排序方式: 共有71条查询结果,搜索用时 15 毫秒
61.
Kim R. Dunbar Steven C. Haefner Calvin E. Uzelmeier Anthony Howard 《Inorganica chimica acta》1995,240(1-2):527-534
Rh(I) and Ir(I) complexes of the type [Rh(cod)(η2-TMPP)]1+ (1) and M(cod)(η2-TMPP-O) (M = Rh (2), Ir (3); cod = cyclooctadiene; TMPP = tris(2,4,6-trimethoxyphenyl)phosphine; TMPP-O = mono-demethylated form of TMPP) have been isolated from reactions of [M(cod)Cl]2 with M′BF4 (M′ = Ag+, K+, Na+) followed by addition of the tertiary phosphine ligand. This chemistry is dependent on the identity of the metal, as both the cationic phosphine complex and the neutral phosphino-phenoxide compound are stable for Rh(I), whereas only the latter is stable for Ir(I). The three complexes have been characterized by IR and NMR (1H and 31P) spectroscopies as well as by cyclic voltammetry. The 1H NMR spectrum of [Rh(cod)(η2-TMPP)]1+ (1) is in accord with the formula and reveals that the TMPP phenyl rings are undergoing rapid exchange between coordinated and non-coordinated modes; the corresponding spectra of 2 and 3 support free rotation about the P---C bonds of the unbound phenyl rings with no fluxionality of the bound demethylated ring. The 31P{1H} NMR spectrum of the neutral species 2 exhibits a significant upfield shift with respect to the analogous cationic compound 1. This shielding is the result of improved electron donation to the metal from a phenoxide group as compared to an ether substituent. In situ addition of CO to the reaction between TMPP and [Rh(cod)Cl]2 or [Ir(cod)Cl]2 in the presence of M′BF4 results in the isolation of the monocarbonyl species [Rh(TMPP)(η2-TMPP)(CO)][BF4] (5) and the stable dicarbonyl compound [Ir(TMPP)2(CO)2][BF4] (4), respectively. Single crystal X-ray data for . The geometry of 4 is square planar, with essentially ideal angles for the mutually trans disposed phosphine and carbonyl ligands, as found in earlier studies for the analogous Rh dicarbonyl compound. The 1H NMR spectrum of 4 supports the assignment of magnetically equivalent phosphorus nuclei in solution. The results of this study indicate that cyclooctadiene is a particularly strong ligand for monovalent late transition metals ligated by TMPP, to the extent that it is inert with respect to substitution in the absence of π-acceptor ligands such as carbon monoxide. 相似文献
62.
O'Neil SV Wang Y Laufersweiler MC Oppong KA Soper DL Wos JA Ellis CD Baize MW Bosch GK Fancher AN Lu W Suchanek MK Wang RL De B Demuth TP 《Bioorganic & medicinal chemistry letters》2005,15(24):5434-5438
Two novel 8,6-fused bicyclic peptidomimetic ring systems were synthesized utilizing olefin metathesis as the key reaction for the formation of the eight-membered ring. Both peptidomimetic scaffolds were further elaborated into potent ICE inhibitors, with numerous compounds exhibiting caspase-1 IC50s less than 10 nM. 相似文献
63.
《Bioorganic & medicinal chemistry letters》2014,24(1):103-107
We described here the first tetradecapeptide somatostatin-analogue where the disulfide bridge has been replaced by a carbon–carbon double bond. This analogue was prepared using microwave assisted ring closing metathesis (RCM) using the 2nd generation Grubbs as catalyst. Under our optimized conditions the cyclization between allylGly 3 and 14 proceeded in moderate yield, excellent cyclic/linear ratio and very high Z-double bond selectivity. NMR studies also demonstrated that the conformational flexibility of this peptide is increased in comparison to that of the natural hormone. Remarkably, this alkene-bridged somatostatin analog is highly selective against somatostatin receptors 1 and 5, suggesting that conformational rigidity is not required for the efficient interaction of somatostatin analogues with these two receptors. 相似文献
64.
《Bioorganic & medicinal chemistry》2014,22(9):2791-2798
When inhibitors of enzymes that utilize isoprenoid pyrophosphates are based on the natural substrates, a significant challenge can be to achieve selective inhibition of a specific enzyme. One element in the design process is the stereochemistry of the isoprenoid olefins. We recently reported preparation of a series of isoprenoid triazoles as potential inhibitors of geranylgeranyl transferase II but these compounds were obtained as a mixture of olefin isomers. We now have accomplished the stereoselective synthesis of these triazoles through the use of epoxy azides for the cycloaddition reaction followed by regeneration of the desired olefin. Both geranyl and neryl derivatives have been prepared as single olefin isomers through parallel reaction sequences. The products were assayed against multiple enzymes as well as in cell culture studies and surprisingly a Z-olefin isomer was found to be a potent and selective inhibitor of geranylgeranyl diphosphate synthase. 相似文献
65.
66.
A new efficient catalytic system was investigated for the epoxidation of various olefins by cis-dioxo-bis[2-(2′-hydroxyphenyl)-oxazolinato]molybdenum(VI), cis-[MoO2(phox)2], and TBHP as oxidizing agent. Using this system as catalyst for the oxidation of aliphatic substrates at 80 °C gives the epoxide as the sole product with yields up to 100% and turnover frequency up to 5000 h−1. The efficiency of the catalyst is strongly influenced by the nature of solvent, reaction time and temperature, and a significant increase in the epoxide yields is observed in higher temperatures and longer reaction times. 相似文献
67.
Concise synthesis of stagonolide-F by ring closing metathesis approach and its biological evaluation
The first total synthesis of 9-membered macrolide, stagonolide-F (3), starting from commercially available 1,5-pentane diol is reported. A combination of Jacobsen’s hydrolytic kinetic resolution (HKR) and Sharpless epoxidation is used for the creation of two stereogenic centers, while ring-closing metathesis (RCM) strategy was used for the construction of the lactone ring. The molecule synthesized exhibited potent antifungal, antibacterial and cytotoxic activities against all the tested strains. 相似文献
68.
Hans H. Brintzinger 《Rendiconti Lincei》2007,18(4):257-269
Recent developments, present state of art and future potentials of polyolefin production by means of metallocene and other
organometallic catalysts are outlined with a view toward practical applicability.
Riassunto Catalizzatori efficienti e selettivi per la produzione di poliolefine: approfondimenti e sfide aperte. Vengono passati in rassegna gli sviluppi recenti, lo stato presente dell'arte e le future prospettive della produzione delle poliolefine mediante metalloceni ed altri catalizzatori organometallici, con particolare riguardo alla possibilità di applicazioni pratiche相似文献
69.
R.M. Gauvin A. Arbaoui E. Gautier A. Mortreux E. Berrier G. Nowogrocki 《Inorganica chimica acta》2009,362(1):277-3345
We describe the fast one-pot synthesis of a chelating diamido dichloride titanium compound through sequential addition of the protonated ligand and triethylamine to TiCl4. The bisamido complex has been structurally characterized. A monoamido intermediate has been isolated. 相似文献
70.
《Journal of enzyme inhibition and medicinal chemistry》2013,28(6):805-812
Some fused dihydrooxepino[f]-, [g]-, and [h]coumarins were obtained from the ring-closing metathesis of the corresponding o-allyl-allyloxycoumarins under the treatment with the first generation Grubbs’ catalyst. These compounds were tested in vitro for their antioxidant activity, and they present significant scavenging activity. They were also showed to inhibit in vitro soybean lipoxygenase. 相似文献