β-Ketonitrosamines. Synthetic Equivalents of α-Methylene Alkylamino Anions (−CH2NHR)

Abstract

β-Ketonitrosamines are important in the study of nitrosamine metabolism, carcinogenesis and in vivo alkylation. The enhanced acidity of protons at the α-carbon, as well as the ease of fragmentation of the title compounds establishes them as synthetic equivalents of α-methylene alkylamino anions (^?CH₂NHR). Anion formation is carried out with powered sodium hydroxide-sodium carbonate in DMF or THF at 25°C. Reaction with an alky halide gives a good yield of the alkylated product. Retro-Claisen cleavage in aqueous basic media gives the corresponding dialkyl-nitrosamine or, with D₂O, the deuterated analog.     

The Effects of Added Hydrogen on a Helium Atmospheric-Pressure Plasma Jet Ambient Desorption/Ionization Source

We present mass spectrometric data demonstrating the effect that hydrogen has on a helium-based dielectric-barrier discharge (DBD) atmospheric-pressure plasma jet used as an ambient desorption/ionization (ADI) source. The addition of 0.9 % hydrogen to the helium support gas in a 35-W plasma jet increased signals for a range of test analytes, with enhancement factors of up to 68, without proportional increases in background levels. The changes in signal levels result from a combination of changes in the desorption kinetics from the surface and increased ion production in the gas phase. The enhancement in ADI-MS performance despite the quenching of key plasma species reported in earlier studies suggests that ionization with a H₂/He plasma jet is the result of an alternate mechanism involving the direct generation of ionized hydrogen.      

New cytotoxic diterpenes from rondeletia panamensis (rubiaceae)

From the wood stem and stem bark of the Panamanian plant Rondeletia panamensis (Rubiaceae), three novel diterpenes have been isolated. The structure of oxidopanamensin (2) was determined by single crystal X-ray crystallography of the diacetate derivative. Panamensin (4) was correlated with oxidopanamensin (2) by epoxidation under alkali conditions and with rondeletin (6) by hydrogenation to 14,15-dihydrorondeletin (8). Of the three isolates, panamensin (4) and oxidopanamensin (2) were cytotoxic in the KB test system but rondeletin was inactive.     

Influence of transport properties in electric field gradient focusing

Miniaturized devices for electric field gradient focusing (EFGF) were developed that consist of a cylindrical separation channel surrounded by an acrylic-based polymer hydrogel. The ionic transport properties of the hydrogel enable the manipulation of the electric field inside the separation channel. A changing cross-section design was used in which the hydrogel is shaped such that an electric field gradient is established in the separation channel. One of the challenges with this type of EFGF device has been that experimental resolution between protein analytes is lower than theoretically predicted. In order to investigate this phenomenon, a mathematical transport model was developed using FEMLAB. Model results and experimental observations showed that the reduced performance was caused by concentration gradients formed in the EFGF channel, and that these concentration gradients were the result of an imbalance in cation transport between the open separation channel and the hydrogel. Removing acidic impurities from the monomers that form the hydrogel reduced this tendency and improved the resolution. These transport-induced concentration gradients can be used to establish electric field gradients that may be useful for sample pre-concentration. Both the results of simulation and experiments demonstrate how transport-induced concentration gradients lead to the establishment of electric field gradients.     

Interactions of a propeller with a stator-induced circumferentially varying flow

The interactions of a circumferentially varying stator cascade and a downstream fixed pitch propeller were investigated experimentally. The global performance of the components and the coupled system were systematically investigated through force and moment measurements on the propulsor model in a water tunnel. In addition, the wake of the cyclic stator cascade with and without the propeller was investigated downstream from a propulsor model using the Stereoscopic PIV technique. A cyclic distribution of the stators’ deflections resulted in non-axisymmetric distributions of the flow field downstream of the stator array. The stator distribution alone produced a significant side force that increased linearly with stator pitch amplitude. When a propeller was incorporated downstream from the cyclic cascade, the side force from the stator cascade was reduced, but a small normal force and pitching moment were created. The generation of these secondary forces and moments can be related to the redistribution of the tangential flow from the cyclic cascade into the axial direction by the retreating and advancing blade states of the fixed pitch propeller.     

Efficient immobilization of a cadmium chemosensor in a thin film: generation of a cadmium sensor prototype

[reaction: see text] The development of an ion-selective chemosensor for Cd(2+) allows generation of a "real-time" sensor. Immobilization of the chemosensor on quartz was achieved in a simple monolayer and in a thin film using a polymer intermediary. As intended, the thin film contains much more chemosensor than the monolayer and provides measurable responses to aqueous Cd(2+) concentrations below 1 microM. Alkali and alkaline earth ions do not interfere with Cd(2+) sensing; Zn(2+) and Cu(2+) are potential interferents.     

Edulisones A and B, two epimeric benzo[b]oxepine derivatives from the bark of Aglaia edulis

Two benzo[b]oxepine derivatives, edulisones A (1) and B (2), were isolated from the bark of Aglaia edulis, collected in Indonesia. The relative stereochemistry of 1 was determined by single-crystal X-ray diffraction analysis. Treatment of compounds 1 and 2 with lithium hydroxide produced the same hydrolysis products, 1a and 1b, as a result of cleavage of the pyrrolidine ring to an alkylated amide mixture in each case, which demonstrated that these substances are epimeric at their 2-aminopyrrolidine moiety.     

Novel cytotoxic 1H-cyclopenta[b]benzofuran lignans from Aglaia elliptica

Bioassay-guided fractionation of the stems and fruits of Aglaia elliptica using human oral epidermoid carcinoma (KB) cells, led to the isolation of five cyclopenta[b]benzofurans, constituted by methyl rocaglate (1) and four novel compounds (2–5), along with three known dammarane triterpenoids. Compound 5 possesses an unusual formyl ester substituent at the C-1 position. The structures of the novel compounds were established on the basis of spectroscopic methods. Compounds 1–5 were found to be very potent cytotoxic substances when evaluated against a panel of human cancer cell lines.     

The Effects of Added Hydrogen on Noble Gas Discharges Used as Ambient Desorption/Ionization Sources for Mass Spectrometry

We demonstrate the effectiveness of using hydrogen-doped argon as the support gas for the dielectric barrier discharge (DBD) ambient desorption/ionization (ADI) source in mass spectrometry. Also, we explore the chemistry responsible for the signal enhancement observed when using both hydrogen-doped argon and hydrogen-doped helium. The hydrogen-doped argon was tested for five analytes representing different classes of molecules. Addition of hydrogen to the argon plasma gas enhanced signals for gas-phase analytes and for analytes coated onto glass slides in positive and negative ion mode. The enhancements ranged from factors of 4 to 5 for gas-phase analytes and factors of 2 to 40 for coated slides. There was no significant increase in the background. The limit of detection for caffeine was lowered by a factor of 79 using H₂/Ar and 2 using H₂/He. Results are shown that help explain the fundamental differences between the pure-gas discharges and those that are hydrogen-doped for both argon and helium. Experiments with different discharge geometries and grounding schemes indicate that observed signal enhancements are strongly dependent on discharge configuration.

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