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  • 1
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A procedure was developed for the biosynthetic preparation of 15N-labelled guanosine and inosine through the action of a mutant Bacillus subtilis strain. Crude [N2,1,3,7,9-15N]guanosine and [1,3,7,9-15N]inosine were isolated from the culture filtrate by precipitation and anion-exchange chromatography (Scheme 1). No cell lysis and no enzymatic degradation was necessary. The per-isobutyrylated derivatives 1 and 2 were isolated from a complex mixture, purified by virtue of their different lipophilicity, and separated in three steps involving normal-and reversed-phase silica-gel chromatography. One litre of complex nutrient medium yielded 8.44 mmol of guanosine derivative and 2.84 mmol of inosine derivative with high average 15N enrichment (83.5 and 91.9 atom-%, resp.). [N6,1,3,7,9-15N]Adenosine (4) was obtained from 2′,3′,5′-tri-O-isobutyryl[1,3,7,9-15N]inosine (1) through the ammonolysis of its 1,2,4-triazolyl derivative with aqueous 15NH3 (Scheme 2).
    Additional Material: 4 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 567-571 
    ISSN: 0899-0042
    Keywords: enantiomer separation ; chromatographic resolution ; peak integration ; peak size ratio ; calibration curve ; determination of optical purity ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chromatographic quantitation of very low amounts of an enantiomer in the presence of its antipode can be an extraordinary challenge. If resolution of the peaks is not complete even at extreme mass ratios an integrator will yield inaccurate results due to geometric effects. A given resolution can be adequate for peaks of similar size but result in severe overlap if one of the signals is markedly smaller. If tailing occurs, which is more the rule than the exception, the problem is especially severe for last eluted small peaks. Additional obstacles are detector nonlinearity and other sources of unsatisfactory calibration curves, overloading phenomena, and the possible lack of standards of highest optical purity. These problems have been studied by computer simulations and the liquid chromatographic separation of (R,S)-phenylethyl naphthoic acid amide on a chiral stationary phase. © 1995 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
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  • 3
    ISSN: 0947-3440
    Keywords: Antibiotics ; Sorangium cellulosum ; Macrolides ; Mass spectrometry ; X-ray structure analysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two novel metabolites, sorangiolide A (1) and B (2), were isolated from the mother liquors and side fractions of the sorangicin A pilot-scale production. Their structures were elucidated by 2D-NMR spectroscopy and mass spectrometry as 18-membered macrolactones with a C11-carboxylic acid side chain. Sorangiolide B (2) differs from A (1) by an additional hydroxyl group at C-6 in the side chain. The absolute configuration of sorangiolide A (1) was established by X-ray structure analysis. The sorangiolides show a weak antibiotic activity against Gram-positive bacteria.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0947-3440
    Keywords: 4H-Pyrazole synthesis ; Dimethoxycarbene ; Diels-Alder reactions, „inverse“ ; Isopyrazolium ketal cations ; Phthalazinecarboxylates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,6-Diphenyl-1,2,4,5-tetrazine (6) reacts with dimethoxycarbene (7), generated from the 1,3,4-oxadiazoline 8, to yield the 4H-pyrazole 10. This is alkylated to the N-methyl-4H-pyrazolium tetrafluoroborate 12 in high yield. The alkylated, cationic azine system of 12 serves as electron-deficient diene in a [4+ + 2] cycloaddition with inverse electron demand and reacts diastereoselectively with several cyclic olefins as electron-rich dienophiles. The initially formed cationic [4+ + 2] adduct, e.g. 15, is unstable and rearranges probably via 16 to a racemic phthalazinecarboxylic ester of type 17. The crystal structures of the epoxyphthalazinecarboxylic ester 25 and of the trans-annulated cycloocta[d]pyridazine 27 were determined by X-ray diffraction. In contrast to the cyclic olefins, cyclooctyne (28) reacts with the pyrazolium cation 12 to yield the cyclooctapyridiazinium tetrafluoroborate 30 via the cycloadduct 29.
    Additional Material: 2 Ill.
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  • 5
    ISSN: 0947-3440
    Keywords: Cinnamic acids ; Cyclophanes ; Topochemistry ; Cycloadditions ; Photochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pseudo-gem cinnamophane dicarboxylic acid 1 was shown to undergo a stereospecific [2 + 2] photocycloaddition in the solid state, generating the truxinic acid derivative 2 in 100% chemical yield; the reaction can proceed to completion because it is not an “independent site” solid state reaction. The X-ray structure of 1 reveals that its molecules are associated in dimers formed from four almost linear hydrogen bonds. A salient feature is the intramolecular centre-to-centre distance between the reacting double bonds of ≈3.37 Å, the smallest known to date. In contrast to trans-cinnamic acid, the topochemical [2 + 2] photocycloaddition occurs also in solution, with a quantitative chemical yield and a quantum yield of ≈0.55 (in methanol).
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  • 6
    Publication Date: 2019-07-13
    Description: We present interstellar gas-phase abundances of zinc and chromium in the Milky Way for comparison with the abundances of these elements in damped Ly-alpha systems at redshifts near z approximately 2. We make use of both IUE (International Ultraviolet Explorer) and GHRS (Goddard High Resolution Spectrograph) archival information in deriving the Milky Way values and find that the average difference in (Zn/H) and (Cr/Zn) between the Milky Way and damped Ly-alpha systems at large N(H1) is about 0.9 dex. The Zn/H values we find for the Milky Way are approximately -0.2 to -0.7 dex below solar and are due in large part to depletion of Zn onto dust grains. The amount of this gas-phase depletion is variable and depends upon the H1 column density and molecular fraction of the gas. Milky Way sight lines having low molecular fractions have values of (Zn/H) within approximately 0.2 dex of the solar value. Combined with larger values of (Cr/Zn) found for the damped Ly-alpha systems, this result confirms that measures of (Zn/H) should accurately reflect the lower gas-phase abundances of Zn found in these systems.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 445; 1; p. L27-L30
    Format: text
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