- Concise synthesis and applications of enantiopure spirobiphenoxasilin-diol and its related chiral ligands
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The development of chiral architectures for chiral ligand and catalyst discovery is essential for asymmetric catalysis. Herein, we report the concise synthesis of a Si-centered spirocyclic skeleton, spirobiphenoxasilin-diol (SPOSiOL), and its derived chiral ligands. Using the chemical resolution method, the optical SPOSiOL could be obtained in high yield on a gram scale. Preliminary studies indicated that this ligand scaffold has great potential in transition metal-catalyzed asymmetric reactions. This finding further highlights that the Si-centered spirocyclic scaffolds are of great value in asymmetric catalysis. This journal is
- Liu, Tao,Wang, Biqin,Wang, Peng,Wu, Yichen,Xu, Wen-Qiang,Yang, Lei
-
supporting information
p. 13365 - 13368
(2021/12/17)
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- New chiral ferrocene/indole-based diphosphine ligands for Rh-catalyzed asymmetric hydrogenation of functionalized olefins
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Convenient synthesis of a new family of chiral ferrocene/indole-based diphosphine ligands, (Rc,Rp)-IndoFerroPhos (L), from (Sc,Rp)-PPFA and 2-(diphenylphosphino)indole has been described. These new ligands exhibited high efficiency in the Rh-catalyzed asymmetric hydrogenation of functionalized olefins including α-dehydroamino acid esters, α-enamides and dimethyl itaconate, in which up to >99% yield and 98% ee were achieved.
- Abbas, Zaheer,Ali, Aijaz,Hu, Xiang-Ping,Hu, Xin-Hu,Xu, You-Wei
-
-
- Topology-Based Functionalization of Robust Chiral Zr-Based Metal-Organic Frameworks for Catalytic Enantioselective Hydrogenation
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The design and development of robust and porous supported catalysts with high activity and selectivity is extremely significant but very challenging for eco-friendly synthesis of fine chemicals and pharmaceuticals. We report here the design and synthesis of highly stable chiral Zr(IV)-based MOFs with different topologies to support Ir complexes and demonstrate their network structures-dependent asymmetric catalytic performance. Guided by the modulated synthesis and isoreticular expansion strategy, five chiral Zr-MOFs with a flu or ith topology are constructed from enantiopure 1,1′-biphenol-derived tetracarboxylate linkers and Zr6, Zr9, or Zr12 clusters. The obtained MOFs all show high chemical stability in boiling water, strongly acidic, and weakly basic aqueous solutions. The two flu MOFs featuring the dihydroxyl groups of biphenol in open and large cages, after sequential postsynthetic modification with P(NMe2)3 and [Ir(COD)Cl]2, can be highly efficient and recyclable heterogeneous catalysts for hydrogenation of α-dehydroamino acid esters with up to 98% ee, whereas the three ith MOFs featuring the dihydroxyl groups in small cages cannot be installed with P(NMe2)3 to support the Ir complex. Incorporation of Ir-phosphorus catalysts into Zr-MOFs leads to great enhancement of their chemical stability, durability, and even stereoselectivity. This work therefore not only advances Zr-MOFs as stable supports for labile metal catalysts for heterogeneous asymmetric catalysis but also provides a new insight into how highly active chiral centers can result due to the framework topology.
- Jiang, Hong,Zhang, Wenqiang,Kang, Xing,Cao, Ziping,Chen, Xu,Liu, Yan,Cui, Yong
-
supporting information
p. 9642 - 9652
(2020/07/02)
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- Synthesis of constrained tetracyclic peptides by consecutive CEPS, CLIPS, and oxime ligation
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In Nature, multicyclic peptides constitute a versatile molecule class with various biological functions. For their pharmaceutical exploitation, chemical methodologies that enable selective consecutive macrocyclizations are required. We disclose a combination of enzymatic macrocyclization, CLIPS alkylation, and oxime ligation to prepare tetracyclic peptides. Five new small molecular scaffolds and differently sized model peptides featuring noncanonical amino acids were synthesized. Enzymatic macrocyclization, followed by one-pot scaffold-assisted cyclizations, yielded 21 tetracyclic peptides in a facile and robust manner.
- Streefkerk, Dieuwertje E.,Schmidt, Marcel,Ippel, Johannes H.,Hackeng, Tilman M.,Nuijens, Timo,Timmerman, Peter,Van Maarseveen, Jan H.
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supporting information
p. 2095 - 2100
(2019/04/11)
-
- BABIPhos Family of Biaryl Dihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation
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Novel bidentate phosphine ligands BABIPhos featuring a biaryl bis-dihydrobenzooxaphosphole core are presented. Their synthesis was achieved via Pd-catalyzed reductive homocoupling of dihydrobenzooxaphosphole aryl triflates. An efficient route toward various analogues was also established, giving access to phosphines with different electronic and steric properties. The newly obtained ligands demonstrated high efficiency and selectivity in Rh-catalyzed asymmetric hydrogenation of di- and trisubstituted enamides. This new class of ligands is complementary to previously described bidentate benzooxaphosphole ligands BIBOP.
- Li, Guisheng,Zatolochnaya, Olga V.,Wang, Xiao-Jun,Rodríguez, Sonia,Qu, Bo,Desrosiers, Jean-Nicolas,Mangunuru, Hari P. R.,Biswas, Soumik,Rivalti, Daniel,Karyakarte, Shuklendu D.,Sieber, Joshua D.,Grinberg, Nelu,Wu, Ling,Lee, Heewon,Haddad, Nizar,Fandrick, Daniel R.,Yee, Nathan K.,Song, Jinhua J.,Senanayake, Chris H.
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supporting information
p. 1725 - 1729
(2018/04/14)
-
- MULTICYCLIC PEPTIDES AND METHODS FOR THEIR PREPARATION
-
The invention relates to methods for preparing a compound comprising a peptide attached to a molecular scaffold whereby multiple peptide loops are formed, to compounds that can be obtained with such methods and uses thereof.
- -
-
Page/Page column 53
(2018/06/30)
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- Facile Cu(ii)-mediated conjugation of thioesters and thioacids to peptides and proteins under mild conditions
-
The bioconjugation of peptide derivatives such as polypeptides, peptide-based probes and proteins is a vibrant area in many scientific fields. However, reports on metal-mediated chemical methods towards native peptides especially non-engineering protein modification under mild conditions are still limited. Herein, we describe a novel Cu(ii)-mediated strategy for the conjugation of thioesters/thioacids to peptides under mild conditions with high functional group tolerance. Based on this strategy, polypeptides, even peptide-based fluorescent probes, can be efficiently constructed. Finally, the selective modification of lysine residues of native Ub with thioesters could be realized and complete conjugation of Ub could be achieved even under equivalent Cu(ii). These promising results could greatly expand Cu(ii)-mediated reaction strategies on chemical biology and molecular imaging.
- Sun, Yao,Lyu, Zhenbin,Wang, Zhiqiang,Zeng, Xiaodong,Zhou, Hui,Xu, Fuchun,Chen, Ziyang,Xu, Yuling,Xu, Ping,Hong, Xuechuan
-
supporting information
p. 3610 - 3614
(2018/05/26)
-
- Ultrasound-Promoted Enantioselective Decarboxylative Protonation of α-Aminomalonate Hemiesters by Chiral Squaramides: A Practical Approach to Both Enantiomers of α-Amino Esters
-
Herein, we report an ultrasound-promoted enantioselective decarboxylative protonation reaction of α-aminomalonate hemiesters 1 in the presence of chiral cinchona-derived squaramide Br?nsted bases under mild conditions, which afforded both the (S)- and (R)-enantiomers of α-amino acid derivatives 2 in excellent yields (> 90 %) and excellent enantioselectivities (up to 98 % ee).
- Some, Surajit,Bae, Han Yong,Kim, Mun Jong,Zhang, Yong Jian,Song, Choong Eui
-
supporting information
p. 4562 - 4565
(2017/08/30)
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- Thioamide-substituted cinchona alkaloids as efficient organocatalysts for asymmetric decarboxylative reactions of MAHOs
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A new class of thioamide-substituted cinchona derivatives is reported. A convergent and practical approach was developed to insert the thioamide functional group onto the cinchonidine from readily available dithioesters. These organocatalysts were effective in asymmetric decarboxylative Mannich and protonation reactions of α-amido-substituted malonic acid half oxyesters (MAHOs), affording α,β- and α-amino acid derivatives, respectively, in good yields and stereoselectivities.
- Singjunla, Yuttapong,Pigeaux, Morgane,Laporte, Romain,Baudoux, Jér?me,Rouden, Jacques
-
supporting information
p. 4319 - 4320
(2018/08/24)
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- Towards a universal organocatalyst for the synthesis of enantioenriched phenylalanine derivatives by enantioselective decarboxylative protonation
-
Access to enantioenriched non-proteogenic phenylalanine derivatives is described using the enantioselective decarboxylative protonation reaction of amidohemimalonate esters catalysed by various cinchona-based compounds. This study compares the catalytic efficiency as well as the enantioselectivity induced by three types of common organocatalysts, namely thioureas, squaramides and bis-cinchona squaramides. One of the main outcome of this work is the observation of a significant influence of the N-protecting group of the hemimalonate on its interaction with the catalyst. This methodology carried out under mild conditions exhibits good substrate scope and functional group tolerance. A substoichiometric amount of catalyst can also be used in certain cases while affording good yields and selectivities.
- Pigeaux, Morgane,Laporte, Romain,Harrowven, David C.,Baudoux, Jér?me,Rouden, Jacques
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supporting information
p. 4599 - 4603
(2016/09/23)
-
- Urea treated subtilisin as a biocatalyst for transformations in organic solvents
-
Abstract Subtilisin lyophilized from its solution in aqueous buffer in the presence of 6 M urea showed up to 50-fold increase (as compared to lyophilized subtilisin not subjected to urea treatment) in its initial rate of a transesterification reaction in anhydrous n-hexane. The lyophilization time controlling the extent of 'drying' was an important parameter. The urea treated subtilisin had five times shorter half life during heating at 100 C in hexane. The change in conformation was also reflected in its 92-fold higher activity at 15 C as compared to merely 28-fold higher activity at 45 C. The comparative enantioselectivity of urea treated subtilisin during kinetic resolution of 1-phenylethanol was expectedly lower. Its enantioselectivity during kinetic resolution of a natural substrate N-acetyl-(R,S)-phenylalanine ethyl ester in hexane was higher. Urea treated subtilisin also showed higher catalytic promiscuity during an aldol condensation. CD studies in both far UV and near UV region were also carried out to compare the two structures.
- Mukherjee, Joyeeta,Mishra, Prasant,Gupta, Munishwar N.
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p. 1976 - 1981
(2015/03/30)
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- An eco-benign and highly efficient procedure for N-acylation catalyzed by heteropolyanion-based ionic liquids using carboxylic acid under solvent-free conditions
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An eco-benign and highly efficient route for N-acylation of amines has been developed by treating amines with corresponding carboxylic acids in the presence of 2 mol % of heteropolyanion-based ionic liquids as catalysts under solvent-free conditions. This practical reaction could tolerate a wide range of substrates. Thus, various N-acylation products including N-acyl α-amino acid derivatives were obtained in moderate to excellent yields at 70 C to 120 C. Moreover, recycling studies revealed that heteropolyanion-based ionic liquids were easily reusable for this N-acylation. This method provides a green and much improved protocol over the existing methods.
- Chen, Zhikai,Fu, Renzhong,Chai, Wen,Zheng, Hao,Sun, Lin,Lu, Qiang,Yuan, Rongxin
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p. 2237 - 2245
(2014/03/21)
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- Self-disproportionation of enantiomers of non-racemic chiral amine derivatives through achiral chromatography
-
Efficient self-disproportionation of enantiomers of several non-racemic chiral amines was achieved through conversion to N-acetamides and subsequent MPLC using an achiral column. The MPLC of these non-racemic N-acetamide derivatives gave the chart having a clear boundary between two fractions. Thus, in the less polar fraction, remarkable enantiomer enrichment was observed (>99%ee), while the ee of more polar fraction was considerably reduced. The magnitude of the enantiomer enrichments and depletions strongly depended on substituent on the amino group.
- Nakamura, Tsuyoshi,Tateishi, Kaori,Tsukagoshi, Shiori,Hashimoto, Saori,Watanabe, Shotaro,Soloshonok, Vadim A.,Ace?a, José Luis,Kitagawa, Osamu
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experimental part
p. 4013 - 4017
(2012/07/14)
-
- Nickel-catalyzed reductive cleavage of aryl-oxygen bonds in alkoxy- and pivaloxyarenes using hydrosilanes as a mild reducing agent
-
A nickel-catalyzed reductive deoxygenation of aryl alkyl ethers and aryl pivalates has been developed. Hydrosilanes serve as a mild reducing agent. The present protocol allows the use of a pivalate group as a robust and traceless steering group in arene functionalization reactions. The Royal Society of Chemistry.
- Tobisu, Mamoru,Yamakawa, Ken,Shimasaki, Toshiaki,Chatani, Naoto
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supporting information; experimental part
p. 2946 - 2948
(2011/04/24)
-
- Resolution of N-protected amino acid esters using whole cells of Candida parapsilosis ATCC 7330
-
Whole cells of Candida parapsilosis ATCC 7330 were used for the resolution of N-acetyl amino acid esters. Excellent enantioselectivities (E = 40 to >500) were achieved for the resolution of N-protected protein and non-protein amino acid esters giving good yields (28-50%) and high enantiomeric excesses (up to >99%) for both enantiomers.
- Stella, Selvaraj,Chadha, Anju
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experimental part
p. 457 - 460
(2010/06/21)
-
- Concurrent esterification and N-acetylation of amino acids with orthoesters: A useful reaction with interesting mechanistic implications
-
The concurrent esterification and N-acetylation of amino acids has been studied with triethyl orthoacetate (TEOA) and triethyl orthoformate (TEOF). In a surprising finding, only 1 equiv of TEOA in refluxing toluene was necessary to convert l-proline and l-phenylalanine into the corresponding N-acetyl ethyl esters in good yield. The same transformation using TEOF was not effective. Stereochemical outcome and stoichiometric studies as well as structural variation of the amino acids in this reaction provided unexpected mechanistic insight.
- Gibson, Sarah,Romero, Dickie,Jacobs, Hollie K.,Gopalan, Aravamudan S.
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scheme or table
p. 6737 - 6740
(2011/02/25)
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- A chiral bidentate phosphoramidite (Me-BIPAM) for Rh-catalyzed asymmetric hydrogenation of α-dehydroamino esters, enamides, and dimethyl itaconate
-
High performance of Me-BIPAM for enantioselective hydrogenation of α-dehydroamino esters, enamides, and dimethyl itaconate was demonstrated. [Rh(Me-BIPAM)(diene)]X (diene = cod, nbd; X = BF4, PF6, SbF6) gave optically active β-aryl α-amino esters up to 99% ee, 1-arylethylamines up to 97% ee, methyl 2-acetylaminobutanoate with 90% ee, and dimethyl 2-methylsuccinate with 97% ee under 0.3-0.8 MPa dihydrogen with 0.1-1 mol % catalyst loading.
- Kurihara, Kazunori,Yamamoto, Yasunori,Miyaura, Norio
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experimental part
p. 3158 - 3160
(2009/08/09)
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- Novel chiral phosphine-phosphoramidite ligands derived from 1-naphthylamine for highly efficient Rh-catalyzed asymmetric hydrogenation
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A new chiral phosphine-phosphoramidite ligand (S)-HY-Phos 1 has been prepared from 1-naphthylamine via a two-step transformation, and successfully applied in the Rh-catalyzed asymmetric hydrogenation of various functionalized olefins, including α-(acetamido)cinnamates, enamides and α-enol ester phosphonates, in which up to 98% ee, 99% ee and 99% ee were achieved, respectively.
- Yu, Sai-Bo,Huang, Jia-Di,Wang, Dao-Yong,Hu, Xiang-Ping,Deng, Jun,Duan, Zheng-Chao,Zheng, Zhuo
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p. 1862 - 1866
(2008/12/21)
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- Chiral 1,2,3,4-tetrahydro-1-naphthylamine-derived phosphine-phosphoramidite ligand (THNAPhos): Application in highly enantioselective hydrogenations of functionalized C=C bonds
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We have recently reported a new chiral 1,2,3,4-tetrahydro-1-naphthylamine- derived phosphine-phosphoramidite ligand, (Rc,Ra)- THNAPhos, that is highly efficient in the rhodium-catalyzed asymmetrichydrog enation of a broad range of aenol ester phosphonates. To further demonstrate the utility of THNAPhos in asymmetric hydrogenation, in this paper, we describe its new application in the asymmetrichy drogenation of α-dehydroamino acid esters, enamides, dimethyl itaconate and α-enamido phosphonates. The results disclosed that the Rh/(Rc,Ra)-THNAPhos complex is highly effective for the enantioselective hydrogenation of these kinds of functionalized C=C olefins, affording the corresponding hydrogenation product in excellent enantioselectivities (normally over 99% ee).
- Qiu, Min,Hu, Xiang-Ping,Wang, Dao-Yong,Deng, Jun,Huang, Jia-Di,Yu, Sai-Bo,Duan, Zheng-Chao,Zheng, Zhuo
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scheme or table
p. 1413 - 1418
(2009/06/18)
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- Highly enantioselective decarboxylative protonation of α- aminomalonates mediated by thiourea Cinchona alkaloid derivatives: Access to both enantiomers of cyclic and acyclic α-aminoacids
-
Equation Presented Thiourea derived cinchona alkaloids promote the asymmetric decarboxylase protonation of cyclic, acyclic, or bicyclic α-aminomalonate hemiesters under mild and metal-free conditions to afford enantioenriched aminoesters in high yields and enantioselectivities up to 93%. Both enantiomers of the aminoesters have been synthesized with the same selectivity when using organic base 3 and its pseudoenantiomer 6 derived from quinine.
- Amere, Mukkanti,Lasne, Marie-Claire,Rouden, Jacques
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p. 2621 - 2624
(2008/02/10)
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- Copper-catalyzed oxidative desulfurization-oxygenation of thiocarbonyl compounds using molecular oxygen: An efficient method for the preparation of oxygen isotopically labeled carbonyl compounds
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A novel copper-catalyzed oxidative desulfurization reaction of thiocarbonyl compounds, using molecular oxygen as an oxidant and leading to formation of carbonyl compounds, has been developed, and the utility of the process is demonstrated by its application to the preparation of a carbonyl-18O labeled sialic acid derivative. The Royal Society of Chemistry.
- Shibahara, Fumitoshi,Suenami, Aiko,Yoshida, Atsunori,Murai, Toshiaki
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p. 2354 - 2356
(2008/02/09)
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- Unsymmetrical ferrocenylethylamine-derived monophosphoramidites: Highly efficient chiral ligands for Rh-catalyzed enantioselective hydrogenation of enamides and α-dehydroamino acid derivatives
-
A new family of unsymmetrical ferrocenylethylamine-derived monophosphoramidites were synthesized and successfully applied in the Rh-catalyzed enantioselective hydrogenation of a range of enamides and α-dehydroamino acid esters, and ee values of up to 99.5% were obtained for both types of substrate. These results suggest that unsymmetrical amine-derived monophosphoramidites can also exhibit excellent enantioselectivity for a broad range of substrates, comparable to or higher than those of the most efficient symmetrical amine-derived monophosphoramidites reported thus far.
- Zeng, Qing-Heng,Hu, Xiang-Ping,Duan, Zheng-Chao,Liang, Xin-Miao,Zheng, Zhuo
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p. 393 - 396
(2007/10/03)
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- New unsymmetrical hybrid ferrocenylphosphine-phosphoramidite ligands derived from H8-BINOL for highly efficient Rh-catalyzed enantioselective hydrogenation
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A series of new H8-BINOL-derived unsymmetrical hybrid ferrocenylphosphine-phosphoramidite ligands have been synthesized and successfully used in Rh-catalyzed asymmetric hydrogenations. The same or higher enantioselectivities (99.9% ee) were achieved in the hydrogenation of dimethyl itaconate and α-dehydroamino acid esters as those obtained with BINOL-derived analogues. However, slightly lower enantioselectivities (99.0% ee) were obtained in the hydrogenation of enamides.
- Zeng, Qing-Heng,Hu, Xiang-Ping,Duan, Zheng-Chao,Liang, Xin-Miao,Zheng, Zhuo
-
p. 1233 - 1238
(2007/10/03)
-
- Mechanistic study on nitrosation-deaminocyclization of mono-carbamoylated vicinal amino alcohols and diols: a new preparative in situ formation of ethanediazo hydroxide for the ethylation of carboxylates under mild conditions
-
While the cyclization of N-carbamoylamino alcohols into oxazolidinones via the activation with NO(1+) underwent smoothly, we found that similar reactions of vicinal diol monocarbamates were very slow. Mechanistic studies by means of time-resolved IR measurements of the former reaction suggested that the initial O-nitrosation was the rate-determining step. Indeed, the introduction of an ethyl group on the nitrogen terminus of diol monocarbamate promoted the desired cyclic carbonate formation. The concomitantly formed ethanediazo hydroxide, the precursor of the protonated form of diazoethane, was evidenced by trapping with p-nitrobenzoic acid as an ethyl ester. The formation of ethyl ester accelerates the reaction in an irreversible manner. Based on an elaboration of the substrates and reaction conditions, 2,3-dimethyl-2,3-butanediol mono-N-ethyl-N-nitrosocarbamate, which is easily prepared in situ from the corresponding ethylcarbamate and t-butyl nitrite, was developed as a new ethylation reagent of various carboxylic acids under mild conditions.
- Suzuki, Masumi,Sugai, Takeshi
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p. 1217 - 1228
(2007/10/03)
-
- α-amino acid derivatives by enantioselective decarboxylation
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The methodology of enantioselective decarboxylation was applied to 2-aminomalonic acid derivatives in order to obtain enantio-enriched amino acid derivatives. Full conversion was achieved stirring racemic N-acetylated 2-aminomalonic hemiesters in THF at 70 °C with 10 mol % of a chiral base for 24 h. The catalyst may be recycled. Whereas the commercially available cinchona alkaloids gave poor results, benzamide and benzenesulfonamide derivatives of 9-amino(9-deoxy)epicinchonine turned out to be effective catalysts. The best result was obtained with 2-N-acetylamino-2-ethoxy-carbonyl-3-phenylpropionic acid as the starting material and N-(9-deoxyepicinchonine-9-yl)-4-methoxybenzamide as the chiral base to give ethyl N-acetyl-L-phenylalaninate in 70% ee. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Brunner, Henri,Baur, Markus A.
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p. 2854 - 2862
(2007/10/03)
-
- The enzyme-catalysed stereoselective transesterification of phenylalanine derivatives in supercritical carbon dioxide
-
The subtilisin Carlsberg catalysed transesterification of N-acetyl phenylalanine methyl ester (1), N-acetyl phenylalanine ethyl ester (2), N-trifluoroacetyl phenylalanine methyl ester (3) and N-trifluoroacetyl phenylalanine ethyl ester (4) was studied in supercritical carbon dioxide. The water content of the reaction affects the reactivity of the system; for the transesterification of the methyl esters with ethanol the optimum concentration of water was determined to be about 0.74 M, while for the transesterification of the ethyl esters with methanol the optimum concentration of water was about 1.3 M. The conversion is also dependent upon the concentration of alcohol; for ethanol, 2% v/v gives the maximum conversion, whilst for methanol, only 0.8-1. 2% v/v is required. This is probably due to a difference in the solubility of the substrates in the two alcohol/supercritical carbon dioxide mixtures. The reaction is highly stereoselective, in all cases no evidence for reaction of the D-isomer could be detected by chiral gas chromatography.
- Smallridge, Andrew J.,Trewhella, Maurie A.,Wang
-
p. 259 - 262
(2007/10/03)
-
- Competitive formation of 10- and 7-membered hydrogen-bonded rings of proline-containing model peptides
-
Intramolecularly hydrogen-bonded structures of proline-containing model peptides with a sequence of N-tert-butoxycarbonyl-prolyl-Xaa-NHCH3 [Xaa = Gly (glycyl), Ala (alanyl), Phe (phenylalanyl), Leu (leucyl), Ile (isoleucyl), and Val (valyl)] were studied by proton nuclear magnetic resonance and infrared spectroscopy. Variation of chemical shifts of amide protons with composition change of DMSO-d6/CDCl3 mixed solvents were found to be a good measure of intramolecular hydrogen bonding of peptides in CDCl3 solution. It has been shown that 10- and 7-membered hydrogen-bonded rings, which should have the β- and γ-turn like structures in proteins, respectively, form competitively with each other. It is suggested that the equilibrium between the two hydrogen-bonded rings is determined by steric hindrance due to a side chain of the Xaa residue. Free energies for formation of the 10- and 7-membered hydrogen-bonded rings, ΔG10 and ΔG7, were estimated from the solvent composition-dependent change of the chemical shifts. A good correlation between ΔG10 and the occurrence frequencies of residues Xaa at the (i + 2)th position for the β-turns in proteins has been found.
- Jin, Yusuke,Tonan, Kenji,Ikawa, Shun-Ichi
-
p. 2795 - 2802
(2007/10/03)
-
- A new family of chelating diphosphines with a transition metal stereocenter in the backbone: Novel applications of "chiral-at-rhenium" complexes in rhodium-catalyzed enantioselective alkene hydrogenations
-
The title compounds are accessed by sequences starting with racemic and enantiomerically pure [(η5-C5H5)Re(NO)(PPh3) (CH3)]. Reactions with chlorobenzene/HBF4, PPh2H, and tBuOK give the phosphido complex [(η5-C5H5)Re(NO) (PPh3)(PPh2)] (3). Reactions with Ph3C+BF4-,PPh2H, and tBuOK give the methylene homologue [(η5-C5H5)Re(NO)(PPh3) (CH2PPh2)] (9). Treatment of 3 or 9 with nBuLi or tBuLi and then PPh2Cl gives the diphosphido systems [(η5-C5H4PPh2)Re(NO) (PPh3)-((CH2)nPPh2)] (n = 0/1, 5/11). Reactions of 5 and 11 with [Rh(NBD)Cl]2/AgPF6 (NBD = norbornadiene) give the rhenium/rhodium chelate complexes [(η5-C5H4-PPh2)Re(NO) (PPh3)((μ-CH2)nPPh 2)Rh-(NBD)]+PF6- (n = 0/1, 6+/12+ PF6-; 30-32% overall from commercial Re2(CO)10). The crystal structures of 6+ PF6- and 12+ PF6- are compared to those of 3 and 9, and other rhodium complexes of chelating bis(diphenylphosphines). The chiral pockets defined by the PPh2 groups show unusual features. Four alkenes of the type (Z)-RCH=C(NHCOCH3)CO2R′ are treated with H2 (1 atm) and (R)-6+ PF6- or (S)-12+ PF6- (0.5 mol%) in THF at room temperature. Protected amino acids are obtained in 70-98% yields and 93-82 % ee [(R)-6+ PF6-] or 72-60% ee [(S)-12+ PF6- ]. Pressure and temperature effects are defined, and turnover numbers of > 1600 are realized.
- Kromm, Klemenz,Zwick, Bill D.,Meyer, Oliver,Hampel, Frank,Gladysz, John A.
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p. 2015 - 2027
(2007/10/03)
-
- Metal-catalyzed acyl transfer reactions of enol esters: Role of Y5(OiPr)13O and (thd)2Y(OiPr) as transesterification catalysts
-
(equation presented) Primary and secondary alcohols react with vinyl or isopropenyl acetate at room temperature in the presence of catalytic amounts (0.05-1 mol percent) of Y5(OiPr)13O to give the corresponding esters. In selected cases, the yttrium catalyst promotes the selective O-acylation of amino alcohols without the formation of the amide. Enol esters also react with α-amino acid esters in the absence of a catalyst, at room temperature, to give the corresponding amides.
- Lin, Mei-Huey,RajanBabu
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p. 997 - 1000
(2007/10/03)
-
- New chiral diphosphinites: Synthesis of Rh complexes. Heterogenisation on zeolites
-
New diphosphinite ligands derived from (2S,4R), (2S,4S)-1-benzyl-4-hydroxy-4-phenyl-2-(1,1-diphenylmethyl)pyrrolidinylmethanol and (2S,4R), (2S,4S)-1-(3-triethoxysilyl)propylaminocarbonyl-4-hydroxy-4-phenyl-2-(1,1- diphenylmethyl)pyrrolidi nylmethanol have been prepared in high yields (60-80%) and reacted with [RhCl(cod)]2 to yield cationic [Rh(diphosphinite)(cod)]+ complexes. Those metal complexes bearing a triethoxysilyl group were covalently bonded to USY-zeolite by controlled hydrolysis and Rh-heterogenised complexes were obtained. A comparative study (homogeneous versus supported) for the catalytic activity and selectivity in hydrogenation and hydroformylation reactions was made, obtaining an enhanced performance for heterogenised catalysts; moreover, those catalysts can be recycled in successive runs, by a simple filtration, without a significant loss of activity.
- Fuerte,Iglesias,Sanchez
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p. 186 - 194
(2007/10/03)
-
- Enzymatic reaction in supercritical fluid carbon dioxide using dry-ice
-
New enzymatic reactions in supercritical fluid carbon dioxide catalyzed by lipases (PPL, Lipase MY, Candida cylindracea Lipase), and Proteases (subtilisin Carlsberg, subtilisin 8397, immobilized papain) with high efficiency and yields in a simple high pressure reactor using readily available dry-ice have been developed.
- Yu, Hui-Ming
-
p. 647 - 650
(2007/10/03)
-
- Heterogenised catalysts on zeolites. Synthesis of new chiral Rh(I) complexes with (2S,4R)-trans-4-RCOO-2-(t-butylaminocarbonyl) pyrrolidines and (2S,4S)-cis-4-RCONH-2-(t-butylaminocarbonyl) pyrrolidines. Heterogenisation on silica and a USY-zeolite and study of the role of support on their catalytic profile in hydrogenation of olefins
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Novel chiral ligands (2S,4R)-2-(t-butylaminocarbonyl)-4-[3-(alkylaminocarbonyl)propanoyloxy]pyrrolidine and (2S,4S)-cis-4-(alkylaminocarbonylamino)-2-(t-butyl-aminocarbonyl)pyrrolidine (4a,b; 9a,b), (a: alkyl = t-butyl; b: alkyl = 3-triethoxysilylpropyl) and their rhodium complexes were synthesised and characterised. The reactions of [{Rh(cod)Cl}2] and [RhCl(PPh3)3] with the chiral ligands in the presence of a non-coordinating anion (PF-6) gave the cationic complexes [Rh(L2)(ligand)][PF6] (L2 = cod, PPh3). The structures of these complexes were elucidated by elemental analyses, IR spectroscopy and 1H, 13C and 31P NMR measurements. The metal complexes bearing a triethoxysilyl group were covalently bonded to silica and modified USY-zeolite and Rh-heterogenised complexes were obtained. A comparative study (homogeneous versus supported) was made for the catalytic activity in hydrogenation reactions.
- Corma,Iglesias,Mohino,Sanchez
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p. 147 - 156
(2007/10/03)
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- Selectivity and Specificity in Substrate Binding to Proteases: Novel Hydrolytic Reactions Catalysed by α-Chymotrypsin Suspended in Organic Solvents with Low Water Content and Mediated by Ammonium Hydrogen Carbonate
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α-Chymotrypsin suspended in organic solvents with low water content catalysed hydrolytic reactions in the presence of ammonium hydrogen carbonate.Molecular modelling studies were carried out and structure-reactivity relationships were established by studying the hydrolysis of amino acid derivatives and analogues.The enzyme was found to be stereoselective with respect to the hydrolysis of L-amino acid derivatives, but no stereoselectivity was observed when α-hydroxy esters were used as substrates.A general procedure for the resolution of aromatic amino acid esters is given.The results are interpreted in terms of molecular modelling based on X-ray crystallographic data and literature data.
- Ricca, Jean-Marc,Crout, David H. G.
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p. 1225 - 1234
(2007/10/02)
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- New Rhodium Complexes anchored on Modified USY Zeolites. A Remarkable Effect of the Support on the Enantioselectivity of Catalytic Hydrogenation of Prochiral Alkenes
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Rh-complexes with N-based chiral ligands, when anchored on a modified USY-zeolite which contains profuse supermicropores, produce a remarkable increase of enantioselectivity (>95percent) in the hydrogenation of N-acyldehydrophenylalanine derivatives and represent a truly heterogeneous counterpart of the homogeneous organometallic catalysts.
- Corma, A.,Iglesias, M.,Pino, C. del,Sanchez, F.
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p. 1253 - 1255
(2007/10/02)
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- Synthesis of chiral Rh-bichep complexes, highly efficient catalysts for asymmetric hydrogenations
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Chiral cationic and neutral Rh complexes RhX(bichep)(nbd) (X=Cl,ClO4; NBD=norbornadiene;bichep=2,2′-bis(dicyclohexylphosphino)-6,6'-dimethyl-l, r-biphenyl) are highly active and excellent catalysts for enantioselective hydrogenation of prochiral olefms and ketones under mild reaction conditions.
- Chiba, Takeshi,Miyashita, Akira,Nohira, Hiroyuki,Takaya, Hidemasa
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p. 4745 - 4748
(2007/10/02)
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- Accelerated esterification of aminoacids with lipoglycosylated α-chymotrypsin in polar solvents
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A lipodisaccharide possessing a reactive aldopentose function, the 6-O-octyl-β-D-galactopyranosyl-(1→5)-L-arabinose (5), has been prepared. The reductive alkylation of four of the lysine residues of the bovine α-chymotrypsin led to a lipo-1-deoxyglycytolated enzyme. This modified protein efficiently catalyzed the synthesis of N-acetyl aminoacid ethyl esters in different solvents with 2.5-3% water contents. Compared to the native enzyme, enhanced esterification rates were determined, particularly in tetrahydrofuran, ethyl acetate and acetonitrile.
- Cabaret, Daniel,Maillot, Sophie,Wakselman, Michel
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p. 2131 - 2134
(2007/10/02)
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- Asymmetric Hydrogenation Using Diphenylphosphinite Derivatives of Carbohydrates as the Chiral Ligand of Rhodium Catalysts
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Diphenylphosphinite derivatives of carbohydrates (L-rhamnose, D-mannitol, and cellulose), which have asymmetric centers on the skeletons were synthesized.Asymmetric hydrogenations of prochiral substrates using rhodium catalysts with the prepared chiral phosphinite ligand were carried out to obtain chiral substances in 8-78percent optical yield.
- Yamashita, Mitsuji,Naoi, Manabu,Imoto, Hiroyuki,Oshikawa, Tatsuo
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p. 942 - 944
(2007/10/02)
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- BIOCATALYTICAL TRANSFORMATIONS II. ENANTIOSELECTIVE HYDROLYSIS OF N-ACETYL-FLUORO-PHENYLALANINE-ETHYLESTERS BY LYOPHILISED YEAST
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The three nuclear substituted monofluoro D-N-acetylphenylalanine-ethylesters were obtained in excellent yield via enantioselective hydrolysis of their respective racemates by use of lyophilised yeast (Saccharomyces cerevisiae Hansen).
- Csuk, Rene,Glaenzer, Brigitte I.
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- ENANTIOSELECTIVE HYDROLYSIS BY BAKER'S YEAST - II. ESTERS OF N-ACETYL AMINO ACIDS
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D-N-Acetyl amino acid esters were obtained via enantioselective hydrolysis of their racemates by use of fermenting yeast.Evidence is given that proteinases are the enzymes involved.
- Glaenzer, B. I.,Faber, K.,Griengl, H.
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p. 771 - 778
(2007/10/02)
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- ENANTIOSELECTIVE HYDROLYSIS BY BAKER'S YEAST
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Optically active N-acetylamino acid esters were obtained by enantioselective hydrolysis of their racemates using fermenting baker's yeast.
- Glaenzer, B.I.,Faber, K.,Griengl, H.
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p. 4293 - 4294
(2007/10/02)
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- Synthesis of Sugar Derivatives of Tervalent Phosphorus Compounds and Their Application to Homogeneous Asymmetric Hydrogenation
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Diphenylphosphine and diphenylphosphinite derivatives of sugars such as methyl 6-deoxy-4-C-(diphenylphosphino)-2,3-O-isopropylidene-α-L-talopyranoside, methyl 4-O-(diphenylphosphino)-2,3-O-isopropylidene-α-L-rhamnopyranoside, methyl 4-C,4-O-(diphenylphosphino)-2,3-O-isopropylidene-α-L-talopyranoside, 6-deoxy-6-C-(diphenylphosphino)-1,2:3,5-di-O-isopropylidene-α-D-glucofuranose, and 6-O-(diphenylphosphino)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose were synthesized by the reaction of diphenylphosphine-sodium dihydrobis(2-methoxyethoxy)aluminate (SDMA) and/or diphenylphosphinous chloride-triethylamine with sugar derivatives.Homogeneous asymmetric hydrogenations of several prochiral olefins (α-acetylaminocinnamic acid, methyl α-acetylaminocinnamate, α-benzoylaminocinnamic acid, itaconic acid, and tiglic acid) were carried out using rhodium(I) catalysts with the tervalent chiral phosphorus derivatives of sugars.The highest optical yield for all the five substrates was obtained when di-μ-chloro-bis(cyclooctadiene)dirhodium(I) and 6-O-(diphenylphosphino)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose were used.The advantages of this method are the simplicity in the synthesis of the chiral phosphorus compound and the comparatively high optical yield in the asymmetric hydrogenation of olefins.
- Yamashita, Mitsuji,Hiramatsu, Koji,Yamada, Manabu,Suzuki, Nobuyoshi,Inokawa, Saburo
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p. 2917 - 2921
(2007/10/02)
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