- No-caririeir-added 11C-labelling of benzenoid compounds in ring positions by condensation of nitro-[11C]methane with pyrylium salts
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A new synthesis is described for three no-carrier-added nitro-[1-11C] benzenes 3a-c by condensation of nitro-[11C]methane (1) with the appropriate pyrylium salts 2a-c in the presence of a base such as t-BuOK in t-BuOH. For synthesizing 4-nitro-[4-11C]anisole (3a), tetrabutylammonium fluoride was successfully used as an auxiliary base. The best results were obtained in the synthesis of 3a. The conversion of 1 with 4-methoxypyrylium perchlorate (2a) yielded 3a of a radiochemical purity of up to 82% and a mean specific radioactivity of 30 GBq/μmol (0.8 Ci/μmol) within 20 min. Related to 1, the reproducible radiochemical yields of 3a are in the range of 77 ± 5% (decay-corrected). 2,6-Dimethyl-4-methoxy-nitro[1-11C]benzene (3b) was prepared by reaction of 1 with 2,6-dimethyl-4-methoxypyrylium perchlorate (2b) in radiochemical yields of about 37% (decay-corrected) within 10 min. 2-Nitro-[2-11C]mesitylene (3c) was obtained by condensation of 1 with 2,4,6-trimethylpyrylium tetrafluoroborate (2c) in radiochemical yields of about 29% (decay-corrected) within 20 min. 13C/11C Co-labelling experiments were carried out in order to confirm the identity of 3a-c and the position of the label.
- Maeding,Steinbach,Johannsen
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- Substituent effects on aromatic stacking interactions
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Synthetic supramolecular zipper complexes have been used to quantify substituent effects on the free energies of aromatic stacking interactions. The conformational properties of the complexes have been characterised using NMR spectroscopy in CDCl3, and by comparison with the solid state structures of model compounds. The structural similarity of the complexes makes it possible to apply the double mutant cycle method to evaluate the magnitudes of 24 different aromatic stacking interactions. The major trends in the interaction energy can be rationalised using a simple model based on electrostatic interactions between the π-faces of the two aromatic rings. However, electrostatic interactions between the substituents of one ring and the π-face of the other make an additional contribution, due to the slight offset in the stacking geometry. This property makes aromatic stacking interactions particularly sensitive to changes in orientation as well as the nature and location of substituents. This journal is The Royal Society of Chemistry.
- Cockroft, Scott L.,Perkins, Julie,Zonta, Cristiano,Adams, Harry,Spey, Sharon E.,Low, Caroline M. R.,Vinter, Jeremy G.,Lawson, Kevin R.,Urch, Christopher J.,Hunter, Christopher A.
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p. 1062 - 1080
(2007/12/27)
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- Amidinoureas substituted in both the urea and amidino nitrogen positions
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A method of inducing blood pressure reduction in humans and mammals by administering 2,6-disubstituted phenyl N-alkyl amidinoureas in which the phenyl ring is additionally substituted by a hydroxy, alkoxy, aralkoxy, alkenyloxy, alkynyloxy, acyloxy or halo acyloxy group and a novel class of amidinourea compounds having pharmaceutical uses, including blood pressure lowering activity.
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- Nitration in Aqueous Nitric Acid: the Rate Profile and the Limiting Reaction Rates
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Rate coefficients for the nitration of a series of quaternary ammonium ions have been used to establish a rate profile for reaction in 63.7percent-100percent nitric acid at 25 deg C and to estimate the concentration of nitronium ions in the aqueous media.The kinetics of nitration of a series of reactive aromatic aromatic compounds (mainly phenolic ethers) in aqueous nitric acid have been analysed in terms of a first-order rate coefficient and the zeroth-order rate of formation of the nitronium ion.The first-order rate coefficients approach a limiting value as the reactivity of the aromatic substrate is increased and this value is as expected for the rate-limiting formation of an encounter pair (ArH*NO2+).The lifetime of nitronium ions in 60.4percent nitric acid (t1/2 ca. 5 x 10-8 s) has been calculated from the zeroth-order rate at 25 deg C and used to show that the formation of the encounter pair (ArH*NO2+) occurs by the diffusion together of the components, not by pre-association.The studies on the more reactive aromatic compounds were carried out in the presence of hydrazine since this was shown to prevent the nitrous-acid catalysed reactions previously observed.
- Draper, Mark R.,Ridd, John H. A.
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