High-Performance Liquid Chromatography of 2′-5′Oligoadenylates and Related Oligonucleotides

Abstract

HPLC has been used for the analysis and separation of the components of p_x (A2′p)_n A (x = 1 to 3, n = 1 to ≥4). Weak anion exchange columns give excellent resolution, but their instability in phosphate buffers makes them impractical for routine use. Reverse phase chromatography using C18 columns provides a satisfactory alternative method. For preliminary analysis of crude material, ammonium phosphate pH7.0 with a linear 1:1 methanol/H₂O gradient gives a good basic separation of the individual oligomers. Resolution of the 5′ mono-, di-and triphosphorylated oligomers or of the nonphosphorylated components can be obtained using ammonium phosphate pH6.0 and potassium phosphate pH6.5 buffers respectively. The C18 columns are very stable and any one column will give retention times reproducible within 0.2%.     

Determination of 2′,3′-Dideoxyinosine in Plasma by High Performance Liquid Chromatography

Abstract

A high performance liquid chromatography analysis method has been developed for the quantitation of 2′,3′-dideoxyinosine (DDI) in plasma. Proteins were precipitated from plasma samples with acetonitrile containing the internal standard, 6-methylaminopurine riboside. The treated samples were evaporated to dryness and reconstituted in mobile phase for the analysis. Separation of the components was achieved on a 5 μm octadecylsilane column with ultraviolet detection at 254 nm. The method was validated at nine concentrations between 0.015 and 150 μg/mL. Using 500 μL of human plasma, the limit of quantitation was 120 ng/mL and the limit of detection was 60 ng/mL. The mean intra-day precision of the method was 1.6%. The mean accuracy of the method was within 2% of the actual values. This method is currently being used for pharmacokinetic studies in the rat.     

Effects of Explicit and Implicit Solvent Models on the Hydrolysis Cleavage of N-Glycosidic Bond in 8-Oxo-7,8-dihydro-2?-deoxyguanosine

8-Oxoguanine(8-oxoG), a critical mutagenic DNA lesion induced by reactive oxygen species, gives rise to a G·C→T·A transversion during replication and thereby must be repaired. The effects of explicit and implicit solvent molecules on the hydrolysis cleavage of N-Glycosidic bond in 8-oxo-7,8-dihydro-2'-deoxyguanosine(8-oxo-dG) have been systematically clarified in the present work based upon two types of computational models. Detailed potential energy surface(PES) scans and full unconstraint optimizations for all the representative points on PESs were carried out at the B3LYP/6-31+G(d) level of theory. The effect of implicit solvent was tested by single-point calculation at the SCRF/IEF-PCM model. The results illustrate that the direct hydrolysis model involving one explicit water molecule can't provide a complete depiction of the hydrolysis process of 8-oxo-dG, attributed to the insufficiency of nucleophile activation and leaving group stabilization. The expansion hydrolysis model involving four explicit water molecules, however, facilitates discrete proton transfer and therefore produces smooth reaction surfaces for both the dissociative(SN1) and concerted(SN2) pathways. The presence of the implicit solvent substantially lowers all activation energies and the SN1 process is more favorable than the SN2 process. The data and insights present here agree well with the experimental results and have given out a baseline for the enzymatic deglycosylation reaction of 8-oxo-dG.     

Development and Validation of High‐Performance Liquid Chromatographic Method for Estimation of Lercanidipine in Rabbit Serum

Abstract

A new, simple, and sensitive reverse‐phase liquid chromatographic method was developed and validated for the estimation of Lercanidipine hydrochloride in rabbit serum using UV detector under isocratic conditions. After subjecting serum to simple and efficient one‐step extraction procedure, 100 µl of sample was injected onto high‐performance liquid chromatography system. The detector response was linear in the concentration range of 25–1000 ng/ml. The developed method was validated as per standard guidelines. Validation demonstrated accuracy, precision, and selectivity of the proposed method. The drug was found to be stable under various processing and storage conditions.     

A Sensitive High Performance Liquid Chromatography Assay for Trospectomycin. An Aminocyclitol Antibiótic,in Human Plasma and Serum

Abstract

This report describes a sensitive, selective and robust assay for the quantification of trospectomycin, an aminocyclitol antibiotic, in human plasma and serum.

This is the first published High Performance Liquid Chramatography (HELC) bioanalytical method for a member of this class of compound.

The method involves the selective solid phase extraction of 6′-n-propyl spectinomycin and the internal standard 6′-n-butyl spectinonycin from 0.5 ml of biofluid, efficient reversed phase high pressure liquid chromatography with post column oxidation, reaction with o-phthaldialdehyde and fluorescence detection. The limit of quantification from 0.5 ml of biofluid is 10 ng/ml.     

High Pressure Liquid Chromatography Assay for Determination of 18-β-Glycyrrhetinic Acid in Plasma

Abstract

This report presents a useful high pressure chromatography assay for determination of the proposed chemopreventive agent 18-β-glycerrhetinic acid (GA) in murine and human plasma. Drug was released from plasma proteins through precipitation with a mixture of sodium bisulfate and sodium chloride after which it was extracted with acetonitrile. Standard calibration curves of GA covered the concentration range of 2.5 to 120 μg/ml. The lower limit of detection was 0.5 μg/ml. No endogenous plasma constituents from plasma were found to interfere with the determination of GA. Recover of GA from plasma was greater than 95% over a concentration range of 20 to 100 μg/ml. Linearity of the assay was excellent; within-run precision showed a C.V. of 4.2% at 25 μg/ml, 5.6% at 20 μg/ml and 3.4% at 120 μg/ml. Between-run assay precision and accuracy was also considered to be excellent. The specificity, sensitivity and reproducibility of the procedure are adequate for proposed clinical pharmacology studies of this agent.     

Determination of the Flavonoids from Ginkgo Biloba Extract by High Performance Liquid Chromatography

Today Ginkgo biloba extract (GBE) is one of the most widely used food supplements and herbal medicines. The amounts of flavone glycosides, one of the key active components in GBE, vary according to the source of the ginkgo leaves and the extraction and enrichment procedures used to prepare the extract. A typical GBE contains from 22% to 27% of flavone glycosides. Ginkgo flavone glycosides are a group of small complex molecules that can be hydrolyzed to give kaempferol, quercetin and isor…     

Conformational Properties of the Phosphate Rings of Neutral Phosphoramidate Derivatives of Ribo- and 2′-Deoxyribonucleoside Cyclic 3′,5′-Monophosphates

Abstract

An investigation of the effects of changing the nature of X, nitrogen base (B), and amino substituent (R₂N) on the equilibrium 1?2 was carried out.

The influence of the above structural changes on the time-averaged coupling constants J_AP and J_BP, determined at 300 MHz, were used to follow changes in K_eq. With constant R₂N, small effects from variation of X and B were found. A large range in K_eq arose from changes in the steric size of R₂N. These results will be related to the question of the ease of chair to twist interconversion of the phosphate ring essential to the biological activities of the naturally occurring diesters, cAMP and cGMP.     

Enhanced Catalytic Performance of Quasi-HKUST-1 for the Tandem Imine Formation

Copper-based metal-organic framework (Cu₃(BTC)₂(H₂O)₃]_n⋅nH₂OMeOH (HKUST-1) has been subjected to thermolysis under air atmosphere at different temperatures ranging from 100 to 300 °C. This treatment produces the partial removal of ligands, the generation of structural defects and additional porosity in a controlled way. The resulting defective materials denoted according to the literature as quasi-MOFs, were subsequently employed as heterogeneous catalysts in the one pot synthesis of N-benzylideneaniline from aniline and benzyl alcohol in open air as terminal oxidant at 70 °C under base- and dehydrating agent-free conditions. The Q-HKUST catalysts calcined at 240 °C (QH-240) was the most efficient in the series, promoting imine synthesis. Data from Knoevenagel condensation of malononitrile shows that in QH-240 the distances of Cu ions in HKUST-1 cavities are preserved, increasing the Knoevenagel activity, but a strong rearrangement takes place at 300 °C or above. The unsaturated copper active sites with simultaneous presence of micro- and mesopores in QH-240 are responsible for this excellent catalytic performance. The effective parameters on catalytic activity of QH-240 including deligandation temperature, the amount of catalyst, the ratio of reactants, and reaction temperature as well as the stability and recyclability of the catalyst were also investigated. The possible mechanism used by QH-240 follows alcohol aerobic oxidation and subsequent anaerobic condensation of aldehyde intermediate with aniline.     

Separation of the α-Tocopherol Model Compound 2,2,5,7,8-Pentamethyl-6-Chromanol from its Oxidation Products by High Performance Liquid Chromatography

Abstract

A rapid method is described for the separation of the α-tocopherol model compound, 2,2,5,7,8-pentamethyl-6-chromanol (6), from 9 of its oxidation products in a single 35 minute run. Separated derivatives of 6, in order of elution, included the 5-cholesteroxymethyl (1), spirotrimer (2), spirodimer (3), 5-formyl (4), 5-ethoxymethyl (5), dihydroxydimer (7), chroman dione (8), quinone (9) and pyrano xanthene (10). A normal phase system, using gradient elution is employed, the eluent being monitored at 290 nm. The minimum detection limit for compounds 1–8 was 0.1 μg per injection and for compounds 9 and 10 it was 0.3 μg per injection.     

High‐Performance Liquid Chromatographic Determination of Parecoxib in Human Plasma and Pharmaceutical Formulations

Abstract

A simple and sensitive RP‐HPLC method for the determination of parecoxib (PXB) in human plasma and pharmaceutical formulations has been developed and validated. The separation of PXB and the internal standard, ibuprofen (IBF) was achieved on a CLC C₁₈ (5 μ, 25 cm×4.6 mm i.d.) column using UV detector at 200 nm. The mobile phase consisted of acetonitrile‐water (92:8 v/v). The linear range of detection was found to be 0.9–18.4 µg/ml (r=0.9985). Intra‐ and inter‐day assay relative standard deviations were observed to be less than 0.3%. The method has been applied successfully for the determination of PXB in spiked human plasma and pharmaceutical preparations. Analytical parameters were calculated and complete statistical evaluation is incorporated.     

Synthesis of 4′-substituted 2′-deoxy-4′-thiocytidines and its evaluation for antineoplastic and antiviral activities

4′-Azido- (7), 4′-C-fluoromethyl- (8) 4′-C-ethynyl- (9) and 4′-C-cyano- (10) 2′-deoxy-4′-thiocytidines have been synthesized. In this study, it was found that the isolated yield of 4′-thiouracil nucleoside 13 in a Lewis acid-promoted Vorbrüggen-type glycosidation utilizing 12 was better than that of the electrophilic glycosidation reaction between silylated uracil and 11. This improved result prompted us to perform the glycosidation utilizing 36 and 43 for the synthesis of 37 and 44. Introduction of the azido group was carried out by nucleophilic substitution in the 4′-benzoyloxy derivative 22a. On the other hand, 9 and 10 were synthesized by way of the chemical manipulation of the hydroxymethyl group at the 4′-position of 46.Evaluation of the antineoplastic activity of 2 and 7–10 against human B-cell (CCRF-SB) and T-cell leukemia (Molt-4) cell lines revealed that 4′-azido- (7) and 4′-C-fluoromethyl- (8) derivatives exhibited cytotoxic activity whereas no cytotoxicity was observed in the 4′-C-ethynyl- (9) and 4′-C-cyano- (10) derivatives as well as the parent compound 2. Compound 7 was also found to possess promising antiviral activity against VZV and HSV-1 without any cytotoxity against HEL host cells. It is noteworthy that 7 exhibited potent inhibitory activities against the thymidine kinase-deficient (TK^?) mutant of VZV and HSV-1.     

A Simple and Rapid Reversed Phase High Performance Liquid Chromatographic Method for Quantification of Alprazolam and α-Hydroxyalprazolam in Plasma

Abstract

A simple and rapid reversed-phase liquid chromatographic method for the determination of alprazolam and a-hydroxyalprazolam in plasma is described. Flunictrazepam was used as internal standard. Plasma samples were buffered with sodium borate and extracted with dichloromethane /n-pentane 4:6 v/v for 60 sec on a vortex apparatus. Extraction solvent was evaporated to dryness and extraction residues were reconstituted in the mobile phase. Samples were chromatographed on a 5μ Lichrospher RP-18 column (25cm × 4mm i. d) using acetonitrile/water 40:60 v/v as the mobile phase. The column effluent was monitored at 230nm. The lower limit of detection was 1ng/ml for alprazolam and a-hydroxyalprazolam while the lower limit of quantification was 2ng/ml for both compounds. Peak height and plasma     

Development and Validation of Liquid Chromatography Method for the Separation of Valdecoxib and its SC‐77852 Impurity

Abstract

A reversed‐phase liquid chromatography method has been developed for the separation of valdecoxib and impurity SC‐77852. The best results were achieved using a mobile phase—methanol: 1% water solution TEA (52∶48 v/v), pH 7.35 (adjusted with 85% orthophosphoric acid), column temperature 24°C. Separation was carried out on XTerra? RP₁₈ (150 mm×4,6 mm), particle size 5 µm, flow rate 1 ml/min, using detection on 220 nm. The method was statistically validated for its selectivity, linearity, precision (repeatability), and robustness. Quantitation and detection limits were determined for both valdecoxib and SC‐77852. Method robustness was further evaluated by performing full factorial design experiment. Validated method was used for assay of valdecoxib and SC‐77852 in Bextra^® film‐coated tablets.     

High Pressure Liquid Chromatography Determination of the 5′-Terminal Residue of Small RNA Molecules

Abstract

Under the appropriate conditions, high pressure liquid chromatography of alkaline hydrolysates of short RNAs allows the identification of the 5′-end group under the form of a nucleoside 5′, 3′(2′)-bisphosphate. The separation conditions were elaborated with an artificial mixture of nucleoside mono-and bisphosphates, tested with an alkaline hydrolysate of Escherichia coli 5 S rRNA, and applied to the identification of the Artemia salina 5 S rRNA end group.     

A Comparative Study of the Separation of the Tryptic Peptides of the β-Chain of Normal and Abnormal Hemoglobins by Reversed Phase High Performance Liquid Chromatography

Abstract

The separation of the tryptic peptides of the human hemoglobin A β-chain by reversed phase high performance liquid chromatography under different elution conditions on several microparticulate alkylsilica supports is described. Similar methods have been used to separate the tryptic peptides of β-chain hemoglobin variants including HbC, HbE, and Hb (Kempsey). Selectivity differences which can be achieved under the different chromatographic conditions have been exploited to permit the assignment of all the anticipated peptide fragments derived from the tryptic digestion of these β-chain Hb-variants.     

An Automated Method for the Determination of Enoximone and Its Major Sulfoxide Metabolite in Plasma Using Robotic Technology–High Performance Liquid Chromatography

Abstract

An automated analytical procedure for the determination of enoximone, a new cardiotonic agent, and its major oxidative metabolite in plasma using robotic technology is described. A Zymark robot is used to perform all the operations of solid phase extraction including column pretreatment, internal standard addition, sample mixing, sample pipetting, column rinsing, drying and sample elution. The processed sample is injected directly into the high performance liquid chromatography system which is equipped with an ultraviolet absorption detector. The assay has good precision and accuracy, equivalent to the manual method it replaces, and yet provides higher throughput of sample.     

Experimental Design Optimization of Solid‐Phase Microextraction Conditions for the Determination of Heterocyclic Aromatic Amines by High‐Performance Liquid Chromatography

Abstract

Solid‐phase microextraction, using Carbowax‐Templated Resin fiber, coupled with high performance liquid chromatography ultra violet/diode array detector (HPLC‐UV/DAD) has been optimized for the determination of the heterocyclic aromatic amines (HAs). Three variables (absorption time, soaking time, and desorption time) were considered as factors in the optimization process. Interactions between analytical factors and their optimal levels were investigated using two level factorial and Doehlert matrix designs. Absorption time and soaking time were significant variables, and 15 min for each one of the variables was chosen for the best response. The optimized procedure allowed the determination of HAs with detection limits that ranged from 1.58 to 16.8 ng/L (except PhIP: 23.8 ng/L). The reproducibility of the method (n=5), expressed as relative standard deviation was between 2.21% and 28.3%. The method was applied to the analysis of a meat extract sample and the range of recoveries for the amines was 64.14%–112.72%.     

Formation of lithiated gold and its use for the preparation of reference electrodes — an EQCM study

Lithiated gold wires can be used to build reference electrodes with outstanding potential stabilities over several days and even over the course of one year. These electrodes are well suited for investigations in the context of lithium-ion batteries (LIBs). In this work, a detailed procedure for the preparation of such electrodes with tailored mechanical properties, which can be fitted gastight into electrochemical cells using commercially available fittings, is given. The electrochemical lithiation process is studied using the electrochemical quartz crystal microbalance (EQCM) technique, and the differences in lithiation of wire type and thin film type gold electrodes are discussed. All experiments were carried out with two different electrolytes, namely, a LiPF₆ and a lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based electrolyte, and we conclude that for a higher lithiation rate and long-term stability, the use of LiTFSI-based electrolyte in the preparation phase is beneficial. The EQCM data provides a better insight in the analysis of film formation processes, like the buildup of the solid electrolyte interphase (SEI) during the lithiation, the rate of deposition of metallic lithium, or additional information on the kinetics of Li-Au alloy formation.