- Synthesis and reactivity of 1,2- and 1,3-diphosphanes that contain four chiral rhenium fragments: Architecturally novel tetrametallo-DMPE and -DMPP species that are unprivileged ligands for enantioselective catalysis
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Reactions of enantiopure (S)-[(η5-C5H 5)Re(NO)(PPh3)-(=CH2)]+ PF 6- [(S)-2] and PH2CH2(CH 2)nCH2PH2 (0.5 equiv.) give (S ReSRe)-[(η5-C5H 5)Re(NO)(PPh3){CH2PH2CH 2(CH2)n-CH2PH2CH 2}(Ph3P)(ON)Re(η5-C5H 5)]2+ 2PF6- [n = 0/1, (S ReSRe)-3/4; 65-62/77-58%]. Reaction of racemic 2 (BF 4- salt) and PH2(CH2) 2PH2 (0.5 equiv.) gives the meso and rac diastereomers of 3 (BF4- salts) in 28% and 38% yields after crystallization. Treatments of (SReSRe)-3/4 with fBuOK and then (S)-2 give the tetrarhenium complexes (SReSReS ReSRe)[{(η5-C5H 5)Re(NO)(PPh3)(CH2)}2{PHCH 2(CH2)n-CH2PH}{(CH 2)(Ph3P)(ON)Re(η5-C5H 5)}2]2+ 2PF6- [n = 0/1, (SReSReSReSRe)-7/8; 89-88/98-87%]. The crystal structure of (SReSReSReS Re)-7 is determined and its conformation analyzed. Reactions of (SReSReSReSRe)-7/8 and tBuOK give air-sensitive diphosphanes (SReSReSReS Re)-{(η5-C5H5)Re(NO)-(PPh 3)(CH2)}2{PCH2(CH2) nCH2P}{(CH2)(Ph3P)(ON) Re(η5-C5H5)}2 [n = 0/1, (S ReSReSReSRe)-9/10; 92/62%]. Additions of (a) PhIO give the corresponding dioxides (72/62 %), and (b) [Rh(NBD)2]+ PF6- give the corresponding chelates [(P-P)-Rh(NBD)]+ PF6- (75/82%) (NBD = norbornadiene). These catalyze hydrogenations of protected dehydroamino acids and hydrosilylations of propiophenone with only modest enantioselectivities. Similar results are obtained when (SReS ReSReSRe)-9/10 are applied in rhodium-catalyzed conjugate additions of aryl boronic acids, or palladium-catalyzed allylic alkylations. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Kromm, Klemenz,Eichenseher, Sandra,Prommesberger, Markus,Hampel, Frank,Gladysz
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- The methoxymethyl cation cleaves peptide bonds in the gas phase
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Methoxymethyl cations and simple N-acyl amino acids and dipeptides react in the gas phase to form [M + MeOCH2]+ ions which fragment via a number of pathways including amide bond cleavage.
- Freitas, Michael A.,O'Hair, Richard A. J.,Dua, Suresh,Bowie, John H.
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- Enhancement of water solubility of poorly water-soluble drugs by new biocompatible N-acetyl amino acid N-alkyl cholinium-based ionic liquids
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The major challenge of the pharmaceutical industry is to find potential solvents for poorly water-soluble drug molecules. Ionic liquids (ILs) have attracted this industry as (co-) solvents due to their unique physicochemical and biological properties. Herein, a straightforward approach for the enhancement of the water solubility of paracetamol and sodium diclofenac is presented, using new biocompatible N-acetyl amino acid N-alkyl cholinium-based ionic liquids as co-solvents (0.2–1 mol%). These new ionic liquids were able to increase the water solubility of these drugs up to four times that in pure water or in an inorganic salt solution. In the presence of these ILs, the drugs lipophilicity (log P was not significantly changed for paracetamol, but for sodium diclofenac it was possible to decrease significantly its lipophilicity. Concerning cytotoxicity in human dermal fibroblasts it was observed that ILs did not show a significant toxicity, and were able to improve cell viability compared with the respective precursors.
- Jesus, Ana R.,Soromenho, Mário R.C.,Raposo, Luís R.,Esperan?a, José M.S.S.,Baptista, Pedro V.,Fernandes, Alexandra R.,Reis, Patrícia M.
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- Amphoteric, water-soluble polymer-bound hydrogenation catalysts
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The synthesis of a water soluble polymer-bound hydrogenation catalyst that is homogeneous and active in basic aqueous media but insoluble and inactive in weakly acidic media is described. This catalyst is also active in organic solvents. In water, the catalyst can be recovered by acidifying the solution to a pH 5. In acetonitrile, the catalyst can be recovered by solvent (ether) precipitation. Activities of the catalyst are comparable to but in every case slightly lower than those of a structurally similar low molecular weight catalyst. Recovery and reuse of the polymeric catalyst is simpler and more efficient.
- Bergbreiter, David E.,Liu, Yun-Shan
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- Racemization of Optically Active Aromatic N-Acetylamino Acids and Asymmetric Transformation of N-Acetyl-2-(4-hydroxyphenyl)glycine via Salt Formation with Optically Active α-Methylbenzylamine
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The racemization rates of N-acetyl-(S)-tyrosine, N-acetyl-(S)-phenylalanine, N-acetyl-(R)-2-(4-hydroxyphenyl)glycine , N-acetyl-(R)-2-phenylglycine, and N-acetyl-(S)-alanine were measured by use of (RS)-α-methylbenzylamine as base-catalyst.The first-order rate constant for racemization tended to increase with an increase in the polar substituent constant of the N-acetylamino acid side chain.The racemization appeared to be subject to the inductive effect by the side chain.An asymmetric transformation of (RS)-AcHpg by using (R)-MBA, based on the result of racemization, gave an optically pure salt of (R)-AcHpg with (R)-MBA by successive use of the filtrate as the solvent.Optically pure (R)-2-(4-hydroxyphenyl)glycine was separated from the salt in 87-90percent yield based on the starting (RS)-AcHpg.In addition, the asymmetric transformation of (R)-AcHpg was achieved by using (S)-MBA to give optically pure (S)-Hpg in 80percent yield after purification of the salt of (S)-AcHpg with (S)-MBA followed by hydrolysis.
- Shiraiwa, Tadashi,Sakata, Shinji,Natsuyama, Hisashi,Fujishima, Keiko,Miyazaki, Hideya,et al.
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- Synthesis and reactivity of cationic iridium(I) complexes of cycloocta-1,5-diene and chiral dithioether ligands. Application as catalyst precursors in asymmetric hydrogenation
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New chiral dithioether compounds (-)-2,2-dimethyl-4,5-bis(isopropylsulfanylmethyl)-1,3-dioxolane (-)-diospr and (+)-2,2-dimethyl-4,5-bis(phenylsulfanylmethyl)-1,3-dioxolane (+)-diosph were prepared from diethyl (+)-L-tartrate. An alternative synthetic method for preparing the previously described bis(methylsulfanylmethyl) dithioether (-)-diosme was devised. By co-ordinating of the dithioethers to different (cycloocta-1,5-diene)iridium(I) compounds chiral cationic complexes [Ir(cod){(-)-diosme}]BF4 1, [Ir(cod){(-)-diospr}]BF4·CH2Cl2 2 and [Ir(cod){(+)-diosph}]BF4 3 were synthesized and then studied by 1H, 13C NMR and FAB mass spectrometry. The complexes reacted with CO to give the corresponding binuclear tetracarbonyls [Ir2(μ-L)2(CO)4][BF]2 4-6. The dithioether ligands were replaced by PPh3 in 1-3 providing [Ir(cod)(PPh3)2]BF4. The addition of H2 to complexes 1 and 2 at -70°C gave cis-dihydridoiridium(III) complexes [IrH2(cod){(-)-L}]BF4 7 and 8 which are in equilibrium in solution with the parent complexes, depending on the temperature. Two possible diastereomers were distinguished for 8 at low temperatures. Complexes 1-3 were active precursors in the asymmetric hydrogenation of different prochiral dehydroamino acid derivatives and itaconic acid, at room temperature under an atmospheric pressure of H2, and the highest enantiomeric excess obtained was 47%.
- Dieguez, Montserrat,Orejon, Aranzazu,Masdeu-Bulto, Anna M.,Echarri, Raouf,Castillon, Sergio,Claver, Carmen,Ruiz, Aurora
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- Cationic iridium complexes with chiral dithioether ligands: Synthesis, characterisation and reactivity under hydrogenation conditions
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A series of cationic IrI complexes containing chiral dithioether ligands have been prepared in order to study the influence of the sulfur substituents and the metallacycle size on the acetamidoacrylate hydrogenation reaction. In the case of complexes 6, 7 and 10, a mixture of diastereomers is observed in solution due to the sulfur inversion processes. In contrast, this fluxional behaviour is efficiently controlled by using bicyclic ligands which inhibit the S-inversion in complexes 8 and 9. The solid-state structure of complex 10b shows only one diastereomer with the sulfur substituents in a relative anti disposition and in an overall configuration of SCS CSSSS at the coordinated dithioether ligand. Iridium com plexes containing seven- and six-membered metallacycles (6b-d, 7b,c, 10a,b) react with the substrate through S-ligand substitution, and the rate of this substitution is related to the position of the fluorine atom on the aromatic ring. On the contrary, complexes containing a bismetallacycle (8 and 9) are not displaced by the substrate. The catalytic hydrogenation activity of complexes 8 and 9 is analysed in terms of the high stability of the corresponding dihydride complexes (13 and 14). In both cases, only two of the four possible diastereomeric dihydride species are formed in solution. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).
- Flores-Santos, Leticia,Martin, Erika,Aghmiz, Ali,Dieguez, Montserrat,Claver, Carmen,Masdeu-Bulto, Anna M.,Munoz-Hernandez, Miguel Angel
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- Minisci-Type Alkylation of N-Heteroarenes by N-(Acyloxy)phthalimide Esters Mediated by a Hantzsch Ester and Blue LED Light
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A synthetic method that enables the Hantzsch ester-mediated Minisci-type C2-alkylation of quinolines, isoquinolines and pyridines by N-(acyloxy)phthalimide esters (NHPI) under blue LED (light emitting diode) light (456 nm) is described. Achieved under mild reaction conditions at room temperature, the metal-free synthetic protocol was shown to be applicable to primary, secondary and tertiary NHPIs to give the alkylated N-heterocyclic products in yields of 21–99%. On introducing a chiral phosphoric acid, an asymmetric version of the reaction was also realised and provided product enantiomeric excess (ee) values of 53–99%. The reaction mechanism was delineated to involve excitation of an electron-donor acceptor (EDA) complex, formed from weak electrostatic interactions between the Hantzsch ester and NHPI, which generates the posited radical species of the redox active ester that undergoes addition to the N-heterocycle.
- Kyne, Sara Helen,Li, Jiacheng,Siang Tan, Suan,Wai Hong Chan, Philip
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supporting information
(2022/01/11)
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- 1,3,2-Diazaphospholenes Catalyze the Conjugate Reduction of Substituted Acrylic Acids
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The potent nucleophilicity and remarkably low basicity of 1,3,2-diazaphospholenes (DAPs) is exploited in a catalytic, metal-free 1,4-reduction of free α,β-unsaturated carboxylic acids. Notably, the reduction occurs without a prior deprotonation of the carboxylic acid moiety and hence does not consume an additional hydride equivalent. This highlights the excellent nucleophilic character and low basicity of DAP-hydrides. Functional groups such as Cbz group or alkyl halides which can be problematic with classical transition-metal catalysts are well tolerated in the DAP-catalyzed process. Moreover, the transformation is characterized by a low catalyst loading, mild reaction conditions at ambient temperature as well as fast reaction times and high yields. The proof-of-principle for a catalytic enantioselective version is described.
- Reed, John H.,Cramer, Nicolai
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p. 4262 - 4266
(2020/07/13)
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- Reactivity of α-Amino Acids in the Reaction with Esters in Aqueous–1,4-Dioxane Media
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The kinetics of the reaction of a series of α-amino acids with 4-nitrophenyl acetate, 4-nitrophenyl benzoate, and 2,4,6-trinitrophenyl benzoate in aqueous 1,4-dioxane medium has been studied. Kinetics of the reactions involving 4-nitrophenyl acetate and 2,4,6-trinitrophenyl benzoate has complied with the Br?nsted dependence and revealed linear correlation between rate constant logarithm and the energy difference of the frontier orbitals of α-amino acids anions.
- Kochetova,Kustova,Kuritsyn
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- Synthetic method of vardenafil hydrochloride impurities
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The invention discloses a synthetic method of vardenafil hydrochloride impurities, which relates to the technical field of pharmaceutical and chemical industry. The synthetic method comprises the following steps: taking alanine (A) as a raw material to react with acetic anhydride, generating 2-acetaminopropionic acid (B), enabling the 2-acetaminopropionic acid (B) to react with ethyl oxalyl monochloride, and generating a reaction product (C); enabling 2-ethoxybenzamidine hydrochloride (D) to react with hydrazine hydrate, generating a reaction product (E), enabling the reaction product (E) to react with the reaction product (C), and generating an impurity intermediate I (F); and enabling the impurity intermediate I (F) to generate an impurity intermediate II (G) under the effect of phosphorus oxychloride; performing sulfonation reaction on the impurity intermediate II (G) to generate a reaction product (H); and dropwise adding N-ethylpiperazine into the reaction product (H) to obtain a target product (I) 4-ethoxy-3-(3,4-dihydro-5-methyl-4-oxo-7-propylimidazole[5,1-f][1,2,4]-trizone-ketone) benzenesulfonic acid. The method is low in production cost, low in requirement on reaction conditions, favorable for the industrialized production and higher in purity of target products.
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Paragraph 0034; 0046; 0054; 0062; 0070; 0078
(2018/04/01)
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- The Enantioselective Dakin-West Reaction
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Here we report the development of the first enantioselective Dakin-West reaction, yielding α-acetamido methylketones with up to 58 % ee with good yields. Two of the obtained products were recrystallized once to achieve up to 84 % ee. The employed methylimidazole-containing oligopeptides catalyze both the acetylation of the azlactone intermediate and the terminal enantioselective decarboxylative protonation. We propose a dispersion-controlled reaction path that determines the asymmetric reprotonation of the intermediate enolate after the decarboxylation.
- Wende, Raffael C.,Seitz, Alexander,Niedek, Dominik,Schuler, S?ren M. M.,Hofmann, Christine,Becker, Jonathan,Schreiner, Peter R.
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supporting information
p. 2719 - 2723
(2016/02/27)
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- Direct C-H alkylation of naphthoquinones with amino acids through a revisited Kochi-Anderson radical decarboxylation: Trends in reactivity and applications
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In our ongoing research program into the discovery of new anticancer drugs, we were interested in the preparation of naphthoquinone scaffolds bearing aminoalkyl side-chains. Following this aim, we revisited the Kochi-Anderson radical decarboxylation of amino acids in order to set up a versatile route to the direct functionalization of naphthoquinones. The best reaction conditions were applied to a selected series of compounds in a systematic methodological study which allowed us to establish important trends in reactivity. We found that α-substituted β-amino acids were the most suitable substrates for the radical addition. In contrast, α-amino acids gave modest results. The influence of the amine protecting groups on the reaction outcome has also been studied. This practical procedure allows the introduction of various unsymmetrical moieties, including orthogonally protected linear aminoalkyl chains or chiral dipeptidic chains, and opens the door to a wide scope of easily accessible chemical diversity.
- Naturale, Guillaume,Lamblin, Marc,Commandeur, Claude,Dessolin, Jean,Felpin, Francois-Xavier
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supporting information
p. 5774 - 5788,15
(2020/09/15)
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- Convenient method for reduction of C-N double bonds in oximes, imines, and hydrazones using sodium Borohydride-Raney ni system
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(Chemical Equation Presented) A practical method has been developed for reduction of C-N double bond in oximes, imines, and hydrazones with sodium borohydride catalyzed by Raney Ni. The reactions were carried out in basic aqueous solution, and the desired products were obtained in moderate yields after a simple procedure. This method can be applied to synthesize simpler aliphatic or aromatic amines and its analogs. Copyright Taylor & Francis Group, LLC.
- Yang, Yihua,Liu, Shouxin,Li, Junzhang,Tian, Xia,Zhen, Xiaoli,Han, Jianrong
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experimental part
p. 2540 - 2554
(2012/07/27)
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- Benzimidazole and imidazole inhibitors of histone deacetylases: Synthesis and biological activity
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A series of N-hydroxy-3-[3-(1-substituted-1H-benzoimidazol-2-yl)-phenyl]-acrylamides (5a-5ab) and N-hydroxy-3-[3-(1,4,5-trisubstituted-1H-imidazol-2-yl)-phenyl]-acrylamides (12a-s) were designed, synthesized, and found to be nanomolar inhibitors of human histone deacetylases. Multiple compounds bearing an N1-piperidine demonstrate EC50s of 20-100 nM in human A549, HL60, and PC3 cells, in vitro and in vivo hyperacetylation of histones H3 and H4, and induction of p21waf. Compound 5x displays efficacy in human tumor xenograft models.
- Bressi, Jerome C.,Jong, Ron de,Wu, Yiqin,Jennings, Andy J.,Brown, Jason W.,O'Connell, Shawn,Tari, Leslie W.,Skene, Robert J.,Vu, Phong,Navre, Marc,Cao, Xiaodong,Gangloff, Anthony R.
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experimental part
p. 3138 - 3141
(2010/09/03)
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- Regioselective synthesis of tetrasubstituted pyrroles by 1,3-dipolar cycloaddition and spontaneous decarboxylation
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We developed a novel regioselective synthesis of tetrasubstituted pyrroles via the classic 1,3-dipolar cycloaddition of α,β-unsaturated benzofuran-3(2H)-one and azlactones (1) followed by spontaneous decarboxylation. The complete regiochemical control of tetrasubstituted pyrroles was confirmed by the orthogonal synthesis of complementary regioisomers (7a and 7b) simply by using different azlactones (1a and 1b, respectively).
- Kim, Yongju,Kim, Jonghoon,Park, Seung Bum
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supporting information; experimental part
p. 17 - 20
(2009/08/07)
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- One-pot o-nitrobenzenesulfonylhydrazide (NBSH) formation-diimide alkene reduction protocol
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A one-pot protocol for the formation of 2-nitrobenzenesulfonylhydrazide (NBSH) from commercial reagents and subsequent alkene reduction is presented. The transformation is operationally simple and generally efficient for effecting diimide alkene reductions. A range of 16 substrates have been reduced, highlighting the unique chemoselectivity of diimide as a reduction system.
- Marsh, Barrie J.,Carbery, David R.
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supporting information; experimental part
p. 3186 - 3188
(2009/09/08)
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- Inverted supercritical carbon dioxide/aqueous biphasic media for rhodium-catalyzed hydrogenation reactions
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An inverted supercritical carbon dioxide (scCO2)/aqueous biphasic system has been used as reaction media for Rh-catalysed hydrogenation of polar substrates. Chiral and achiral CO2-philic catalysts were efficiently immobilised in scCO2 as the stationary phase, while the polar substrates and products were contained in water as the mobile phase. Notably, product separation and catalyst recycling were conducted without depressurisation of the autoclave, The catalyst phase was reused several times with high conversion and product recovery of more than 85%. Loss of rhodium and phosphorus by leaching were found to be below the detection limit after the first two cycles in the majority of repetitive experiments. The reaction conditions were optimised with a minimum of experiments by using a simplex algorithm in a sequential optimisation. Total turnover numbers (TTNs) of up to 1600, turnover frequencies (TOFs) of up to 340 h-1 and ee's up to 99% were obtained in repetitive batch operations. The scope of the devised catalytic system has been investigated and a semicontinuous reaction setup has been implemented. The chiral ligand (R,S)-3-H2F6-BINAPHOS allowed highly enantioselective hydrogenation of itaconic acid and methyl-2-acetamidoacrylate combined with a considerable catalyst stability in these reaction media.
- Burgemeister, Katja,Francio, Giancarlo,Gego, Volker H.,Greiner, Lasse,Hugl, Herbert,Leitner, Walter
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p. 2798 - 2804
(2008/02/04)
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- Second generation artificial hydrogenases based on the biotin-avidin technology: Improving activity, stability and selectivity by introduction of enantiopure amino acid spacers
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We report on our efforts to create efficient artificial metalloenzymes for the enantioselective hydrogenation of N-protected dehydroamino acids using either avidin or streptavidin as host proteins. Introduction of chiral amino acid spacers - phenylalanine or proline - between the biotin anchor and the flexible aminodiphosphine moiety 1, combined with saturation mutagenesis at position S112X of streptavidin, affords second generation artificial hydrogenases displaying improved organic solvent tolerance, reaction rates (3-fold) and (S)-selectivities (up to 95% ee for N-acetamidoalanine and N-acetamidophenylalanine). It is shown that these artificial metalloenzymes follow Michaelis-Menten kinetics with an increased affinity for the substrate and a higher kcat than the protein-free catalyst (compare k cat 3.06 min-1 and KM 7.38 mM for [Rh(COD)Biot-1]+ with kcat 12.30 min-1 and KM 4.36 mM for [Rh-(COD)Biot-(R)-Pro-1]+ ? WT Sav). Finally, we present a straightforward protocol using Biotin-Sepharose to immobilize artificial metalloenzymes (> 92% ee for N-acetamidoalanine and N-acetamidophenylalanine using [Rh(COD)Biot-(R)-Pro-1]+ ? Sav S112W).
- Rusbandi, Untung E.,Lo, Cheikh,Skander, Myriem,Ivanova, Anita,Creus, Marc,Humbert, Nicolas,Ward, Thomas R.
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p. 1923 - 1930
(2008/09/18)
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- Substituted imidazotriazinones
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The present invention relates to new substituted imidazotriazinones, processes for their preparation, and their use for the production of medicaments, in particular for improving perception, concentration power, learning power and/or memory power.
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- pH effects on reaction rates in rhodium catalysed hydrogenation in water
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The compound [Rh(DPPBTS)(NBD)][O3SCF3] 1 (DPPBTS = tetrasulfonated 1,4-bis(diphenylphosphino)butane, NBD = norbornadiene) has been prepared. On reaction of 1 with H2 different complexes [Rh(DPPBTS)(H2O)3-(H)]2+, [Rh(DPPBTS)(H2O)]+ or [Rh(DPPBTS)(OH)]2 are formed depending on the pH of the aqueous solution. Addition of α-acetamidoacrylic acid (AAA) to an aqueous solution of [Rh(DPPBTS)(H2O)2]+ affords a substrate complex in which the co-ordination mode of AAA is pH dependent, i.e. it co-ordinates via the double bond and the amide carbonyl at a pH below the pKa of AAA, or via the double bond and the carboxylate group at a pH higher than the pKa. The co-ordination mode has a dramatic effect on the rate of hydrogenation of AAA catalysed by 1, being extremely fast at a pH below the pKa of the substrate (270 000 mol h-1), but approximately 2000 times slower at a pH higher than the pKa. The hydrogenation rate is zero order in olefin concentration at pH 4.7 and a kH/kD isotope effect of 1.25 has been observed at pH 4.5. These observations indicate that the oxidative addition of H2 is the rate determining step in the hydrogenation using 1 as a catalyst, and that the mechanism is the same in water as in organic solvents.
- Malmstroem, Torsten,Wendt, Ola F.,Andersson, Carlaxel
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p. 2871 - 2875
(2007/10/03)
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- Ferrocenyl diphosphines as ligands for homogeneous catalysts
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Compounds of formula I STR1 wherein R1 is C1 -C8 alkyl, phenyl or phenyl which is substituted by 1 to 3 C1 -C4 alkyl or C1 -C4 alkoxy groups; R2 and R3 are identical and are C1 -C12 alkyl, C5 -C12 cycloalkyl or C1 -C4 alkyl- or C1 -C4 alkoxy-substituted C5 -C12 cycloalkyl, or phenyl which is substituted by one to three identical or different members selected from the group consisting of C1 -C4 alkyl, C1 -C4 alkoxy, --SiR4 R5 R6, halogen, --SO3 M, --CO2 M, --PO3 M,--NR7 R8 and --[≈ NR7 R8 R9 ]X? ; or R2 and R3 are different and are C1 -C12 alkyl, C5 -C12 cycloalkyl, C1 -C4 alkyl- or C1 -C4 alkoxy-substituted C5 -C12 cycloalkyl, phenyl or phenyl which is substituted by one to three identical or different members selected from the group consisting of C1 -C4 alkyl, C1 -C4 alkoxy, --SiR4 R5 R6, halogen, --SO3 M, --CO2 M, --PO3 M2, --NR7 R8 and --[≈NR7 R8 R9 ]X? ; or the group --PR2 R3 is a radical of formula II STR2 and R4, R5 and R6 are each independently of one another C1 -C12 alkyl or phenyl, R7 and R8 are H, C1 -C2 alkyl, phenyl or R7 and R8, taken together, are tetramethylene, pentamethylene or 3-oxa-1,5-pentylene, R9 is H or C1 -C4 alkyl, M is H or an alkali metal, X? is the anion of a monobasic acid, and * is a stereogenic carbon atom, in the form of their racemates and diastereoisomers or mixtures of diastereoisomers. Rhodium and iridium complexes with these ligands are suitable for use as homogeneous enantioselective catalysts for the hydrogenation of prochiral compounds containing carbon double bonds or carbon/hetero atom double bonds.
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- Group 6 anionic ·-hydride complexes [HM2(CO)10]- (M = Cr, Mo, W): New catalysts for hydrogenation and hydrosilylation
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Group 6 anionic ·-hydride complexes catalyze hydrogenation of conjugated olefins, aldehydes, ketoesters, and alkynes, and hydrosilylation of aldehydes and conjugated olefins with high regio- and stereoselectivity. Ketones are converted into silyl ethers and silyl enol ethers with monohydrosilanes and dihydrosilanes, respectively.
- Fuchikami, Takamasa,Ubukata, Yumiko,Tanaka, Yasutaka
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p. 1199 - 1202
(2007/10/02)
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- Process for synthesis of N-acetylglycine
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An N-acetylglycine is manufactured by reacting paraformaldehyde with an acetamide and carbon monoxide in the present of a cobalt-containing catalyst promoted by a sulfoxide or dinitride compounds. The presence of sulfoxide or dinitrile ligands are essential for the high yield synthesis of N-acetylglycine and good cobalt recovery.
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- Chiral phosphorus compounds, a process for their manufacture and their application to the catalysis of enantioselective synthesis reactions
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Chiral phosphorus-containing ligands comprising at least one amine radical and at least one dihydrocarbylphosphinoxy radical of the formula W=OP (R)2, in which R is a hydrocarbon radical selected from the group consisting of alkyl, aryl, and cycloalkyl radicals, wherein the ligand is selected from the group consisting of: those of the formula STR1 those of the formula STR2 those of the formula STR3 those of the formula STR4 in which formulae: R1 and R2 are selected from the group consisting of a hydrogen atom and hydrocarbon radicals; R3 and R4, which must be different from one another, are selected from the group consisting of a hydrogen atom and hydrocarbon radicals that may or may not carry at least one functional group selected from the group consisting of the alcohol, thiol, thioether, amine, imine, acid, ester, amide, and ether functional groups; and R5 and R6 are selected from the group consisting of hydrogen atoms and hydrocarbon radicals that may or may not contain functional groups. A process for their manufacture comprises reacting an optically active amino alcohol, in a hydrocarbon solvent at a temperature between -50° and 80° C. and under an inert gas atmosphere, with at least one compound of the formula P(R)2 Y in which Y is chosen from among the halogen atoms and amine radicals, the compound being present in a molar ratio, relative to the amino alcohol, greater than or equal to the number of P(R)2 groups to be introduced into the chiral molecule. The chiral phosphorous-containing ligands are used by reacting at least one organic compound that does not possess a center of asymmetry with (A), on the one hand, at least one transition metal complex of formula MZq in which M is a metal in group VIII of the Periodic Classification, q is the coordination number of the metal M, and Z is an atom or molecule capable of complexing the metal M and (B), on the other hand, at least one ligand L.
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- RHODIUM CATALYZED REDUCTIVE ESTERIFICATION REACTIONS
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Reductive esterification occurs when unsaturated acids are treated with hydrogen in alcohol using either rhodium trichloride or the dimer of chloro(1,5-hexadiene)rhodium(I) as the catalyst.Saturated acids containing appropriate functional groups are also esterified under the same conditions.
- Lin, Ivan J. B.,Zahalka, Hayder A.,Alper, Howard
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p. 1759 - 1762
(2007/10/02)
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- A defense Mechanism against Pathogenic Bacteria in the Digestive Tracts of Silkworm Larvae-in vitro Evidence of the Formation of Caffeoquinone, a True Antibacterial Substance, and Synergism of Amino Compounds
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For the defense mechanism against pathogenic bacteria in the digestive tracts of silkworm larvae reared on mulberry leaves, in vitro evidence of the formation of atrue antibacterial substance was obtained. caffeic acid (CA) derived from chlorogenic acid (ChA)was converted into caffeoquinone (CQ) by base-catalyzed oxidation in a buffer solution (pH 10.0).CQ was trapped as 6'phenylsulfonylcaffeic acid (6'sulfone) by the addition of benzenesulfinic acid (BSA).The synergetic effects of amino compounds on the antibacterial activity of CQ are discussed in detail, and the probable reactions of CA with amino and thiol compounds in the alkaline solution are proposed.
- Nakano, Hidenori,Tahara, Satoshi,Iizuka, Toshihiko,Mizutani, Junya
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p. 549 - 556
(2007/10/02)
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- Functionalized DL-Amino Acid Derivatives. Potent New Agents for the Treatment of Epilepsy
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Structural analogues of the potent known anticonvulsant agent N-acetyl-DL-alanine N-benzylamide (1a) have been prepared (16 examples).The pharmacological activities of these products were evaluated in the maximal electroshock seizure (MES), the subcutaneous pentylenetetrazole seizure threshold (sc Met), and the rotorod (Tox) tests.The median effective doses (ED50) and the median toxic doses (TD50) for the most active compounds by both intraperitoneal and oral administration are reported.The most active compounds were N-acetyl-DL-phenylglycine N-benzylamide (1d) and N-acetyl-DL-alanine N-m-fluorobenzylamide (1m) along with the parent compound 1a.The ED50 values in the MES test for these three compounds compared well with phenobarbital, while their high TD50 values contributed to their large protective indexes, which approached that of phenytoin.When tested against four convulsant agents, compounds 1a and 1d displayed activity profiles significantly different from those reported for conventionally used antiepileptic drugs.
- Conley, Judith D.,Kohn, Harold
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p. 567 - 574
(2007/10/02)
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- A general and accurate nmr determination of the enantiomeric purity of α-aminoacids and α-aminoacid derivatives
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Derivatization of α-aminoacids, α-aminoesters and α-aminolactones as N-acetyl derivatives allow the accurate NMR determination of the enantiomeric purity. In these conditions the major coordination site with a chiral shift reagent will correspond to the NMR observation site. Experimental factors leading to the highest ΔΔδ values are ascertained. No straightforward correlation with absolute configurations can be established.
- Calmes, Monique,Daunis, Jacques,Jacquier, Robert,Verducci, Jean
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p. 2285 - 2292
(2007/10/02)
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- Mechanism of formation of serine β-lactones by Mitsunobu cyclization: synthesis and use of L-serine stereospecifically labelled with deuterium at C-3
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The ring closure of N-benzyloxycarbonyl-L-serine (1) under Mitsunobu conditions (Ph3P, dimethyl azodicarboxylate, -78 deg C) to give the corresponding β-lactone (2) is shown by deuterium and oxygen-18 labelling studies to proceed by hydroxy group activation, in contrast to analogous cyclizations of more hindered β-hydroxy acids, which usually occur by carboxy group activation.Samples of 1 stereospecifically labelled with deuterium at C-3 were prepared by hydrogenation of (Z)-2-acetamido-3-methoxyacrylic acid (9) with deuterium, followed by selective Acylase I deacetylation of the 2S isomer, removal of the protecting groups, and N-acylation of the resulting L-serine with benzyl chloroformate.Mitsunobu cyclizations of this 3R deuterated N-acyl serine, of the analog lg, and of the derivative 1f show that lactonization occurs with inversion of configuration at C-3, loss of the hydroxy oxygen, and retention of the carboxy oxygens.Similar labelling experiments demonstrate that aqueous sodium hydroxide opens the β-lactone ring by exclusive attack at the carbonyl to regenerate 1, whereas acidic hydrolysis proceeds primarily by attack of water at the C-3 methylene group of 2.This information allows interconversion of L-serines that are stereospecifically labelled at C-3 with hydrogen isotopes and affords access to other labelled β-substituted alanines.
- Ramer, Shawn E.,Moore, Richard N.,Vederas, John C.
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p. 706 - 713
(2007/10/02)
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