Results 1 - 10 of 1431
Results 1 - 10 of 1431. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] A variety of physical and chemical properties of nitro compounds is determined by the characteristics of their molecular structure. We have carried out a series of works on the theoretical study of the IR absorption spectra of molecules containing nitro groups. In this work have studied the theoretical frequencies of the normal vibrations and the normal intensity of the IR absorption spectrum of 2,4,6-tenonitrozole molecule.
[en] CB 1954 (2,4-dinitro-5-aziridinyl benzamide) is a radiosensitizer which is up to 10 times more efficient in vitro than would be predicted on the basis of its electron affinity. In order to determine the contribution of the various functional groups comprising the molecule to overall sensitizing efficiency, nine structural analogues have been studied. Taken together, the data suggest that multiple mechanisms of radiosensitization may contribute to the abnormal radiosensitizing efficiency of CB 1954 and its analogues. This has implications for the further design and development of novel radiosensitizing drugs. (author)
[en] A brief survey of types of chemicals used as radiosensitizers for hypoxic cells is given together with an account of the quantitative structure-activity relationships in design of radiosensitizers, and a review of some aspects of imidazole chemistry. Attempts to prepare compounds of value as radiosensitizers are described. These compounds are either of the conventional type in that they contain nitro substituents as an aromatic nucleus or unconventional in that they have more than one electron-withdrawing substituent, each substituent taken separately being a less powerful electron-withdrawing group than the nitro group. Nitroimidazoles are important radiosensitizers but neuro-toxicity accompanies their use. The preparations of imidazoles having acid, ester, amide, cyano, aldehyde and ketone, carboxylic acid hydrazide and trifluoromethyl groups are described. It is interesting that the two of these compounds that were assessed showed high electron-affinity but very poor radiosensitizing properties. Some bicyclic systems carrying electron-withdrawing substituents were prepared. Sometimes the nitro substituent was included and the imidazole moiety featured in some of the bicyclic systems. (author)
[en] The published data on nitro derivatives of 1,3,5-triazine, belonging to the class of high-energy substances, have been systematised for the first time. The properties of C-nitrotriazines, nitraminotriazines and nitroalkyltriazines are considered. The data on the synthesis of previously unknown trisubstituted 1,3,5-triazines containing various functional groups including trinitromethyl groups are generalised.
[en] The mechanism of enhanced radiosensitization by nitroheterocyclics after a preincubation period under hypoxic conditions was investigated. The hypothesis that this phenomenon was caused by glutathione depletion was tested. The phenomena of enhanced radiosensitization by nitroheterocyclics after a preincubation period under hypoxic conditions is potentially of importance therapeutically because essentially nonlethal preradiation exposures to the electron affinic drugs cause a much larger radiation sensitization than would otherwise be expected. We have investigated this interesting property of several 2-nitroimidazoles to determine its possible cause and to test various hypotheses about maximizing its possible therapeutic benefit. In view of many observations that thiols are depleted by incubation of cells with nitroimidazoles under hypoxic conditions, we have specifically investigated this aspect of the preincubation effect. Depletion of glutathione was either enhanced by an overnight incubation with buthionine sulfoximine or minimized by preincubation with a 2-nitroimidazole which is sterically inhibited from causing thiol depletion. When conditions were chosen which minimized variations in cellular glutathione content during the preincubation period, no preincubation effect was observed. At low, therapeutically relevant radiation doses, where 2-nitroimidazoles are less efficient sensitizers, the preincubation effect may be even more important, but thiol depletion still minimizes its impact in this region of the dose-response curve. These results suggest that the preincubation effect is caused by a open-quotes self-sensitizationclose quotes involving the known enhancement of radiation sensitization by thiol depletion. 16 refs., 5 figs
[en] On the basis of our previous work, a new approach, nitro group charge method (NGCM) is established and applied to understand, evaluate and predict the properties of nitro compounds or explosives, including molecular stability, impact sensitivity and nitrating reaction. At first, the more negative nitro charges (QNitro) correspond to the more stable nitro compounds. Secondly, for all nitro explosives in which the R-Nitro bond is the weakest, QNitro can be regarded as a structural parameter to assess and predict the impact sensitivity. The more negative QNitro means the higher H50. Thirdly, the conditions, the velocities and the products' occurrence ratios of some nitrating reactions can be approximately evaluated and compared using NGCM: the more negative QNitro corresponds to the easier and the faster reaction, and the higher occurrence ratio. Meanwhile, this idea of using charges on common atoms or groups to investigate related properties can be generalized to some other systems such as azide explosives
[en] Data on new methods for the synthesis of fused azines by nucleophilic attack on the unsubstituted carbon atom of azines and nitroarenes are generalised. The review surveys tandem reactions of azines with binucleophiles comprising nucleophilic addition AN-AN nucleophilic addition-substitution AN-SipsoN, and nucleophilic substitutions SHN-SipsoN and SHN-SHN. Intramolecular SHN reactions of azines and nitroarenes and other methods for the synthesis of fused heterocycles based on SHN nucleophilic substitution are also discussed. The bibliography includes 69 references.
[en] The data on the synthesis, chemical transformations and practical use of aliphatic nitro alcohols published over the last 25 years are described systematically and analysed. The bibliography includes 316 references.
[en] Hydropalladium carboxylates, formed from π-allylpalladium chloride dimer plus carboxylic acids, have been shown to catalyze cyclization of structurally diverse enediynes to form the corresponding six- or five-membered rings depending upon the reaction conditions. Some enediynes having an oxygen linker in an appropriate position under the similar condition yielded the corresponding cyclopropanation products in highly stereoselective manner. A study using deuterated formic acid has proven that the alkylpalladium intermediates formed in our conditions were reduced by the pendant formate ligand. The dienediyne 10 yielded only the tricyclic product 12 in 67% yield, although it was expected to form the cyclic product 11. All these cyclizations seemed to occur via the corresponding alkylpalladium intermediates I, which could proceed to the corresponding cyclic products depending on the reaction conditions and the substrates. The study using deuterated formic acid could provide an important information to understand the present cyclization mechanism. Overall the present study could play an important role in developing new synthetic methodologies for constructing complex polycyclic compounds