Gradient reversed-phase high-performance liquid chromatographic separation of naturally occurring retinoids

A gradient reversed-phase high-performance liquid chromatographic technique is described for the facile separation and quantitation of the naturally occurring retinoids: retinoic acid, retinol, and retinyl esters. An octadecylsilane column (Waters mu Bondapak C18) is used, with gradient elution from methanol--water (80:20) (solvent A) to 70% or 100% methanol--tetrahydrofuran (50:50) (solvent B) at 2.0 ml/min; detection is by absorbance at 325 nm. Analysis can be completed, with return to starting conditions, in 25-30 min. The method is inherently flexible: retinyl esters can be eluted as a group, with little resolution, by gradient to 100% solvent B, or mostly resolved by gradient to 70% solvent B; separation of retinoids more polar than retinoic acid can be achieved by use of greater proportions of water in solvent A. The separation of vitamin A compounds from extracts of human, rat, and pig liver and from rat kidney by this technique is described.     

Rapid and high-throughput purification of salvianolic acid B from Salvia miltiorrhiza Bunge by high-performance counter-current chromatography

A large-scale purification of salvianolic acid B from Salvia miltiorrhiza Bunge is presented. The method development began with selection of the solvent system, then optimization of the operating parameters and ended up with linear scale-up from an analytical to a preparative instrument. Three factors were used for method optimization and scale-up estimation: purity, process throughput and process efficiency. Preparation was achieved using a two-phase solvent system comprising hexane–ethyl acetate–methanol–acetic acid–water (1:5:1.5:0.00596:5, v/v). This preparation yielded 475 mg of salvianolic acid B with a purity of 96.1% from 1.5 g of crude extract. The process throughput of crude was 2.23 g/h while process efficiency per gram of target compound was 0.769 g/h. Two factors—process environmental risk factor and process evaluation factor were used for evaluation of the separation process.     

Investigation on isobaric vapor–liquid equilibrium for acetic acid + water + methyl ethyl ketone + isopropyl acetate

Isobaric vapor–liquid equilibrium (VLE) data for acetic acid + water, acetic acid + methyl ethyl ketone (MEK), MEK + isopropyl acetate, acetic acid + MEK + water and acetic acid + MEK + isopropyl acetate + water are measured at 101.33 kPa using a modified Rose cell. The nonideal behavior in vapor phase of binary systems measured in this work is analyzed through calculating fugacity coefficients since mixture containing acetic acid deviates from ideal behavior seriously in vapor phase due to the associating effect of acetic acid. Combined with Hayden–O’Connell (HOC) equation, the VLE data of the measured binary systems for acetic acid + water, acetic acid + MEK and MEK + isopropyl acetate are correlated by the NRTL and UNIQUAC models. The NRTL model parameters obtained from correlating data of binary system are used to predict the VLE data of the ternary and quaternary systems, and the predicted values obtained in this way agree well with the experimental values.     

Liquid + liquid equilibria for the quaternary systems of (water + acetic acid + mixed solvent) at 298.2 K and atmospheric pressure

Liquid–liquid equilibrium (LLE) data for the quaternary systems of [water + acetic acid + mixed solvent (dipropyl ether + diisopropyl ether)] were measured at 298.2 K and atmospheric pressure, using various compositions of mixed solvent. Binodal curves and tie-lines for the quaternary systems have been determined in order to investigate the effect of solvent mixture, dipropyl ether (DPE) and diisopropyl ether (IPE), on extracting acetic acid from aqueous solution. A comparison of the extracting capabilities of the mixed solvents was made with respect to distribution coefficients, separation factors, and solvent free selectivity bases. Reliability of the data was confirmed by using the Othmer–Tobias and Hand plots. The tie-lines were also correlated using the UNIFAC model. The average root-mean-square deviations between the observed and calculated mass fractions for the studied systems were in the range of 10–14%.     

Electrochemical Amination of Benzene in Aqueous Solutions of Sulfuric Acid and an Organic Solvent

Electrolysis of the Ti(IV)–NH₂OH–C₆H₆ system in 11 M H₂SO₄ reveals that out of four organic solvents—methanol, formic acid, acetonitrile, and acetic acid—only the last two meet conditions imposed on solvents to be used in indirect cathodic amination of aromatic compounds. They improve the aromatic substrate solubility in the catholyte and affect the process mechanism, determining, together with other factors, the substitution's rate and selectivity.     

Kinetics and mechanism of the oxidation of glycine by N-bromosuccinimide

A systematic kinetic study on the oxidation of glycine by N-bromosuccinimide (NBS) in presence of mercuric acetate in acetic acid—water media has been made. Near first order dependence inNBS and glycine and near inverse first order dependence in hydrogen ion concentrations have been observed. A negligible ionic strength effect and a positive dielectric effect have been observed. Various rate parameters have been computed and hydrocyanic acid identified as the end product. On the basis of the kinetic data, a mechanism of the reaction has been proposed.With 3 Figures     

Use of high-performance liquid chromatography to quantitative thymine-containing pyrimidine dimers in DNA

We have developed two high-performance liquid chromatographic systems for the measurement of pyrimidine dimers in hydrolysates of DNA. Normal-phase chromatography on an NH₂ column in methanol—ethyl acetate (3:97) at an elution rate of 2.0 ml/min allowed quantitaion of thymine-containing (thymine-thymine plus thymine-uracil) pyrimidine dimers at levels as low as 0.1% of the total radioactivity as thymine in DNA. This system was unaffected by the presence of up to 1 mg of contaminating protein (bovine serum albumin) or 40 μg of DNA in hydrolysates prepared for chromatography. Reversed-phase chromatography on a μBondapak C₁₈ column allowed measurement of thymine-thymine dimers at concentrations as low as 0.02% of the total radioactivity. With 0.1% tetrahydrofuran in wateras the solvent at a flow-rate of up to 0.6 ml/min, thymine—thymine, thymine—uracil, and uracil—uracil dimers were completely resolved. We were not able to quantitate the latter two dimeric forms, however, owing to the presence of other radioactive components of undefined origin that eluted concomitantly with the uracil-containing dimers.     

Simultaneous Determination of Cefuroxime Axetil and Cefuroxime in Pharmaceutical Preparations by Thin-Layer Chromatography and Densitometry

Summary Conditions have been established for identification and quantification of cefuroxime axetil and cefuroxime by thin-layer chromatography and densitometry. Good separation of these compounds was achieved on silica gel by use of chloroform–ethyl acetate–glacial acetic acid–water, 4:4:4:1 (v/v), as mobile phase. UV densitometry was used to detect spots on chromatograms. Under these conditions the limits of detection for cefuroxime axetil and cefuroxime were 40 ng and 30 ng, respectively. Recoveries of cefuroxime axetil and cefuroxime were 99.93% and 97.94%, respectively.     

Separation of synthetic cycloalkylated bases, nucleosides and nucleotides by reversed-phase high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography was used to determine the elution profiles of a series of synthetic cycloalkylated bases, nucleosides, and their corresponding 5'-monophosphates. A 70% aqueous methanol solution proved to be the most efficient solvent system for the separation of a mixture of the bases, all of which were eluted in times ranging from 3.3 to 4.8 min at a flow-rate of 0.8 ml/min. Subsequently, the same percentage of methanol solvent, at 0.8 ml/min, eluted the nucleoside mixture as well, with retention times ranging from 3.3 to 5.0 min. Optimum separation and resolution were achieved with 70% methanol at a flow-rate of 0.6 ml/min for a mixture of the base and nucleoside series. A phosphate buffer, containing acetonitrile-tetrabutylammonium ion, was used to analyze the 5'-monophosphate derivatives. Elution times ranged from 2.6 to 6.1 min at a flow-rate of 1.0 ml/min. Three variables were considered in order to determine optimum conditions for separation and resolution: (a) the percentage of methanol in the solvent; (b) flow-rate of solvent; and (c) the size of the cycloalkylated group of each synthetic analogue. The procedures and conditions described herein have potential use as a monitoring system to detect modified nucleic acid derivative which are prevalent in the body fluids of patients with certain metabolic disorders.     

Application of solid-phase extraction for determination of phenolic compounds in barrique wines

A fast, selective and sensitive chromatographic method has been developed for determination of gallic, protocatechuic, p-hydroxybenzoic, vanillic, caffeic, syringic, p-coumaric, benzoic, ferulic, sinapic, cinnamic, and ellagic acids and p-hydroxybenzaldehyde, vanillin, syringaldehyde, 2-furfural, 5-methylfurfural, and 5-methoxyfurfural. The compounds from untreated wine samples were pre-concentrated and cleaned using solid-phase extraction on RP-105 polymeric sorbent. The cartridge was conditioned with methanol and water. Co-extracted ballast substances were rinsed from the sorbent with 0.1 mol L^–1 hydrochloric acid–methanol, 1:4 (v/v). Retained phenolic compounds were selectively eluted with diethyl ether. A linear mobile phase gradient containing 0.3% acetic acid and methanol was used for final baseline chromatographic separation on a Hypersil BDS C18 column. Limits of detection (LOD=3s_bl) in the range 5.2 to 181.2 g L^–1, resolution (R) better than 1.7, and repeatability of 2.7–5.1% (RSD for real samples) were achieved. The method was applied for quantification of individual phenolic compounds in barrique wines.     

Isolation and purification of ginkgo flavonol glycosides from Ginkgo biloba leaves by high-speed counter-current chromatography

A high-speed counter-current chromatography method was developed for the separation and purification of bioactive flavonol glycosides from a crude ethanol extract of Ginkgo biloba leaves. The separation was performed with a two-phase solvent system composed of n-hexane-butanol-ethyl acetate-methanol-0.5% acetic acid (1:0.5:3.5:1:4, v/v) and three pure compounds were eluted in high purities in a one-step separation. Their purities were determined by HPLC and identified by MS,(1)H-NMR, and(13)C-NMR.     

Synthesis and properties of 1-aryl-2,5,7-trimethyl-4-oxo-1,4-dihydropyrido[2,3-d]pyrimidines

1-Aryl-2,5,7-trimethyl-4-oxo-1,4-dihydropyrido[2,3-d]pyrimidines are formed from the cyclization of N-acetyl-2-arylamino-4,6-dimethylnicotinonitriles by perchloric acid in a mixture of acetic acid and acetic anhydride. 1-Aryl-2-acetonyl-5,7-dimethyl-4-oxo-1,4-dihydropyrido[2,3-d]pyrimidines areformedonheating2-arylamino-4,6-dimethylnicotinamides with acetic anhydride. These and analogous compounds were obtained by acylation of 1-aryl-2,5,7-trimethyl-4-oxo-1,4-dihydropyrido[2,3-d]pyrimidines with acetic anhydride or benzoyl chloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1234–1236, September, 1992.     

Effect of time and temperature on the preparation of pyrazines in model reactions of the synthesis of aroma-forming substances

The qualitative and quantitative compositions of pyrazines that form in model glucose—ammonia and glucose—ammonia—leucine reactions in a glycerol medium were studied. Reaction conditions were found that ensure the synthesis of 23 alkylpyrazines in total concentration 6 g/kg. The obtained mixture of pyrazines is promising for use in the development of food aroma-forming substances.Institute of Food Substances, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1628–1635, July, 1992.     

Cu(I) camphor coordination polymers: Synthesis and study of the catalytic activity for cyclization of 4‐pentyn‐1‐oic acid

The number of CuCl units per camphor ligand in [{CuCl}₂L]_n was extended to three or four in [{CuCl}₃L]_n ( 2 ) or [{CuCl}₄L]_n ( 1 ). The Hartree‐Fock ab initio calculations support the polymeric structure of 1 and 2 that catalyze the cyclization of 4‐pentyn‐1‐oic acid ( A ) forming 5‐methylenedihydrofuran‐2(3H)‐one ( B ) and/or 2‐methyl‐5‐oxotetrahydrofuran‐2‐ylpent‐4‐ynoate ( C ). The catalytic activity of 1 , 2 and other polynuclear Cu(I) complexes ( 3–5 ) was evaluated under solvent free conditions and/or solution. In the absence of solvent, catalyst 2 displays the highest activity and selectivity (75.8/23.1, C to B ratio, at 5.4% loading) while 4 reaches the highest level of A → B conversion (97.5 %) in solution. Selected reactions were followed by NMR and the kinetic constants calculated. A mechanism is proposed based on the equations used for the calculations. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3316–3323     

Separation of acidic and neutral lipids by aminopropyl-bonded silica gel column chromatography.

The separation of acidic and neutral lipids by aminopropyl-bonded silica gel column chromatography is presented. Total lipid extracts from Escherichia coli and human spermatozoa were loaded onto pre-packed aminopropyl-bonded silica gel columns and the lipids separated into four fractions. Non-polar lipids including cholesterol esters, triglycerides, diglycerides, monoglycerides and cholesterol, were eluted with 4 ml of isopropanol-chloroform (1:2, v/v) (fraction 1); free fatty acids were eluted with 4 ml of 2% acetic acid in diethyl ether (fraction 2); neutral polar lipids, including phosphophatidylethanolamine, phosphatidylcholine, sphingomyelin and neutral glycolipids, were eluted with 4 ml of methanol (fraction 3); and, finally, polar acidic lipids, including phosphatidylglycerol, cardiolipin, phosphatidylinositol, phosphatidylserine, seminolipid lipid A and acidic glycosphingolipids, were eluted with 4 ml of chloroform-methanol-0.8 M sodium acetate (60:30:4.5, v/V/V) (fraction 4). The recoveries for the different lipids ranged between 89 and 98% and the intra-assay variation, expressed as the standard deviation, was less than 5%.     

Synthesis and biological application of pyranopyrimidine derivatives catalyzed by efficient nanoparticles and their nucleoside analogues

Abstract

Nanoparticles supply an environmentally friendly procedure for the synthesis of pyrano[2,3-d]pyrimidines by the one-pot three-component condensation reaction of thiobarbituric acid and malononitrile with pyrrol-2-carboxaldehyde. The catalyst could be easily recovered using an external magnet and reused for six cycles with almost consistent activity. A facile synthesis of a new series of cyclic and acyclic nucleosides of pyrano[2,3-d]pyrimidines derivatives was performed. The synthesis of poly heterocyclic compounds starting from pyrano[2,3-d]pyrimidines derivatives was achieved. Structures of the newly synthesized compounds were confirmed on the bases of elemental analyses and spectral data (IR, ¹H NMR, ¹³C NMR, and mass spectra). Compound 6 exhibited the most potent biological activity.     

Design and Optimization of Ecofriendly One-Pot Synthesis of 2,4,5-Triaryl-1H-imidazoles by Three-Component Condensation Using Response Surface Methodology

Phase-transfer-catalyzed, highly versatile, and high-yielding protocol for the synthesis of 2,4,5-triaryl-1H-imidazoles was developed through response surface methodology (RSM). The effects of different solvents, reaction paths, and phase-transfer catalysts (PTCs) in different concentrations were envisioned. Three independent variables (catalyst, catalyst loading, and solvent volume) identified by one-factor-at-a-time (OFAT) study were screened through full factorial design at two levels. The analysis of variance results suggested the significance of catalyst PEG400 and solvent glacial acetic acid at 5 h reaction. The optimum reaction conditions suggested by the RSM were the use of PEG400 (10.61 mol%) and glacial acetic acid (10.71 mL) for 5 h cycloocondensation. The experimental yield of 4,5-diphenyl-2-nitrophenyl-1H-imidazole (97%) was in agreement with predicted yield (97.5%).     

Some observations on catalytic conductometric titrations

Conductometric and high-frequency conductometric methods for the determination of the endpoint of catalytic titrations were developed. Titrations of sodium acetate were made in a mixture of acetic anhydride and acetic acid (7:3–11:3) which was 0.05–0.1 mol dm⁻³ in sodium perchlorate. Integral and derivative titration curves were recorded in both coulometric and volumetric titrations. Different acylation reactions, as well as dehydration of formic acid, were used as the indicator reactions. The optimal conditions of determination—choice of volume ratio of acetic anhydride to acetic acid, rate of the titrating reagent addition, concentration of sodium perchlorate, and concentration of several alcohols, water, and formic acid as components of the indicator reactions—were determined. Using the catalytic conductometric method, amounts of 0.04–11 mg of sodium acetate were determined with a relative standard deviation of less than 0.8 and 1.6% in volumetric and coulometric addition, respectively. Using the catalytic high-frequency conductometric method, amounts of 1–11 mg of sodium acetate were determined with relative standard deviation less than 0.5% (volumetrically) or less than 1.4% (coulometrically). The obtained results were compared with those of potentiometric and catalytic thermometric titrations.     

Synthesis and spectral and luminescent properties of 3-formyl-7-dialkylaminocoumarins

By means of the Vilsmeier reaction, starting with various 4-substituted 7-dialkylaminocoumarins having an open position 3, the corresponding 3-formyl derivatives have been obtained, and their spectral and luminescence characteristics have been studied. The ¹³C NMR spectra and acid—base properties of a number of the synthesized compounds have been examined.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1480–1487, November, 1991.     

Novel approach for developing urinary nucleosides profile by capillary electrophoresis-mass spectrometry

A simple, rapid and efficient capillary electrophoresis-mass spectrometry (CE-MS) method was developed to analyze urinary nucleosides for the first time. The composition of CE buffer and MS parameters were systematically optimized. The optimum buffer was 150 mM acetic acid containing 15% methanol and 15% ethanol. The optimum MS parameters were: methanol containing 0.5% acetic acid was selected as the sheath liquid and the flow rate was 5 microL/min; the flow rate and temperature of drying gas were 6L/min and 150 degrees C, respectively; the pressure of nebulizing gas was 2 psig; and the fragmentor and ESI voltage were 100 V and 4000 V, respectively. Under the optimum CE-MS conditions, the urinary nucleosides were separated within 18 min. The linearity between the relative peak areas and the corresponding concentration of nine nucleosides markers were excellent. The limits of detection (S/N=3) of markers were 0.00862-3.82 nmol/mL. The optimum CE-MS method was applied to analyze urine from 20 bladder cancer patients and 20 healthy volunteers. Considering the standards of many nucleosides cannot be obtained, it is not the ratios of the concentrations of nucleosides to that of creatinine in the literatures, but the ratios of the relative peak area of nucleosides to the concentration of creatinine that used for pattern recognition. And, the statistical analysis result indicated this method was feasible.