- β-Indolyloxy Functionalized Aspartate Analogs as Inhibitors of the Excitatory Amino Acid Transporters (EAATs)
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The excitatory amino acid transporters (EAATs) mediate uptake of the major excitatory neurotransmitter l-glutamate (Glu). The essential functions governed by these transporters in regulating the central Glu level make them interesting therapeutic targets in a wide range of neurodegenerative and psychiatric disorders. l-Aspartate (Asp), another EAAT substrate, has served as a privileged scaffold for the development of EAAT inhibitors. In this study, we designed and synthesized the first β-indolyloxy Asp analogs 15a-d with the aim to probe a hitherto unexplored adjacent pocket to the substrate binding site. The pharmacological properties of 15a-d were characterized at hEAAT1-3 and rEAAT4 in a conventional [3H]-d-Asp uptake assay. Notably, thiophene analog 15b and the para-Trifluoromethyl phenyl analog 15d were found to be hEAAT1,2-preferring inhibitors exhibiting IC50values in the high nanomolar range (0.21-0.71 μM) at these two transporters versus IC50values in the low micromolar range at EAAT3,4 (1.6-8.9 μM). In summary, the results presented herein open up for further structure-Activity relationship studies of this new scaffold.
- Liu, Na,Jensen, Anders A.,Bunch, Lennart
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Read Online
- An optimized synthetic route for the preparation of the versatile chiral building block 1,4-di-O-benzylthreitol
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An improved five-step procedure has been applied to synthesize enantiopure l- and d-1,4-di-O-benzylthreitol out of readily available l- and d-tartaric acid. Through the use of modern reagents and enhanced work-up conditions these useful auxiliaries were o
- Meier, Bettina,Kollroser, Manfred,Presser, Armin
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Read Online
- Selective Monoacylation of Diols and Asymmetric Desymmetrization of Dialkyl meso-Tartrates Using 2-Pyridyl Esters as Acylating Agents and Metal Carboxylates as Catalysts
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With 2-pyridyl benzoates as acylating agents and Zn(OAc)2 as a catalyst, 1,2-diols, 1,3-diols, and catechol were selectively monoacylated. Furthermore, the highly enantioselective desymmetrization of meso-tartrates was achieved for the first time, utilizing 2-pyridyl esters and NiBr2/AgOPiv/Ph-BOX in CH3CN or CuCl2/AgOPiv/Ph-BOX in EtOAc catalyst systems (up to 96% ee). The latter catalyst system was also effective for the kinetic resolution of dibenzyl dl-tartrate.
- Hashimoto, Yuki,Michimuko, Chiaki,Yamaguchi, Koki,Nakajima, Makoto,Sugiura, Masaharu
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p. 9313 - 9321
(2019/08/12)
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- Enantioselective Dihydroxylation of Alkenes Catalyzed by 1,4-Bis(9-O-dihydroquinidinyl)phthalazine-Modified Binaphthyl–Osmium Nanoparticles
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A series of unprecedented binaphthyl–osmium nanoparticles (OsNPs) with chiral modifiers were applied in the heterogeneous asymmetric dihydroxylation of alkenes. A remarkable size effect of the OsNPs, depending on the density of the covalent organic shells, on the reactivity and enantioselectivity of the dihydroxylation reaction was revealed. Successful recycling of the OsNPs was also demonstrated and high reaction efficiency and enantioselectivity were maintained.
- Zhu, Jie,Sun, Xiao-Tao,Wang, Xiao-Dong,Wu, Lei
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p. 1788 - 1792
(2018/04/30)
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- Chiroptical properties of 2,2’-bioxirane
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The two enantiomers of 2,2′-bioxirane were synthesized, and their chiroptical properties were thoroughly investigated in various solvents by polarimetry, vibrational circular dichroism (VCD), and Raman optical activity (ROA). Density functional theory (DFT) calculations at the B3LYP/aug-cc-pVTZ level revealed the presence of three conformers (G+, G?, and cis) with Gibbs populations of 51, 44, and 5% for the isolated molecule, respectively. The population ratios of the two main conformers were modified for solvents exhibiting higher dielectric constants (G? form decreases whereas G+ form increases). The behavior of the specific optical rotation values with the different solvents was correctly reproduced by time-dependent DFT calculations using the polarizable continuum model (PCM), except for the benzene for which explicit solvent model should be necessary. Finally, VCD and ROA spectra were perfectly reproduced by the DFT/PCM calculations for the Boltzmann-averaged G+ and G? conformers.
- Daugey,De Rycke,Brotin,Buffeteau
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supporting information
p. 342 - 350
(2018/01/15)
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- Mechanistically Driven Development of an Iron Catalyst for Selective Syn-Dihydroxylation of Alkenes with Aqueous Hydrogen Peroxide
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Product release is the rate-determining step in the arene syn-dihydroxylation reaction taking place at Rieske oxygenase enzymes and is regarded as a difficult problem to be resolved in the design of iron catalysts for olefin syn-dihydroxylation with potential utility in organic synthesis. Toward this end, in this work a novel catalyst bearing a sterically encumbered tetradentate ligand based in the tpa (tpa = tris(2-methylpyridyl)amine) scaffold, [FeII(CF3SO3)2(5-tips3tpa)], 1 has been designed. The steric demand of the ligand was envisioned as a key element to support a high catalytic activity by isolating the metal center, preventing bimolecular decomposition paths and facilitating product release. In synergistic combination with a Lewis acid that helps sequestering the product, 1 provides good to excellent yields of diol products (up to 97% isolated yield), in short reaction times under mild experimental conditions using a slight excess (1.5 equiv) of aqueous hydrogen peroxide, from the oxidation of a broad range of olefins. Predictable site selective syn-dihydroxylation of diolefins is shown. The encumbered nature of the ligand also provides a unique tool that has been used in combination with isotopic analysis to define the nature of the active species and the mechanism of activation of H2O2. Furthermore, 1 is shown to be a competent synthetic tool for preparing O-labeled diols using water as oxygen source.
- Borrell, Margarida,Costas, Miquel
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supporting information
p. 12821 - 12829
(2017/09/25)
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- Highly Enantioselective Iron-Catalyzed cis-Dihydroxylation of Alkenes with Hydrogen Peroxide Oxidant via an FeIII-OOH Reactive Intermediate
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The development of environmentally benign catalysts for highly enantioselective asymmetric cis-dihydroxylation (AD) of alkenes with broad substrate scope remains a challenge. By employing [FeII(L)(OTf)2] (L=N,N′-dimethyl-N,N′-bis(2-methyl-8-quinolyl)-cyclohexane-1,2-diamine) as a catalyst, cis-diols in up to 99.8 % ee with 85 % isolated yield have been achieved in AD of alkenes with H2O2as an oxidant and alkenes in a limiting amount. This “[FeII(L)(OTf)2]+H2O2” method is applicable to both (E)-alkenes and terminal alkenes (24 examples >80 % ee, up to 1 g scale). Mechanistic studies, including18O-labeling, UV/Vis, EPR, ESI-MS analyses, and DFT calculations lend evidence for the involvement of chiral FeIII-OOH active species in enantioselective formation of the two C?O bonds.
- Zang, Chao,Liu, Yungen,Xu, Zhen-Jiang,Tse, Chun-Wai,Guan, Xiangguo,Wei, Jinhu,Huang, Jie-Sheng,Che, Chi-Ming
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supporting information
p. 10253 - 10257
(2016/08/24)
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- Cis-Dihydroxylation of electron deficient olefins catalysed by an oxo-bridged diiron(III) complex with H2O2
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Room temperature oxidation of olefins catalysed by a symmetrical (μ-oxo)(μ-hydroxo)diiron(III) complex (1) based on the amino pyridyl ligand bpmen (bpmen = N,N′-dimethyl-N,N′-bis(2-pyridyl methyl)ethane-1,2-diamine) with hydrogen peroxide under the conditions of limiting substrate is described. Excellent substrate conversions have been achieved under ambient reaction conditions. The olefin oxidation efficacy of the 1/H2O2 system has been found to get improved in presence of acetic acid. The catalytic system has been shown to oxidise electron-deficient olefins to the corresponding cis-diols, while epoxidation is favoured in case of electron-rich olefins. The μ-oxo diiron(III) core of the catalyst 1 has been found be regenerated after the catalytic turnovers. Addition of a second batch of substrate and oxidant at the end of the olefin oxidation results in the formation of almost identical amounts of epoxides/diols. Moreover, the regenerated catalyst exhibits a significantly higher preference towards the oxidation of electron-deficient olefins.
- Kejriwal, Ambica,Biswas, Sachidulal,Biswas, Achintesh N.,Bandyopadhyay, Pinaki
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- Sesquiterpene dimers esterified with diverse small organic acids from the seeds of Sarcandra glabra
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11 new sesquiterpene dimers, sarglabolides A-K (1-11), and five known ones were isolated from the seeds of Sarcandra glabra. Their structures were elucidated by spectroscopic data analysis and chemical evidence. Sarglabolide A (1) was verified to exclusively possess a seventeen-membered macrocyclic ester ring formed by the scaffold of the sesquiterpene dimer and small organic acids, different from the eighteen-membered rings of the other reported analogues. The chiral small organic acid moieties were assigned to l-malic acid, d-malic acid, and d-tartaric acid based on the combination of spectroscopy, chemical derivatization and HPLC analysis. Dimers 1, 12 and 13 can significantly inhibit NO production in LPS-induced macrophages with IC50 values at 3.04, 4.65 and 2.33 μmol/L, respectively.
- Wang, Peng,Luo, Jun,Zhang, Yang-Mei,Kong, Ling-Yi
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p. 5362 - 5370
(2015/07/15)
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- Design of Highly Stable Iminophosphoranes as Recyclable Organocatalysts: Application to Asymmetric Chlorinations of Oxindoles
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A new family of tartaric acid derived chiral iminophosphoranes has been developed as highly effective organocatalysts in the asymmetric chlorinations of 3-substituted oxindoles with a high level of enantioselectivity. Importantly, these catalysts are air- and moisture-stable. Recovery of the catalyst after simple chromatographic separation for reuse in the model reaction was achieved; the catalyst can be recycled six times without loss of any enantioselectivity. Several advantages of this catalytic process are high conversion after a very short reaction time at ambient temperature, low catalytic loading, and scale-up to multigram quantities with an excellent enantiomeric excess value of >99%, which meets the enantiomeric purity required for pharmaceutical purposes.
- Gao, Xing,Han, Jianwei,Wang, Limin
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supporting information
p. 4596 - 4599
(2015/09/28)
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- Synthesis and the absolute configuration of both enantiomers of 4,5-dihydroxy-3-(formyl)cyclopent-2-enone acetonide as a new chiral building block for prostanoid synthesis
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The synthesis of both enantiomers of 4,5-dihydroxy-3-(formyl)cyclopent-2-enone acetonide (5) was accomplished in five steps starting from meso-tartaric acid (6). The key steps involved are preparation of the isopropylidene protected 3-[(dimethoxyphosphoryl)methyl]-4,5-dihydroxycyclopent-2-enone (9), resolution of the diastereoisomeric products 10 of the Horner reaction of racemic 9 with (R)-glyceraldehyde acetonide and the final regioselective ozonolysis of the exocyclic carbon-carbon double bond of the separated dienones 10 leading to both enantiomeric title compounds 5. The absolute configuration of both enantiomers was initially assigned based on the comparison of the chiroptical properties obtained from the DFT calculations with the experimental data and finally confirmed by X-ray analysis.
- Lukasik, Beata,Mikolajczyk, Marian,Bujacz, Grzegorz,Zurawiski, Remigiusz
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p. 807 - 816
(2015/02/19)
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- Enantioselective construction of 6-substituted-α,β-unsaturated- δ-lactone: Total synthesis of anti-bacterial agent (-)-cleistenolide
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An efficient and straightforward stereoselective synthesis of α,β-unsaturated lactone (1) cleistenolide is described. The synthesis was started from commercially available d-tartaric acid and completed within 13 steps with an overall yield of 7.92%. The cis-olefin was generated from Still-Gennari protocol and one of the hydroxyl groups was from dihydroxylation methodology. All the reactions were very clean and the products were obtained in very good yields.
- Ghogare, Ramesh S.,Wadavrao, Sachin B.,Narsaiah, A. Venkat
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p. 5674 - 5676
(2013/09/24)
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- General and efficient α-oxygenation of carbonyl compounds by TEMPO induced by single-electron-transfer oxidation of their enolates
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A generally applicable method for the synthesis of protected α-oxygenated carbonyl compounds is reported. It is based on the single-electron-transfer oxidation of easily generated enolates to the corresponding α-carbonyl radicals. Coupling with the stable free radical TEMPO provides α-(piperidinyloxy) ketones, esters, amides, acids or nitriles in moderate-to-excellent yields. Enolate aggregates influence the outcome of the oxygenation reactions significantly. Competitive reactions have been analyzed and conditions for their minimization are presented. Chemoselective reduction of the products led to either N-O bond cleavage to α-hydroxy carbonyl compounds or reduction of the carbonyl functionality tomonoprotected 1,2-diols or O-protected amino alcohols. The oxygenation of enolates proves to be the most general and effective methodology for the synthesis of O-protected α-oxy carbonyl compounds and nitriles A. The scope and limitations of the electron-transfer-induced radical coupling reaction with TEMPO are presented. The reaction pathways are outlined. Methods for the deprotection to α-hydroxy carbonyl compounds B are provided and discussed. Copyright
- Dinca, Emanuela,Hartmann, Philip,Smrcek, Jakub,Dix, Ina,Jones, Peter G.,Jahn, Ullrich
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supporting information
p. 4461 - 4482
(2012/10/30)
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- Investigation of tartaric acid amide formation by thermolysis of tartaric acids with alkylamines
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N,N'-dialkyltartramides were obtained by conventional thermolysis at 200 °C without a solvent, of the L-, D- or meso-tartaric acids with butyl-, hexyl- and octylamine, respectively. The products proved in all cases to be mixtures of all the possible stereoisomers, in ratios that depended on the stereochemistry of the tartaric acid applied, retaining an excess of the configuration of the starting material. Isomerization of the initially formed diamide did not take place under the reaction conditions. Mechanistically the transformation was rationalized in terms of two competing pathways - the direct substitution of the alkylamine into the carboxylic acid group, - in competition with ketene formation and subsequent amide formation. As a method for stereoselective synthesis of optically active N,N'-dialkyltartramides, the method may be considered obsolete and of little practical value; however, it provided new insight into the mechanisms of amide formation. ARKAT-USA, Inc.
- Gonzalez, Susana V.,Carlsen, Per
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experimental part
p. 325 - 336
(2011/08/22)
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- Olefin cis-dihydroxylation with bio-inspired iron catalysts. evidence for an FeII/FeIV catalytic cycle
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Iron(II) complexes of a series of N-acylated dipyridin-2-ylmethylamine ligands (R-DPAH) have been investigated as catalysts for the cis-dihydroxylation of olefins to model the action of Rieske dioxygenases that catalyze arene cis-dihydroxylation. The Rieske dioxygenases have a mononuclear iron active site coordinated to a 2-histidine-1-carboxylate facial triad motif. The R-DPAH ligands are designed to provide a facial N,N,O-ligand set that mimics the enzyme active site. The iron(II) complexes of the R-DPAH ligands activate H 2O2 to effect the oxidation of olefin substrates into cis-diol products. As much as 90% of the H2O2 oxidant is converted into cis-diol, but a large excess of olefin is required to achieve the high conversion efficiency. Reactivity and mechanistic comparisons with the previously characterized Fe(TPA)/H2O2 catalyst/oxidant combination (TPA = tris(pyridin-2-ylmethyl)amine) lead us to postulate an FeII/FeIV redox cycle for the Fe(R-DPAH) catalysts in which an FeIV(OH)2 oxidant carries out the cis-hydroxylation of olefins. This hypothesis is supported by three sets of observations: (a) the absence of a lag phase in the conversion of the H 2O2 oxidant into a cis-diol product, thereby excluding the prior oxidation of the Fe(II) catalyst to an Fe(III) derivative as established for the Fe(TPA) catalyst; (b) the incorporation of H218O into the cis-diol product, thereby requiring O-O bond cleavage to occur prior to cis-diol formation; and (c) the formation of cis-diol as the major product of cyclohexene oxidation, rather than the epoxide or allylic alcohol products more commonly observed in metal-catalyzed oxidations of cyclohexene, implicating an oxidant less prone to oxo transfer or H-atom abstraction.
- Oldenburg, Paul D.,Feng, Yan,Pryjomska-Ray, Iweta,Ness, Daniel,Que Jr., Lawrence
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experimental part
p. 17713 - 17723
(2011/03/17)
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- Cis-dihydroxylation of alkenes with oxone catalyzed by iron complexes of a macrocyclic tetraaza ligand and reaction mechanism by ESI-MS spectrometry and DFT calculations
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[FeIII(L-N4Me2)Cl2]+ (1, L-N4Me2 = N,N′-dimethyl-2,11-diaza[3.3](2,6) pyridinophane) is an active catalyst for cis-dihydroxylation of various types of alkenes with oxone at room temperature using limiting amounts of alkene substrates. In the presence of 0.7 or 3.5 mol % of 1, reactions of electron-rich alkenes, including cyclooctene, styrenes, and linear alkenes, with oxone (2 equiv) for 5 min resulted in up to >99% substrate conversion and afforded cis-diol products in up to 67% yield, with cis-diol/epoxide molar ratio of up to 16.8:1. For electron-deficient alkenes including α,β-unsaturated esters and α,β-unsaturated ketones, their reactions with oxone (2 equiv) catalyzed by 1 (3.5 mol %) for 5 min afforded cis-diols in up to 99% yield with up to >99% substrate conversion. A large-scale cis-dihydroxylation of methyl cinnamate (9.7 g) with oxone (1 equiv) afforded the cis-diol product (8.4 g) in 84% yield with 85% substrate conversion. After catalysis, the L-N4Me2 ligand released due to demetalation can be reused to react with newly added Fe(ClO4)2?4H2O to generate an iron catalyst in situ, which could be used to restart the catalytic alkene cis-dihydroxylation. Mechanistic studies by ESI-MS, isotope labeling studies, and DFT calculations on the 1-catalyzed cis-dihydroxylation of dimethyl fumarate with oxone reveal possible involvement of cis-HO-Fe V O and/or cis-O FeV O species in the reaction; the cis-dihydroxylation reactions involving cis-HO-FeV O and cis-O FeV O species both proceed by a concerted but highly asynchronous mechanism, with that involving cis-HO-FeV O being more favorable due to a smaller activation barrier.
- Chow, Toby Wai-Shan,Wong, Ella Lai-Ming,Guo, Zhen,Liu, Yungen,Huang, Jie-Sheng,Che, Chi-Ming
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experimental part
p. 13229 - 13239
(2010/12/19)
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- A structural and functional model for dioxygenases with a 2-His-1-carboxylate triad
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(Chemical Equation Presented) An attractive model: The iron complex shown on the left models the 2-His-1-carboxylate active sites of Rieske dioxygenases both in terms of structure and function. 18O-labeling studies of olefin dihydroxylation support the involvement of a high-valent iron-oxo species.
- Oldenburg, Paul D.,Ke, Chun-Yen,Tipton, A. Alex,Shteinman, Albert A.,Que Jr., Lawrence
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p. 7975 - 7978
(2007/10/03)
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- Supported ruthenium nanoparticle catalyst for cis -dihydroxylation and oxidative cleavage of alkenes
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The present invention relates to the use of nanosized metal particles (e.g., ruthenium) grafted on inert solid support for oxidation of alkenes. The supported metal catalyst can effect cis-dihydroxylation and oxidative cleavage of alkenes to give the respective cis-diols and carbonyl products.
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Page/Page column 3; 5
(2008/06/13)
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- Boric acid catalyzed chemoselective esterification of α- hydroxycarboxylic acids
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Boric acid catalyzes the selective esterification of α- hydroxycarboxylic acids without causing significant esterification to occur with other carboxylic acids. The procedure is simple, high-yielding, and applicable to the esterification of α-hydroxy carboxylates in the presence of other carboxylic acids including β-hydroxyacids within the same molecule.
- Houston, Todd A.,Wilkinson, Brendan L.,Blanchfield, Joanne T.
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p. 679 - 681
(2007/10/03)
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- Synthesis of L-lyxo-phytosphingosine and its 1-phosphonate analogue using a threitol acetal synthon
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The first synthesis of an isosteric phosphonate analogue of the aminotriol lipid phytosphingosine (3), together with an improved synthesis of (2S,3S,4S)-phytosphingosine (2), are described. A key intermediate is 3-pentylidene acetal 9, which was prepared in two steps from dimethyl 2,3-0-benzylidene-D-tartrate (7).
- Lu, Xuequan,Byun, Hoe-Sup,Bittman, Robert
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p. 5433 - 5438
(2007/10/03)
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- Ruthenium nanoparticles supported on hydroxyapatite as an efficient and recyclable catalyst for cis-dihydroxylation and oxidative cleavage of alkenes
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Impregnation of hydroxyapatite with colloidal ruthenium results in the formation of a catalyst that effects cis-dihydroxylation and oxidative cleavage of alkenes to their respective cis-1,2-diols and carbonyl products in good to excellent yields (see scheme). The supported ruthenium catalyst can be easily recycled and reused for consecutive reaction runs without significant deterioration of the catalytic activities. R1, R2 = H, alkyl, aryl.
- Ho, Chi-Ming,Yu, Wing-Yiu,Che, Chi-Ming
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p. 3303 - 3307
(2007/10/03)
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- A mild and effective method for the transesterification of carboxylic acid esters
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An extraordinarily versatile transesterification of simple or highly functionalized esters of aliphatic and aromatic carboxylic acids in high yields is catalyzed by dibutyltin oxide [Eq. (1)]. The reaction is compatible with several functional groups, for example, acetals, ketals, aliphatic bromides, enol ethers, urethanes, as well as free hydroxy, phenolic, and amino groups, and even with water.
- Baumhof, Patrick,Mazitschek, Ralph,Giannis, Athanassios
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p. 3672 - 3674
(2007/10/03)
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- Synthesis of a chiral aziridine derivative as a versatile intermediate for HIV protease inhibitors.
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[reaction: see text] Chiral aziridine derivative 1 was prepared from D-tartaric acid. This compound could be utilized as a common intermediate for the synthesis of hydroxyethylamine class HIV protease inhibitors such as saquinavir, amprenavir, or nelfinavir.
- Kim,Bae,So,Yoo,Chang,Lee,Kang
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p. 2349 - 2351
(2007/10/03)
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- Studies toward the synthesis of pinolidoxin, a phytotoxic nonenolide from the fungus Ascochyta pinodes. Determination of the configuration at the C-7, C-8, and C-9 chiral centers and stereoselective synthesis of the C6- C18 fragment
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The absolute stereochemistry at the C-7, C-8, and C-9 chiral centers of pinolidoxin (1) has been determined by chemical and spectral methods. First, the synthesis of four stereoisomeric fully benzoylated 2,3-erythro-1,2,3,4- heptanetetrols, corresponding to the C6-C18 portion of the natural substance, has been accomplished starting from meso-tartaric acid. As next step, the selection of the synthetic tetrabenzoate possessing 'natural' stereochemistry (10a') suitable for absolute configuration determination, has been carried out by correlation with its 'natural' homologue derived from degradation of pinolidoxin. Determination of the stereochemistry at the title chiral centers has been carried out by application of the Mosher's method both to 7a', a compound stereochemically related to 10a', and to pinolidoxin itself. The stereoselective synthesis of a protected form of the C6-C18 portion of pinolidoxin, to be used in its total synthesis, has also been accomplished starting from commercially available D-erythronolactone.
- De Napoli, Lorenzo,Messere, Anna,Palomba, Daniela,Piccialli, Vincenzo,Evidente, Antonio,Piccialli, Gennaro
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p. 3432 - 3442
(2007/10/03)
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- Rhutenium-Catalyzed cis-Dihydroxylation of Alkenes: Scope and Limitations
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Oxidative ruthenium catalysis (0.07 molequiv RuCl3*(H2O)3, 1.5 molequiv NaIO4, EtOAc/CH3CN/H2O 3:3:1), beyond the usual C-C bond cleavage to give dicarbonyls, have been shown to syn-dihydroxylate a wide range of alkenes (except for strained bicyclic alkenes, sterically hindered trisubstituted alkenes, and most tetrasubstituted alkenes) to give vicinal diols rapidly (within minutes) and efficiently.The minor products are the usual oxidative fission products, namely, ketones and aldehydes or carboxylic acids, and sometimes ketols.Longer reaction times lower the yields of most diols, probably owing to oxidative glycol cleavage.Reactions with substrates containing one or more electron-withdrawing groups in conjugation with or adjacent to the alkene moiety are generally slower but give better yields.The diastereoselectivity of the present "flash" dihydroxylation, anti to the existing α-stereogenic center, with cycloalkenes is excellent whereas that with acyclic alkenes is moderate to poor.Sodium metaperiodate is still the best co-oxidant for the catalytic reaction.Aqueous acetonitrile (approximately 86percent) as an alternative solvent system was found to give better yields of 1,2-diols than the original solvent system in some cases. - Keywords: alkenes, catalysis, dihydroxylations, electrophilicity, ruthenium compounds.
- Shing, Tony K. M.,Tam, Eric K. W.,Tai, Vincent W.-F.,Chung, Ivan H. F.,Jiang, Qin
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- Asymmetric Dihydroxylation of Olefins with a Simple Chiral Ligand
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A C2 symmetrical chiral ligand derived from (R,R)-trans-1,2-diaminocyclohexane is highly effective in the asymmetric cis-dihydroxylation of aromatic and aliphatic di- and trisubstituted olefins under stoichiometric conditions.
- Hanessian, Stephen,Meffre, Patrick,Girard, Mario,Beaudoin, Serge,Sanceau, Jean-Yves,Bennani, Youssef
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p. 1991 - 1993
(2007/10/02)
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- Asymmetric Dihyroxylation of Alkenes with Osmium Tetroxide: Chiral N,N'-Dialkyl-2,2'-bipyrrolidine Complex
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Asymmetric osmylation of alkenes by using N,N'-dialkyl-2,2'-bipyrrolidines as the chiral ligands shows a high asymmetric induction and a marked dependence of the enantioselectivity on both the N-alkyl group and the reaction solvent.
- Hirama, Masahiro,Oishi, Tohru,Ito, Sho
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p. 665 - 666
(2007/10/02)
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- A Study of Stereoselective Hydrolysis of Symmetrical Diesters with Pig Liver Esterase
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Pig liver esterase (PLE) catalyzed hydrolysis of dimethyl esters of symmetrical dicarboxylic acids, including meso-diacids, cis-1,2-cycloalkanedicarboxylic acids, and diacids with a prochiral center, was studied with 14 substrates.The products of these stereoselective hydrolyses are chiral monoesters of dicarboxylic acids, with an enantiomeric excess (e.e.) from 10percent to 100percent.Some of these optically active monoesters are valuable synthons in natural products synthesis.An additivity pattern of α- and β-substituents with the glutaric esters on the stereoselectivity of enzymatic hydrolysis was observed.Analysis of the experimental results leads to a model of enzyme stereoselectivity of diester hydrolysis in which the substitution pattern at α- and β-C-atoms is found to determine the absolute configuration of the resulting monoester.
- Mohr, Peter,Waespe-Sarcevic, Nada,Tamm, Christoph,Gawronska, Krystyna,Gawronsky, Jacek K.
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p. 2501 - 2511
(2007/10/02)
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- Stoffwechselproducte von Mikroorganismen. Strukturaufklaerung von Elaiophylin: Spektroskopische Untersuchungen und Abbau
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The structure of the antibiotic elaiophylin (azalomycin B) was elucidated by extended spectroscopic investigations and chemical degradation.Elaiophylin (26) is a macrodiolide with a 16 membered dilactone ring.The synthesis of 7-acetoxy-6-ethyl-3-octanone (14), the acetyl derivative of an important degradation product, is described.
- Kaiser, Hanspeter,Keller-Schierlein, Walter
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p. 407 - 424
(2007/10/02)
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- STEREOCHEMISTRY OF α,α'-DIFLUOROSUCCINIC ACIDS
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Treatment of both dimethyl (-)-D-tartrate (IVa) and dimethyl (+)-L-tartrate (Va) with sulfur tetrafluoride gave dimethyl meso-α,α'-difluorosuccinate (Ia).The same reagent converted dimethyl meso-tartrate (IIIa) to a racemic mixture of dimethyl D- and L-α,α'-difluorosuccinate (IIa).This outcome resulting from the replacement of hydroxyl by fluorine with inversion of configuration at one and retention of configuration at the other chiral carbon atom can be rationalized by assuming the formation of a cyclic intermediate.This is opened by a subsequent SN2 reaction with fluoride ion followed by a four-center displacement of sulfuroxy group by fluorine.The respective configuration of the dimethyl α,α'-difluorosuccinates Ia and IIa were established by (1)H and (19)F NMR using an optically active chemical shift reagent and confirmed by converting the esters to the corresponding acids and these in turn to the cis- and trans-α,α'-difluorosuccinic anhydrides, respectively.
- Bell, H. M.,Hudlicky, M.
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p. 191 - 200
(2007/10/02)
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