- Phenylalanyl-tRNA synthetase of Escherichia coli K 10. Multiple enzyme-aminoacyl-tRNA complexes as a consequence of substrate specificity.
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The interaction between Phe-tRNA(Phe) or other acyl-tRNA derivatives thereof and phenylalanyl-tRNA synthetase of Escherichia coli K 10 has been investigated by nonequilibrium dialysis, by fluorescence titration in the presence of 2-p-toluidinylnaphthalene-6-sulfonate, by the kinetics of the aminoacylation of tRNA(Phe), and by the kinetics of the catalytic hydrolysis of Phe-tRNA(Phe). Phe-tRNA(Phe), or derivatives thereof, forms two types of complexes with the synthetase. One type involves the attachment of the phenylalanyl moiety to the phenylalanine-specific site of the enzyme, and the other type, to the tRNA(Phe)-specific binding site. They resemble alternative modes of a destabilized enzyme-product complex and are predicted on the basis of thermodynamic considerations. The two modes of binding of acyl-tRNA compete with each other. The attachment of Phe-tRNA(Phe) to the phenylalanine-specific site dominates. At equilibrium, this complex is present at a fourfold higher concentration than the other type of complex. The HNO2 deaminated Phe-tRNA(Phe) binds exclusively to the site specific for L-phenylalanine. On the contrary, Ile-tRNA(Phe) adds at 94.1% to the tRNA(Phe)-specific site. The association of Phe-tRNA(Phe) with this site leads to enzymatic hydrolysis into L-phenylalanine and tRNA(Phe). The complex involving the phenylalanine-specific site is hydrolytically unproductive. L-Phenylalanine acts as an activator of the hydrolysis by occupying the amino acid specific site and by shifting the equilibrium between the complexes toward the binding ot Phe-tRNA(Phe) at the tRNA(Phe)-specific site. The association of Phe-tRNA(Phe) at the phenylalanine-specific site does not interfere sterically with the binding of free tRNA(Phe). The sequential addition of free and aminoacylated tRNA(Phe) exhibits negative cooperativity. Such a mechanism could help to expel the product from the enzyme.
- Guentner,Holler
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Read Online
- ISOLATION OF β-PHENYLLACTIC ACID RELATED COMPOUNDS FROM PSEUDOMONAS SYRINGAE
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Three metabolites, weakly phytotoxic on apple and bean leaves, have been isolated from Pseudomonas syringae pv papulans culture filtrates and their structures established by spectroscopic analysis.The trivial names of papuline, o-hydroxynitropapuline and papulinone were assigned to the three active substances.Papuline was the methylester of β-phenyllactic acid, and o-hydroxynitropapuline was its meta-hydroxy-para-nitro disubstituted derivative.Papulinone, a new β-lactone structurally related to β-phenyllactic acid, was identified as 4-(1-hydroxy-2-phenylethyl)-4-carbomethoxyoxyetan-2-one.
- Evidente, Antonio,Iacobellis, Nicola S.,Scopa, Antonio,Surico, Giuseppe
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Read Online
- Trifluoromethanesulonic acid catalyzed alkylation of arenes with methyl (2R)-glycidate
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Methyl (R)-glycidate (= methyl (R)-oxiranecarboxylate; 2) in superacidic trifluoromethanesulfonic acid medium reacts with electron-rich arenes to give α-hydroxy-β-arylpropanoate derivatives 3a-3f with high stereospecificity. At the same time, the observed
- Linares-Palomino, Pablo J.,Prakash, G. K. Surya,Olah, George A.
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Read Online
- Enantioselective Synthesis of 3-Fluorochromanes via Iodine(I)/Iodine(III) Catalysis
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The chromane nucleus is common to a plenum of bioactive small molecules where it is frequently oxidized at position 3. Motivated by the importance of this position in conferring efficacy, and the prominence of bioisosterism in drug discovery, an iodine(I)/iodine(III) catalysis strategy to access enantioenriched 3-fluorochromanes is disclosed (up to 7:93 e.r.). In situ generation of ArIF2 enables the direct fluorocyclization of allyl phenyl ethers to generate novel scaffolds that manifest the stereoelectronic gauche effect. Mechanistic interrogation using deuterated probes confirms a stereospecific process consistent with a type IIinv pathway.
- Daniliuc, Constantin G.,Gilmour, Ryan,Neufeld, Jessica,Sarie, Jér?me C.,Thiehoff, Christian
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supporting information
p. 15069 - 15075
(2020/06/17)
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- Stereodivergence in the Ireland-Claisen Rearrangement of α-Alkoxy Esters
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A systematic investigation into the Ireland-Claisen rearrangement of α-alkoxy esters is reported. In all cases, the use of KN(SiMe3)2 in toluene gave rearrangement products corresponding to a Z-enolate intermediate with excellent diastereoselectivity, presumably because of chelation control. On the other hand, chelation-controlled enolate formation could be overcome for most substrates through the use of lithium diisopropylamide (LDA) in tetrahydrofuran (THF).
- Podunavac, Ma?a,Lacharity, Jacob J.,Jones, Kerry E.,Zakarian, Armen
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supporting information
p. 4867 - 4870
(2018/08/24)
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- Enantioselective, Catalytic Vicinal Difluorination of Alkenes
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The enantioselective, catalytic vicinal difluorination of alkenes is reported by II/IIII catalysis using a novel, C2-symmetric resorcinol derivative. Catalyst turnover via in situ generation of an ArIIIIF2 species is enabled by Selectfluor oxidation and addition of an inexpensive HF–amine complex. The HF:amine ratio employed in this process provides a handle for regioselective orthogonality as a function of Br?nsted acidity. Selectivity reversal from the 1,1-difluorination pathway (geminal) to the desired 1,2-difluorination (vicinal) is disclosed (>20:1 in both directions). Validation with electron deficient styrenes facilitates generation of chiral bioisosteres of the venerable CF3 unit that is pervasive in drug discovery (20 examples, up to 94:06 e.r.). An achiral variant of the reaction is also presented using p-TolI (up to >95 % yield).
- Scheidt, Felix,Sch?fer, Michael,Sarie, Jér?me C.,Daniliuc, Constantin G.,Molloy, John J.,Gilmour, Ryan
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supporting information
p. 16431 - 16435
(2018/11/23)
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- Stereoselective Oxidation of Titanium(IV) Enolates with Oxygen
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A novel approach to synthesize enantiomerically pure α-hydroxy carboxylic derivatives is reported. A highly stereoselective oxidation of titanium(IV) enolates from chiral N -acyloxazolidinones is performed with oxygen under simple experimental conditions
- Gómez-Palomino, Alejandro,Romea, Pedro,Urpí, Fèlix
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p. 2721 - 2726
(2018/06/08)
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- Amidation of unactivated ester derivatives mediated by trifluoroethanol
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A catalytic amidation protocol mediated by 2,2,2-trifluoroethanol has been developed, facilitating the condensation of unactivated esters and amines, furnishing both secondary and tertiary amides. The complete scope and limitations of the method are described, along with modified conditions for challenging substrates such as acyclic secondary amines and chiral esters with retention of chiral integrity.
- McPherson, Christopher G.,Caldwell, Nicola,Jamieson, Craig,Simpson, Iain,Watson, Allan J. B.
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supporting information
p. 3507 - 3518
(2017/04/26)
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- Solvent-induced chirality switching in the enantioseparation of regioisomeric hydroxyphenylpropionic acids via diastereomeric salt formation with (1R,2S)-2-amino-1,2-diphenylethanol
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The enantioseparation of three hydroxyphenylpropionic acid isomers via diastereomeric salt formation with (1R,2S)-2-amino-1,2-diphenylethanol has been demonstrated. The racemates of all three acid isomers were successfully separated with high efficiency (0.56–0.84) after single crystallization. For 2-hydroxy-3-phenylpropionic acid 4, the configuration of the less-soluble salt was controlled by the crystallization solvent: the (R)-4 salt was crystallized from water, while 2-propanol afforded the (S)-4 salt. The chiral recognition mechanism of the three acids was discussed based on the crystal structures of the diastereomeric salts.
- Kodama, Koichi,Nagata, Jun,Kurozumi, Nobuhiro,Shitara, Hiroaki,Hirose, Takuji
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supporting information
p. 460 - 466
(2017/03/23)
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- Stereoselective synthesis of hantupeptins A, B and C common fragment
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The stereoselective synthesis of the common fragment of Hantupeptine A, B and C is described using N-methylation of aminoacids, HATU mediated coupling reaction and diazotization of L-phenylalanine.
- Srinivas,Sunitha,Rao, C. Govind
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p. 1239 - 1242
(2017/04/28)
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- Asymmetric transfer hydrogenation of α-azido acrylates
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The asymmetric transfer hydrogenation of α-azido acrylates has been explored, a range of α-hydroxy esters are produced with good enantioselectivities (80-90% ee). The reaction was conducted in the wet HCO2H/NEt3 with Ru-TsDPEN A.
- Ji, Yang,Xue, Ping,Ma, Dan-Dan,Li, Xue-Qiang,Gu, Peiming,Li, Rui
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p. 192 - 194
(2015/02/05)
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- A chemoselective oxidation of monosubstituted ethylene glycol: Facile synthesis of optically active α-hydroxy acids
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A mild and efficient method for the synthesis of optically active α-hydroxy acids through chemoselective oxidation of monosubstituted ethylene glycols using the TEMPO-NaOCl reagent system is described. It is evident from our studies that the solvent, pH and reaction temperature are very crucial for the success of this oxidation. The versatility of this method has been demonstrated with a variety of aliphatic, aromatic and carbohydrate substrates bearing various functional groups. the Partner Organisations 2014.
- Chinthapally, Kiran,Baskaran, Sundarababu
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p. 4305 - 4309
(2014/06/23)
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- Synthesis of biologically relevant compounds by ruthenium porphyrin catalyzed amination of benzylic C-H bonds
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Herein we report the catalytic activity of ruthenium porphyrin complexes to promote the amination of benzylic C-H bonds by aryl azides, yielding α- and β-amino esters. The catalytic methodology is also effective to synthesize two derivatives of methyl l-3-phenyllactate in order to convert one of them into the corresponding β-lactam. The catalytic experimental conditions have been optimized on the basis of a preliminary mechanistic investigation which underlines the pivotal role of the substrate concentration to maximize the reaction productivity.
- Zardi, Paolo,Caselli, Alessandro,Macchi, Piero,Ferretti, Francesco,Gallo, Emma
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supporting information
p. 2210 - 2218
(2014/06/09)
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- Synthesis of new chiral ionic liquids from α-hydroxycarboxylic acids
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New functionalized optically active N-methylimidazolium ionic liquids with an asymmetric center at the β-position to the imdazole ring were synthesized as bromide salts from optically active α-hydroxycarboxylic acids. The bromide anions were exchanged by carboxylate anions with Amberlite IRA 400 ionic exchange resin.
- Poterala, Marcin,Plenkiewicz, Jan
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experimental part
p. 294 - 299
(2011/05/17)
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- A novel one-pot procedure for the stereoselective synthesis of α-hydroxy esters from ortho esters
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A novel one-pot procedure for the stereoselective synthesis of a-hydroxy esters from ortho esters was developed. Key steps were multiheteroatom Cope rearrangements of O-acylated N-hydroxy-L-tert-leucinol-derived oxazoline N-oxides leading to a-acyloxy oxazolines and, after methanolysis, to the target molecules in 67-80% yield and 94-98% ee.
- Breunlng, Matthias,Haeuser, Tobte,Tanzer, Eva-Maria
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supporting information; experimental part
p. 4032 - 4035
(2009/12/09)
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- Synthesis of a regular 24-membered cyclodepsipeptide by direct amide cyclization
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Aminoisobutyric Acid, Crystal Structure The synthesis of a 24-membered cyclic depsipeptide with an alternating sequence of phenyllactic acid and α-aminoisobutyric acid (Aib) is described. The linear precursor was prepared via the 'azirine/oxazolone method
- K?ttgen, Peter,Linden, Anthony,Heimgartner, Heinz
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experimental part
p. 689 - 698
(2009/12/26)
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- Phase-transfer-catalyzed asymmetric acylimidazole alkylation
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(Chemical Equation Presented) 2-Acylimidazoles are alkylated under phase-transfer conditions with cinchonidinium catalysts at -40°C with allyl and benzyl electrophiles in high yield with excellent enantioselectivity (79 to >99% ee). The acylimidazole substrates are made in three steps from bromoacetic acid via the N-acylmorpholine adduct. The catalyst is made in high purity allowing for S-product formation (6-20 h) under mild conditions, consistent with an ion-pair mechanism. The products are readily converted to useful ester products using methyltriflate and sodium methoxide, via a dimethylacylimidazolium intermediate without racemization. The process is efficient, direct, and amenable to other electrophiles and transformations that proceed through an enolate intermediate.
- Andrus, Merritt B.,Christiansen, Michael A.,Hicken, Erik J.,Gainer, Morgan J.,Bedke, D. Karl,Harper, Kaid C.,Mikkelson, Shawn R.,Dodson, Daniel S.,Harris, David T.
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p. 4865 - 4868
(2008/03/14)
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- Synthesis of Nα-Z, Nβ-Fmoc or Boc protected α-hydrazinoacids and study of the coupling reaction in solution of Nα-Z-α-hydrazinoesters
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The preparation of chiral orthogonally protected Nα-Z, Nβ-Fmoc- or Boc-α-hydrazinoacids derivatives, directly suitable for SPPS, is described in six steps with good yields starting from the corresponding α-aminoacids. The coupling reaction assays performed in liquid phase between Nα-Z-hydrazinoesters and N-Fmoc-α-aminoacids demonstrated the low reactivity of the hydrazinoester derivatives. However, we found that the acid fluoride method allowed the formation of hydrazinodipeptides almost quantitatively.
- Bouillon, Isabelle,Brosse, Nicolas,Vanderesse, Régis,Jamart-Grégoire, Brigitte
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p. 2223 - 2234
(2007/10/03)
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- Stereoselective β-hydroxy-α-amino acid synthesis via an ether-directed, palladium-catalysed aza-Claisen rearrangement
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A highly diastereoselective synthesis of (2S,3S)-β-hydroxy-α- amino acids has been developed from enantiopure α-hydroxy acids using a MOM-ether-directed, palladium(II)-catalysed, aza-Claisen rearrangement of allylic acetimidates to effect the key step. This highly stereoselective process gave allylic amides in diastereomeric ratios of up to 14 : 1. Problems associated with the isolation of 1,3-products (anti-Claisen) from sterically demanding substrates via an in situ palladium(0)-catalysed rearrangement process were overcome by the addition of a re-oxidant, p-benzoquinone, leading to cleaner reactions and improved yields of the 3,3-products (Claisen). The target β-hydroxy-α-amino acids are an important class of natural products that are also components of more complex organic compounds with significant biological properties. The Royal Society of Chemistry 2005.
- Fanning, Kate N.,Jamieson, Andrew G.,Sutherland, Andrew
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p. 3749 - 3756
(2007/10/03)
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- Asymmetric phase-transfer catalyzed glycolate alkylation, investigation of the scope, and application to the synthesis of (-)-ragaglitazar
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Asymmetric glycolate alkylation using a protected acetophenone surrogate under solid-liquid phase-transfer conditions is a new approach to the synthesis of 2-hydroxy esters and acids. Diphenylmethyloxy-2,5-dimethoxyacetophenone 1 with a trifluorobenzyl ci
- Andrus, Merritt B.,Hicken, Erik J.,Stephens, Jeffrey C.,Karl Bedke
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p. 9470 - 9479
(2007/10/03)
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- Synthesis and application of phosphinoferrocenylaminophosphine ligands for asymmetric catalysis
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(Chemical Equation Presented) A new class of bidentate ligands utilizing a phosphine-aminophosphine structure has been prepared on a ferrocenylethyl backbone in a straightforward and scalable fashion from acetylferrocene. The unique property of the α-ferrocenyl carbonium ion that allows the replacement of a variety of "leaving groups" with retention of configuration greatly facilitates the synthesis, and a number of ligands have been prepared by varying the nitrogen and phosphorus substituents on the aminophosphine. These readily prepared phosphinoferrocenylaminophosphines, known as BoPhoz ligands, show surprising hydrolytic and air stability, with no degradation after 3 years open to the air. The rhodium complexes of these ligands show exceedingly high enantioselectivities (generally > 95% ee) and activities often in excess of 50 000 catalyst turnovers per hour for the asymmetric hydrogenation of a wide variety of dehydro-α-amino acid and itaconic acid derivatives. They also show high activity and good to excellent enantioselectivity for the hydrogenation of a number of α-ketoesters.
- Boaz, Neil W.,Mackenzie, Elaine B.,Debenham, Sheryl D.,Large, Shannon E.,Ponasik Jr., James A.
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p. 1872 - 1880
(2007/10/03)
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- PROCESS FOR PRODUCING OPTICALLY ACTIVE 2-SUBSTITUTED CARBOXYLIC ACID
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The present invention relates to a process for efficiently producing an optically active 2-bromocarboxylic acid and an optically active 2-sulfonyloxycarboxylic acid, which are important in the production of medicinal compounds and so forth. An optically active 2-sulfonyloxycarboxylic acid ester is subjected to deprotection under acid conditions to obtain an optically active 2-sulfonyloxycarboxylic acid. A metal bromide is caused to act on the acid to brominate it with configuration inversion at position 2 to thereby produce an optically active 2-bromocarboxylic acid. The resultant optically active 2-bromocarboxylic acid is isolated/purified by subjecting it to a step in which the acid is crystallized and separated as a salt with a base. Thus, an optically active 2-bromocarboxylic acid having a high chemical purity and high optical purity can be produced.
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- Phase-transfer-catalyzed asymmetric glycolate alkylation
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Asymmetric surrogate glycolate alkylation has been performed under phase-transfer conditions. Diphenylmethyloxy-2,5-dimethoxyacetophenone with trifluorobenzyl cinchonidinium catalyst and cesium hydroxide provided alkylation products at -35°C in high yield
- Andrus, Merritt B.,Hicken, Erik J.,Stephens, Jeffrey C.
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p. 2289 - 2292
(2007/10/03)
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- Simple deprotection of acetal type protecting groups under neutral conditions
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Heating acetals with ethylene glycol causes the deprotection of acetal type protecting groups. When acetals such as MOM ethers, MEM ethers, and THP ethers were heated in ethylene glycol or propylene glycol, solvolysis proceeded smoothly to produce alcohols in excellent yield. This reaction is a very promising method for chemoselective deprotection of acetal type protecting groups.
- Miyake, Hideyoshi,Tsumura, Takatsugu,Sasaki, Mitsuru
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p. 7213 - 7215
(2007/10/03)
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- Characterization of an abeo-taxane: Brevifoliol and derivatives
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Brevifoliol is a natural diterpene isolated from Taxus baccata Nutt. A series of brevifoliol 1 derivatives, 2-8 and 10, were prepared for characterization and semisynthesis purposes and included the introduction of acetyl, Troc, and TES groups at C-5 and C-13. Derivatives 16-20 of 5-acetylbrevifoliol 2 were obtained via esterification with cinnamic acid, with both 2S-(-)- and 2R-(+)-3-phenyllactic acid, and with N-benzoyl-(2′ R,3′S)-3′-phenylisoserine at C-13. Brevifoliol compounds 12, 13, and 15 with either 2S-(-)-phenyllactate moieties at C-5 and C-13 or an N-benzoyl-(2′R,3′S)-3′-phenylisoserinyl at C-13 were also prepared. An abeo-taxane structure for 1 was clearly defined from the 13C NMR analysis of the 5-acetyl-13-oxo derivative 8 and from the conversion of 1 into 10, a conformationally restrained compound having a C-13, C-15 oxygen bridge. The biological activity of each of these derivatives is being studied.
- Tremblay, Steve,Soucy, Chantal,Towers, Neil,Gunning, Philip J.,Breau, Livain
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p. 838 - 845
(2007/10/03)
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- Process research of (R)-cyclohexyl lactic acid and related building blocks: A comparative study
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(S)-Cyclohexyl lactic acid is a component of the selective E-selectin inhibitor 2 ((S)-cHexLact-2-0-(3-Galβ(1→3)ddGlc-(4→1)αFuc). We describe the evaluation of various synthetic routes to this building block: (A) diazotation of phenylalanine followed by phenyl ring hydrogenation; (B) phenyl ring hydrogenation of phenyl alanine followed by diazotation; (C) acidic hydrolysis of the cyanohydrin derived from phenylacetaldehyde, enantiomeric resolution of the resulting, racemic phenyl lactic acid via diasteromeric salt formation and phenyl ring hydrogenation; (D) enantioselective dihydroxylation of a cinnamate ester, followed by hydrogenation of the benzylic hydroxy group and the aromatic nucleus; (E) enantioselective biocatalytic reduction of phenylpyruvic acid, followed by phenyl ring hydrogenation. The development of (2R)-2-0-(4-nitrophenyl)sulfonyl-cyclohexyl lactic acid p-bromobenzylester 21 as a buidling block with improved crystallinity and stability is also described.
- Storz, Thomas,Dittmar, Peter,Fauquex, Pierre Francois,Marschal, Philippe,Lottenbach, Willy Urs,Steiner, Heinz
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p. 559 - 570
(2013/09/05)
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- A novel application of a [3+2] cycloaddition reaction for the synthesis of the piperazinone rings of pseudotheonamides A1 and A2
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A novel approach to synthesize the piperazinone ring system of pseudotheonamide A1 and A2 is described. The key step is the intramolecular [3+2] cycloaddition reaction of a suitably orientated azide and an α,β-unsaturated ester.
- Gurjar, Mukund K,Karmakar, Sukhen,Mohapatra, Debendra K,Phalgune, Usha D
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p. 1897 - 1900
(2007/10/03)
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- 4-aryl-1-oxa-9-thia-cyclopenta (b) fluorenes
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This invention provides compounds of Formula I having the structure wherein B and D are each, independently, hydrogen, halogen, —CN, alkyl of 1-6 carbon atoms, aryl, or aralkyl of 6-12 carbon atoms; R1is hydrogen, alkyl of 1-6 carbon atoms, —CH
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Page column 20
(2008/06/13)
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- A Practical Method for Optical Resolution of Racemic Alcohols or Esters via Lipase-Catalyzed Transformation and Sulfation
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Optically active esters were conveniently obtained from the corrasponding racemic alcohols or esters by lipase-catalyzed transformation, followed by sulfation. Sulfation by sulfurtrioxide pyridine complex enabled facile isolation of optically active esters by extraction instead of laborious column chromatography. The method would be especially adventageous on a large scale.
- Yamano, Toru,Kikumoto, Fumio,Yamamoto, Shozo,Miwa, Katsuhiko,Kawada, Mitsuru,Ito, Tatsuya,Ikemoto, Tomomi,Tomimatsu, Kiminori,Mizuno, Yukio
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p. 448 - 449
(2007/10/03)
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- 2(3H)-and 2(5H)-furanones. VII. Chirality transfer on the tetronic acid templates
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The chirality transfer on the β-tetronic acid templates has been examined via highly diastereoselective alkylation or the Michael reaction at the α-position of the acids. Synthetic utility of this transfer procedure was demonstrated by the formal synthesis of (+)-cassiol and enantiodivergent synthesis of O-methyljoubertiamine.
- Momose, Takefumi,Toyooka, Naoki,Nishio, Morihiro,Shinoda, Hiroyuki,Fujii, Hiromi,Yanagino, Hironobu
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p. 1321 - 1343
(2007/10/03)
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- Direct catalytic asymmetric aldol reaction
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The direct catalytic asymmetric aldol reaction using aldehydes and unmodified ketones is described for the first time herein. This reaction was first found to be promoted by 20 mol % of anhydrous (R)-LLB (L = lanthanum, L = lithium, B = (R)-binaphthol moiety) at -20 °C, giving a variety of aldol products in ee's ranging from 44 to 94%. This asymmetric reaction has been greatly improved by developing a new heteropolymetallic asymmetric catalyst [(R)-LLB, KOH, and H2O]. Using 3-8 mol % of this catalyst, a variety of direct catalytic asymmetric aldol reactions were again found to proceed smoothly, affording aldol products in ee's ranging from 30 to 93% and in good to excellent yields. Interestingly, the use of this new heteropolymetallic asymmetric catalyst has realized a diastereoselective and enantioselective aldol reaction using cyclopentanone for the first time. It is also noteworthy that a variety of aldehydes, including hexanal, can be utilized for the current direct catalytic asymmetric aldol reaction. Chiral aldehydes containing α-hydrogen including (S)-hydrocinnamaldehyde-α-d have been found to produce the corresponding aldol products with negligible racemization (0-4%) at the α-position. One of the aldol products has been successfully converted to the key synthetic intermediates of epothilone A and bryostatin 7. The possible structure of the heteropolymetallic catalyst is also discussed. Finally, mechanistic studies have revealed a characteristic reaction pathway, namely that the reaction is kinetically controlled and the rate-determining step is the deprotonation of the ketone. This is consistent with the fact that the reaction rate is independent of the concentration of the aldehyde.
- Yoshikawa, Naoki,Yamada, Yoichi M. A.,Das, Jagattaran,Sasai, Hiroaki,Shibasaki, Masakatsu
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p. 4168 - 4178
(2007/10/03)
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- Rh-DuPHOS-catalyzed enantioselective hydrogenation of enol esters. Application to the synthesis of highly enantioenriched α-hydroxy esters and 1,2-diols
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The asymmetric hydrogenation of α-(acetyloxy)- and α- (benzoyloxy)acrylates 4 catalyzed by cationic rhodium-DuPHOS complexes has been examined. A wide range of substrates (4) were prepared via a convenient Horner-Emmons condensation protocol, and subsequently hydrogenated under mild conditions (60 psi of H2) at substrate-to-catalyst ratios (S/C) of 500. Overall, enol ester substrates 4 were reduced by the cationic Et-DuPHOS-Rh catalysts with very high levels of enantioselectivity (93-99% ee). Importantly, substrates 4 bearing β-substituents could be employed as E/Z isomeric mixtures with no detrimental effect on the selectivity. Labeling studies indicated that no significant E/Z isomerization of the substrates occurs during the course of these reactions. Details concerning optimization of the reaction, interesting solvent effects, and deprotection procedures for the synthesis of highly enantioenriched α-hydroxy esters and 1,2-diols also are provided.
- Burk, Mark J.,Kalberg, Christopher S.,Pizzano, Antonio
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p. 4345 - 4353
(2007/10/03)
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- Tributyltin hydride-induced free radical deoxygenation of the cyclic thionocarbonates of threo-2,3-dihydroxy esters and ketones
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A practical and enantiospecific method for the synthesis of optically pure β-hydroxy esters and ketones is described. The key reaction is free radical deoxygenation of the cyclic thionocarbonates of threo-2,3-dihydroxy esters and ketones with tributyltin
- Rho, Ho-Sik
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p. 3887 - 3893
(2007/10/03)
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- Synthesis of optically pure 4-alkenyl- or 4-alkanyl-2-hydroxytetronic acids
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The present invention relates to a method for synthesis of optically pure 4-alkenyl or 4-alkanyl-2-hydroxytetronic acids from an optically pure aldehyde. The invention further relates to the use of such optically pure compounds as potent inhibitors of pla
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- Optically pure 4-alkenyl- or 4-alkanyl-2-hydroxytetronic acids and pharmaceutical use thereof
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The present invention relates to a method for synthesis of optically pure 4-alkenyl or 4-alkanyl-2-hydroxytetronic acids from an optically pure aldehyde. The invention further relates to the use of such optically pure compounds as potent inhibitors of pla
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- Synthesis of Peptidosulfinamides and Peptidosulfonamides: Peptidomimetics Containing the Sulfinamide or Sulfonamide Transition-State Isostere
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Synthetic routes are described toward the preparation of α- as well as β-substituted aminoethanesulfinyl chlorides, starting from either an aldehyde or from an amino acid derivative.The sulfinyl chlorides are used as building blocks for the preparation of homochiral α- or β-substituted sulfinamide and sulfonamide transition-state isosteres.The methodology has been applied to the synthesis of peptidosulfonamide peptidomimetics such as a hapten needed for the generation of antibodies and potential HIV protease inhibitors.In addition, the β-substituted aminoethanesulfinyl chlorides were used as building blocks for the preparation of a tetrapeptidosulfonamide, which can be considered as a biopolymer mimetic, employing a repetition of a cycle of three reactions: coupling of the sulfinyl chloride to the N-terminus of the growing peptidosulfonamide, oxidation to the sulfonamide, and deprotection of the N-terminus.
- Moree, Wilna J.,Marel, Gijs A. van der,Liskamp, Rob J.
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p. 5157 - 5169
(2007/10/02)
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- Stereoselective Protonation of Carbanions, 4. Enantioselective Protonation of Lactone Enolates
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The prochiral lithium enolates derived from the five-membered lactones rac-1 and rac-2 were protonated by 37 OH- and 21 NH-chiral proton sources in THF at -78 deg C.The enantioselectivities, determined directly from the reaction mixture by chiral HPLC, ar
- Gerlach, Uwe,Haubenreich, Thomas,Huenig, Siegfried
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p. 1969 - 1980
(2007/10/02)
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- A New Entry to 1,3-Polyols, 2-Amino 1,3-Polyols, and β-(1-Hydroxyalkyl)isoserines Using Azetidinone Frameworks as Chiral Templates via Iterative Asymmetric Cycloaddition Reactions
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A new entry to polyfunctional compounds based on an iterative asymmetric cycloaddition reaction of ketenes to O-protected α-hydroxy aldehyde derived imines is described for the first time.
- Palomo, Claudio,Aizpurua, Jesus M.,Urchegui, Raquel,Garcia, Jesus M.
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p. 1646 - 1648
(2007/10/02)
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- Enantioselectivity of carbonic anhydrase catalyzed hydrolysis of mandelic methyl esters
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We report the first enantioselective hydrolysis of esters catalyzed by caebonic anhydrase.We found that mandelic methyl esters are good substrates for carbonic anhydrase.The R enantiomers are better substrates and enantiomeric excess values are moderate (40-51percent).
- Chenevert, Robert,Letourneau, Martin
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p. 314 - 316
(2007/10/02)
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- Hydroxyacetic acid derivatives for the treatment of diabetic complications
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Racemic and chiral (2R,4R)-4-c-hydroxy-2-4-(substituted)chroman(and thiochroman)-4-acetic acids and their pharmaceutically acceptable salts, their use in the treatment of diabetic complications and intermediates therefor.
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- ENZYME-MEDIATED ASYMMETRIC HYDROLYSIS OF α-BENZYLOXYCARBOXYLIC ESTERS
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Incubation of dl-α-benzyloxycarboxylic esters with grown cells of a bacterium, Corynebacterium equi IFO 3730, afforded the chiral esters of high optical purities via asymmetric hydrolysis.This reaction has been revealed to have a wide applicability to alkene- and arylalkene-carboxylic esters.
- Kato, Yasuo,Ohta, Hiromichi,Tsuchihashi, Gen-ichi
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p. 1303 - 1306
(2007/10/02)
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- Asymmetric Oxidation of Ester and Amide Enolates Using New (Camphorylsulfonyl)oxaziridines
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The first asymmetric oxidation of ester and amide lithium enolates 5 to optically active α-hydroxycarbonyl compounds 6 is reported using new, easily prepared, stable (camphorylsulfonyl)oxaziridines (+)-(2R,8aS)-3 and (-)-(2S,8aR)-4.Either enantiomer of 6 can be readily obtained because the configuration of the oxaziridine three-membered ring determines the product stereochemistry.
- Davis, Franklin A.,Haque, M. Serajul,Ulatowski, Terrance G.,Towson, James C
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p. 2402 - 2404
(2007/10/02)
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- A SYNTHON FOR CHIRAL GLYCOLATE ENOLATE (ROC-HCOOR'): A CAMPHOR-BASED OXAZOLINE
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Alkylations of the anion (7a) derived from a camphor-based oxazoline proceed in good yield.Hydrolysis affords the corresponding α-hydroxy acids in high ee.
- Kelly, T. Ross,Arvanitis, Argyrios
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- Peptide Sweeteners. 3. Effect of Modifying the Peptide Bond on the Sweet Taste of L-Aspartyl-L-phenylalanine Methyl Ester and Its Analogues
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A series of analogues designed to assess the importance of the amide bond in the dipeptide sweetener L-aspartyl-L-phenylalanine methyl ester has been synthesized and tested.The peptide bond was methylated, replaced by an ester bond, or reversed.All of the
- MacDonald, Scott A.,Willson, C. Grant,Chorev, Michael,Vernacchia, Fred S.,Goodman, Murray
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p. 413 - 420
(2007/10/02)
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