Dibenzyl Structuresin a Macromolecular Chain. III. Dibenzyldiisocyanates Reactivity

The reactivity of the 2,2′-, 2,4′-, 4,4′-dibenzyldiisocyanate (2,2′-, 2,4′-, 4,4′-DBDI) with n-butanol in benzene has been studied. The concentrations of all species were monitored by using high performance liquid chromatography (HPLC). The reactivity of 4,4′-DBDI is similar to that of 4,4′-diphenylmethanediisocyanate (4,4′-MDI). Very strong intramolecular catalytic effects were noticed in the case of 2,2′-DBDI, probably due to the variable molecular geometry. These effects are responsible for the whole reaction pattern. The 2,4′-DBDI NCO ortho and para groups reactivities are different and comparable to that of 2,4-toluylenediisocyanate (2,4-TDI).     

Semi-targeted residue screening in complex matrices with liquid chromatography coupled to high resolution mass spectrometry: current possibilities and limitations

Some twenty cultured fish samples were analyzed for possible residues of veterinary drugs with high resolution mass spectrometry (single stage Orbitrap) coupled to ultra performance liquid chromatography. Quantitative analysis based on external standards covered 110 analytes. Some 116 additional compounds were monitored without having access to reference materials. Detection was based on calculated exact masses and narrow mass windows. Furthermore, a number of semi-targeted techniques were evaluated and compared to corresponding triple quadrupole precursor scan experiments. Single stage high resolution mass spectrometry was used to monitor compound specific product ions (without relying on a previous precursor selection). The capabilities of neutral loss searches based on exact masses were shown by detecting small concentrations of incurred oxytetracycline residues. High resolution mass spectrometry provided more sensitivity and selectivity than corresponding tandem quadrupole precursor and neutral loss scans. The currently limiting factor is the not adequate performance of the available software used for data mining. The high number of false positives that were produced, when searching for chlorine isotopic patterns, was clearly linked to the fact that the utilized software does not perform a peak deconvolution, but simply investigates one individual spectrum after another.     

Development of an improved high resolution mass spectrometry based multi-residue method for veterinary drugs in various food matrices

Multi-residue methods for veterinary drugs or pesticides in food are increasingly often based on ultra performance liquid chromatography (UPLC) coupled to high resolution mass spectrometry (HRMS). Previous available time of flight (TOF) technologies, showing resolutions up to 15,000 full width at half maximum (FWHM), were not sufficiently selective for monitoring low residue concentrations in difficult matrices (e.g. hormones in tissue or antibiotics in honey). The approach proposed in this paper is based on a single stage Orbitrap mass spectrometer operated at 50,000 FWHM. Extracts (liver and kidney) which were produced according to a validated multi-residue method (time of flight detection based) could not be analyzed by Orbitrap because of extensive signal suppression. This required the improvement of established extraction and clean-up procedures. The introduced, more extensive deproteinzation steps and dedicated instrumental settings successfully eliminated these detrimental suppression effects. The reported method, covering more than 100 different veterinary dugs, was validated according to the EU Commission Decision 2002/657/EEC. Validated matrices include muscle, kidney, liver, fish and honey. Significantly better performance parameters (e.g. linearity, reproducibility and detection limits) were obtained when comparing the new method with the older, TOF based method. These improvements are attributed to the higher resolution (50,000 versus 12,000 FWHM) and the superior mass stability of the of the Orbitrap over the previously utilized TOF instrument.     

Stereoselective Syntheses of Tetrahydrolipstatin and of an Analogue,Potent Pancreatic-Lipase Inhibitors Containing a β-Lactone Moiety

Tetrahydrolipstatin ( 1 ) and itsanalogue 2 are representatives of a new class of pancreatic-lipase inhibtors. Two stereoselective synthetic approaches are described.     

Flüssigphasen-Epitaxie zur Herstellung von Ga1−xAlxP-Heterostrukturen für optische Wellenleiter-Modulatoren

Ohne Zusammenfassung     

Buchbesprechungen

Ohne Zusammenfassung     

The aromatic amino acid constituent of echinocandin B: 3, 4-dihydroxyhomotyrosine (author's transl)]

The aromatic amino acid constituent of Echinocandin B: 3,4-Dihydroxyhomotyrosine. The antifungal antibiotic echinocandin B gave upon treatment of its tetrahydroderivative with anhydrous trifluoroacetic acid and subsequent methanolysis the tripeptide threonyl-(4-hydroxyprolyl)-(4-oxohomotyrosine) methyl ester ( 8 ), which could be hydrolysed to 4-oxohomotyrosine ( 11 ). These facts together with the earlier described hydrolysis of the antibiotic to 1-amino-3-p-hydroxyphenyl-2-propanone ( 6 ) and the reductive hydrolysis to homotyrosine suggested the presence of 3,4-dihydroxyhomotyrosine ( 14 ) as a constituent amino acid of echinocandin B. This was confirmed by a degradation of the intact tetrahydro-polypeptide with perjodate yielding p-hydroxybenzaldehyde and by the isolation of free 3,4-dihydroxyhomotyrosine upon mild acidic treatment of the tetrahydro-polypeptide.     

Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6-Oxo-isophoron. V. Synthese von Astacin

Technical Procedure for the synthesis of Carotenoids and Related Compounds from 6-Oxo-isophorone

1 Teil 4 dieser Reihe: [1].

. V. Synthesis of Astacene Starting from optically inactive astaxanthin intermediates, the highly oxygenated carotenoid astacene was synthesized in seven steps (55% overall yield from 6-oxo-isophorone). Key features of the new approach are base- and acid-catalyzed rearrangements of acetylenic intermediates such as those described in Schemes 2, 7 and 8.