- Mixing and matching chiral cobalt- and manganese-based calix-salen catalysts for the asymmetric hydrolytic ring opening of epoxides
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Homochiral oligomeric salen macrocycles possessing aromatic spacers have been prepared as new calix-salen derivatives. The corresponding cobalt and manganese complexes were synthesized and characterized, and their catalytic activities have been studied in the challenging hydrolysis of meso epoxides. While manganese calix-salen complexes were not active in the studied reactions, the dual heterobimetallic system, using an equimolar combination of cobalt and manganese calix-salen derivatives proved to be more enantioselective than the sole cobalt system. Furthermore, as heterogeneous complexes, the catalytic mixture could be easily recovered by simple filtration and successfully reengaged in subsequent catalytic runs. Interestingly, no need for cobalt reactivation was noticed to maintain maximum efficiency of this dual system. The matched Co/Mn dual catalyst was also used to promote the dynamic hydrolytic kinetic resolution of epibromohydrin.
- Dandachi, Hiba,Zaborova, Elena,Kolodziej, Emilie,David, Olivier R.P.,Hannedouche, Jér?me,Mellah, Mohamed,Jaber, Nada,Schulz, Emmanuelle
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p. 246 - 253
(2017/03/01)
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- Chiral calix-salen cobalt complexes, catalysts for the enantioselective dynamic hydrolytic kinetic resolution of epibromohydrin
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New calix-salen cobalt (III) complexes were synthesized as a mixture and as pure trimer or tetramer complexes. These cyclic complexes were used as catalysts to promote the dynamic hydrolytic kinetic resolution (HKR) of epibromohydrin in order to evaluate the effect of the cyclic structures size on the cooperative bimetallic interactions. Since the obtained catalysts were easily recovered from the reaction mixture by simple filtration, their efficiency was evaluated in recycling procedures. It was found that both cyclic oligomer complexes (trimer and tetramer) and the mixture of calix-salen complexes delivered the expected diol with high enantioselectivity and yield. Tetramer calix-salen cobalt complex proved to be the most active and selective catalyst of the series. In this case, an optimal conformation to allow the formation of bimetallic species activating respectively both the epoxide and water as nucleophile is probably responsible for an efficient dual activation.
- Dandachi, Hiba,Nasrallah, Houssein,Ibrahim, Farah,Hong, Xiang,Mellah, Mohamed,Jaber, Nada,Schulz, Emmanuelle
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p. 457 - 462
(2014/12/10)
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- Continuous enantioselective kinetic resolution of terminal epoxides using immobilized chiral cobalt-salen complexes
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Jacobsen's cobalt-salen complex was covalently immobilized on polymer carriers that are part of different technical setups (polymer powder, composite Raschig rings, PASSflow microreactors) and employed for the enantioselective ring opening of terminal epoxides with water and phenols. The polymer-supported catalysts showed good activity and stereoselectivity and could be used repeatedly after a simple reactivation protocol in both batch as well as continuous-flow modes. Georg Thieme Verlag Stuttgart.
- Solodenko, Wladimir,Jas, Gerhard,Kunz, Ulrich,Kirschning, Andreas
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p. 583 - 589
(2007/12/25)
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- Hydrolytic kinetic resolution of epoxides catalyzed by chromium(III)-endo, endo-2,5-diaminonorbornane-salen [Cr(III)-DIANANE-salen] complexes. Improved activity, low catalyst loading
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The hydrolytic kinetic resolution (HKR) of terminal epoxides, using chiral chromium(III)-salen catalysts based on DIANANE (endo,endo-2,5-diaminonorbornane) , was studied. A broad substrate scope was found for the chromium(III)-DIANANE catalysts, and very low loadings (down to 0.05 mol%) were needed to achieve high enantiomeric purities of both the remaining epoxides and the product diols (up to >99% ee). Besides monosubstituted epoxides, 2-methyl-2-n-pentyloxirane, which is an example for 2,2-disubstituted epoxides, could be ring-opened in an asymmetric fashion with water in the presence of an electronically tuned chromium-(III)-DIANANE complex.
- Berkessel, Albrecht,Ertuerk, Erkan
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p. 2619 - 2625
(2007/10/03)
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- Process for the preparation of protected 3-amino-1,2-dihydroxypropane acetal and derivatives thereof
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A process for producing protected 3-amino-1,2-dihydroxypropane acetal, particularly in chiral forms, for use as an intermediate in the preparation of various 3-carbon compounds which are chiral. In particular, the present invention relates to the process for preparation of 3-amino-1,2-dihydroxypropane isopropylidene acetal. The protected 3-amino-1,2-dihydroxypropane acetal is a key intermediate to the preparation of chiral 3-carbon compounds which in turn are intermediates to various pharmaceuticals.
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- Polymer-supported chiral Co(salen) complexes: Synthetic applications and mechanistic investigations in the hydrolytic kinetic resolution of terminal epoxides
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This paper describes the synthesis of polystyrene- and silica-bound chiral Co(salen) complexes and their application in asymmetric catalysis. A general method for the covalent attachment of salen complexes to both types of support has been devised, and the corresponding immobilized cobalt derivatives are shown to be efficient and highly enantioselective catalysts for the hydrolytic kinetic resolution (HKR) of terminal epoxides. These systems provide practical solutions to certain technical difficulties associated with the isolation of reaction products from the HKR. Removal of the supported catalyst by filtration and repeated recycling is demonstrated with no loss of reactivity or enantioselectivity. The enantioselective addition of phenols to terminal epoxides mediated by this catalyst system provides a facile, high-yielding synthesis of the corresponding enantioenriched aryl ethers. The immobilized catalysts have been adapted to a continuous flow process for the generation of reaction products in high yield and ee, requiring only very simple techniques for product purification. The mechanism by which these catalysts perform highly efficient and enantioselective epoxide ring opening has been addressed using a silica- bound Co(salen) complex. A dramatic correlation between the degree of catalyst site-isolation and reaction rate has been observed, consistent with a cooperative bimetallic mechanism in these reactions.
- Annis, D. Allen,Jacobsen, Eric N.
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p. 4147 - 4154
(2007/10/03)
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- Design and synthesis of a novel class of nucleotide analogs with anti- HCMV activity
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A novel class of cyclic nucleotide analogs has shown anti-HCMV activity. The synthesis as well as structure - activity relationship studies are presented.
- Nguyen-Ba, Paul,Lee, Nola,Mitchell, Helen,Chan, Laval,Quimpere, Miguel
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p. 3555 - 3560
(2007/10/03)
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- Anti-viral compounds
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Nucleotide analogues having the general formula (I) and pharmaceutically acceptable derivatives: STR1 wherein n is 0 or an integer; X is O or S, CH2, CH-halogen, CH--N3, or C=CH2 ; Q and U are independently selected from: O, S, and CH(Ra) wherein Ra is hydrogen, OH, halogen, N3, NH2, SH, carboxyl, C1-6 alkyl or Ra is CH2 (Rb) wherein Rb is hydrogen, OH, SH, NH2, C1-6 alkyl or carboxyl; or both Q and U are CH when Q and U are linked by a double bond; Z is selected from: O, a C1-6 alkoxy, a C1-6 thioalkyl, a C1-6 aminoalkyl, (CH2)m wherein m is 0 or an integer, and N(Rc)2 wherein both Rc are independently hydrogen or a C1-6, alkyl; and R2 is a purine or pyrimidine base or an analogue or derivative thereof are disclosed. Members of this series of analogues possess anti-viral activity.
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- New polymer supported cinchona alkaloids for heterogeneous catalytic asymmetric dihydroxylation of olefins
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Two new polymeric cinchona alkaloid derived ligands were synthesized and utilized in the asymmetric dihydroxylation of olefins, exhibiting high enantioselectivities in the case of aliphatic terminal olefins under heterogeneous phase.
- Nandanan,Sudalai,Ravindranathan
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p. 2577 - 2580
(2007/10/03)
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- Eine neue Ligandenklasse fuer die asymmetrische Dihydroxylierung von Olefinen
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Keywords: Asymmetrische Dihydroxylierungen; Chirale Liganden; Chinchonaalkaloide; Katalyse; Osmiumverbindungen
- Becker, Heinrich,Sharpless, K. Barry
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p. 447 - 449
(2007/10/03)
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- Short and Practical Syntheses of (R)-(-)-Carnitine and (R)-(-)-γ-Amino-β-hydroxybutyric Acid (GABOB)
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Short and practical syntheses of (R)-(-)-carnitine and (R)-(-)-γ-amino-β-hydroxybutyric acid have been developed, both commencing with the catalytic asymmetric dihydroxylation of allyl bromide.
- Kolb, Hartmuth C.,Bennani, Youssef L.,Sharpless, K. Barry
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p. 133 - 141
(2007/10/02)
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- Degradation of 2,3-Dichloro-1-propanol by a Pseudomonas sp.
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A bacterium that assimilates 2,3-dichloro-1-propanol was isolated from soil by enrichment culture.The strain was identified as Pseudomonas sp. by the taxonomic studies.The strain converted 2,3-dichloro-1-propanol to 3-chloro 1,2-propanediol, releasing chloride ions.The conversion was stereospecific because the residual 2,3-dichloro-1-propanol and formed 3-chloro-1,2-propanediol gave optical rotation.The resting cells converted various halohydrins to the dehalogenated alcohols, and cell-free extracts had strong epoxyhydrolase activity.These results indicated that the strain assimilated 2,3-dichloro-1-propanol via 3-chloro-1,2-propanediol, glycidol and glycerol.The possibility to manufacture optically active 2,3-dichloro-1-propanol is discussed.
- Kasai, Naoya,Tsujimura, Kazuya,Unoura, Kinya,Suzuki, Toshio
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p. 3185 - 3190
(2007/10/02)
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- ENANTIOMERE DER 2,2'-DINITROBIPHENYL-6,6'-DICARBONSAEURE ALS STEREOSELEKTIV WIRKSAME, REVERSIBLE SCHUTZGRUPPEN-II. STEREOSELEKTIVE SYNTHESEN VON LIPIDGRUNDKOERPERN ODER -BAUSTEINEN
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S-(-)-1,1'-diphenyl-2,2'-dinitro-6,6'-dicarboxylic acid (1) is used as an axial-chiral protecting group for the primary hydroxy group of glycerol and glycerol derivatives.Diesters of 1 were formed which have the largest distance between the nitro groups and the nucleophilic substituents on glycerol.After hydrogenolytical removal of the protecting group asymmetric glycerol derivatives were obtained with approximately 10percent enantiomeric excess.Hydroxybromination of 12 resulted mainly in he anti-Markovnikov 13a instead of the Markovnikov product 13b expected, which was present only in traces.This deviation is discussed.
- Mueller, H. K.,Burgold, J.
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p. 1533 - 1538
(2007/10/02)
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