- Group 4 metallocene complexes bearing cholestanol-derived substituents at the Cp-rings-their synthesis and use in propene polymerization catalysis
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Two series of Group 4 bent metallocene complexes bearing cholestanol-derived substituents at their Cp-rings have been prepared. 5α-Cholestan-3α-ol was converted to the 3α-mesylate.Nucleophilic substitution with CpNa, followed by deprotonation and treatment with ZrCl4(THF)2 gave bis5-5α-cholestan-3β-yl)cyclopentadienyl>zirconium dichloride 3β-5. 5α-Cholestan-3-one 6 was converted to the corresponding fulvene, methyl lithium was added and deprotonation and addition to ZrCl4(THF)2 furnished bis5-(3β-methyl-5α-cholestan-3α-yl)cyclopentadienyl>zirconium dichloride (11b).Treatment of the chiral Cp-substituted zirconocene dichlorides with a large excess of methyl alumoxane gave homogeneous Ziegler catalysts.Propene polymerization proceeded with overall stereochemical chain end control to give partly isotactic polypropylene.Keywords: Zirconium; Cholestanol; Polymerization
- Erker, Gerhard,Mollenkopf, Christoph
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- Nickel-Catalyzed Cyanation of Unactivated Alkyl Sulfonates with Zn(CN)2
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Cyanation of unactivated primary and secondary alkyl mesylates with Zn(CN)2 catalyzed by nickel has been developed. The reaction provides an efficient route for the synthesis of alkyl nitriles with wide substrate scope, good functional group tolerance, and compatibility with heterocyclic compounds. Mechanistic studies indicate that alkyl iodide generated in situ serves as the reactive intermediate and the gradual release of alkyl iodide is crucial for the success of the reaction.
- Xia, Aiyou,Lv, Peizhuo,Xie, Xin,Liu, Yuanhong
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supporting information
p. 7842 - 7847
(2020/11/02)
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- Predictable Selectivity in Remote C?H Oxidation of Steroids: Analysis of Substrate Binding Mode
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Predictability is a key requirement to encompass late-stage C?H functionalization in synthetic routes. However, prediction (and control) of reaction selectivity is usually challenging, especially for complex substrate structures and elusive transformations such as remote C(sp3)?H oxidation, as it requires distinguishing a specific C?H bond from many others with similar reactivity. Developed here is a strategy for predictable, remote C?H oxidation that entails substrate binding to a supramolecular Mn or Fe catalyst followed by elucidation of the conformation of the host-guest adduct by NMR analysis. These analyses indicate which remote C?H bonds are suitably oriented for the oxidation before carrying out the reaction, enabling prediction of site selectivity. This strategy was applied to late-stage C(sp3)?H oxidation of amino-steroids at C15 (or C16) positions, with a selectivity tunable by modification of catalyst chirality and metal.
- Olivo, Giorgio,Capocasa, Giorgio,Ticconi, Barbara,Lanzalunga, Osvaldo,Di Stefano, Stefano,Costas, Miquel
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supporting information
p. 12703 - 12708
(2020/06/02)
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- Ruthenium nanoparticles ligated by cholesterol-derived NHCs and their application in the hydrogenation of arenes
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Herein we present ruthenium nanoparticles (Ru-NPs) stabilized with two rigid NHC ligands derived from cholesterol. The obtained nanoparticles were fully characterized and applied in the hydrogenation of various aromatic compounds under mild conditions. Interestingly, the more bulky ligand gives a slightly lower ligand coverage and a faster catalyst.
- Rakers, Lena,Martínez-Prieto, Luis M.,López-Vinasco, Angela M.,Philippot, Karine,Van Leeuwen, Piet W. N. M.,Chaudret, Bruno,Glorius, Frank
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p. 7070 - 7073
(2018/07/05)
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- Addressable Cholesterol Analogs for Live Imaging of Cellular Membranes
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Cholesterol is an essential component of most biological membranes and serves important functions in controlling membrane integrity, organization, and signaling. However, probes to follow the dynamic distribution of cholesterol in live cells are scarce and so far show only limited applicability. Herein, we addressed this problem by synthesizing and characterizing a class of versatile and clickable cholesterol-based imidazolium salts. We show that these cholesterol analogs faithfully mimic the biophysical properties of natural cholesterol in phospholipid mono- and bilayers, and that they integrate into the plasma membrane of cultured and primary human cells. The membrane-incorporated cholesterol analogs can be specifically labeled by click chemistry and visualized in live-cell imaging experiments that show a distribution and behavior comparable with that of endogenous membrane cholesterol. These results indicate that the cholesterol analogs can be used to reveal the dynamic distribution of cholesterol in live cells. Cholesterol is an important component of biological membranes, but probes recording its dynamic intracellular distribution are scarce. Rakers et al. developed cholesterol-derived imidazolium salts mimicking properties of natural cholesterol. Following specific labeling via click chemistry, one of the cholesterol analogs was shown to incorporate into cellular membranes equivalent to endogenous cholesterol.
- Rakers, Lena,Grill, David,Matos, Anna L.L.,Wulff, Stephanie,Wang, Da,B?rgel, Jonas,K?rsgen, Martin,Arlinghaus, Heinrich F.,Galla, Hans-Joachim,Gerke, Volker,Glorius, Frank
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p. 952 - 12,961
(2018/05/08)
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- Evaluation of steroidal amines as lipid raft modulators and potential anti-influenza agents
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The influenza A virus (IFV) possesses a highly ordered cholesterol-rich lipid envelope. A specific composition and structure of this membrane raft envelope are essential for viral entry into cells and virus budding. Several steroidal amines were investigated for antiviral activity against IFV. Both, a positively charged amino function and the highly hydrophobic (C log P ≥ 5.9) ring system are required for IC50 values in the low μM range. An amino substituent is preferential to an azacyclic A-ring. We showed that these compounds either disrupt or augment membrane rafts and in some cases inactivate the free virus. Some of the compounds also interfere with virus budding. The antiviral selectivity improved in the series 3-amino, 3-aminomethyl, 3-aminoethyl, or by introducing an OH function in the A-ring. Steroidal amines show a new mode of antiviral action in directly targeting the virus envelope and its biological functions.
- Agarwal, Sameer,Schroeder, Cornelia,Schlechtingen, Georg,Braxmeier, Tobias,Jennings, Gary,Kn?lker, Hans-Joachim
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p. 5165 - 5169
(2013/09/12)
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- Iron(III)-catalyzed halogenations by substitution of sulfonate esters
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A novel halogenation reaction from sulfonates catalyzed by iron(III) is described. The reaction can be performed as a stoichiometric or a catalytic version. This reaction provides a convenient strategy for the efficient access to structurally diverse secondary chlorides, bromides and iodides. The stereochemical course of the reaction is governed by the substrate and the experimental conditions. Secondary alcohols modified as quisylates or pysylates are substantially more reactive. Aliphatic quisylates proceed with overall inversion of configuration under catalytic conditions. Chemoselectivity in bismesylates was observed in favour of the secondary mesylate. Additionally, based on the experimental results, a possible catalytic cycle for the halogenation has been proposed.
- Ortega, Nuria,Feher-Voelger, Andres,Brovetto, Margarita,Padron, Juan I.,Martin, Victor S.,Martin, Tomas
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supporting information; experimental part
p. 963 - 972
(2011/06/20)
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- Inversion of secondary chiral alcohols in toluene with the tunable complex of R3N{single bond}R′COOH
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The SN2 reaction of enantiomerically pure sulfonates with the tunable complex of R3N-R′COOH in toluene has been extensively studied. It was revealed that the molar ratio of the tertiary amines and carboxylic acids in the complex of R3NR′COOH is crucial for the SN2 reaction, and should be tuned for each sulfonate to give the best yield. Fifteen sulfonates 1 and 3-13 (Scheme 2) were prepared and transformed into 22 corresponding inverted esters 2 and 14-24 (Scheme 2) in good to high yields.
- Shi, Xiao-Xin,Shen, Chun-Li,Yao, Jian-Zhong,Nie, Liang-Deng,Quan, Na
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experimental part
p. 277 - 284
(2010/05/18)
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- Practical synthesis of 3β-amino-5-cholestene and related 3β-halides involving i-steroid and retro-i-steroid rearrangements
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(Equation Presented) Derivatives of 3β-amino-5-cholestene (3β-cholesterylamine) are of substantial interest as cellular probes and have potential medicinal applications. However, existing syntheses of 3β-amino-5-cholestene are of limited preparative utility. We report here a practical method for the stereoselective preparation of 3β-amino-5- cholestene, 3β-chloro-5-cholestene, 3β-bromo-5-cholestene, and 3β-iodo-5-cholestene from inexpensive cholesterol. A sequential i-steroid/retro-i-steroid rearrangement promoted by boron trifluoride etherate and trimethylsilyl azide converted cholest-5-en-3β-ol methanesulfonate to 3β-azido-cholest-5-ene with retention of configuration in 93% yield.
- Sun, Qi,Cai, Sutang,Peterson, Blake R.
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supporting information; experimental part
p. 567 - 570
(2009/07/18)
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- Synthesis and antimicrobial evaluation of water-soluble, dendritic derivatives of epimeric 5α-cholestan-3-amines and 5α-cholestan-3-yl aminoethanoates
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To examine the effect of negatively charged steroidal amphiphiles on antimicrobial activity, two pairs of epimeric, dendritic tricarboxylato amphiphiles - 4-(2-carboxyethyl)-4-[3-(5α-cholestan-3-yl)ureido]heptanedioic acid (1) and 4-(2-carboxyethyl)-4-[3-(5α-cholestan-3-yloxycarbonylmethyl)ureido]heptanedioic acid (2) - were synthesized. A broad antimicrobial screen of 11 microbes revealed that these amphiphiles only showed good activity against a methicillin-resistant isolate of Staphylococcus aureus (MRSA) and modest activity against an unrelated strain of S. aureus. The best activity, a minimal inhibitory concentration (MIC) of 27 μM, was found for the 3β epimer of 1 against MRSA.
- Sugandhi, Eko W.,Slebodnick, Carla,Falkinham III, Joseph O.,Gandour, Richard D.
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p. 615 - 626
(2008/02/04)
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- Chloromethanesulfonate as an efficient leaving group: Rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles
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The chloromethanesulfonate (monochlate) served as an efficient leaving group for rearrangement of the carbon-carbon bond and conversion of alcohols into azides and nitriles. The treatment of the monochlate 16a with zinc acetate in dioxane at 90 °C effected migration of the 4α-methyl group to give alkene 17a. Upon similar treatment of the monochlates 22a, 25a, 28a, and 31a with zinc acetate, the carbon-carbon bonds antiperiplanar to the hydroxyl groups efficiently migrated to afford the alkenes 23a, 26a-c, 29a,b, and 32a, respectively. In the case of the diol 40, the monochlate was converted into the ketone 41 via a rearrangement-ring expansion. The reaction of the monochlates 44a, 47a, 49a, 52a, and 57a with sodium azide or lithium azide in N,N-dimethylformamide efficiently afforded the azides with inversion of the configuration. The introduction of a nitrile group to the sterically hindered alcohol 59 was performed in high yield by the reaction of the monochlate 60a with sodium cyanide.
- Shimizu, Takeshi,Ohzeki, Tomoya,Hiramoto, Katsuya,Hori, Nobuyuki,Nakata, Tadashi
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p. 1373 - 1385
(2007/10/03)
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- Efficient method for inversion of secondary alcohols by reaction of chloromethanesulfonates with cesium acetate
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Inversion of a variety of secondary alcohols using the (chloromethylsulfonyl)oxy group as a favorable leaving group with cesium acetate in the presence of 18-crown-6 has been performed to give the inverted acetates in high yields.
- Shimizu, Takeshi,Hiranuma, Sayoko,Nakata, Tadashi
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p. 6145 - 6148
(2007/10/03)
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- EFFICIENT INVERSIONS OF SECONDARY ALCOHOLS USING CESIUM ACETATE AND 18-CROWN-6
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Reaction of alcohol mesylate with cesium acetate and 18-crown-6 in benzene is an effective method for the inversion of cyclopentyl and cyclohexyl alcohols.
- Torisawa, Yasuhiro,Okabe, Hiromitsu,Ikegami, Shiro
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p. 1555 - 1556
(2007/10/02)
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- Photolyse d' arenesulfonates d' alkyle. Influence des bases et mecanisme de la reaction
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Photolysis of alkyl arenesulfonates in various solvents leads to the corresponding alkyl alcohols in good chemical yields.Aromatic hydrocarbons and sulfur dioxide are also characterized in the reaction mixture.In the first step, homolysis of the C-S bond takes place from the sulfonate excited in a singlet state.In basic medium the reaction becomes cleaner and more efficient.Thr quenching of the fluorescence by NaOH, with 3 β-cholestanyl p-toluenesulfonate, seems to be diffusioncontrolled.The role of the base is discussed.
- Pete, Jean-Pierre,Portella, Charles
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p. 275 - 282
(2007/10/02)
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