Ethyl-(r)-(4-methylphenylsulfinyl)-n-methoxy acetimidate a useful chiral acetate equivalent in aldol type condensations

Ethyl N-methoxyacetimidate was metallated by lithium amides and reacted with (-)-(S)-menthyl p-toluenesulfinate to afford, in excellent yield, (R) - (4-methylphenylsulfinyl)-ethyl-N-methoxy acetimidate (2). Compound (2) was tested in aldol-type condensations with various aldehydes, and the adducts, after desulfurization, were converted into optically active β-hydroxyesters with good ?80%) e.e. The stereochemical outcome of the reaction of benzaldehyde was found to be dramatically affected by changing either the counterion of the enolate from lithium to zirconium or by going from kinetic to thermodynamic control.     

Transfer reaction and molecular weight distribution in the anionic polymerization of formaldehyde

The anhydrous formaldehyde polymerization is examined. The influence of initiator and monomer concentration on the molecular weight and molecular weight distribution are emphasized. A mechanism for the transfer to the monomer is introduced. This mechanism is confirmed by experimental results and leads to the formation of formyl end groups. The influence of various initiators on the transfer reaction also is evaluated.     

Competitive Na(+) and Rb(+) binding in the minor groove of DNA

Sequence-dependent coordination of alkali ions to the nucleotide bases in the minor groove of AT-tract B-DNA has recently been inferred from X-ray crystallography, solution NMR and computer simulations. Here, we present new (23)Na and (87)Rb magnetic relaxation dispersion (MRD) data that demonstrate competitive and long-lived binding of Na(+) and Rb(+) ions in the minor groove of the B-DNA duplex [d(CGCGAATTCGCG)](2). The Na(+)/Rb(+) selectivity of the minor groove is found to be weak, consistent with local structural flexibility. The ion occupancies derived from the MRD data are substantially higher than previously reported, suggesting that groove-bound ions significantly influence the energetics and structural polymorphism of DNA in vivo. For example, in the presence of 0.20 M Na(+) and 0.56 M Rb(+) at 4 degrees C, the ApT site in the minor groove is occupied by a Rb(+) ion, a Na(+) ion, or a water molecule 40, 10, and 50% of the time, respectively. In the absence of Rb(+), the Na(+) occupancy increases to 50%. At 4 degrees C, the mean residence time of groove-bound ions is 0.2 +/- 0.1 micros for Rb(+) and 10 ns to 100 micros for Na(+). A shorter correlation time of 2 ns is attributed to counterions bridging cross-strand phosphate groups.     

Catalytic, enantioselective allylation of α-iminoesters promoted by silver(I) complexes of chiral imines

The catalytic enantioselective addition of allyltributylstannane to N-protected α-iminoesters promoted by silver(I) trifluoromethanesulfonate in the presence of chiral imine ligands was studied. After testing several chiral imines derived from 1,2-diaminocyclohexane and binaphthyl diamine a very simple experimental procedure was developed that allowed us to obtain optically active homoallylic amines in very high yields and enantioselectivities up to 71%.     

Study of carbon,hydrogen and nitrogen determination by combustion-gas chromatography

Summary The method for carbon-hydrogen-nitrogen determination based on dynamic rapid combustion of the sample, gas chromatographic separation and thermal-conductivity measurement of the gases N₂, CO₂ and H₂O is critically considered and improved. In order to achieve instantaneous combustion of all types of organic compounds, oxidizable metallic containers are used for the sample and dropped in the hot combustion zone while the carrier gas is momentarily enriched with pure oxygen. Flash combustion of the sample is followed by catalytic oxidation on a newly developed active catalyst. This reagent, adsorption-free and thermally resistent, consists of pure chromic oxide, mechanically compressed and granulated. Copper treated with silver is used as reducing reagent. Unwanted gases are eliminated with Co₃O₄ containing silver, and by utilizing the chemiadsorption properties of the column packing. Measurements are made by integrating and printing the electrical signal. The analytical process is controlled by means of a potentiometric recorder. The increased combustion capacity, the practical absence of blanks and the very extended linearity of response of the detector make possible CHN determination in sample sizes of 0.1–3 mg. Except for sample weighing and calculation of results from the printed integration values, all the operations are automatically controlled by a preset programme.

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Zusammenfassung Das Verfahren zur Bestimmung von C, H und N, das auf der dynamischen Schnellverbrennung der Probe, der gaschromatographischen Trennung und Wärmeleitfähigkeitsmessung der Gase N₂, CO₂ und H₂O beruht, wurde kritisch überdacht und verbessert. Um die sofortige Verbrennung aller Arten organischer Verbindungen zu erzielen, wurden die in oxydierbaren Metallbehältern eingewogenen Proben in die heiße Zone des Verbrennungsrohres eingeführt, während gleichzeitig das Transportgas kurzfristig mit Sauerstoff angereichert wurde. Die Verbrennung erfolgt durch katalytische Oxydation an einem neu entwickelten Kontakt, der nicht adsorbiert, hitzebeständig ist und aus reinem, gepreßtem und gekörntem Chromoxid besteht. Versilbertes Kupfer dient als Reduktionsmittel. Störende Gase werden mit silberhältigem Co₃O₄ sowie durch Chemisorption an der Säulenfüllung entfernt. Die elektrischen Signale werden integriert und ausgedruckt. Der ganze analytische Vorgang wird durch einen Spannungsschreiber kontrolliert. Die erhöhte Verbrennungskapazität, das praktisch vollständige Fehlen eines Blindwertes sowie die weitgehende Linearität der Detektoranzeige erlauben CHN-Bestimmungen in nur 0,1 bis 3 mg Probe. Abgesehen von der Einwaage und der Berechnung der Resultate aus den ausgedruckten Werten verlaufen alle Vorgänge automatisch und programmiert.

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Dedicated to the memory of Dr. Wolfgang Schöniger.     

Microbial growth and air pollution in carbonate rock weathering. Preliminary results of a in situ experimental study

Preliminary results on limestone weathering caused by air pollution and microbial colonization are presented in this study. Outdoor exposure experimental assays were performed on Scaglia limestone samples. Samples were exposed in two areas in Perugia (Italy) that differ for degree of urban air pollution. At different times of exposure, ranging from 1 to 12 months, microbial contamination and textural modifications of sampled surfaces were evaluated by microbiological procedures, X-ray diffraction, and scanning electron microscopy. After one year of exposure a significant fungal colonization and the presence of weathering products (i.e. gypsum) were detected on sampled surfaces.     

Liquid chromatographic determination of triasulfuron in soil

Two extraction methods were developed for the determination of triasulfuron in soil. Method I included extraction with methanol-phosphate buffer at pH 7 (2 + 1, v/v), liquid-liquid partition with dichloromethane, and cleanup on a liquid chromatographic Si adsorption solid-phase extraction tube. In Method II, Extrelut was added and the sample was then extracted with acetonitrile. In both cases, the extracts were analyzed by liquid chromatography (LC) with UV detection and the LC peak was confirmed by LC/mass spectrometry (MS). The 2 methods were tested on 3 soils having different physicochemical characteristics. Method I gave 83% average recovery and a determination limit of 0.4 microg/kg soil. Method II gave 67% average recovery and a determination limit of 2 microg/kg soil. Examples of application of Method I to field samples are reported.     

2,6-Pyridinedimethanol from 2,6-lutidine. A comparison of chlorination and oxidation routes

Chlorination of lutidine to 2,6-bis(chloromethyl)pyridine, or its catalytic oxidation to 2,6-pyridinedicarboxaldehyde, respectively, followed by hydrolysis or by hydrogenation to the end product, were investigated as possible routes for the title process. In both cases interesting overall yields were obtained. The choice between the routes seems then to depend more on economical, rather than on chemical considerations.

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2,6- () 2,6- , . . , , , .

     

EPR study of iron-doped MFI zeolite and silicalite catalysts: effect of treatments after synthesis

The systematic study of iron-doped MFI zeolite and MFI silicalite by X- and Q-band EPR spectroscopy is reported in this paper. Both samples, which contain Fe(III) ions in the MFI lattice, underwent three sequential treatments—calcination, steaming, and washing with sodium dithionite solution—which are needed to make the catalyst active by extracting iron ions from the lattice. EPR spectra could be simulated by assuming a broad distribution of spin-spin (zero-field) coupling parameters. The simulation parameters depend on sample history and reproduce the selective intensity changes that are observed in X-band spectra after each treatment. In particular, the distribution width decreases by calcining and steaming samples and then it increases by treating with aqueous dithionite solution. This is in agreement with the view that iron ions are extracted from the framework by calcining and by steaming and may form relatively large iron oxide particles which become smaller after the chemical treatment. We have also studied the temperature dependence of the EPR spectra. The most interesting results are from the steamed samples. Their behavior has been interpreted as due to the presence of superparamagnetic single domain particles of iron oxide. This agrees with the view that iron oxide particles form during steaming.     

High-performance liquid chromatography/tandem mass spectrometry for the quantitative analysis of a novel taxane derivative (BAY59-8862) in biological samples and characterisation of its metabolic profile in rat bile samples

A sensitive, specific, accurate and reproducible high-performance liquid chromatography (HPLC) analytical method was developed and validated for the quantification of the novel oral taxane analogue BAY59-8862 in mouse plasma and tissue samples. A fully automated solid-phase extraction procedure was applied to the plasma after internal standard (IS) addition, with only 0.2 mL volume of the sample loaded on a CN-Sep-pak cartridge. In the case of the tissues a very simple acetonitrile extraction was used to recover BAY59-8862 and its internal standard from liver. The procedure for the quantification of BAY59-8862 and its IS (IDN5127) is based on high-performance liquid chromatography/ion spray-tandem mass spectrometry, operating in selected ion monitoring mode. The retention times of BAY and IS were 7.21 and 10.36 min, respectively. In both plasma and tissue specimens the assay was linear in the range 50-5000 ng/mL (ng/g). The overall precision and accuracy were assessed on three different days. The results for plasma were within 6.1% (precision) and between 99 and 112% (accuracy), and for the liver samples within 7.3% and between 104 and 118%, respectively. The LOD was 5 ng/mL and 20 ng/g in the plasma and liver, respectively. In addition, the biliary excretion of the compound in rats was studied. The study showed that an oxidative chemical reaction was the preferred metabolic pathway for biliary excretion, and two sets of mono- and dihydroxylated metabolites were detected by LC/ISP-MS/MS experiments. With this method, BAY59-8862 pharmacokinetic was determined in mice. The combined results demonstrate that the methodology can be considered a valid approach to conduct pharmacokinetic and metabolic studies during preclinical and clinical investigations.