The structures of lignans from Gmelina arborea Linn

Five new lignans isolated from Gmelina arborea Linn have been characterised. The parent compound arboreol, is 2a,6e-dipiperonyl-1e,2e-dihydroxy-3,7-dioxabicyclo-[3,3,0]-octane. It is accompanied by its 2-O-methyl ether, the 2-O-ethyl ether and its 2-epimer, isoarboreol,. The fifth substance, gmelanone, is the first reported example of a lignan derived from 3,6-dioxabicyclo-[3,2,1]-octane.     

Rapid Liquid Chromatographic – Tandem Mass Spectrometric Method for the Quantification of Pentoxifylline in Human Plasma

A simple, rapid, sensitive and selective liquid chromatography / tandem mass spectrometry method was developed and validated for the quantification of pentoxifylline, a haemorheological agent. The analyte and internal standard, tamsulosin were extracted by liquid-liquid extraction with ethyl acetate and were separated using an isocratic mobile phase on a reverse phase C₁₈ column. The analytes were analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M+H]⁺ ions, m/z 279/138 for pentoxifylline and m/z 409/228 for the IS. The assay exhibited a linear dynamic range of 2–1000 ng mL⁻¹ for pentoxifylline in human plasma. The lower limit of quantification was 2 ng mL⁻¹ with a relative standard deviation of less than 10%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 1.5 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies. Revised: 4 and 20 October 2005     

Characteristics of La-modified Ni-Al2O3 and Ni-SiO2 catalysts for COx-free hydrogen production by catalytic decomposition of methane

Hydrotalcite precursors of La modified Ni-Al₂O₃ and Ni-SiO₂ catalysts prepared by co-precipitation method and the catalytic activities were examined for the production of CO_x-free H₂ by CH₄ decomposition. Physico-chemical characteristics of fresh, reduced and used catalysts were evaluated by XRD, TPR and O₂ pulse chemisorptions, TEM and BET-SA techniques. XRD studies showed phases due to hydrotalcite-like precursors in oven dried form produced dispersed NiO species upon calcination in static air above 450 °C. Raman spectra of deactivated samples revealed the presence of both ordered and disordered forms of carbon. Ni-La-Al₂O₃ catalyst with a mole ratio of Ni : La : Al = 2 : 0.1 : 0.9 exhibited tremendously high longevity with a hydrogen production rate of 1300 mol_H2 ·mol^?1_Ni. A direct relationship between Ni metal surface area and hydrogen yields was established.     

Characteristics of La-modified Ni-Al2O3 and Ni-SiO2 catalysts for COx-free hydrogen production by catalytic decomposition of methane

Hydrotalcite precursors of La modified Ni-Al2O3 and Ni-SiO2 catalysts prepared by co-precipitation method and the catalytic activities were examined for the production of COx-free H2 by CH4 decomposition. Physico-chemical characteristics of fresh, reduced and used catalysts were evaluated by XRD, TPR and O2 pulse chemisorptions, TEM and BET-SA techniques. XRD studies showed phases due to hydrotalcite-like precursors in oven dried form produced dispersed NiO species upon calcination in static air above 450 C. Raman spectra of deactivated samples revealed the presence of both ordered and disordered forms of carbon. Ni-La-Al2O3catalyst with a mole ratio of Ni : La : Al = 2 : 0.1 : 0.9 exhibited tremendously high longevity with a hydrogen production rate of 1300 molH2 mol 1 Ni. A direct relationship between Ni metal surface area and hydrogen yields was established.     

A stability-indicating ultra-performance liquid chromatographic method for estimation of related substances and degradants in paliperidone active pharmaceutical ingredient and its pharmaceutical dosage forms

A simple, linear gradient, rapid, precise and stability-indicating analytical method was developed for the estimation of related substances and degradants of paliperidone API and tablets. The chromatographic separations were achieved using an Acquity ultra-performance liquid chromatograph (BEH 100 mm, 2.1 mm, 1.7 μm C-18 column) employing 0.01 M potassium dihydrogen phosphate buffer (pH 2.0) as mobile phase A and acetonitrile-water (9:1) as mobile phase B. A linear gradient (mobile phase A, mobile phase B in the ratio of 84:16) with a 0.45 mL/min flow rate was chosen. All six impurities were eluted within five minutes of run time. The column temperature was maintained at 25 °C and a detector wavelength of 238 nm was employed. Paliperidone was exposed to thermal, photolytic, hydrolytic and oxidative stress conditions. The stressed samples were analyzed by the proposed method. Considerable degradation of the analyte was observed when it was subjected to oxidative conditions and impurity F was found to be the major degradant. Peak homogeneity data of paliperidone obtained by photodiode array (PDA) detection demonstrated the specificity of the method in the presence of degradants. The method was validated with respect to linearity, precision, accuracy, ruggedness, robustness, limit of detection and limit of quantification.     

On the dependence of a characterization of proteomics maps on the number of protein spots considered

We have reexamined the numerical characterization of proteomics maps based on the construction of novel distance matrices associated with the nearest neighbor graph for the protein spots. In particular we consider dependence of a characterization of proteomics map on the number of proteins considered in the analysis. We examined a collection of proteomics maps in which we approximately doubled the number of spots to be used for quantitative analysis, considering cases of maps having 30, 50, 100, 250, 500, and 1054 protein spots. For each case we have compared the similarity-dissimilarity results for five proteomics maps of rat liver cells associated with the control group and four proliferators administrated by intraperitoneal injection. We found that proteins maps based on a set of about the 250 most abundant proteins spots suffice for a satisfactory numerical characterization of such maps.     

A short and efficient synthetic protocol for the synthesis of 5-substituted-4,6-dioxo-pyrrolo[2,3-d]pyrimidines

A short and efficient synthesis for 5-substituted-4,6-dioxo-pyrrolo[2,3-d]pyrimidines has been developed by the cyclocondensation of α,α-dibromoaldehydes with 2,4-diamino-6-hydroxypyrimidine under mild basic conditions in good yields. Application of this protocol has been demonstrated in the synthesis of a metabolite of Pemetrexed disodium, a novel multi-targeted antifolate.     

Kinetics and mechanism of quinolinium dichromate mediated oxidation of sugar alcohols in Bronsted acid media

Bronsted acid catalyzed oxidation of certain sugar alcohols (polyols) has been studied by quinolinium dichromate (QDC) using aqueous sulfuric, perchloric, and hydrochloric acids at different temperatures. At constant acidity, reaction kinetics revealed the second-order kinetics with a first order in [Alcohol] and [QDC]. Zucker-Hammett, Bunnett, and Bunnett-Olsen criteria were used to analyze acid-dependent rate accelerations. Bunnett-Olsen plots of (log k + H_ν) versus (H_ν + log [H⁺]), and (log k) versus (H_ν + log [H⁺]) afforded slope values (ϕ and ϕ^*, respectively) > 0.47, suggesting that a water molecule acts as a prton transfer agent in the slow step of the mechanism in the oxidation of alcohols by QDC in the presence of aqueous sulfuric, perchloric, and hydrochloric acids.