Chemoselective Suzuki–Miyaura reactions of 4-trifluoromethylsulfonyloxy-6-bromocoumarin

Suzuki–Miyaura reactions of 4-trifluoromethylsulfonyloxy-6-bromocoumarin provide a convenient access to arylated coumarins. The reactions proceed with excellent chemoselectivity in favour of position 4.     

Synthesis and mass spectral studies of a coumarin analog of chloramphenicol

Preparation of dl-threo-2-dichloroacetamido-1-(3-coumarinyl)propane-1,3-diol ( 7 ) is discussed. The structures of the final compound ( 7 ) as well as its two precursors ( 5 and 6 ) were confirmed by ir and nmr studies. Because of the larger side chain, the coumarin analog ( 7 ) breaks down in a well defined manner upon electron impact. Its mass spectral fragmentation patterns are described.     

A heterocyclic analog of leucine-enkephalin

A series of di-, tri-, tetra- and pentapeptide analogs of leucine-enkephalin have been prepared in which the initial tyrosinylglycine fragment has been replaced by the 5,6-dihydro-5,5-dimethyl-2-oxo-3-phenyl-1(2H)-pyrazineacetic acid moiety.     

A new spectrophotometric method for assay of chloramphenicol

Summary Ninhydrin in the presence of SnCl₂ in 0.2M citrate buffer (pH 5) is proposed as a new reagent for the Spectrophotometric assay of chloramphenicol (CP), CP esters and CP in pharmaceutical formulations such as tablets, capsules, eye drops, eye ointments, ear drops and injections. The method is based on hydrolysis of chloramphenicol with 4M NaOH and subsequent treatment with ninhydrin reagent. The resulting violet colour exhibits maximum absorption at 570 nm. The Beer's law limits, molar absorptivity, effect of time and reagent concentration, and interference studies are reported.

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Eine neue spektrophotometrische Methode zur Bestimmung von Chloramphenicol

Zusammenfassung Für die spektrophotometrische Bestimmung von Chloramphenicol (CP) und CP-Estern in pharmazeutischen Präparaten (Tabletten, Pillen, Augentropfen, Augensalben, Ohrentropfen und Injektionspräparaten) wurde als neues Reagens Ninhydrin mit SnCl₂ in 0,2M Citratpuffer (pH 5) vorgeschlagen. Das Verfahren beruht auf der Hydrolyse von CP mit 4M NaOH und nachfolgender Behandlung mit dem Ninhydrinreagens. Die sich dabei ergebende Violettfärbung hat ihr Absorptionsmaximum bei 570 nm. Die Gültigkeitsgrenzen des Beerschen Gesetzes, die molare Absorbanz, der Einfluß der Zeit und der Reagenskonzentration sowie die Störfaktoren wurden angegeben.

     

A new pyrimidine analog of m-tyrosine

Synthesis of the hitherto unknown -(6-hydroxypyrimidyl-4)alanine, a pyrimidine analog of m-tyrosine, is effected. It is based on conversion of ethyl -(6-methoxypyrimidyl-4)pyrotartrate to an -hydroxyimino derivative followed by reduction of the latter in acid medium. The synthesis of -(6-hydroxypyrimidyl-4)alanine completes the preparation of the series of all theoretically possible pyrimidine analogs of m-tyrosine.A comparative study of amino acids I-Ic is in hand. The authors are very grateful to Prof. M. A. Prokof'ev for his continued interest in the present work.     

A simple oxidation of formycin to oxoformycin and oxoformycin B. Synthesis of 6-methyloxoformycin,A C-nucleoside analog of doridosine

A simple, high-yield procedure has now been developed for the direct oxidation of formycin to oxoformycin and oxoformycin B. Treatment of formycin (1) with bromine/water provided oxoformycin (8) . A similar treatment of formycin B (4) gave oxoformycin B (6) . Upon prolonged exposure of either 1 or 8 to bromine/water at reflux temperature, conversion to 6 occurred in good yield. Application of this procedure to 1-methylformycin (2) , 1-methylformycin B (5) and 2-methylformycin (17) gave 1-methyloxoformycin (9) , 1-methyloxoformycin B (7) and 2-methyloxoformycin (18) , respectively. Deamination of 8 and 9 with nitrosyl chloride also gave 6 and 7 , respectively. This selective oxidation of 6-methylformycin gave 7-amino-6-methyl-3-β-D-ribofuranosylpyrazolo[4,3-d]pyrimidin-5(4H)-one (10) , a C-nucleoside analog of doridosine. A similar oxidation of 1,6-dimethylformycin B (11) gave 1,6-dimethyloxoformycin B (12) . This direct introduction of the 5-oxo function into the pyrazolo[4,3-d]pyrimidine ring appears to be due to the attack of Br⁺ at N(4), followed by the addition of water to C(5) and subsequent elimination of hydrogen bromide from the transient intermediate 3 .     

一种合成柔红霉素糖基类似物的新方法

与很多蒽环类抗生素一样,柔红霉素分子中含有3-氨基2,3,6-三脱氧己糖单元,糖基部分对药物分子的活性起着至关重要的作用.本文介绍了一种合成柔红霉素糖基类似物的新方法.     

A comparison of pulser-based analog and digital spectrometers

We have begun a program of updates to the instruments used by the Radiation Measurements Laboratory at the Idaho National Laboratory. This laboratory supports the Advanced Test Reactor as well as many other programs throughout the INL. The first step in this upgrade is the updating of the gamma-ray spectrometry systems. Currently, these gamma-ray spectrometers use a standard spectroscopy amplifier and a pulser-based ADC. We have performed a series of tests to determine if a digital-signal processor-based system can replace these analog electronics, with little to no loss in performance.     

Chemiluminescence immunoassay for chloramphenicol

In recent years, various chemiluminescent clinical immunoassay kits have been widely applied to the detection of hormones. However, a kit for chloramphenicol (CAP) is often absent from most commercial product lists, even though it is important to control the levels of CAP residues in foodstuffs too. Therefore, we describe a simple, solid-phase chemiluminescence immunoassay (CLIA) for the measurement of CAP in foodstuffs. A rabbit anti-CAP IgG is passively adsorbed onto the walls of polypropylene plates. The labeled antigen is horseradish peroxidase (HRP) conjugate of CAP. Luminol solution is used as the substrate of HRP. The light yield is inversely proportional to the concentration of CAP. The method has a similar sensitivity (0.05 ng/ml), specificity, precision, and accuracy to a conventional enzyme immunoassay (EIA). The intra-assay and inter-assay CVs of ten samples were <8% and <20%, respectively, and the analytical recovery of the method was 87–100%. The experimental correlation coefficient of dilution was found to be 0.999 using milk supernatant as buffer. The detection limit for the method was 0.1–10 ng/ml, and it displayed good linearity.