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Reported Reactions (reported + reaction)
Selected AbstractsImproved synthesis of [18F]fluoromethyl tosylate, a convenient reagent for radiofluoromethylationsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2005Timothy R. Neal Abstract The utility of [18F]fluoromethyl tosylate as an [18F]fluoromethylation reagent has been reexamined. The preparation of this potentially useful compound from the reaction of bis(tosyloxy) methane with 18F- was reported several years ago, but it had not found use as a labeling reagent. When the reported reaction of bis(tosyloxy) methane with 18F- was carried out, [18F]fluoromethyl tosylate was formed along with [18F]tosyl fluoride. The product ratio depended upon reaction conditions, with the yield of [18F]fluoromethyl tosylate usually in the range of 25,40%. Addition of a small amount of water to the reaction mixture resulted in a significant increase in the yield of [18F]fluoromethyl tosylate. Reaction conditions were defined that produced a yield of 71±6% of [18F]fluoromethyl tosylate (decay corrected). The product was conveniently purified by alumina chromatography. Reaction of [18F]fluoromethyl tosylate with the (des-fluoromethyl) fluticasone propionate thioacid precursor produced [18F]fluticasone propionate in improved yield (16%, from fluoride in production-scale runs) over other synthesis methods. Similarly, formation of [18F]choline, [18F]fluoromethionine and N- ([18F]fluoromethyl)spiperone from the reaction of [18F]fluoromethyl tosylate with corresponding precursors was examined. Copyright © 2005 John Wiley & Sons, Ltd. [source] Latex allergy: diagnosis and managementDERMATOLOGIC THERAPY, Issue 4 2004James S. Taylor ABSTRACT:, Latex allergy is an IgE-mediated immediate hypersensitivity response to natural rubber latex (NRL) protein with a variety of clinical signs ranging from contact urticaria, angioedema, asthma, and anaphylaxis. Major allergens include dipped latex products such as gloves and balloons. In highest risk for NRL allergy are patients with spina bifida, but health care workers and others who wear latex gloves are also at risk. NRL allergic patients may also react to fruits/foods, especially banana, kiwi, and avocado. Diagnosis is made by a positive latex RAST and/or skin prick test or challenge test to NRL. Allergen avoidance and substitution and the use of latex-safe devices including synthetic gloves (vinyl, synthetic polyisoprene, neoprene, nitrile, block polymers, or polyurethane) are essential for the affected patient. Accommodation in the workplace may include the use of powder-free, low-allergen NRL gloves or synthetic gloves. These preventive measures have significantly reduced the prevalence of reported reactions to NRL. Hyposensitization is not yet feasible. [source] Synthetic popularity reflects chemical reactivityJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2009Bartlomiej Kowalczyk Abstract Large and diverse databases of chemical reactions contain statistically significant information about the propensities of molecules to undergo specific chemical transformations. It is shown that this information can be quantified to reflect reaction thermodynamics/kinetics and can be used to construct primitive (yet accurate) reactivity indices from the counts of reported reactions involving molecules/molecular positions of interest. These indices correlate with frontier orbital (FO) populations or Hammett , and , parameters for a range of reactions involving aromatic substrates. These findings suggest that large chemical databases are not only a historical repository of chemical knowledge but also tools with which one can make useful chemical predictions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Asymmetric Sulfonium Ylide Mediated Cyclopropanation: Stereocontrolled Synthesis of (+)-LY354740CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Varinder K. Aggarwal Prof. Abstract The reaction of ester-stabilized sulfonium ylides with cyclopentenone to give (+)- 5 ((1S,5R,6S)-ethyl 2-oxobicyclo[3.1.0]hexane-6-carboxylate), an important precursor to the pharmacologically important compound (+)-LY354740, has been studied using chiral sulfides operating in both catalytic (sulfide, Cu(acac)2, ethyl diazoacetate, 60,°C) and stoichiometric modes (sulfonium salt, base, room temperature). It was found that the reaction conditions employed had a major influence over both diastereo- and enantioselectivity. Under catalytic conditions, good enantioselectivity with low diastereoselectivity was observed, but under stoichiometric conditions low enantioselectivity with high diastereoselectivity was observed. When the stoichiometric reactions were conducted at high dilution, diastereoselectivity was reduced. This indicated that base-mediated betaine equilibration was occurring (which is slow relative to ring closure at high dilution). Based on this model, conditions for achieving high enantioselectivity were established as follows: use of a preformed ylide, absence of base, hindered ester (to reduce ylide-mediated betaine equilibration), and low concentration. Under these conditions high enantioselectivity (95,% ee) was achieved, albeit with low diastereocontrol. Our model for selectivity has been applied to other sulfonium ylide mediated cyclopropanation reactions and successfully accounts for the diastereoselectivity observed in all such reported reactions to date. [source] | ||||||||||