- Automated solid-phase radiofluorination using polymer-supported phosphazenes
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The polymer supported phosphazene bases PS-P2 tBu and the novel PS-P2 PEG allowed for efficient extraction of [18F]F- from proton irradiated [18O]H 2O and subsequent radiofluorination of a broad range of substrates directly on the resin. The highest radiochemical yields were obtained with aliphatic sulfonates (69%) and bromides (42%); the total radiosynthesis time was 35-45 min. The multivariate analysis showed that the radiochemical yields and purities were controlled by the resin load, reaction temperature, and column packing effects. The resins could be reused several times with the same or different substrates. The fully automated on-column radiofluorination methodology was applied to the radiosynthesis of the important PET radiotracers [18F]FLT and [18F]FDG. The latter was produced with 40% yield on a 120 GBq scale and passed GMP-regulated quality control required for commercial production of [18F]FDG. The combination of compact form factor, simplicity of [18F]F- recovery and processing, and column reusability can make solid phase radiofluorination an attractive radiochemistry platform for the emerging dose-on-demand instruments for bedside production of PET radiotracers.
- Mathiessen, Bente,Zhuravlev, Fedor
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- Development of Chiral Organosuperbase Catalysts Consisting of Two Different Organobase Functionalities
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In the field of chiral Br?nsted base catalysis, a new generation of chiral catalysts has been highly anticipated to overcome the intrinsic limitation of pronucleophiles that are applicable to the enantioselective reactions. Herein, we reveal conceptually new chiral Br?nsted base catalysts consisting of two different organobase functionalities, one of which functions as an organosuperbase and the other as the substrate recognition site. Their prominent activity, which stems from the distinctive cooperative function by the two organobases in a single catalyst molecule, was demonstrated in the unprecedented enantioselective direct Mannich-type reaction of α-phenylthioacetate as a less acidic pronucleophile. The present achievement would provide a new guiding principle for the design and development of chiral Br?nsted base catalysts and significantly broaden the utility of Br?nsted base catalysis in asymmetric organic synthesis.
- Kondoh, Azusa,Oishi, Masafumi,Terada, Masahiro,Tezuka, Hikaru
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supporting information
p. 7472 - 7477
(2020/03/19)
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- Phosphazenes: Efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide
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Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h-1 with a TON of 759. It is also shown that unexpectedly, N,N-dimethylformamide can reduce CO2 to a mixture of silyl formates, acetals and methoxides in the absence of any catalyst.
- Courtemanche, Marc-André,Légaré, Marc-André,Rochette, étienne,Fontaine, Frédéric-Georges
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supporting information
p. 6858 - 6861
(2015/04/14)
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- Extremely strong, uncharged auxiliary bases; monomeric and polymer-supported polyaminophosphazenes (P2-P5)
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The syntheses and properties of novel, extremely strong uncharged polyaminophosphazene bases up to a high level of steric hindrance are described. Most of the systems were readily prepared in up to molar quantities and conveniently recovered from their salts. They are of appreciable to high chemical and thermal stability. Crystal structures of their salts were determined in order to parametrize a force field, which is utilized in molecular modeling studies. The latter offer a rationalization of the high conformational mobility of these systems. These bases cover a range of ca. 15 pK units in basicity and extend the range of uncharged auxiliary bases by ca. 19 pK units up to DMSOpKBH+ values of 34-35. They are proposed as a novel class of auxiliary bases for deprotonation of very low acidic compounds where chemists have been so far left to classical metalorganic bases. Depending on the basicity range and the degree of steric protection of the basic center, these systems are particularly applicable to E2 elimination or to in situ generation of highly reactive "naked" anions. VCH Verlagsgesellschaft mbH, 1996.
- Schwesinger, Reinhard,Schlemper, Helmut,Hasenfratz, Christian,Willaredt, Juergen,Dambacher, Tim,Breuer, Thomas,Ottaway, Carol,Fletschinger, Michael,Boele, Joachim,Fritz, Hans,Putzas, Dietmar,Rotter, Heinz W.,Bordwell, Frederick G.,Satish, Amruthur V.,Ji, Guo-Zen,Peters, Eva-Maria,Peters, Karl,Von Schnering, Hans Georg,Walz, Leonhard
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p. 1055 - 1081
(2007/10/03)
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