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141.
Delest B Nshimyumukiza P Fasbender O Tinant B Marchand-Brynaert J Darro F Robiette R 《The Journal of organic chemistry》2008,73(17):6816-6823
A divergent and regioselective synthesis of 1,2,4- and 1,2,5-trisubstituted imidazoles from a readily available (two steps) common intermediate has been developed. This methodology is based on the regiocontrolled N-alkylation of 1-(N,N-dimethylsulfamoyl)-5-iodo-2-phenylthio-1H-imidazole (10). When this intermediate is engaged in reaction with methyl triflate, selective formation of the corresponding 1,2,5-trisubsituted 1H-imidazole is observed. NMR studies have revealed that this regioselectivity can be accounted for by in situ rapid isomerization of 10 into its 1,2,4-isomer (13) followed by regiospecific N-alkylation of the latter. Conversely, when key intermediate 10 is slowly added to Meerwein's salt, isomerization can be constrained and regiospecific N-alkylation of 10 leads to 1,2,4-trisubstituted 1H-imidazole with a high selectivity. The general character of this methodology has been illustrated by showing that iodine in position 4 or 5 could be easily substituted by an aryl group by Suzuki coupling, whereas the phenylthio group at position 2 could, after oxidation into sulfone, be displaced by nucleophilic substitution. 相似文献
142.
Schelter EJ Veauthier JM Graves CR John KD Scott BL Thompson JD Pool-Davis-Tournear JA Morris DE Kiplinger JL 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(26):7782-7790
Reaction of two equivalents of [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) or [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) with 1,4-dicyanobenzene leads to the formation of the novel 1,4-phenylenediketimide-bridged bimetallic organoactinide complexes [{(C(5)Me(4)Et)(2)(Cl)U}(2)(mu-{N==C(CH(3))-C(6)H(4)-(CH(3))C==N})] (8) and [{(C(5)Me(5))(2)(Br)Th}(2)(mu-{N==C(CH(3))-C(6)H(4)- (CH(3))C==N})] (9), respectively. These complexes were structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy. Metal-metal interactions in these isovalent bimetallic systems were assessed by means of cyclic voltammetry, UV-visible/NIR absorption spectroscopy, and variable-temperature magnetic susceptibility. Although evidence for magnetic coupling between metal centers in the bimetallic U(IV)/U(IV) (5f(2)-5f(2)) complex is ambiguous, the complex displays appreciable electronic communication between the metal centers through the pi system of the dianionic diketimide bridging ligand, as judged by voltammetry. The transition intensities of the f-f bands for the bimetallic U(IV)/U(IV) system decrease substantially compared to the related monometallic ketimide chloride complex, [(C(5)Me(5))(2)U(Cl){-N==C(CH(3))-(3,4,5-F(3)-C(6)H(2))}] (11). Also reported herein are new synthetic routes to the actinide starting materials [(C(5)Me(4)Et)(2)U(CH(3))(Cl)] (6) and [(C(5)Me(5))(2)Th(CH(3))(Br)] (7) in addition to the syntheses and structures of the monometallic uranium complexes [(C(5)Me(4)Et)(2)UCl(2)] (3), [(C(5)Me(4)Et)(2)U(CH(3))(2)] (4), [(C(5)Me(4)Et)(2)U{-N==C(CH(3))-C(6)H(4)-C==N}(2)] (10), and 11. 相似文献
143.
The site-specific recognition of abasic sites and single base bulges in duplex DNA by sterically expansive rhodium metalloinsertors has been investigated. Through DNA photocleavage experiments, Rh(bpy)2(chrysi)3+ is shown to bind both abasic sites and single base bulges site-specifically and, upon irradiation, to cleave the backbone of the defect-containing DNA. Photocleavage titrations reveal that the metal complex binds DNA containing an abasic site with high affinity (2.6(5) x 106 M-1), comparably to the metalloinsertor and a CC mismatch. The complex binds single base bulge sites with lower affinity (approximately 105 M-1). Analysis of cleavage products and the correlation of affinities with helix destabilization suggest that Rh(bpy)2(chrysi)3+ binds both lesions via metalloinsertion, as observed for Rh binding at mismatched sites, a binding mode in which the mismatched or unpaired bases are extruded from the helix and replaced in the base stack by the sterically expansive ligand of the metalloinsertor. 相似文献
144.
Gadolinium chelate coated gold nanoparticles as contrast agents for both X-ray computed tomography and magnetic resonance imaging 总被引:1,自引:0,他引:1
Alric C Taleb J Le Duc G Mandon C Billotey C Le Meur-Herland A Brochard T Vocanson F Janier M Perriat P Roux S Tillement O 《Journal of the American Chemical Society》2008,130(18):5908-5915
Functionalized gold nanoparticles were applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. These particles were obtained by encapsulating gold cores within a multilayered organic shell which is composed of gadolinium chelates bound to each other through disulfide bonds. The contrast enhancement in MRI stems from the presence of gadolinium ions which are entrapped in the organic shell, whereas the gold core provides a strong X-ray absorption. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in the lungs, spleen, and liver. 相似文献
145.
146.
Ito FM Petroni JM de Lima DP Beatriz A Marques MR de Moraes MO Costa-Lotufo LV Montenegro RC Magalhães HI Pessoa Cdo O 《Molecules (Basel, Switzerland)》2007,12(2):271-282
Part of our research program concentrates on the discovery of new bioactive compounds prepared either by total synthesis or molecular transformation of compounds with bioactivity profiles. In this work we have focused our interest on chemical transformations of the Diels-Alder adduct tricyclo[6.2.1.0(2,7)]undeca-4,9-dien-3,6-dione in order to obtain cage-like compounds and derivatives, followed by an evaluation of their biological activity. 相似文献
147.
A cyclometalated complex of Ir(III) is covalently tethered to DNA oligonucleotides and serves as both a photooxidant and photoreductant in the study of DNA-mediated hole transport (HT) and electron transport (ET). Spectroscopic and melting temperature studies support intercalation of the tethered complex into the DNA duplex through the functionalized dppz ligand. Using these tethered assemblies, ET and HT is initiated in DNA by the same photoredox probe. Cyclopropylamine substituted bases, N4-cyclopropylcytosine (CPC) and N2-cyclopropylguanine (CPG) are used as kinetically fast electron and hole traps to probe the resulting electron migration processes after direct irradiation of the tethered Ir assembly. Oxidation of CPG and CPC is promoted efficiently by HT from photoexcited Ir(III) when the modified bases are positioned in the purine strands of the A-tract. In contrast, when CPC is embedded in a pyrimidine tract, ET to yield reductive decomposition is observed. Thus, the Ir(III)-tethered DNA assembly containing cyclopropyl-modified bases provides a unique model system to explore the two DNA-mediated electron migration processes using the same photoredox probe and the same DNA bridge. 相似文献
148.
149.
150.
Kondo Y Morey JV Morgan JC Naka H Nobuto D Raithby PR Uchiyama M Wheatley AE 《Journal of the American Chemical Society》2007,129(42):12734-12738
Sequential reaction of HTMP (= 2,2,6,6-tetramethylpiperidine) with nBuLi and Et2Zn affords unsolvated polymer chains of EtZn(micro-Et)(micro-TMP)Li 6. The scope of this reagent in directed ortho metalation (DoM) chemistry has been tested by its reaction with N,N-diisopropylnaphthamide in THF to give EtZn(micro-C10H6C(O)NiPr2-2)2Li.2THF 7. Data reveal that 6 has undergone reaction with 2 equiv of aromatic tertiary amide and imply that it exhibits dual alkyl/amido basicity. DFT calculations reveal that direct alkyl basicity is kinetically disfavored and instead point to a stepwise mechanism whereby 6 acts as an amido base, liberating HTMP during the first DoM event. Re-coordination of the amine at lithium then incurs the elimination of EtH. Reaction of the resulting alkyl(amido)(arylamido)zincate with a second equivalent of N,N-diisopropylnaphthamide eliminates HTMP and affords 7. Both DoM steps involve the exhibition of amido basicity and each reveals a low kinetic barrier to reaction. Understanding of this reaction sequence is tested by treating 6 with N,N-diisopropylbenzamide in THF. On the basis of theory and experiment, the presence of THF solvent (in place of stronger Lewis bases) combined with the use of a sterically less congested aromatic amide is expected to encourage threefold, stepwise reaction. Isolation and characterization of the resulting tripodal zincate Zn(micro-C6H4C(O)NiPr2-2)3Li.THF 8 bears this out and suggests a significant new level of control in zincate-induced DoM chemistry through the combination of experiment and DFT studies. 相似文献