- Asymmetric catalytic sulfoxidation by a novel v IV 8 cluster catalyst in the presence of serum albumin: A simple and green oxidation system
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A novel VIV8 cluster formulated as [V8O12(OH)4(CH3O)4(DAC)4]·7CH3OH (1) (DAC = 1,2-diaminocyclohexane) has been constructed successfully. Enantioselective oxidation of a series of alkyl aryl sulfides catalyzed by 1 is tested in an aqueous medium in the presence of serum albumin. The catalytic procedure is found to be simple and environmentally friendly. The influences of the parameters such as concentration of catalyst and oxidant, pH, and reaction time on the thioanisole as models are investigated. Under optimum conditions, 1 exhibits high conversion (up to 99%), excellent chemoselectivity (≥90% in all cases) and moderate enantioselectivity (up to 75% ee). After binding with serum albumin, the catalytic activity of 1 is promoted. The bovine serum albumin (BSA) and pig serum albumin (PSA) molecules have a more positive effect on the catalytic activity.
- Tang, Jie,Yao, Peng-Fei,Xu, Xiao-Ling,Li, Hai-Ye,Huang, Fu-Ping,Nie, Qing-Qing,Luo, Mei-Yi,Yu, Qing,Bian, He-Dong
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- An efficient silica supported Chitosan@vanadium catalyst for asymmetric sulfoxidation and its application in the synthesis of esomeprazole
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A new type of silica supported Chitosan@vanadium complex was used as a highly active heterogeneous catalyst for asymmetric oxidation of aryl alkyl sulfides. With the economic aqueous H2O2(30%) as the oxidant, the oxidation products were obtained in high yields (up to 95%) with good enantioselectivities (up to 68% ee). It is noted that the marketed drug Nexium (first proton-pump inhibitor, esomeprazole) could be synthesized easily by the newly developed asymmetric sulfoxidation reaction. In addition, the highly active catalyst can be reused five times without losing its catalytic activity.
- Shen, Chao,Qiao, Jun,Zhao, Linwei,Zheng, Kai,Jin, Jianzhong,Zhang, Pengfei
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- Altering 2-Hydroxybiphenyl 3-Monooxygenase Regioselectivity by Protein Engineering for the Production of a New Antioxidant
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2-Hydroxybiphenyl 3-monooxygenase is a flavin-containing NADH-dependent aromatic hydroxylase that oxidizes a broad range of 2-substituted phenols. In order to modulate its activity and selectivity, several residues in the active site pocket were investigated by saturation mutagenesis. Variant M321A demonstrated altered regioselectivity by oxidizing 3-hydroxybiphenyl for the first time, thus enabling the production of a new antioxidant, 3,4-dihydroxybiphenyl, with similar ferric reducing capacity to the well-studied piceatannol. The crystal structure of M321A was determined (2.78 ?), and molecular docking of the 3-substituted phenol provided a rational explanation for the altered regioselectivity. Furthermore, HbpA was found to possess pro-S enantioselectivity towards the production of several chiral sulfoxides, whereas variant M321F exhibited improved enantioselectivity. Based on the biochemical characterization of several mutants, it was suggested that Trp97 stabilized the substrate in the active site, Met223 was involved in NADH entrance or binding to the active site, and Pro320 might facilitate FAD movement.
- Bregman-Cohen, Almog,Deri, Batel,Maimon, Shiran,Pazy, Yael,Fishman, Ayelet
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- A convenient approach to chiral sulfoxides by enantioselective oxidation with a steroidal furylhydroperoxide
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The introduction of a steroidal residue into a position distant from the reaction center shows a beneficial effect on the reactivity of secondary furylhydroperoxides: chiral sulfoxides are obtained by asymmetric oxidation of sulfides and/or kinetic resolution of racemic sulfoxides with reduced reaction times and high enantiomeric excesses.
- Palombi, Laura,Bonadies, Francesco,Pazienza, Alessandro,Scettri, Arrigo
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- Substituent effects and mechanism elucidation of enantioselective sulfoxidation catalyzed by vanadium Schiff base complexes
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The effects of substituents of the Schiff base ligands on oxovanadium-catalyzed enantioselective sulfoxidation were first systematically studied, and a rational mechanism of enantioselective sulfoxidation based on our experimental data and the reported da
- Zeng, Qingle,Wang, Heqing,Weng, Wen,Lin, Wenshi,Gao, Yuxing,Huang, Xiantong,Zhao, Yufen
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- Sulfide oxidation catalyzed vanadyl complexes of N-salicylidene α-amino acids at low catalyst loading
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Sulfoxides are extensively used in chemical and pharmaceutical industries. Various catalytically synthetic methods were reported, but in common 1-10 (mol)% catalyst loading were demanded. Sulfide oxidation catalyzed by vanadyl complexes of N-salicylidene α-amino acids with catalyst loading as low as 0.03 (mol)% gave high yields at room temperature with aqueous hydrogen peroxide as an oxidant, which is a green, solvent-free, energy-saving and easy-operated protocol. In contrast, vanadyl complexes of N-salicylidene amino alcohols could not, even at 0.1 (mol)%. The possible reason is that the stronger acidity of N-salicylidene α-amino acids makes their vanadyl complexes stable to aqueous hydrogen peroxide. This rule may be used in designing other high efficient catalysts, especially with aqueous hydrogen peroxide as an oxidant.
- Zeng, Qingle,Weng, Wen,Xue, Xinghua
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- Reactivity of furylhydroperoxides in asymmetric oxidation and kinetic resolution
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Furylhydroperoxides can be successfully employed in the enantioselective oxidation of allylic alcohols and sulfides under Sharpless-type conditions. Their kinetic resolution provides a mean both to chiral furylhydroperoxides and furylalcohols.
- Lattanzi, Alessandra,Bonadies, Francesco,Scettri, Arrigo
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- Stereoselective sulfoxidation catalyzed by achiral Schiff base complexes in the presence of serum albumin in aqueous media
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Four coordination complexes ML derived from an achiral Schiff base ligand (H2L = 2,2′-[(1,2-ethanediyl)bis(nitrilopropylidyne)]bisphenol) have been synthesized and characterized. A method is described for the enantioselective oxidation of a series of aryl alkyl sulfides using the coordination complexes in the presence of serum albumins (SAs) in an aqueous medium at ambient temperature. The mixture of metal complexes with serum albumins is useful for inducing asymmetric catalysis. The complex, albumin source and substrate influence stereoselective sulfoxidation. At optimal pH with the appropriate oxidant, some of ML/SA systems are identified as very efficient catalysts, giving the corresponding sulfoxides in excellent chemical yield (up to 100%) and good enantioselectivity (up to 94% ee) in certain cases. UV–visible spectroscopic data provide evidence that stronger binding between the complex and serum albumin lead to higher enantioselectivity.
- Tang, Jie,Yao, Pengfei,Huang, Fuping,Luo, Meiyi,Wei, Yi,Bian, Hedong
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- Synthesis of a renewable hydroperoxide from (+)-norcamphor: Influence of steric modifications of the bicyclic framework on asymmetric sulfoxidation
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A renewable tertiary hydroperoxide has been efficiently synthesized in 83% overall yield starting from commercially available (+)-endo-2-norborneol. This oxygen donor, derived from (+)-norcamphor, when employed in Ti(Oi-Pr) 4-catalyzed sulfoxidations, proved to be considerably more reactive when compared to a previously reported camphor-derived hydroperoxide. Reduced steric hindrance of the new oxidant lowered the level of asymmetric induction achieved in the oxidation, but stereoconvergent kinetic resolution has been exploited to improve enantioselectivity. Excellent recovery (95%) of the tertiary alcohol at the end of the sulfoxidation provides a highly advantageous chiral resource saving protocol.
- Lattanzi, Alessandra,Iannece, Patrizia,Scettri, Arrigo
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- Kinetic resolution and asymmetric oxidation as combined routes to chiral sulfoxides
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Non-racemic sulfoxides are accessible through a modified Sharpless kinetic resolution of racemic sulfoxides. Furthermore, thanks to enantioconvergence of asymmetric oxidation and kinetic resolution a successful improvement of e.e. is achievable.
- Lattanzi, Alessandra,Bonadies, Francesco,Senatore, Angela,Soriente, Annunziata,Scettri, Arrigo
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- Iron-Catalyzed Asymmetric Sulfide Oxidation with Aqueous Hydrogen Peroxide
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An iron in the fire: Iron-based catalysts promote the asymmetric oxidation of alkyl aryl sulfides to the corresponding sulfoxides with up to 90% ee (see scheme). Simple hydrogen peroxide (30% in water) serves as the terminal oxidant.
- Legros, Julien,Bolm, Carsten
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- Chloroperoxidase-Catalyzed Asymmetric Synthesis: Enantioselective Reactions of Chiral Hydroperoxides with Sulfides and Bromohydration of Glycals
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This paper describes the use of chloroperoxidase (CPO) from Caldariomyces fumago in the oxidation of sulfides to prepare (R)-sulfoxides with excellent ee (97-100percent) and yield (66-92percent) using H2O2 as oxidant.When racemic 1-phenylethyl hydroperoxides were used in the oxidation of sulfides, the corresponding (R)-alcohol generated from the oxidant and the unreacted (S)-hydroperoxide were recovered with high enantiomeric purity.The enantioselectivity in the enzymatic asymmetric oxidation was found to depend on the concentration of the substrate and enzyme.Chloroperoxidase was also used in the regioselective bromohydration of certain saccharide glycals with KBr and H2O2 to give the corresponding 2-deoxy-2-bromo saccharides.
- Fu, Hong,Kondo, Hirosato,Ichikawa, Yoshitaka,Look, Gary C.,Wong, Chi-Huey
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- ASYMMETRIC OXIDATION OF SULFIDES MEDIATED BY CHIRAL TITANIUM COMPLEXES: MECHANISTIC AND SYNTHETIC ASPECTS
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Asymmetric oxidation of sulfides by hydroperoxides mediated by chiral titanium complexes was further developed.The effect of water was discussed as well as steric and electronic factors of aryl groups in aryl-S-alkyl oxidation.When aryl is replaced by 1-alkyne, the sulfoxude is still obtained with hihg ee.The enantioselectivity of oxidation is enhanced by using cumene hydroperoxide instead of t-butyl hydroperoxide (up to 96percent).The asymmetric oxidation was also run under catalytic conditions (with respect to the titanium complex) and beneficial effects were observed in the presence of molecular sieves in the reaction medium.
- Zhao, S. H.,Samuel, O.,Kagan, H. B.
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- Catalytic enantioselective oxidation of sulfides to sulfoxides with a renewable hydroperoxide
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The catalytic asymmetric oxidation of prochiral sulfides can be conveniently performed by using an easily accessible and renewable furyl hydroperoxide in the presence of the chiral Ti(O-i-Pr)4/BINOL/H2O system.
- Massa, Antonio,Lattanzi, Alessandra,Siniscalchi, Francesca R,Scettri, Arrigo
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- Bi2O3 catalyzed asymmetric oxidation of sulfides
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Bismuth based catalytic system for the asymmetric oxidation of alkyl and aryl benzyl sulfides using t-BuOOH as the oxidant has been investigated. This method affords sulfoxides with high enantioselectivities (up to 98% ee) and good yields in reasonable time. The over oxidized product namely the sulfone was not observed. The described method has wide range of applications, exhibits chemoselectivity/enantioselectivity, and proceeds under mild and environmentally friendly reaction conditions.
- Malik, Payal,Chakraborty, Debashis
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- Vanadium-catalyzed enantioselective sulfoxidation and concomitant, highly efficient kinetic resolution provide high enantioselectivity and acceptable yields of sulfoxides
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Simple, inexpensive, preformed vanadium-Schiff base complexes were facilely prepared and used in enantioselective sulfoxidation. Both the amount of aqueous H2O2 and reaction time greatly influenced the ee values and yields of chiral sulfoxides. High enantioselectivities (up to 99% ee) and reasonable yields (>40%) for various chiral sulfoxides were achieved by combining enantioselective sulfoxidation and appropriate concomitant kinetic resolution.
- Zeng, Qingle,Wang, Heqing,Wang, Tongjian,Cai, Yimin,Weng, Wen,Zhao, Yufen
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- Asymmetric Oxidation of Sulphides, catalysed by Chloroperoxidase
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Chloroperoxidase oxidation of sulphides affords the corresponding sulphoxides having the (R) absolute configuration in up to 92percent enantiomeric excess (e.e.).
- Colonna, Stefano,Gaggero, Nicoletta,Manfredi, Amedea,Casella, Luigi,Gullotti, Michele
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- Molybdenum-catalyzed enantioselective sulfoxidation controlled by a nonclassical hydrogen bond between coordinated chiral imidazolium-based dicarboxylate and peroxido ligands
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Chiral alkyl aryl sulfoxides were obtained by molybdenum-catalyzed oxidation of alkyl aryl sulfides with hydrogen peroxide as oxidant in mild conditions with high yields and moderate enantioselectivities. The asymmetry is generated by the use of imidazoli
- Carrasco, Carlos J,Montilla, Francisco,Galindo, Agustín
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- Asymmetric counteranion-directed iron catalysis: A highly enantioselective sulfoxidation
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A highly active and enantioselective ion-pair sulfoxidation catalyst, consisting of an achiral iron(III)-salen cation and a chiral phosphate counteranion, mediates the oxidization of various sulfides with high yields and enantioselectivities. The enantioselectivities observed, especially for electron-poor substrates, represent the best results so far in manganese and iron-salen systems. This work represents the first application of our concept of asymmetric counteranion-directed catalysis (ACDC) to iron catalysis. Copyright
- Liao, Saihu,List, Benjamin
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- Chiral Ligands in Hypervalent Iodine Compounds: Synthesis and Structures of Binaphthyl-Based λ3-Iodanes
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Several novel binaphthyl-based chiral hypervalent iodine(III) reagents have been prepared and structurally analysed. Various asymmetric oxidative reactions were applied to evaluate the reactivities and stereoselectivities of those reagents. Moderate to excellent yields were observed; however, very low stereoselectivities were obtained. NMR experiments indicated that these reagents are very easily hydrolysed in either chloroform or DMSO solvents leading to the limited stereoselectivities. It is concluded that the use of chiral ligands is an unsuccessful way to prepare efficient stereoselective iodine(III) reagents.
- Zhang, Huaiyuan,Cormanich, Rodrigo A.,Wirth, Thomas
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supporting information
(2021/12/22)
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- Two enantiocomplementary Baeyer-Villiger monooxygenases newly identified for asymmetric oxyfunctionalization of thioether
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Two enantiocomplementary Baeyer-Villiger monooxygenases RaBVMO and AmBVMO were identified by genome mining for the asymmetric sulfoxidation. Both recombinant BVMOs have optimal pH of 9.0 and temperature of 35 °C. The half-lives of RaBVMO and AmBVMO at 30 °C were 24.4 and 24.6 h. RaBVMO and AmBVMO exhibited broad substrate spectrum and could catalyze the oxidization of various compounds including fatty ketones, cyclic ketones, and thioethers. Kinetic parameters analysis revealed that both RaBVMO and AmBVMO displayed higher catalytic efficiency toward thioanisole than cyclohexanone. As much as 50 mM thioanisole could be completely oxidized by AmBVMO and RaBVMO with 99% (R) and 95% (S), respectively. Molecular docking analysis further provides evidence for the complementary enantioselectivity of RaBVMO and AmBVMO. Our results demonstrate the potential application of the two novel BVMOs in asymmetric synthesis of sulfoxides.
- Liu, Yafei,Ni, Ye,Wei, Shiyu,Xu, Guochao,Zhou, Jieyu
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- The Stereoselective Oxidation of para-Substituted Benzenes by a Cytochrome P450 Biocatalyst
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The serine 244 to aspartate (S244D) variant of the cytochrome P450 enzyme CYP199A4 was used to expand its substrate range beyond benzoic acids. Substrates, in which the carboxylate group of the benzoic acid moiety is replaced were oxidised with high activity by the S244D mutant (product formation rates >60 nmol.(nmol-CYP)?1.min?1) and with total turnover numbers of up to 20,000. Ethyl α-hydroxylation was more rapid than methyl oxidation, styrene epoxidation and S-oxidation. The S244D mutant catalysed the ethyl hydroxylation, epoxidation and sulfoxidation reactions with an excess of one stereoisomer (in some instances up to >98 %). The crystal structure of 4-methoxybenzoic acid-bound CYP199A4 S244D showed that the active site architecture and the substrate orientation were similar to that of the WT enzyme. Overall, this work demonstrates that CYP199A4 can catalyse the stereoselective hydroxylation, epoxidation or sulfoxidation of substituted benzene substrates under mild conditions resulting in more sustainable transformations using this heme monooxygenase enzyme.
- Chao, Rebecca R.,Lau, Ian C.-K.,Coleman, Tom,Churchman, Luke R.,Child, Stella A.,Lee, Joel H. Z.,Bruning, John B.,De Voss, James J.,Bell, Stephen G.
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p. 14765 - 14777
(2021/09/14)
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- The mutagenesis of a single site for enhancing or reversing the enantio- or regiopreference of cyclohexanone monooxygenases
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The mutagenesis of a "second sphere"switch residue of CHMOAcineto could control its enantio- and regiopreference. Replacing phenylalanine (F) at position 277 of CHMOAcineto into larger tryptophan (W) enabled a significant enhancement of enantio- or regioselectivity toward structurally diverse substrates, moreover, a complete reversal of enantio- or regiopreference was realized by mutating F277 into a range of smaller amino acids (A/C/D/E/G/H/I/K/L/M/N/P/Q/R/S/T/V).
- Hu, Yujing,Xu, Weihua,Hui, Chenggong,Xu, Jian,Huang, Meilan,Lin, Xianfu,Wu, Qi
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supporting information
p. 9356 - 9359
(2020/11/02)
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- Chiral: N, N ′-dioxide-iron(iii)-catalyzed asymmetric sulfoxidation with hydrogen peroxide
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A highly enantioselective sulfoxidation of various sulfides has been achieved by a N,N′-dioxide-iron(iii) complex with 35% aq. H2O2 as the oxidant. The utility of the current method was demonstrated by asymmetric gram-scale synthesis of drug molecule (R)-modafinil. Moreover, a possible working mode was provided to elucidate the chiral induction.
- Dong, Shunxi,Feng, Lili,Feng, Xiaoming,Liu, Xiaohua,Wang, Fang
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supporting information
p. 3233 - 3236
(2020/03/23)
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- Highly Efficient Access to (S)-Sulfoxides Utilizing a Promiscuous Flavoprotein Monooxygenase in a Whole-Cell Biocatalyst Format
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Chiral sulfoxides have gained attention as synthons and precursors for API synthesis. Flavoproteins such as Baeyer-Villiger or styrene monooxygenases mainly provide access to (R)-sulfoxides and often suffer from low selectivity, activity, and/or limited substrate scope. The flavoprotein monooxygenase AbIMO from Acinetobacter baylyi ADP1 initiates indole degradation. Here, AbIMO was expressed recombinantly in E. coli and characterized for its sulfoxidation activity and substrate spectrum. Next to indole and styrene, AbIMO was found to accept numerous alkyl aryl sulfides as substrates, transforming them to (S)-sulfoxides with high enantioselectivity (95 percent to '99 percent for most sulfides). The formulation as a whole-cell biocatalyst allowed specific production rates of up to 370 U gcdw?1 – the highest specific oxygenase activity achieved in whole cells so far – and the preparative synthesis of enantiopure (S)-aryl alkyl sulfoxides. With its extraordinarily high specific activity, high specificity, ease of handling, and high stability (catalyst is stable for '16 days at 4 °C), the designed whole-cell biocatalyst adds enormous value to the portfolio of chemical and biological catalysts for asymmetric sulfoxide synthesis.
- Willrodt, Christian,Gr?ning, Janosch A. D.,Nerke, Philipp,Koch, Rainhard,Scholtissek, Anika,Heine, Thomas,Schmid, Andreas,Bühler, Bruno,Tischler, Dirk
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p. 4664 - 4671
(2020/01/22)
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- Accessing Enantiopure Epoxides and Sulfoxides: Related Flavin-Dependent Monooxygenases Provide Reversed Enantioselectivity
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Enantiopure organic compounds are of major importance for the chemical and pharmaceutical industry. Flavin-dependent group E monooxygenases, composed of monooxygenase and reductase, are known to perform epoxidation of substituted alkenes as well as sulfoxidation in a regio- and enantioselective fashion. Group E is divided into styrene monooxygenases (SMO) and indole monooxygenases (IMO). Hitherto mainly SMOs have been characterized. In this study, we assayed 31 monooxygenases from both types, while 23 of which showed activity. They almost exclusively produced (S)-styrene oxide at high enantiomeric excess with maximum activities of 0.73 μmol min?1 mg?1 (kcat=0.54 s?1). In case of sulfoxidation, we found that the enantioselectivity is contrary between both types. IMOs preferably produce the (S)-enantiomer while SMOs have a tendency to produce the (R)-enantiomer. Sequence analysis and molecular docking of substrates allowed identifying fingerprint motives: SMO N46-V48-H50-Y73-H76-S96 and IMO S46-Q48-M50-V/I73-I76-A96. These form an essential part of the active site while the loop (AS44-51) interacts with the co-substrate and other amino acids direct the substrate. The motives clearly distinguish group E monooxygenases and define the enantioselectivity and thus direct biotechnological applications. Two-hour biotransformations with several sulfides in conjunction with upscale experiments (10 and 100 mg scale) resulted in the identification of promising candidates for the realization of biocatalytic processes.
- Heine, Thomas,Scholtissek, Anika,Hofmann, Sarah,Koch, Rainhard,Tischler, Dirk
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p. 199 - 209
(2019/11/13)
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- Biocatalytical Asymmetric Sulfoxidation by Identifying Cytochrome P450 from Parvibaculum Lavamentivorans DS-1
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Cytochrome P450 monooxygenases (P450s) catalyzed asymmetric sulfoxidation represents a green route for the synthesis of valuable enantiopure sulfoxides, which are potentially interesting synthons in synthetic and pharmaceutical chemistry. Here the potential P450 and redox partner genes from Parvibaculum lavamentivorans DS-1 are screened and co-expressed in Escherichia coli host to construct twenty recombinant P450 strains. By testing the whole-cell biooxidation of thioanisole, P450PL2 (CYP278A4) and P450PL7 (CYP108G3) are identified with excellent S enantioselectivity while P450PL1 (CYP111B1) and P450PL9 (CYP153A26) exhibit the complementary R enantioselectivity. Asymmetric sulfoxidation of sulfides 1 a–1 m is further investigated using the recombinant E. coli strain P450PL2-2 based on the optimal conditions, producing the corresponding enantioenriched sulfoxides with up to 82 % isolated yield and 99 % ee.
- Wu, Kailin,Tang, Linchao,Cui, Haibo,Wan, Nanwei,Liu, Ziyan,Wang, Zhongqiang,Zhang, Shimin,Cui, Baodong,Han, Wenyong,Chen, Yongzheng
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p. 5410 - 5413
(2018/11/23)
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- Asymmetric Sulfinylations of N-Methylephedrine-Modified Tri- or Tetraalkyl Zincates by Symmetric Diaryl Sulfoxides
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Diethylzinc was treated with 1 or 2 equiv. of AlkMgCl or PhMgBr (preferably) or with 1 equiv. of nBuLi (less efficiently) for forming species – plausibly zincates – which were sulfinylated by diaryl sulfoxides to give racemic alkyl aryl sulfoxides in yields reaching 100 %. Dialkylzinc reagents were also activated by treatments with 1 or 2 equiv. of an enantiomerically pure alkylmagnesium β-aminoalkoxide. This worked best when the alkoxide stemmed from a dialkylmagnesium reagent and an equimolar amount of N-methyl-(–)-ephedrine. This second activation mode allowed sulfinylations of what was originally the dialkylzinc reagent with diaryl sulfoxides. This generated alkyl aryl sulfoxides with enantiomeric ratios up to 93:7 in up to 100 % yield.
- Ruppenthal, Simon,Brückner, Reinhard
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p. 2518 - 2530
(2018/06/11)
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- Enantioselective Aromatic Sulfide Oxidation and Tandem Kinetic Resolution Using Aqueous H2O2 and Chiral Iron–Bis(oxazolinyl)bipyridine Catalysts
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An efficient method for the oxidation of aromatic sulfides has been developed by using aqueous H2O2, catalyzed by the in situ generated chiral Fe/6,6′-bis(4-isopropyloxazolin-2-yl)-2,2′-bipyridine (bipybox-iPr) complex. The corresponding sulfoxides were obtained with high enantioselectivities (up to 98.5:1.5 er) and in good yields (up to 61 %) when the mono-oxidation of the sulfides was performed in combination with the kinetic resolution of the sulfoxide into the sulfone.
- Jalba, Angela,Régnier, Noémie,Ollevier, Thierry
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p. 1628 - 1637
(2017/04/06)
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- Peroxygenase-Catalyzed Enantioselective Sulfoxidations
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The performances of the unspecific peroxigenase from Agrocybe aegerita (AaeUPO) in the asymmetric sulfoxidation of substituted aryl alkyl sulfides were here investigated. A small library of differently substituted aryl alkyl sulfoxides was successfully synthesized from the corresponding sulfides in the presence of AaeUPO and H2O2. All the sulfoxides were obtained as (R)-enantiomers, regardless the substitution pattern both on the aromatic ring and the alkyl chain, in up to > 99 % conversion and > 99 % ee. An overview about the biocatalytic entries to chiral sulfoxides is also presented here in form of a comparison between the results obtained with AaeUPO and performances of the chloroperoxidase from Caldariomyces fumago, and three different Baeyer–Villiger monooxygenases. To the best our knowledge, this is the first example of a systematic investigation of the AaeUPO synthetic potential in the asymmetric oxidation of hetero atoms, i.e., the pro-stereogenic sulfur of sulfides.
- Bassanini, Ivan,Ferrandi, Erica Elisa,Vanoni, Marta,Ottolina, Gianluca,Riva, Sergio,Crotti, Michele,Brenna, Elisabetta,Monti, Daniela
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supporting information
p. 7186 - 7189
(2017/12/28)
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- Method for catalyzing asymmetric oxidation of sulfur ether
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The invention provides a method for asymmetrically oxidizing sulfur ether. The sulfur ether is subjected to asymmetric catalytic oxidation reaction by taking a chiral complex formed by a four-tooth nitrogen organic ligand and a metal scandium compound as a catalyst and taking hydrogen peroxide as an oxidizing agent to obtain a corresponding chiral sulfoxide compound, and the yield and the enantioselectivity are more than 90 percent. The reaction has the advantages of cleanness, mild reaction condition, high conversion rate and high enantioselectivity. The method has an industrial prospect.
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Paragraph 0028; 0029; 0030
(2017/08/30)
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- HPLC enantioseparation on a homochiral MOF-silica composite as a novel chiral stationary phase
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The last frontier in the development of chiral stationary phases for chromatographic enantioseparation involves homochiral metal-organic frameworks (MOFs). Using enantiopure (R)-2,2′-dihydroxy-1,1′-binaphthalene-6,6′-dicarboxylic acid as a starting material, we prepared three homochiral MOFs that were further used as chiral stationary phases for high-performance liquid chromatography to separate the enantiomers of various kinds of racemic sulfoxides, sec-alcohols, β-lactams, benzoins, flavanones and epoxides. The experimental results showed excellent performances for enantioseparation, and highlighted that enantioseparation on homochiral MOF columns is practical.
- Tanaka, Koichi,Muraoka, Toshihide,Otubo, Yasuhiro,Takahashi, Hiroki,Ohnishi, Atsushi
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p. 21293 - 21301
(2016/03/08)
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- Efficient HPLC enantiomer separation using a pillared homochiral metal-organic framework as a novel chiral stationary phase
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HPLC enantioseparation of racemates using novel pillared homochiral metal-organic framework-silica composite as chiral stationary phase has been successfully demonstrated.
- Tanaka, Koichi,Hotta, Naoki,Nagase, Shohei,Yoza, Kenji
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supporting information
p. 4891 - 4894
(2016/07/06)
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- Chiral DHIP-Based Metal-Organic Frameworks for Enantioselective Recognition and Separation
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Two chiral porous 2,3-dihydroimidazo[1,2-a]pyridine (DHIP)-based metal-organic frameworks (MOFs) are assembled from an enantiopure dipyridyl-functionalized DHIP bridging ligand. The Zn-DHIP MOF shows a good enantioseparation performance toward aromatic sulfoxides, and the heterogeneous adsorbent can be readily recovered and reused without significant degradation of the separation performance.
- Zhang, Jie,Li, Zijian,Gong, Wei,Han, Xing,Liu, Yan,Cui, Yong
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supporting information
p. 7229 - 7232
(2016/08/09)
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- Bovine serum albumin-cobalt(II) Schiff base complex hybrid: An efficient artificial metalloenzyme for enantioselective sulfoxidation using hydrogen peroxide
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An artificial metalloenzyme (BSA-CoL) based on the incorporation of a cobalt(ii) Schiff base complex {CoL, H2L = 2,2′-[(1,2-ethanediyl)bis(nitrilopropylidyne)]bisphenol} with bovine serum albumin (BSA) has been synthesized and characterized. Attention is focused on the catalytic activity of this artificial metalloenzyme for enantioselective oxidation of a variety of sulfides with H2O2. The influences of parameters such as pH, temperature, and the concentration of catalyst and oxidant on thioanisole as a model are investigated. Under optimum conditions, BSA-CoL as a hybrid biocatalyst is efficient for the enantioselective oxidation of a series of sulfides, producing the corresponding sulfoxides with excellent conversion (up to 100%), chemoselectivity (up to 100%) and good enantiomeric purity (up to 87% ee) in certain cases.
- Tang, Jie,Huang, Fuping,Wei, Yi,Bian, Hedong,Zhang, Wei,Liang, Hong
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p. 8061 - 8072
(2016/06/06)
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- Molybdenum-catalyzed asymmetric sulfoxidation with hydrogen peroxide and subsequent kinetic resolution, using an imidazolium-based dicarboxylate compound as chiral inductor
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A catalytic system based on simple and economic molybdenum compounds and a straightforwardly prepared imidazolium-based dicarboxylate compound, as chirality inductor, was developed for the catalytic asymmetric oxidation of sulfides with hydrogen peroxide. High yields of chiral methyl phenyl sulfoxide and good enantioselectivities (up to 40% ee) were achieved utilizing one equivalent of oxidant in 1?h. By combination of the enantioselective sulfoxidation and the concomitant kinetic resolution an 83% ee was obtained, an excellent enantioselectivity value for a molybdenum catalyst.
- Carrasco, Carlos J.,Montilla, Francisco,Galindo, Agustín
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p. 134 - 136
(2016/07/11)
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- Extreme synergistic mutational effects in the directed evolution of a baeyer-villiger monooxygenase as catalyst for asymmetric sulfoxidation
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Structure-based directed evolution utilizing iterative saturation mutagenesis (ISM) has been applied to phenyl acetone monooxygenase (PAMO), a thermally robust Baeyer-Villiger monooxygenase, in the quest to access a mutant which displays reversed enantioselectivity in the asymmetric sulfoxidation of prochiral thioethers. Whereas WT PAMO leads to 90% ee in the sulfoxidation of p-methylbenzyl methyl thioether with preference for the (S)-sulfoxide, the evolved mutant I67Q/P440F/A442N/L443I is 95% (R)-selective in the reaction of this and other thioethers. Partial deconvolution of the (R)-selective mutant with generation of the respective four single mutants shows that all of them are (S)-selective, which points to pronounced synergism (cooperative nonadditivity) when they interact in concert. Complete deconvolution with formation of all combinatorial forms of the respective double and triple mutants allows the designed construction of a fitness landscape featuring all 24 upward pathways leading from WT to the (R)-selective quadruple mutant. In all 24 trajectories strong cooperative mutational effects were found as well, which indicates that such mutational changes in enzymes constitute nonlinear systems. A theoretical analysis based on induced fit docking explains many of the observed effects on a molecular level.
- Zhang, Zhi-Gang,Lonsdale, Richard,Sanchis, Joaquin,Reetz, Manfred T.
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p. 17262 - 17272
(2015/02/19)
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- Unusually Broad Substrate Profile of Self-Sufficient Cytochrome P450 Monooxygenase CYP116B4 from Labrenzia aggregata
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A new member of the CYP116B subfamily - P450LaMO - was discovered in Labrenzia aggregata by genomic data mining. It was successfully overexpressed in Escherichia coli, purified, and subsequently characterized spectroscopically, and its catalytic properties were assessed. Substrate profiling of the P450LaMO revealed that it was a versatile catalyst, exhibiting hydroxylation and epoxidation activities as well as O-dealkylation and asymmetric sulfoxidation activities. Diverse compounds, including alkylbenzenes, aromatic bicyclic molecules, and terpenoids, were shown to be hydroxylated by P450LaMO. Such diverse catalytic activities are uncommon for the bacterial P450s, and the P450LaMO -mediated stereoselective hydroxylation of inactivated C - H bonds - ubiquitous and relatively unreactive in organic molecules - is particularly unusual. The self-sufficient nature of P450LaMO, coupled with its broad substrate range, highlights it as an ideal template for directed evolution towards various applications.
- Yin, Yue-Cai,Yu, Hui-Lei,Luan, Zheng-Jiao,Li, Ren-Jie,Ouyang, Peng-Fei,Liu, Jing,Xu, Jian-He
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p. 2443 - 2449
(2015/03/03)
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- Unusually Broad Substrate Profile of Self-Sufficient Cytochrome P450 Monooxygenase CYP116B4 from Labrenzia aggregata
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A new member of the CYP116B subfamily - P450LaMO - was discovered in Labrenzia aggregata by genomic data mining. It was successfully overexpressed in Escherichia coli, purified, and subsequently characterized spectroscopically, and its catalytic properties were assessed. Substrate profiling of the P450LaMO revealed that it was a versatile catalyst, exhibiting hydroxylation and epoxidation activities as well as O-dealkylation and asymmetric sulfoxidation activities. Diverse compounds, including alkylbenzenes, aromatic bicyclic molecules, and terpenoids, were shown to be hydroxylated by P450LaMO. Such diverse catalytic activities are uncommon for the bacterial P450s, and the P450LaMO -mediated stereoselective hydroxylation of inactivated C-H bonds - ubiquitous and relatively unreactive in organic molecules - is particularly unusual. The self-sufficient nature of P450LaMO, coupled with its broad substrate range, highlights it as an ideal template for directed evolution towards various applications.
- Yin, Yue-Cai,Yu, Hui-Lei,Luan, Zheng-Jiao,Li, Ren-Jie,Ouyang, Peng-Fei,Liu, Jing,Xu, Jian-He
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p. 2443 - 2449
(2015/08/24)
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- Exploring nicotinamide cofactor promiscuity in NAD(P)H-dependent flavin containing monooxygenases (FMOs) using natural variation within the phosphate binding loop. Structure and activity of FMOs from Cellvibrio sp. BR and Pseudomonas stutzeri NF13
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Flavin-containing monooxygenases (FMOs) catalyse asymmetric oxidation reactions that have potential for preparative organic synthesis, but most use the more expensive, phosphorylated nicotinamide cofactor NADPH to reduce FAD to FADH2 prior to f
- Jensen, Chantel N.,Ali, Sohail T.,Allen, Michael J.,Grogan, Gideon
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p. 191 - 198
(2015/01/09)
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- PROCESS FOR THE ASYMMETRIC OXIDATION OF ORGANIC COMPOUNDS WITH PEROXIDES IN THE PRESENCE OF A CHIRAL ACID CATALYST
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The present invention relates to a process for the asymmetric oxidation of nucleophilic organic compounds, particularly metal-free, with peroxide compounds in the presence of a chiral Bronsted acid catalyst. In one detail, the present invention relates to a process for enantioselective sulfoxidation of thiocompounds with peroxide compounds in the presence of a chiral imidodiphosphate catalyst. In another detail, the present invention relates to a process for enantioselective sulfoxidation of thiocompounds with peroxide compounds in the presence of a chiral phosphoric acid catalyst.
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Page/Page column 25-27
(2013/07/25)
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- A new methodology for the oxidation of sulfides with Fe(III) catalysts
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A variety of sulfides were converted to the corresponding sulfoxide derivatives with 70% t-BuOOH (water) as the oxidant in the presence of catalytic quantity of Fe2(SO4)3. The method described has a wide range of applicati
- Chakraborty, Debashis,Malik, Payal,Goda, Vinod Kumar
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experimental part
p. 21 - 26
(2012/03/11)
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- Chiral phosphoric acid-catalyzed asymmetric oxidation of aryl alkyl sulfides and aldehyde-derived 1,3-dithianes: Using aqueous hydrogen peroxide as the terminal oxidant
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(R)-1,1'-Binaphthyl-2,2'-diol (R-BINOL) derived chiral phosphoric acids have been explored as organocatalysts for the asymmetric oxidation of a series of aryl alkyl sulfides and 1,3-dithianes derived from aldehydes with aqueous hydrogen peroxide (H2O2) as the terminal oxidant. The enantiomerically enriched sulfoxides are obtained in moderate to excellent yield (up to 99%) with excellent diastereoselectivity (up to >99:1 dr) and moderate to good enantioselectivity (up to 91:9 er). In particular, the present protocol stereoselectively provides an efficient access to enantiomerically enriched aryl alkyl sulfoxides and dithioacetal mono-sulfoxides, which strictly restrains the formation of the undesirable by-products: sulfones or disulfoxides. The tracking experiments also verify that this approach proceeds via a direct sulfoxidation process, instead of a kinetic resolution route by overoxidation of the resulting sulfoxides. Copyright
- Liu, Zhao-Min,Zhao, Hua,Li, Mei-Qiu,Lan, Yu-Bao,Yao, Qi-Bo,Tao, Jing-Chao,Wang, Xing-Wang
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supporting information; experimental part
p. 1012 - 1022
(2012/05/20)
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- Titanium complexes of chiral amino alcohol derived Schiff bases as efficient catalysts in asymmetric oxidation of prochiral sulfides with hydrogen peroxide as an oxidant
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An efficient asymmetric oxidation of prochiral sulfides catalyzed by a series of simple in situ generated complexes based on chiral amino alcohol derived Schiff bases with Ti(Oi-Pr)4 was carried out in presence of cheap and environmentally benign oxidant H2O2 at 0 °C. Prochiral sulfides were converted to respective chiral sulfoxides efficiently (conversion, 93%; up to ee, 98%) with this system in 10 h at 0 °C. The present study demonstrated a significant role of steric influence of the substituent attached on both aryl and alkyl moiety on the enantioselectivity. Kinetic studies of the catalytic reaction showed first order dependence on substrate and catalyst whereas it is zero for the oxidant. Kinetic studies in combination with UV-vis. spectral studies were used to propose a catalytic cycle for the sulfoxidation reaction.
- Bera, Prasanta Kumar,Ghosh, Debashis,Abdi, Sayed Hasan Razi,Khan, Noor-Ul Hasan,Kureshy, Rukhsana Ilays,Bajaj, Hari Chandra
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experimental part
p. 36 - 44
(2012/08/07)
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- Exploring the biocatalytic scope of a bacterial flavin-containing monooxygenase
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A bacterial flavin-containing monooxygenase (FMO), fused to phosphite dehydrogenase, has been used to explore its biocatalytic potential. The bifunctional biocatalyst could be expressed in high amounts in Escherichia coli and was able to oxidize indole and indole derivatives into a variety of indigo compounds. The monooxygenase also performs the sulfoxidation of a wide range of prochiral sulfides, showing moderate to good enantioselectivities in forming chiral sulfoxides. The Royal Society of Chemistry 2011.
- Rioz-Martinez, Ana,Kopacz, Malgorzata,De Gonzalo, Gonzalo,Torres Pazmino, Daniel E.,Gotor, Vicente,Fraaije, Marco W.
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experimental part
p. 1337 - 1341
(2011/04/23)
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- New chiral molybdenum complex catalyzed sulfide oxidation with hydrogen peroxide
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Six new cis-dioxomolybdenum(VI) complexes of chiral Schiff-base ligands, derived from condensation of various amino alcohols and substituted salicylaldehydes, have been prepared and characterized by NMR, IR, ESI-MS and single crystal X-ray diffraction techniques. The geometry around the molybdenum center is distorted octahedral in which a tridentate Schiff-base ligand with two anionic oxygens and one neutral imine nitrogen occupies meridional position. The octahedral geometry of the cis-dioxomolybdenum center is additionally completed by a coordinated labile solvent molecule. In some complexes the sixth site is found to be vacant where the relatively bulky substituents hinder the coordination of the solvent. These complexes are tested for catalytic enantioselective sulfoxidation reactions using hydrogen peroxide as oxidant at low temperature which shows high selectivity along with good to moderate enantiomeric excess. ESI-MS study of the reaction mixture indicates the formation of oxoperoxoMo(VI) complexes during catalysis. The steric effect originated from the substituent on chiral ligand on the catalytic reaction is also discussed. It is found that the substituents at the β position of the amino alcohol seem to greatly influence the enantioselectivity of the oxidation reactions.
- Chakravarthy, Rajan Deepan,Suresh, Kotapati,Ramkumar, Venkatachalam,Chand, Dillip Kumar
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experimental part
p. 57 - 63
(2011/10/30)
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- Organocatalytic asymmetric synthesis of sulfoxides from sulfenic acid anions mediated by a cinchona -derived phase-transfer reagent
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Preliminary results concerning a conceptually novel route to chiral sulfoxides based on the asymmetric alkylation of sulfenate salts with alkyl halides mediated by a chiral phase-transfer catalyst are described. As a representative example, o-anisyl methyl sulfoxide was produced in 96% yield and with an enantiomeric excess of 58% using commercial cinchonidinium derivative 2a.
- Gelat, Fabien,Jayashankaran, Jayadevan,Lohier, Jean-Francois,Gaumont, Annie-Claude,Perrio, Stephane
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p. 3170 - 3173
(2011/08/06)
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- Planar chiral flavinium salts - Prospective catalysts for enantioselective sulfoxidation reactions
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A novel planar chiral flavinium salt, 3-benzyl-5-ethyl-10-(8- phenylnaphthalen-1-yl)isoalloxazinium perchlorate (2b), which bears a phenyl cap that covers one side of the isoalloxazinium skeleton plane, has been prepared as a potential catalyst for the enantioselective H2O2 oxidation of sulfides. The rate of H2O2 oxidation of sulfides in the presence of racemic 2b is comparable to that of the reaction catalysed by 5-ethyl-3,10-dimethylisoalloxazinium perchlorate, which indicates that the bulky shielding substituent does not influence the catalytic activity of the flavinium unit. The turnover frequency for the oxidation of thioanisole with hydrogen peroxide with 2b is 870 h-1. The enantiomerically pure salts (+)-2b and (-)-2b were prepared from the pure enantiomers (+)-3b and (-)-3b of 3-benzyl-10-(8-phenylnaphthalen-1-yl)isoalloxazine (3b) obtained by HPLC separation of racemic 3b on a chiral stationary phase. The enantiomerically pure salts (+)-2b and (-)-2b catalyse the H2O2 oxidation of para-substituted thioanisoles with enantiomeric excesses of 34-44%. The highest enantioselectivity (54% ee) was observed in the oxidation of methyl naphthyl sulfide.
- Jurok, Radek,Cibulka, Radek,Dvorakova, Hana,Hampl, Frantisek,Hodacova, Jana
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experimental part
p. 5217 - 5224
(2010/11/02)
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- Photopromoted Ru-catalyzed asymmetric aerobic sulfide oxidation and epoxidation using water as a proton transfer mediator
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Ru(NO)-salen complexes were found to catalyze asymmetric aerobic oxygen atom transfer reactions such as sulfide oxidation and epoxidation in the presence of water under visible light irradiation at room temperature. Oxidation of sulfides including alkyl aryl sulfides and 2-substituted 1,3-dithianes using complex 2 as the catalyst proceeded with moderate to high enantioselectivity of up to 98% ee, and epoxidation of conjugated olefins using complex 3 as the catalyst proceeded with good to high enantioselectivity of 76-92% ee. Unlike biological oxygen atom transfer reactions that need a proton and electron transfer system, this aerobic oxygen atom transfer reaction requires neither such a system nor a sacrificial reductant. Although the mechanism of this oxidation has not been completely clarified, some experimental results support the notion that an aqua ligand coordinated with the ruthenium ion serves as a proton transfer agent for the oxygen activation process, and it is recycled and used as the proton transfer mediator during the process. Thus, we have achieved catalytic asymmetric oxygen atom transfer reaction using molecular oxygen that can be carried out under ambient conditions.
- Tanaka, Haruna,Nishikawa, Hiroaki,Uchida, Tatsuya,Katsuki, Tsutomu
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supporting information; experimental part
p. 12034 - 12041
(2010/11/04)
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- Vanadium-catalyzed asymmetric oxidation of sulfides using Schiff base ligands derived from ss-amino alcohols with two stereogenic centers
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Novel Schiff base ligands derived from ss-amino alcohols with two stereogenic centers were prepared and. used in the preparation of optically pure sulfoxides by using aqueous hydrogen peroxide as the oxidant. A variety of sulfides were smoothly converted into the corresponding sulfoxides cata-lyzed by the chiral vanadium-Schiff base complex. Good yields (>80%) with excellent: enantioselectivities (>99%ee) were obtained in most cases.
- Wu, Yinuo,Liu, Juntao,Li, Xingshu,Chan, Albert S. C.
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supporting information; experimental part
p. 2607 - 2610
(2009/07/25)
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- Synthesis of chiral sulfoxides by enantioselective sulfide oxidation and subsequent oxidative kinetic resolution using immobilized Ti-binol complex
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Chiral Ti-binol complex was immobilized onto ionic liquid modified SBA-15 and characterized by different physicochemical techniques. The catalyst was found to be highly enantioselective in the heterogeneous asymmetric oxidation of prochiral sulfides to sulfoxides and subsequent oxidative kinetic resolution of the sulfoxides using aqueous tert-butylhydroperoxide as the oxidant. A positive non-linear effect was observed in the oxidation-kinetic resolution of thioanisole using this supported catalyst. The supported catalyst was reused in multiple catalytic runs without any loss of enantioselectivity.
- Sahoo, Suman,Kumar, Pradeep,Lefebvre,Halligudi
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experimental part
p. 111 - 118
(2009/06/17)
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- Synthesis of optically active 2,5-dialkylcyclohexane-1,4-diols and their application in the asymmetric oxidation of sulfides
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A simple and efficient approach to obtain optically pure 1,4-diols was established. The asymmetric oxidation of sulfides to sulfoxides with cumyl hydroperoxide in moderate yields and moderate to high enantioselectivities (up to 84%) catalyzed by chiral Ti/ 1,4-diols complexes has been achieved. A 76% ee value was obtained in the asymmetric synthesis of esomeprazole. Georg Thieme Verlag Stuttgart.
- Sun, Jiangtao,Yang, Minghua,Dai, Zhenya,Zhu, Chengjian,Hu, Hongwen
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scheme or table
p. 2513 - 2518
(2009/04/11)
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- Enantioselective sulfoxidation and kinetic resolution combined protocol mediated by a functionalized (S)-norcamphor-based hydroperoxide/titanium(IV) isopropoxide system
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A functionalized tertiary furyl hydroperoxide derived from (S)-norcamphor has been easily synthesized in good yield and in a highly diastereoselective manner. Good to high enantioselectivities (up to 99% ee) and acceptable to good yields (up to 86%) were achieved for the sulfoxides, by tandem stereoconvergent asymmetric sulfoxidation and kinetic resolution when using the novel hydroperoxide s oxygen donor and chirality source in the presence of catalytic loadings of titanium(IV) isopropoxide as the catalyst.
- Lattanzi, Alessandra,Piccirillo, Sandro,Scettri, Arrigo
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p. 357 - 363
(2008/02/07)
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- Fe(salan)-catalyzed asymmetric oxidation of sulfides with hydrogen peroxide in water
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A new chiral Fe(salan) complex was synthesized, and it was found to serve as an efficient catalyst for asymmetric oxidation of sulfides using hydrogen peroxide in water without surfactant. Not only alkyl aryl sulfides but also various methyl alkyl sulfides were oxidized to the corresponding sulfoxides with high enantioselectivities up to 96% ee. It should be noted that the turnover number of complex 4 amounts to 8000. Copyright
- Egami, Hiromichi,Katsuki, Tsutomu
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p. 8940 - 8941
(2008/02/11)
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- Efficient soluble polymer-supported tartrate/Ti catalyst for asymmetric oxidation of prochiral sulfides
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A group of soluble polymer-supported chiral tartrate ligands was prepared by liquid-phase synthesis with ligand diversity strategy. Moderate to excellent chemical yields and enantiomeric excesses were obtained by using soluble polymer-supported tartrate ester in asymmetric oxidation of prochiral sulfides using Ti(O-i-Pr)4/cumyl hydroperoxide, and the workup was greatly simplified. The influence of substituent in chiral tartrate ligands on the enantioselectivities of the reaction was disclosed.
- Gao, Jinshan,Guo, Hongchao,Liu, Shangzhong,Wang, Min
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p. 8453 - 8455
(2008/03/13)
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- Asymmetric oxidation catalysis by a chiral Al(salalen) complex: Highly enantioselective oxidation of sulfides with aqueous hydrogen peroxide
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(Chemical Equation Presented) Not afraid to get wet: Aluminum(salalen) complexes were found to be water compatible and therefore suitable catalysts for asymmetric oxidation with aqueous hydrogen peroxide. A variety of sulfides underwent the title reaction in the presence of the aluminum(salalen) complex shown to the give the desired sulfoxides with high to excellent enantioselectivity (see scheme; Bn = benzyl).
- Yamaguchi, Tetsufumi,Matsumoto, Kazuhiro,Saito, Bunnai,Katsuki, Tsutomu
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p. 4729 - 4731
(2008/02/09)
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- Oxidative kinetic resolution of alkyl aryl sulfoxides
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Kinetic resolution is observed in the oxidation of racemic alkyl aryl sulfoxides using a combination of VO(acac)2 and ligand 1 in chloroform at 0 °C, conditions previously described for asymmetric oxidation of prochiral sulfides. Kinetic resolution is also observed in toluene as the solvent, although higher temperatures are required. Georg Thieme Verlag Stuttgart.
- Mohammadpoor-Baltork, Iraj,Hill, Mathias,Caggiano, Lorenzo,Jackson, Richard F. W.
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p. 3540 - 3544
(2007/10/03)
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- A re-investigation of Modena's protocol for the asymmetric oxidation of prochiral sulfides
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The reactivity of commercially available or easily accessible hydroperoxides has been conveniently exploited for the achievement of highly efficient and enantioselective catalytic modifications of Modena's protocol for the asymmetric oxidation of sulfides. A notably enhanced enantioselectivity has been obtained by exploiting a concomitant process of stereoconvergent kinetic resolution taking place under catalytic conditions.
- Massa, Antonio,Mazza, Valeria,Scettri, Arrigo
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p. 2271 - 2275
(2007/10/03)
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- Investigations on the iron-catalyzed asymmetric sulfide oxidation
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The development of an enantioselective sulfide oxidation involving a chiral iron catalyst and aqueous hydrogen peroxide as oxidant is described. In the presence of a simple carboxylic acid, or a carboxylate salt, the reaction affords sulfoxides with remarkable enantioselectivities (up to 96% ee) in moderate to good yields. The influence of the structure of the additive on the reaction outcome is reported. In the sulfoxide-to-sulfone oxidation a kinetic resolution (with s = 4.8) occurs, which, however, plays only a negligible role in the overall enantioselective process. Furthermore, a positive nonlinear relationship between the ee of the product and that of the catalyst has been found. On the basis of these observations, a possible catalyst structure is proposed.
- Legros, Julien,Bolm, Carsten
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p. 1086 - 1092
(2007/10/03)
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