共查询到20条相似文献,搜索用时 15 毫秒
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Pascal Buskens 《Inorganica chimica acta》2004,357(6):1969-1974
The carbene-containing non-classical ruthenium hydride complex [(PCy3)Ru(H)2(H2)2(IMes)] 1 (IMes=1,3-Bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) is an active catalyst for H/D exchange in aromatic ketones. It is also capable of combining sp2 C-H bond activation with C-C bond formation. Comparing the chemo- and regio-selectivities of the H/D exchange process and the C-C bond formation clearly indicates that different intermediates are involved in the two processes. High pressure NMR studies provide strong evidence that the key intermediate for the C-C coupling reaction is analogous to that for other ruthenium catalysts reported previously. Catalytic turnover is limited by the instability of this intermediate in the presence of the olefinic coupling partner. 相似文献
3.
Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)2(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)2(CO)H(CCR)] (R = Ph 3, SiMe3, 4) and [Ru(IMes)2(CO)(CCR)2] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)2(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)2(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography. 相似文献
4.
Density-functional calculations have been used to examine the electronic structure and bonding in the recently reported complex [(PMe(3))(CO)(2)Fe(mu-pdt)(mu-CO)Fe(CO)(IMes)](+) (1(+), IMes=1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene). This mixed valent Fe(II)Fe(I) complex features a rotated geometry that places a carbonyl ligand in a semi-bridging position, which makes it an accurate model of the S =(1/2) resting state of the [FeFe]-hydrogenase active site. Calculations indicate that the unpaired electron in this complex lies almost entirely on the rotated iron center, implying that this iron remains in the Fe(I) oxidation state, while the unrotated iron has been oxidized to Fe(II). The frontier molecular orbitals in 1(+) are compared with those in the neutral Fe(I)Fe(I) precursor (PMe(3))(CO)(2)Fe(mu-pdt)(mu-CO)Fe(CO)(IMes) at both its optimized geometry (1) and constrained to a rotated geometry (1(rot)). These theoretical results are used to address the role of the bridging CO ligand in 1(+) and to predict reactivity patterns; they are related back to the intricate biological mechanism of [FeFe]-hydrogenase. 相似文献
5.
Bianca J. van Lierop Amanda N. Whelan Sofianos Andrikopoulos Roger J. Mulder W. Roy Jackson Andrea J. Robinson 《International journal of peptide research and therapeutics》2010,16(3):133-144
Ruthenium-alkylidene catalysed ring closing metathesis (RCM) provides a convenient method for the synthesis of cyclic dicarba
peptide analogues. Sequences devoid of turn-inducing residues, however, can often fail to cyclise. A combination of pseudoproline
(ΨPro) insertion and microwave irradiation can be used to enhance RCM yield in these problematic sequences. This strategy
is illustrated in the synthesis of a dicarba human growth hormone (hGH) fragment. The structural changes associated with cystine
to dicarba replacement were found to change the metabolic profile of the peptide. 相似文献
6.
The asymmetric total syntheses of (R)-(+)- and (S)-(-)-umbelactone were achieved by using the Sharpless asymmetric epoxidation reaction to generate the stereogenic center and a ring-closing metathesis (RCM) for the formation of the lactone structure. Starting from 3-methyl-2-buten-1-ol, the asymmetric total synthesis was achieved in an efficient 6-step protocol with an overall yield of 16%. 相似文献
7.
Mingzhang Gao Min Wang Qi-Huang Zheng 《Bioorganic & medicinal chemistry letters》2018,28(13):2234-2238
The reference standards methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate (5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-methoxybenzamide (5c), and their corresponding desmethylated precursors 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoic acid (6a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-hydroxybenzamide (6b), were synthesized from 5-amino-2,2-difluoro-1,3-benzodioxole and 3-substituted benzoic acids in 5 and 6 steps with 33% and 11%, 30% and 7% overall chemical yield, respectively. Carbon-11-labeled casein kinase 1 (CK1) inhibitors, [11C]methyl 3-((2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)carbamoyl)benzoate ([11C]5a) and N-(2,2-difluoro-5H-[1,3]dioxolo[4′,5′:4,5]benzo[1,2-d]imidazol-6-yl)-3-[11C]methoxybenzamide ([11C]5c), were prepared from their O-desmethylated precursor 6a or 6b with [11C]CH3OTf through O-[11C]methylation and isolated by HPLC combined with SPE in 40–45% radiochemical yield, based on [11C]CO2 and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370–740?GBq/μmol with a total synthesis time of ~40-min from EOB. 相似文献
8.
Patil S Deally A Gleeson B Müller-Bunz H Paradisi F Tacke M 《Metallomics : integrated biometal science》2011,3(1):74-88
From the reaction of 1-methylimidazole (1a), 4,5-dichloro-1H-imidazole (1b(I)) and 1-methylbenzimidazole (1c) with p-cyanobenzyl bromide (2a), non-symmetrically substituted N-heterocyclic carbene (NHC) [(3a-c)] precursors, 5,6-dimethyl-1H-benzimidazole (1d) and 4,5-diphenyl-1H-imidazole (1e) with p-cyanobenzyl bromide (2a) and benzyl bromide (2b), symmetrically substituted N-heterocyclic carbene (NHC) [(3d-f)] precursors were synthesised. These NHC-precursors were then reacted with silver(i) acetate to yield the NHC-silver complexes (1-methyl-3-(4-cyanobenzyl)imidazole-2-ylidene)silver(i)acetate (4a), (4,5-dichloro-1-(4-cyanobenzyl)-3-methyl)imidazole-2-ylidene)silver(i)acetate (4b), (1-methyl-3-(4-cyanobenzyl)benzimidazole-2-ylidene)silver(i)acetate (4c), (1,3-bis(4-cyanobenzyl)5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4d), (1,3-dibenzyl-5,6-dimethylbenzimidazole-2-ylidene) silver(i) acetate (4e) and (1,3-dibenzyl-4,5-diphenylimidazol-2-ylidene) silver(i) acetate (4f) respectively. Three NHC-precursors 3c-e and four NHC-silver complexes 4b and 4d-f were characterised by single crystal X-ray diffraction. Preliminary in vitro antibacterial activity of the NHC-precursors and NHC-silver complexes was investigated against Gram-positive bacteria Staphylococcus aureus, and Gram-negative bacteria Escherichia coli using the qualitative Kirby-Bauer disk-diffusion method. NHC-silver complexes have shown very high antibacterial activity compared to the NHC-precursors. All six NHC-silver complexes were tested for their cytotoxicity through MTT based in vitro tests on the human renal-cancer cell line Caki-1 in order to determine their IC?? values. NHC-silver complexes 4a-f were found to have IC?? values of 6.2 (±1.0), 7.7 (±1.6), 1.2 (±0.6), 10.8 (±1.9), 24.2 (±1.8) and 13.6 (±1.0) μM, respectively. These values represent improved cytotoxicity against Caki-1, most notably for 4c, which is a three times more cytotoxic than cisplatin (IC?? value = 3.3 μM) itself. 相似文献
9.
Wels B Kruijtzer JA Garner K Nijenhuis WA Gispen WH Adan RA Liskamp RM 《Bioorganic & medicinal chemistry》2005,13(13):4221-4227
The synthesis of a novel potent cyclic peptide MC4-ligand by ring-closing metathesis (RCM) is described. Based on the Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH2-MC4 ligand, Ac-Nle-Alg-Lys-D-Phe-Arg-Trp-Alg-NH2 was designed and synthesized followed by cyclization using RCM. Both compounds are high affinity and selective MC4-R-agonists. The cyclic RCM-peptide was more potent in a rat-grooming assay. 相似文献
10.
K C Nicolaou N P King M R Finlay Y He F Roschangar D Vourloumis H Vallberg F Sarabia S Ninkovic D Hepworth 《Bioorganic & medicinal chemistry》1999,7(5):665-697
A Stille coupling strategy has been utilized to complete a total synthesis of epothilone E from vinyl iodide 7 and thiazole-stannane 8h. The central core fragment 7 and its trans-isomer 11 were prepared from triene 15 using ring-closing metathesis (RCM), and were subsequently coupled to a variety of alternative stannanes to provide a library of epothilone analogues 18a-o and 19a-o. The Stille coupling approach was then used to prepare epothilone B analogues from the key macrolactone intermediate 24 which was itself synthesized by a macrolactonization based strategy. 相似文献
11.
Marcus L. Cole David E. Hibbs Cameron Jones Neil A. Smithies 《Inorganica chimica acta》2005,358(1):102-108
The reactions of the N-heterocyclic carbene (NHC) stabilised group 13 trihydride complexes [AlH3(IMeMe)] (1) (IMeMe = 1,3,4,5-tetramethylimidazol-2-ylidene), [AlH3(IiPrMe)] (2) (IiPrMe = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) with three molar equivalents of phenol, and [InH3(IMes)] (3) (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) with one molar equivalent of 1,1,1,5,5,5-hexafluoropentan-2,4-dione (F6acacH) are presented. These render the imidazolium tetraphenoxyaluminate species; [IMeMe · H][Al(OPh)4] (4) and [IiPrMe · H][Al(OPh)4] (5), and 1,3-bis(2,4,6-trimethylphenyl)imidazolium 1,1,1,5,5,5-hexafluoropentan-2,4-dionate; [IMes · H][CH{C(O)CF3}2] (6), the latter leading to metallohydride decomposition. The molecular structures of 4 and 6 are described. 相似文献
12.
Andrea J Robinson Jomana Elaridi Bianca J Van Lierop Selma Mujcinovic W Roy Jackson 《Journal of peptide science》2007,13(4):280-285
Microwave irradiation dramatically improves the efficiency of ring closing metathesis (RCM) reactions of resin-attached peptides and the technology is illustrated by the highly selective synthesis of dicarba analogues of alpha-conotoxin IMI. 相似文献
13.
This critical review is an updated survey of metal-carbenes as potential anticancer chemotherapeutics. We report on the recent advances in the discovery of N-heterocyclic carbenes, acyclic diamino carbenes and abnormal NHCs associated with metals from groups 10 and 11 that displayed antiproliferative activity and emphasize, when possible, their molecular target(s) and their mechanism of action. 相似文献
14.
A series of new ruthenium(II) carbonyl chloride complexes with pyridine-functionalised N-heterocyclic carbenes [Ru(Py-NHC)(CO)2Cl2], [Py-NHC = 3-methyl-1-(2-pyridyl)imidazol-2-ylidene, 1 (1a and 1b); 3-methyl-1-(2-picoyl)imidazol-2-ylidene, 2 (2a and 2b); 3-methyl-1-(2-pyridyl)benzimidazolin-2-ylidene, 3 (3b); 3-methyl-1-(2-picoyl)benzimidazolin-2-ylidene, 4 (4a and 4b); 1-methyl-4-(2-pyridyl)-1,2,4-triazoline-5-ylidene, 5 (5a and 5b)] have been prepared by transmetallation from the corresponding silver carbene complexes and characterized by NMR, IR spectroscopy and elemental analysis. In these complexes with bidentate Py-NHC ligands, one CO ligand is trans to the Py ligand. In 1a, 2a, 4a, and 5a, the NHC ligand is trans to the other CO ligand, thus leaving the two Cl− ligands trans to each other. In 1b, 2b, 3b, 4b, and 5b, the NHC ligands are trans to one Cl− ligand, and the two Cl− ligands are cis to each other. The structures for 1b, 2b, 3b and 4b have been determined by single-crystal X-ray diffraction. These complexes are efficient catalysts in the transfer hydrogenation of acetophenone and their catalytic activities are found to be influenced by electronic effect of the N-heterocyclic carbene ligands. 相似文献
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F. Ekkehardt Hahn Beate Heidrich Alexander Hepp Eduardo Sola 《Inorganica chimica acta》2006,359(15):4840-4846
The reaction of 1-methyl-3-(2-propenyl)imidazolium bromide (1) or 1,3-bis(2-propenyl)-imidazolium bromide (2) with [Ir(μ-OMe)(cod)]2 afforded the five coordinated iridium(I) carbene complexes [IrBr(L)(cod)] (3) (L=1-methyl-3-(2-propenyl)imidazolin-2-ylidene) and (4) (L=1,3-bis(2-propenyl)imidazolin-2-ylidene). The reaction proceeds via an in situ deprotonation of the imidazolium salt. Molecular structure determinations on 3 and 4 confirmed the coordination of the carbene ligands via the carbene carbon atom and one allyl group in both complexes. Treatment of complex 3 with an excess of AgBF4 gave the dinuclear bromo bridged complex [(Ir(μ-Br)(L)(cod)]2BF4 (5) (L=1-methyl-3-(2-propenyl)imidazolin-2-ylidene). The reaction of complex 4 with an excess of AgBF4 led to the mononuclear complex [Ir(L)(cod)]BF4 (6) (L=1,3-bis(2-propenyl)imidazolin-2-ylidene) where both N-allyl substituents are coordinated to the iridium(I) center. 相似文献
17.
The extent and nature of cyclic electron delocalization in free and coordinated cyclopropenylidene carbenes has been analyzed by combined experimental and theoretical charge-density studies. The significant asymmetry of the C-C bond lengths in substituted cyclopropenylidene carbenes was identified as cooperative effect which depends on contributions of both σ- and π-bonding. We show that analyses of (i) the topology of the Laplacian of the electron density distribution and (ii) the out-of-plane atomic quadrupole moments - the charge-density analogues of pπ occupation - allow to distinguish between the influence of σ- and π-electrons on cyclic electron delocalization. These studies hint for pronounced electron localization in the carbene lone pair region which dominates the electronic structure of free cyclopropenylidene carbenes and hinders the establishment of true aromaticity. We further investigated the electron donating/withdrawing ability of cyclopropenylidene ligands relative to N-heterocyclic carbenes. The experimental benchmark systems LCr(CO)5 (L = 2,3-diphenylcyclopropenylidene and 1,2-dimethylimidazol-2-ylidene) show that the cyclopropenylidene ligand clearly displays the higher π-acceptor capability relative to N-heterocyclic carbenes. 相似文献
18.
Akira Matsuda Krzysztof Pankiewicz Bonita K. Marcus Kyoichi.A. Watanabe Jack J. Fox 《Carbohydrate research》1982,100(1):297-302
The first chemical synthesis of 3-methyl-ψ-uridine (5) and its 2′-deoxy analogue (9) has been achieved. ψ-Uridine was trimethylsilylated and the crude product was treated with acetyl chloride, to give the 1-acetyl derivative (3). Crude 3 was methylated with dimethoxymethyldimethylamine and then saponified, to give crystalline 5 in 82% overall yield. Treatment of 5 with 1,3-dichloro-1,1,3,3-tetraiso-propyldisiloxane afforded the 3′,5′-protected product, which was converted into the 2′-O-[(imidazol-1-yl)thiocarbonyl] derivative 7. Reduction of 7 with tributyltin hydride followed by deblocking of the product gave crystalline 2′-deoxy-3-methyl-ψ-uridine (9) in 35% yield from 5. 相似文献
19.
Sebastien Monfette João A. Duarte Silva Eduardo N. dos Santos Deryn E. Fogg 《Inorganica chimica acta》2010,363(3):481-9527
The utility and limitations of 1H NMR methods for monitoring the progress of ring-closing metathesis (RCM) reactions are examined. 1H NMR analysis of RCM reactions that yield macrocyclic and medium-ring products can be more problematic than is generally recognized. Interpretation is complicated by the formation of oligomers with an NMR signature identical or closely similar to that of the diene precursor, the RCM target, or a composite of the two. DOSY-NMR can aid in resolving ambiguities in signal assignment, but reliable quantitation requires ancillary methods. 相似文献
20.
The synthesis of unusual cyclic amino acids, that may be envisaged as proline analogs, is an area of great interest for their
potential applications as scaffolds for the design of bioactive peptidomimetics or units for the creation of novel foldamers.
We have carried out the preparation of cyclic dehydro-β-amino acids starting from allylic carbonates via a two-step allylic
amination/ring closing metathesis (RCM) protocol. The introduction of the allylamino moiety has been carried out either without
a catalyst, through an SN2′ reaction, or in the presence of iridium complexes. The backbone of the allylamino intermediates contains two unsaturations,
thus suggesting that RCM could be a valuable tool for the preparation of dihydropyrrole scaffolds. A similar reaction has
been already reported in the literature for racemic aromatic-substituted substrates, but no examples of enantiopure derivatives
bearing aliphatic chains have been reported. The reaction was optimized by testing different Grubbs’ catalysts and carbamate
nitrogen protecting groups. Moreover, in view of a future application of these dehydro-β-amino acids as central core of peptidomimetics,
the malonate chain was also used to protect nitrogen prior to RCM. 相似文献