- Reactions of benzyltriphenylphosphonium salts under photoredox catalysis
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The development of benzyltriphenylphosphonium salts as alkyl radical precursors using photoredox catalysis is described. Depending on substituents, the benzylic radicals may couple to form C-C bonds or abstract a hydrogen atom to form C-H bonds. A natural product, brittonin A, was also synthesized using this method.
- Boldt, Andrew M.,Dickinson, Sidney I.,Ramirez, Jonathan R.,Benz-Weeden, Anna M.,Wilson, David S.,Stevenson, Susan M.
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supporting information
p. 7810 - 7815
(2021/09/28)
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- Substituted dienes prepared from betulinic acid – Synthesis, cytotoxicity, mechanism of action, and pharmacological parameters
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A set of new substituted dienes were synthesized from betulinic acid by its oxidation to 30-oxobetulinic acid followed by the Wittig reaction. Cytotoxicity of all compounds was tested in vitro in eight cancer cell lines and two noncancer fibroblasts. Almost all dienes were more cytotoxic than betulinic acid. Compounds 4.22, 4.30, 4.33, 4.39 had IC50 below 5 μmol/L; 4.22 and 4.39 were selected for studies of the mechanism of action. Cell cycle analysis revealed an increase in the number of apoptotic cells at 5 × IC50 concentration, where activation of irreversible changes leading to cell death can be expected. Both 4.22 and 4.39 led to the accumulation of cells in the G0/G1 phase with partial inhibition of DNA/RNA synthesis at 1 × IC50 and almost complete inhibition at 5 × IC50. Interestingly, compound 4.39 at 5 × IC50 caused the accumulation of cells in the S phase. Higher concentrations of tested drugs probably inhibit more off-targets than lower concentrations. Mechanisms disrupting cellular metabolism can induce the accumulation of cells in the S phase. Both compounds 4.22 and 4.39 trigger selective apoptosis in cancer cells via intrinsic pathway, which we have demonstrated by changes in the expression of the crucial apoptosis-related protein. Pharmacological parameters of derivative 4.22 were superior to 4.39, therefore 4.22 was the finally selected candidate for the development of anticancer drug.
- Frydrych, Ivo,Urban, Milan,?arek, Jan,Benická, Sandra,D?ubák, Petr,Gurská, Soňa,Hajdúch, Marián,Kotulová, Jana,Li?ková, Barbora,Olejníková, Denisa,Pokorny, Jan
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- Kinetic Study of the Substitution Reactions of Triphenylphosphine with Chlorobenzyl Chlorides, Dimethylbenzyl Chloride, and Methylbenzyl Bromides in Various Two-Phase Organic Solvent/Water Media
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The kinetics of the substitution reactions of triphenylphosphine (TP) with chlorobenzyl chlorides (CBC), 2,5-dimethylbenzyl chloride (DMBC), and methylbenzyl bromides (MBB) in aprotic organic solvent was studied under the extraction by water. The effects of water, agitation, organic solvent, reactant, and temperature were investigated. These reactions take place via the SN2 mechanism and exhibit large and negative entropy of activation. The order of relative activity of solvents is CHCl3 > CH2Cl2 >> C6H6. In CHCl3, the order of relative reactivity of benzyl chloride (BC), benzyl bromide (BB), CBC, DMBC, and MBB toward reaction with TP is 2-MBB > 4-MBB > 3-MBB > BB > DMBC > BC > 2-CBC > 4-CBC > 3-CBC. These reactions produce quantitatively benzyltriphenylphosphonium salts, which are useful for synthesizing Z-form isomers of stilbenes via the two-phase Wittig reaction.
- Shieh, Ruey-Lone,Lin, Ruey-Lih,Hwang, Jiann-Jyh,Jwo, Jing-Jer
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p. 517 - 523
(2007/10/03)
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- Ylidyl-dihalogenphosphane - Strukturbilder einer sich anbahnenden Dissoziation
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The reaction of phosphonium ylides with phosphorus trihalides has been studied for the synthesis of ylidyl-dihalophosphanes (= dihalophosphanyl ylides (Ph3P=CR-PX2 3, X = Cl, and 9, X = Br.Compounds 3, R = aryl, are readily prepared from the phosphonium bromides Br, compounds 3, R = alkyl, SiMe3 or PCl2, and 9 are obtained from silylylides Ph3P=CR-SiMe3, compound 3, R = PPh3(1+) results from the addition of PCl3 to the hexaphenylcarbodiphosphorane.A (β-morpholinovinyl)dichlorophosphane 12 has also been prepared.Ylides 3 are oxidized by sulfur and selenium and are converted to ylidyl-chlorophosphenium (= chlorophosphaalkenyl-phosphonium) salts AlCl4 10.In the 31P-NMR spectra of 3 and 9 the geminal coupling 2JPP indicates the phosphorus lone pair to be synperiplanar to the phosphonio group.In one case the P(III)-C rotation barrier has been estimated from VT-31P-NMR spectra.By X-ray crystallography the structures of 3, R = Me, 2,6-Cl2C6H4, 4-NO2C6H5, PCl2, of 9, R = Me (two molecules), SiMe3, of an ylidyl-selenophosphonyl dichloride (11b), and of 12 have been analyzed.They provide representatives for the full range of rotation from the symmetric conformer with two equal P-X bonds to the conformer with one P-X bond perpendicular to the PCP plane and with this bond being extremely elongated.Thus, they map out the pathway to P-X bond breaking.On this way the initial charge transfer from the ylidic carbon to the antibonding P-X orbital ends up in a ? donation and P-X dissociation. - Key Words: Ylides, dichloro- and dibromophosphanyl-/ Enamines, dichlorophosphanyl-/ Phosphonium ions, chlorophosphaalkenyl-/ Stereoelectronic (anomeric) effect and anionic hyperconjugation
- Schmidpeter, Alfred,Noeth, Heinrich,Jochem, Georg,Schroedel, Hans-Peter,Karaghiosoff, Konstantin
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p. 379 - 394
(2007/10/02)
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- Spatial Structure of 4n? Helicene Dianions
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Helicene dianions, e.g. phenanthrene derivatives, once believed to be non-helical, maintain their chirality as 4n? dianions.Phenanthrene 5, as well as substituted phenanthrene derivatives, undergo a two-electron reduction to form the respective 4n? dianion e.g. 52-/2Li+.Phenanthrene derivatives substituted at the 4- and 5-positions (bay substituents) e.g. 6-11, which are helical, afford stable dianions.These dianions are also prepared by a two-electron reduction of the (4n+2)? electron hydrocarbons and show, in their 1H NMR spectra, a quench of the paratropicity compared to 52- as well as a line shape dependence on their twist angle.The quench of paratropicity was also observed in the closely related charged helicenes derived from the benzochrysene system, i.e. anions 122- and 132-.The twist angles were calculated by MMX and MNDO calculations for the neutral systems, i.e., 5-11, and by MNDO for the dianions.MNDO calculations also included the preferred location of the counter cation.A dynamic NMR spectroscopic study proves experimentally the helicity of anion 112- thus shedding light on the behaviour of this novel class of dianions.
- Frim, R.,Goldblum, A.,Rabinovitz, M.
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p. 267 - 274
(2007/10/02)
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- New Three- and Sixfold Bridged Phenylogous Cyclophanes
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The syntheses of the threefold bridged cyclophanes 4, 5, of the sixfold bridged cyclophane 6, and of the triple-layered cyclophanes 7, 8 are reported.The yields have been optimized by variation of the reaction conditions and by use of the cesium effect.The enantiomer resolution of 7 and the X-ray structural analysis of 4 are discussed.
- Sendhoff, Norbert,Kissener, Wolfram,Voegtle, Fritz,Franken, Sybille,Puff, Heinrich
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p. 2179 - 2186
(2007/10/02)
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