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The design and synthesis of a new diazotransfer reagent, imidazole-1-sulfonyl azide hydrochloride, are reported. This reagent has proven to equal triflyl azide in its ability to act as a "diazo donor" in the conversion of both primary amines into azides and activated methylene substrates into diazo compounds. Crucially, this reagent can be prepared in a one-pot reaction on a large scale from inexpensive materials, is shelf-stable, and is conveniently crystalline. 相似文献
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Goddard-Borger ED Sakaguchi K Reitinger S Watanabe N Ito M Withers SG 《Journal of the American Chemical Society》2012,134(8):3895-3902
Xylanases capable of degrading the crystalline microfibrils of 1,3-xylan that reinforce the cell walls of some red and siphonous green algae have not been well studied, yet they could prove to be of great utility in algaculture for the production of food and renewable chemical feedstocks. To gain a better mechanistic understanding of these enzymes, a suite of reagents was synthesized and evaluated as substrates and inhibitors of an endo-1,3-xylanase. With these reagents, a retaining mechanism was confirmed for the xylanase, its catalytic nucleophile identified, and the existence of -3 to +2 substrate-binding subsites demonstrated. Protein crystal X-ray diffraction methods provided a high resolution structure of a trapped covalent glycosyl-enzyme intermediate, indicating that the 1,3-xylanases likely utilize the (1)S(3) → (4)H(3) → (4)C(1) conformational itinerary to effect catalysis. 相似文献
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SINGLET OXYGEN INDUCES FRANK STRAND BREAKS AS WELL AS ALKALI- AND PIPERIDINE-LABILE SITES IN SUPERCOILED PLASMID DNA 总被引:6,自引:0,他引:6
ED ROBERT BLAZEK JENNIFER G. PEAK MEYRICK J. PEAK 《Photochemistry and photobiology》1989,49(5):607-613
A covalently closed, circular, supercoiled plasmid was exposed to singlet oxygen by a separated-surface sensitizer. For each exposure, the quantity of single oxygen entering the DNA target solution was estimated by its oxidation of histidine. After singlet oxygen exposure, some DNA samples were treated to disclose occult lesions. Agarose gel electrophoresis was then used to resolve the unrelaxed supercoils from the relaxed circular and linear species, and all bands were quantitated fluorometrically. Exposure of supercoiled plasmid DNA to singlet oxygen induced frank DNA strand breaks, alkali-labile sites (pH 12.5, 90 degrees C, 30 min), and piperidine-labile sites (0.4 M, 60 degrees C, 30 min), all in a dose-dependent manner. Yields of alkali-labile and piperidine-labile sites ranged from one to four times the frank strand break yield. Replacement of buffered H2O by buffered D2O as the DNA solvent for singlet oxygen exposures increased DNA lesion yields by a factor of 2.6 (averaged over lesion classes). Our data for the detection of frank strand breaks is at variance with published results from studies in which singlet oxygen was derived from a thermolabile endoperoxide dissolved in the DNA solution. 相似文献
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Goddard-Borger ED Carapito R Jeltsch JM Phalip V Stick RV Varrot A 《Chemical communications (Cambridge, England)》2011,47(34):9684-9686
As part of continued efforts to understand the mechanisms of 1,5-α-l-arabinanases better, some arabinan-like iminosugar oligosaccharides were synthesized. An iminosugar analogue of arabinobiose was found to be a good inhibitor of the arabinanase Arb93A from Fusarium graminearum. Structures were determined for complexes of this inhibitor with wild-type Arb93A and a catalytically inactive mutant. 相似文献
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Fischer N Goddard-Borger ED Greiner R Klapötke TM Skelton BW Stierstorfer J 《The Journal of organic chemistry》2012,77(4):1760-1764
Imidazole-1-sulfonyl azide hydrochloride, an inexpensive and effective diazotransfer reagent, was recently found to be impact sensitive. To identify safer-to-handle forms of this reagent, several different salts of imidazole-1-sulfonyl azide were prepared, and their sensitivity to heat, impact, friction, and electrostatic discharge was quantitatively determined. A number of these salts exhibited improved properties and can be considered safer than the aforementioned hydrochloride. The solid-state structures of the chloride and less sensitive hydrogen sulfate were determined by single-crystal X-ray diffraction in an effort to provide some insight into the different properties of the materials. 相似文献
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