Qingxiang Guo

A Facile and Efficient One‐Pot Synthesis of Dihydropyrimidinones Catalyzed by Magnesium Bromide Under Solvent‐Free Conditions

Abstract Magnesium bromide efficiently catalyzes the three‐component condensation reaction of aldehyde, β‐diketon and urea/thiourea under solvent‐free conditions to afford the corresponding dihydropyrimidinones in high yields and short reaction time.

Synthesis of substituted 1,4-dihydropyridines in water using phase-transfer catalyst under microwave irradiation

Abstract The synthesis of various substituted 1,4‐dihydropyridines has been achieved by the reaction of aldehydes, ethyl/methyl acetoacetates, and ammonium acetate in water using phase‐transfer catalyst under microwave irradiation. Compared to the classical Hantzschs reaction conditions, this new method consistently has the advantage of good yields and short reaction times. Bifunctional compounds containing two units have been synthesized using dialdehyde as precursor in good yields.

Simultaneous Determination of Hydrochlorothiazide and Valsartan in Human Plasma by Liquid Chromatography/Tandem Mass Spectrometry

Abstract A rapid and specific liquid chromatography/tandem mass spectrometry method was described for the simultaneous determination of hydrochlorothiazide and valsartan in human plasma. After extracted from plasma using methanol, hydrochlorothiazide, valsartan and hydroflumethiazide, irbesartan, used as the internal standard, respectively, were chromatographically analyzed on a Phenomenex Kromasil C8 column with water and methanol (27:73, v/v) as the mobile phase. Selected reaction monitoring was specific for mass detection employing negative electrospray ionization. The calibration standards were linear over the concentration range (3.13–800 ng/ml for hydrochlorothiazide and 11.72–3000 ng/ml for valsartan). The method was found to be suitable for application to a pharmacokinetic study after oral administration of dispersible tablet containing 12.5 mg hydrochlorothiazide and 80 mg valsartan to 20 healthy volunteers.

Rapid and sensitive liquid chromatography tandem mass spectrometry method for the quantification of ambroxol in human plasma

A sensitive, specific and rapid high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was described and validated for the quantification of ambroxol in human plasma using enalaprilat as the internal standard (IS). Chromatographic separation was performed on a Lichrospher CN column with a mobile phase of methanol and water (containing 0.1% formic acid) (70:30, v/v). The total run time was 5.0 min for each sample. The analytes was detected by mass spectrometry with electrospray ionization source in positive selected reaction monitoring mode. The precursor-fragment ion reaction for ambroxol was m/z 378.9 --> 263.8, and for IS was m/z 349.0 --> 205.9. The linearity was established over the concentration range of 1.56-400.00 ng/mL. The inter-day and the intra-day precisions were all within 10%. A simple protein precipitation with methanol was adopted for sample preparation. The extraction recoveries of ambroxol and IS were higher than 90.80%. The validated method was successfully applied in pharmacokinetic study after oral administration of 90 mg ambroxol to 24 healthy volunteers.

Determination of ritodrine in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

A simple and sensitive HPLC/MS/MS method was developed and evaluated to determine the concentration of ritodrine (RTD) in human plasma. Liquid-liquid extraction with ethyl acetate was employed as the sample preparation method. The structural analogue salbutamol was selected as the internal standard (IS). The liquid chromatography was performed on a Hanbon Sci. & Tech. Lichrospher CN (150 mm x 4.6 mm, i.d., 5 microm) column (Hanbon, China) at 20 degrees C. A mixture of 0.03% acetic acid and methanol (50:50, v/v) was used as isocratic mobile phase to give the retention time 3.60 min for ritodrine and 2.94 min for salbutamol. Selected reaction monitoring (SRM) in positive ionization mode was employed for mass detection. The calibration functions were linear over the concentration range 0.39-100 ng mL(-1). The intra- and inter-day precision of the method were less than 15%. The lower limit of quantification was 0.39 ng mL(-1). The method had been found to be suitable for application to a pharmacokinetic study after oral administration of 20mg ritodrine hydrochloride tablet to 18 healthy female volunteers. The half-life is 2.54+/-0.67 h.

Determination of Tropisetron in Human Plasma by Liquid Chromatography Tandem Mass Spectrometry

A fast and sensitive liquid chromatography tandem mass spectrometric method has been developed and validated for the determination of tropisetron in human plasma. The HPLC separation was performed on a Phenomenex Synergi Fusion RP80 column using acetonitrile −13 mM ammonium acetate – acetic acid (30:70:0.035, v/v) as the isocratic mobile phase. The assay was linear over the concentration range 0.5–128 ng/mL. The intra- and inter-assay precision was less than 11.6% for tropisetron. The method was successfully used to characterize the pharmacokinetic profiles of tropisetron in 20 healthy volunteers after an intravenous infusion of 5 mg tropisetron.

Sensitive LC‐MS‐MS method for the determination of tiopronin in human plasma

A highly selective and sensitive LC-MS-MS method was developed and validated to quantify tiopronin in human plasma, using fudosteine as the internal standard (IS). L-Cysteine and 1,4-dithiothreitol (DTT) were used as the reducer and the stabilizer to release and stabilify tiopronin from a dimmer and mix forms with endogenous thiols in the treatment of plasma samples. After a simple liquid-liquid extraction with ethyl acetate in acidic condition, the post-treatment samples were analyzed on a C(18) column interfaced with a triple-quadruple tandem mass spectrometer using negative electrospray ionization. Methanol and water (40:60, v/v) were used as the isocratic mobile phase, with 0.2% formic acid and 1.0 mM tris (hydroxymethyl) aminomethane (Tris) in water. The method was validated to demonstrate the specificity, lower limit of quantification, accuracy and precision of measurements. The assay was linear over the concentration range 0.078-10 microg/mL. The correlation coefficients for the calibration curves ranged from 0.9980 to 0.9990. The intra- and inter-day precisions, calculated from quality control samples, were not more than 10.49%. The method was employed in a pharmacokinetic study after oral administration of 200 mg tiopronin tablets to 24 healthy volunteers.

Sensitive LC-ESI/MS/MS assay for the quantification and pharmacokinetic study of roxithromycin in human serum

A simple and sensitive LC-ESI/MS/MS method is developed and evaluated to determine the concentrations of roxithromycin in human serum. Serum proteins are precipitated with methanol with clarithromycin as the internal standard. In order to reduce the pollution of sample, after vortex mixing and centrifugation, the supernatants are diluted with mobile phase before analysis on a Phenomenex Luna CN column (100 mm × 2.0mm i.d., 3 μm). The mobile phase composes of methanol, acetonitrile and 0.1% formic acid and 0.1% ammonium acetate in water (3: 3: 4, v/v/v) at a flow rate of 0.2 mL/min. The linearity ranges from 10 to 20480 ng/mL. The extraction recoveries of roxithromycin range from 97 to 101%. The method is successfully used to pharmacokinetic study of roxithromycin after an oral administration dose of 300 mg roxithromycin tablets to 20 healthy volunteers.

A Synthetic Study of Neutral and Cationic Cholesteryl Derivatives as Gene Vectors

Abstract Some novel neutral and cationic lipids bearing cholesteryl groups were synthesized. These lipids contain ketal units as linker bonds which should be easily biodegradable in cells.