discussed. Chirality 24:606–609, 2012. © 2012 Wiley Periodicals, Inc.     

Bioanalysis and preliminary pharmacokinetics of the acridonecarboxamide derivative GF120918 in plasma of mice and humans by ion-pairing reversed-phase high-performance liquid chromatography with fluorescence detection

We have developed and validated a sensitive and selective method for the determination of the P-glycoprotein modulator GF120918 in murine and human plasma. Chlorpromazine is used as internal standard. Sample pretreatment involves liquid–liquid extraction with tert-butyl methyl ether. Chromatographic separation is achieved by reversed-phase high-performance liquid chromatography using a Symmetry C₁₈ column and detection was accomplished with a fluorescence detector set at excitation and emission wavelengths of 260 and 460 nm, respectively. The mobile phase consists of acetonitrile–50 mM ammonium acetate buffer, pH 4.2 (35:65, v/v). To achieve good separation from endogenous compounds and to improve the peak shape the counter-ion 1-octane sulfonic acid (final concentration 0.005 M) was added to the mobile phase. The lower limit of quantitation was 5.7 ng/ml using 200 μl of human plasma and 23 ng/ml using 50 μl of murine plasma. Within the dynamic range of the calibration curve (5.7–571 ng/ml) the accuracy was close to 100% and within-day and between-day precision were within the generally accepted 15% range. The stability of GF120918 was tested in plasma and blood from mice and humans incubated at 4°C, room temperature, and 37°C for up to 4 h. No losses were observed under these conditions. This method was applied to study the pharmacokinetics of orally administered GF120918 in humans and mice. The sensitivity of the assay was sufficient to determine the concentration in plasma samples obtained up to 24 h after drug administration.     

Solvent extraction of tricyclic amines from blood plas- ma and liquid chromatographic determination

The extraction of seven tricyclic antidepressant amines from human plasma at different pH values was investigated for dichloromethane, diethyl ether and hexane—1-pentanol (95:5). The amines were extracted as bases and back-extracted to sulphuric acid, 0.10 mol/l, prior to the separation by bonded-phase liquid chromatography. Ether and hexane— 1-pentanol (95:5) were most suitable, tertiary amines being best extracted at pH 8, and secondary amines at pH 10. Using ether, both tertiary and secondary amines required 30 min extraction time for a quantitative yield while 15 rain was sufficient for hexane— -1-pentanol (95:5). UV detection allowed concentrations down to 10 ng in 1 ml of plasma to be determined.Three ammonium ions—octylammonium, dimethylammonium, and trimethylammonium - were added as modifiers to the mobile phase containing acetonitrile in phosphoric acid, 0.10 mol/l. In the concentration interval 0.010–0.030 mol/l all of the amine modifiers gave on Polygosil C₈ peak asymmetry factors of sufficiently low magnitude, while on Li- Chrosorb RP-18 this was so only for di- and trimethylammonium in a concentration of 0.030 mol/l.     

Decarboxylation of uroporphyrinogen III by erythrocyte uroporphyrinogen decarboxylase. Evidence for a random decarboxylation mechanism.

The isomeric composition of type-III heptacarboxylic porphyrinogens derived from decarbosylation of uroporphyrinogen III by erythrocyte uroporphyringogen decarboxylase was analysed by h.p.l.c. with electrochemical detection. All four possible isomers were identified, and there were little differences in the proportion of isomers formed by erythrocytes from normal subjects and from patients with sporadic porphyria cutanea tarda. The results provide conclusive evidence that the normal decarboxylation pathway is random in nature, and the fourth isomer only increases when enzyme abnormality is found.