Stereoselective hydrolysis of amino acid esters by dipeptide catalysts and by N-decanoyl-histidine in surfactant aggregate domains

The rate constants of hydrolysis of the enantiomers of amino acid nitrophenyl esters by catalytic domains composed of cationic surfactant aggregates and dipeptide catalysts or Ndecanoyl-L -histidine have been determined at pH 7.30. The dipeptide catalysts shows large rate enhancement and stereoselectivity in aggregate domains. The surfactant structural effects are examined by investigation of the rate constants and stereoselectivities, and the nature of stereoselective catalysis is discussed.     

Three-step synthesis of 4-(2′-hydroxyethyl) azetidin-2-one and its substituted derivatives from 4-acetoxy-2-pyridones

4-(2'-Hydroxyethyl)azetidin-2-one, an important synthetic intermediate for carbapenem, and its substituted derivatives have been synthesized from 4-acetoxy-2-pyridones by photolysis, catalytic hydrogenation, followed by basic hydrolysis in the presence of sodium borohydride.     

Pipette tip solid-phase extraction and gas chromatography – mass spectrometry for the determination of methamphetamine and amphetamine in human whole blood

Methamphetamine and amphetamine were extracted from human whole blood samples using pipette tip solid-phase extraction (SPE) with MonoTip C₁₈ tips, on which C₁₈-bonded monolithic silica gel was fixed. Human whole blood (0.1 mL) containing methamphetamine and amphetamine, with N-methylbenzylamine as an internal standard, was mixed with 0.4 mL of distilled water and 50 μL of 5 M sodium hydroxide solution. After centrifugation, the supernatant was extracted to the C₁₈ phase of the tip (pipette tip volume, 200 μL) by 25 repeated aspirating/dispensing cycles using a manual micropipettor. Analytes retained in the C₁₈ phase were eluted with methanol by five repeated aspirating/dispensing cycles. After derivatization with trifluoroacetic anhydride, analytes were measured by gas chromatography – mass spectrometry with selected ion monitoring in the positive-ion electron impact mode. Recoveries of methamphetamine and amphetamine spiked into whole blood were more than 87.6 and 81.7%, respectively. Regression equations for methamphetamine and amphetamine showed excellent linearity in the range of 0.5–100 ng/0.1 mL. The limits of detection for methamphetamine and amphetamine were 0.15 and 0.11 ng/0.1 mL, respectively. Intra- and interday coefficients of variation for both stimulants were not greater than 9.6 and 13.8%, respectively. The determination of methamphetamine and amphetamine in autopsy whole blood samples is presented, and was shown to validate the present methodology.     

Pipette tip solid-phase extraction and gas chromatography-mass spectrometry for the determination of mequitazine in human plasma

Mequitazine has been found to be extractable from human plasma samples using MonoTip C₁₈ tips, inside which C₁₈-bonded monolithic silica gel was fixed. Human plasma (0.1 mL) containing mequitazine and cyproheptadine as an internal standard (IS) was mixed with 0.4 mL of distilled water and 25 μL of 1 M potassium phosphate buffer (pH 8.0). After centrifugation of the mixture, the supernatant fraction was extracted to the C₁₈ phase of the tip by 25 repeated aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C₁₈ phase were then eluted with methanol by five repeated aspirating/dispensing cycles. Without evaporation and reconstitution, the eluate was injected into a gas chromatograph injector and detected by a mass spectrometer with selected ion monitoring in the positive-ion electron impact mode. The separation of mequitazine and the IS from each other and from impurities was generally satisfactory using a DB-1MS capillary column (30 m × 0.32 mm i.d., film thickness 0.25 μm). The recoveries of mequitazine and the IS spiked into plasma were more than 90.0%. The regression equation for mequitazine showed excellent linearity in the range of 0.2-200 ng 0.1 mL⁻¹, and the detection limit was 0.05 ng 0.1 mL⁻¹of plasma. The intra-day and inter-day coefficients of variation for mequitazine in human plasma were not greater than 8.16 and 9.24%, respectively. Accuracy for the drug was in the range of 90.0-97.4%. The data obtained from determination of mequitazine in human plasma after oral administration of the drug are also presented.     

Determination of the acid value of instant noodles: interlaboratory study

An interlaboratory study was performed to evaluate the method for determining the acid value of instant noodles, based on the Japanese Agricultural Standard (JAS), with extraction of lipid using petroleum ether at a volume of 100 mL to the test portion of 25 g. Thirteen laboratories participated and analyzed 5 test samples as blind duplicates. Statistical treatment revealed that the repeatability (RSDr) of acid value was <6.5%, and the reproducibility (RSDR) of acid value was <9.6%. The HorRat values (RSDR/predicted RSDR) were 1.2-1.8, where the RSDR and the predicted RSDR were obtained in terms of free fatty acids in the noodles per unit weight, using the equation [acid value = percent free fatty acids (as oleic) x 1.99] and the extracted lipid contents. This method was shown to have acceptable precision by the present study.     

Simultaneous determination of ten antihistamine drugs in human plasma using pipette tip solid-phase extraction and gas chromatography/mass spectrometry

Ten antihistamine drugs, diphenhydramine, orphenadrine, chlorpheniramine, diphenylpyraline, triprolidine, promethazine, homochlorcyclizine, cyproheptadine, cloperastine and clemastine, have been found to be extractable from human plasma samples using MonoTip C18 tips, inside which C18- bonded monolithic silica gel was fixed. Human plasma (0.1 mL) containing the ten antihistamines was mixed with 0.4 mL of distilled water and 25 microL of a 1 M potassium phosphate buffer (pH 8.0). After centrifugation of the mixture, the supernatant fraction was extracted to the C18 phase of the tip by 25 repeated aspirating/dispensing cycles using a manual micropipettor. The analytes retained on the C18 phase were then eluted with methanol by five repeated aspirating/dispensing cycles. The eluate was injected into a gas chromatography (GC) injector without evaporation and reconstitution steps, and was detected by a mass spectrometer with selected ion monitoring in the positive-ion electron impact mode. The separation of the ten drugs from each other and from impurities was generally satisfactory using a DB-1MS column (30 m x 0.32 mm i.d., film thickness 0.25 microm). The recoveries of the ten antihistamines spiked into plasma were 73.8-105%. The regression equations for the ten antihistamines showed excellent linearity with detection limits of 0.02-5.0 ng/0.1 mL. The within-day and day-to-day coefficients of variation for plasma were not greater than 9.9%. The data obtained from determination of diphenhydramine and chlorpheniramine in human plasma after oral administration of the drugs are also presented.