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111.
Hirel C Luneau D Pécaut J Ohrström L Bussière G Reber C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(14):3157-3161
The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m space group with a=7.4050(7), c=8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953(2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temperature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by considering a two-dimensional square array of spin S=1/2 antiferromagnetically coupled (J=-10 cm(-1) and g=2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively. 相似文献
112.
Robert Kolodziuk Mustapha Tollabi Catherine Goux-Henry Denis Sinou 《Journal of organometallic chemistry》2003,687(2):384-391
Carbohydrate-substituted phosphines are easily obtained in quite good yields by coupling of protected or non-protected d-glucosamine with the corresponding diphenylphosphino acid. These neutral ligands, in association with palladium acetate, are very active catalysts in the Suzuki cross-coupling reaction. The polyhydroxy phosphines are more active than the peracetylated phosphines. The process tolerates electron-rich as well as electron-poor substituents. Excellent turnovers, up to 97?000 are observed. 相似文献
113.
Coutouli-Argyropoulou E Tsitabani M Petrantonakis G Terzis A Raptopoulou C 《Organic & biomolecular chemistry》2003,1(8):1382-1388
The Sonogashira coupling reaction of ethynylferrocene with adenine, uracil, tyrosine and steroid derivatives was studied; with the exception of tyrosine it was proved to be a good route for the attachment of ferrocene to these representative biomolecules. In addition the transformation of alkynyl uracil to furanopyrimidone derivatives was investigated and the formation of the furanopyrimidone ring was confirmed by an X-ray crystallographic analysis carried out on product 16. 相似文献
114.
Two- or three-component aza Diels-Alder reactions of Danishefsky's diene with imines or aldehydes and amines in water took place smoothly under neutral conditions in the presence of a catalytic amount of an alkaline salt such as sodium triflate to afford dihydro-4-pyridones in high yields. 相似文献
115.
[reaction: see text] The partial reduction of electron-deficient 2,5-disubstituted pyrroles has been developed into a flexible procedure that gives control of relative stereochemistry by variation of the reduction conditions. After the reaction, the pyrroline products were dihydroxylated at C-3,4 to give either the cis or trans isomers; this flexibility means that a variety of polyhydroxylated pyrrolidines can be prepared in a short sequence. Finally, this method was applied to a synthesis of the naturally occurring glycosidase inhibitor DMDP. 相似文献
116.
Dr. Jamal El Bakali Dr. Michal Blaszczyk Dr. Joanna C. Evans Dr. Jennifer A. Boland Dr. William J. McCarthy Imam Fathoni Dr. Marcio V. B. Dias Dr. Eachan O. Johnson Dr. Anthony G. Coyne Prof. Valerie Mizrahi Prof. Tom L. Blundell Prof. Chris Abell Dr. Christina Spry 《Angewandte Chemie (International ed. in English)》2023,62(17):e202300221
The coenzyme A (CoA) biosynthesis pathway has attracted attention as a potential target for much-needed novel antimicrobial drugs, including for the treatment of tuberculosis (TB), the lethal disease caused by Mycobacterium tuberculosis (Mtb). Seeking to identify inhibitors of Mtb phosphopantetheine adenylyltransferase (MtbPPAT), the enzyme that catalyses the penultimate step in CoA biosynthesis, we performed a fragment screen. In doing so, we discovered three series of fragments that occupy distinct regions of the MtbPPAT active site, presenting a unique opportunity for fragment linking. Here we show how, guided by X-ray crystal structures, we could link weakly-binding fragments to produce an active site binder with a KD <20 μM and on-target anti-Mtb activity, as demonstrated using CRISPR interference. This study represents a big step toward validating MtbPPAT as a potential drug target and designing a MtbPPAT-targeting anti-TB drug. 相似文献
117.
Quadrupole mass spectrometry has been employed to characterize the ionic species in the discharges of pure CH4, CH4/H2, and CH4/Ar systems. For pure methane, the major positive ions in the discharge at low pressure (e.g., 0.15 torr) are CH
3
+
, C2H
3
+
, CH
2
+
, C2H
2
+
, CH
4
+
, C2H
4
+
, and C2H
5
+
at high pressure (e.g., 0.5 torr) the major ions are CH
3
+
, C2H
3
+
, C2H
5
+
, C3H
3
+
, C H3H
7
+
, C4H
7
+
, C5H
7
+
, C6H
5
+
, and C7H
7
+
. The relative abundances of C1 ions decrease with increasing pressure, whereas those of higher-order ions increase with pressure. For 5% CH4 + 95% H2 mixture, in addition to those sampling from the pure methane plasma at the lower pressure, H
n
+
ions have also been detected. For 5% CH4 +95% Ar mixture, the principal ions are CH
3
+
, CH
2
+
, CH+, CH
5
+
, Ar+, and ArH+; the ions containing more than two carbon atoms are negligible. In these discharges, the CH
3
+
and C2H
3
+
are the most important positive ions in C1 and C2 ions, respectively. The ions detected are believed to come from the sheath between the electrode and the luminous plasma, and have high kinetic energy. An ion-molecule reaction mechanism is proposed which can well explain the observed main features of ionic products.Died June 1, 1991. 相似文献
118.
Ron Orlando Catherine Fenselau Robert J. Cotter 《Journal of the American Society for Mass Spectrometry》1991,2(3):189-197
Endothermic ion-molecule reactions in a tandem mass spectrometer have been used for a number of years for determining thermodynamic quantities, such as heats of formation and proton affinities, for gaseous ions. Recently, the reactive, endothermic collision has been exploited as an analytical technique for the structural analysis of peptides and other biomolecules. The technique is based upon the endothermic transfer of protons associated with amide bonds to ammonia. This reaction proceeds via a long-lived collision complex. When additional beam energy is supplied, other dissociation channels are opened up, leading to the production of sequence ions for the mass-selected, protonated analyte that are normally observed in high energy collision-induced dissociation spectra. The advantage, however, is that such spectra can be produced at very low beam energies. In this article, the rationale for developing this scheme, and its roots in previous ion-molecule studies, are explored. 相似文献
119.
Improved high-performance liquid chromatographic assay for the determination of ethionamide in serum
A solid-phase extraction (SPE) method was developed to simplify the preparation of human serum prior to high-performance liquid chromatography of ethionamide (ETA). Octadecyl SPE columns were used. Serum constituents were removed from the column with water, and ETA was eluted with methanol. Samples were evaporated to dryness, reconstituted in mobile phase, and assayed. The method is reproducible, with a recovery of ETA of 64%, comparable to the more tedious liquid-liquid extraction method for ETA. 相似文献