ortho-metalation of unprotected 3-bromo and 3-chlorobenzoic acids with hindered lithium dialkylamides

Upon treatment of 3-chloro/bromobenzoic acids with hindered lithium dialkylamides (LDA or LTMP) at -50 degrees C, lithium 3-chloro/bromo-2-lithiobenzoates are generated. These dianions can be trapped as such to afford after electrophilic quenching a variety of simple 2-substituted-3-chloro/bromobenzoic acids. The 3-bromo-2-lithiobenzoate is less stable than the corresponding 3-chloro derivative and partly eliminates lithium bromide, thus setting free lithium 2,3- and 3,4-dehydrobenzoates that can be intercepted in situ with the hindered base.     

Evidence for the intermediacy of arylbenzylnitrenium ions in the thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile

In contrast to the diaryl, dialkyl, alkylaryl, and parent series, nothing is known about the generation and chemical behavior of arylbenzylnitrenium ions. Herein, we report that these species can be generated by a process involving an unprecedented thermal rearrangement of isoxazolidines derived from C,N-diarylnitrones and 2-morpholin-4-yl-acrylonitrile. The products from these reactions are dramatically dependent upon the nature of the nitrone. Most of the observed chemistry originates from the singlet state.     

Near-field analysis of surface waves launched at nanoslit apertures

With the aim of analyzing the properties of the waves that are scattered by nanoslits on metallic surfaces, we provide a direct observation of the near-field in a slit-doublet experiment at optical wavelengths. We show that two distinct waves are involved: a surface plasmon polariton and another wave with a free-space character. From the recorded data, we have extracted the amplitudes and phases of these waves, their damping characteristic lengths and their relative weights as a function of the separation distance from the slit. The analysis is fully supported by a quantitative agreement with vector-theory computational results.     

Past, present and future of mass spectrometry in the analysis of residues of banned substances in meat-producing animals

A residue is a trace (microg kg(-1), ng kg(-1)) of a substance, present in a matrix. Banned substances, such as growth promoters, which are abused in animal fattening and where this article is focused on, may be divided into four major groups: thyreostats, anabolics or anabolic steroids, corticosteroids and beta-agonists or repartitioning agents. The combination of chromatographic techniques with mass spectrometry (GC-MS(n), LC-MS(n), etc.) plays a key role in the production of specific results in residue analysis. In this review, the past, present and future of mass spectrometry in this area are discussed in the light of the impact of these substances on human health and the reliable production of analytical results, ready for challenge in a court.     

Mass spectrometric detection of and similarities between 1-androgens

Regularly new anabolic steroids appear on the black market. In most cases these substances are marketed on websites or are confiscated during inspections. 1,(5alpha)-Androstene-17beta-ol-3-one, also known as 1-testosterone, is one of these substances presented to body-builders as a nutritional supplement or a pro-hormone. 1-Testosterone closely resembles the natural hormone testosterone except for a 1,2-double bound instead of a 4,5-double bound. 1-Androstene-3beta,17beta-diol is transformed into 1-testosterone after oral administration. 1-Testosterone, 1-androstene-3beta,17beta-diol and some other related 'new' anabolic steroids were studied with gas chromatography coupled to mass spectrometry (GC-MS) and Liquid chromatography coupled to tandem mass spectrometry (LC-MS2) methods. Similarities in spectra to known analytes, which may lead to pitfalls in the interpretation of the derivatised analytes, are discussed.     

Phytosterols and anabolic agents versus designer drugs

Cholesterol is a well-known component in fats of animal origin and it also is the precursor of natural hormones. Phytosterols appear in plants and only differ slightly in structure from cholesterol. An important difference however is the low absorption in the gut of phytosterols and their saturated derivatives, the phytostanols. As a result, there is time for all kind of reactions in faecal material inside and outside of the gut. Determination of the abuse of natural hormones may be based on gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Abuse of natural hormones changes the 13C/12C ratio of some metabolites during a relatively long time. The formation of (natural) hormones in the gut may interfere with this method. Designer drugs are mainly known from sports doping. In animal fattening, designer drugs may be used as well. Small changes in the structure of (natural) hormones may lead to a new group of substances asking for new strategies for their detection and the constatation of their abuse.     

Evidence for a trianion intermediate in the metalation of 4-hydroxy-6,7-dimethoxy-8-methyl-2-naphthoic acid. Methodology and application to racemic 5,5'-didesisopropyl-5,5'-dialkylapogossypol derivatives

The metalation of 4-hydroxy-6,7-dimethoxy-8-methyl-2-naphthoic acid (8) affording trianion 6 is presented and applied to the regioselective efficient construction of a series of 5,5'-didesisopropyl-5,5'-dialkylapogossypol derivatives 3 that are potent pan-active inhibitors of antiapoptotic Bcl-2 family proteins.     

Simple Stereocontrolled Synthesis of Methyl 2-Deoxy-d-erythro-hexopyranosid-4-uloses,Thromboxane B2 (TXB2) Precursors,from d-Galactose

Abstract

The stereospecific synthesis of methyl 3-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-2-deoxy-α-d-erythro-hexopyranosid-4-ulose (5) - a Thromboxane B₂ (TXB₂) precursor -starting from D-galactose is described. Facile and established methods including selective benzoylation, oxidation-elimination and a stereocontrolled hydrogenation (Pd/charcoal) were employed effectively.