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Pravat Mondal, Narshinha P Argade
Correction for 'Stereoselective synthesis of (-)-desethyleburnamonine, (-)-vindeburnol and (-)-3-epitacamonine: observation of a substrate dependent diastereoselectivity reversal of an aldol reaction' by Pravat Mondal et al., Org. Biomol. Chem., 2016, DOI: 10.1039/c6ob01438k.
October 24, 2016: Organic & Biomolecular Chemistry
Misato Uraki, Atsushi Kawase, Masahiro Iwaki
1. The effects of adjuvant-induced arthritis (AA) on the stereoselective hepatic disposition and chiral inversion of "profens" have scarcely been investigated. Ibuprofen (IB) undergoes unidirectional chiral inversion from R-IB to S-IB and is metabolized to IB-glucuronide (IB-Glu). 2. We used an in situ perfused rat liver system to clarify the effects of inflammation on the metabolic activities and chiral inversion of IB without protein binding. 3. After dosing of R-IB, AA had minimal effect on the elimination of R-IB from the perfusate...
October 22, 2016: Xenobiotica; the Fate of Foreign Compounds in Biological Systems
Ioannis V Pavlidis, Martin S Weiß, Maika Genz, Paul Spurr, Steven P Hanlon, Beat Wirz, Hans Iding, Uwe T Bornscheuer
The use of transaminases to access pharmaceutically relevant chiral amines is an attractive alternative to transition-metal-catalysed asymmetric chemical synthesis. However, one major challenge is their limited substrate scope. Here we report the creation of highly active and stereoselective transaminases starting from fold class I. The transaminases were developed by extensive protein engineering followed by optimization of the identified motif. The resulting enzymes exhibited up to 8,900-fold higher activity than the starting scaffold and are highly stereoselective (up to >99...
November 2016: Nature Chemistry
Hui Lin, Lin Dong
A novel decahydropyrene synthesis has been successfully developed involving a tandem rhodium-catalyzed C-H activation/intramolecular Diels-Alder reaction/1,3-dipolar cycloaddition cascade process by using diazole as a traceless directing group. The advantage of this one-pot strategy is a quite simple, efficient, highly stereoselective, and unique product structure.
October 21, 2016: Organic Letters
Juying Li, Tuo Huang, Lizong Li, Tengda Ding, Hong Zhu, Bo Yang, Qingfu Ye, Jay Gan
In this study, the fate of paichongding was investigated in three soils with contrasting soil properties. In general, low soil pH has the potential to retard the mineralization and promote the dissipation of paichongding and the formation of its primary transformation product and to accelerate the formation of bound residue. The dissipation of paichongding stereoisomers was very fast and diastereoselective. This selectivity was found only between diastereomers and not between enantiomers and was observed to be soil dependent...
October 21, 2016: Journal of Agricultural and Food Chemistry
Hai-Tao Yang, Yi-Chen Tan, Jie Ge, He Wu, Jia-Xing Li, Yang Yang, Xiao-Qiang Sun, Chun-Bao Miao
The thermal reaction of C60 with aromatic aldehydes and inactive secondary amines for the stereoselective synthesis of trans-1,2,5-trisubstitutedfulleropyrrolidines has been developed. Moreover, when an ortho-hydroxyl group was located at the phenyl ring of the generated fulleropyrrolidines, the Cu(OAc)2-promoted regioselective intramolecular C-O coupling reaction occurred to generate unique tricycles-fused fullerene derivatives.
October 21, 2016: Journal of Organic Chemistry
Michael H Wang, Karl A Scheidt
N-Heterocyclic carbene (NHC) catalysis has emerged as a powerful stratagem in organic synthesis to construct complex molecules primarily by polarity reversal (umpolung) approaches. These unique Lewis bases have been used to generate acyl anions, enolates, and homoenolates in catalytic fashion. Recently, a new strategy has emerged that dramatically expands the synthetic utility of carbene catalysis by leveraging additional activation modes: cooperative catalysis. The careful selection and balance of cocatalysts have led to enhanced reactivity, increased yields, and improved stereoselectivity...
October 20, 2016: Angewandte Chemie
James M Cash, Mathew R Heal, Ben Langford, Julia Drewer
The atmospheric reactions leading to the generation of secondary organic aerosol (SOA) from the oxidation of isoprene are generally assumed to produce only racemic mixtures, but aspects of the chemical reactions suggest this may not be the case. In this review, the stereochemical outcomes of published isoprene-degradation mechanisms contributing to high amounts of SOA are evaluated. Despite evidence suggesting isoprene first-generation oxidation products do not contribute to SOA directly, this review suggests the stereochemistry of first-generation products may be important because their stereochemical configurations may be retained through to the second-generation products which form SOA...
October 20, 2016: Environmental Science. Processes & Impacts
Claire M Young, Daniel G Stark, Thomas H West, James E Taylor, Andrew D Smith
N-Acyl imidazoles and catalytic isothiourea hydrochloride salts function as ammonium enolate precursors in the absence of base. Enantioselective Michael addition-cyclization reactions using different α,β-unsaturated Michael acceptors have been performed to form dihydropyranones and dihydropyridinones with high stereoselectivity. Detailed mechanistic studies using RPKA have revealed the importance of the "imidazolium" effect in ammonium enolate formation and have highlighted key differences with traditional base-mediated processes...
October 20, 2016: Angewandte Chemie
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November 2016: Drug Metabolism and Disposition: the Biological Fate of Chemicals
Nathan Line, Aaron Burns, Sean Butler, Jerry Cashbolm, Craig J Forsyth
Salvinorin A (1) is natural product that in humans is a hallucinogen which binds the human κ-opioid receptor. A total synthesis has been developed that parlays L-(+)-tartaric acid into that of (-)-1 via an unprecedented allylic dithiane intramolecular Diels-Alder reaction to obtain the trans-decalin scaffold. Tsuji allylation set the C9 quaternary center and a late-stage stereoselective chiral ligand-assisted addition of a 3-titanium furan upon a C12 aldehyde / C17 methyl ester established the furanyl lactone moiety...
October 18, 2016: Chemistry: a European Journal
Raphael Gasper, Isabelle Effenberger, Piotr Kolesinski, Barbara Terlecka, Eckhard Hofmann, Andreas Schaller
Dirigent proteins impart stereoselectivity to phenoxy radical coupling reactions in plants and thus play an essential role in the biosynthesis of biologically active natural products. This includes the regio- and enantioselective coupling and subsequent cyclization of two coniferyl alcohol radicals to pinoresinol as the committed step of lignan biosynthesis. The reaction is controlled by dirigent proteins which, depending on the species and protein, direct the reaction to either (+)- or (-)-pinoresinol. We present the crystal structure of the (-)-pinoresinol forming Dirigent Protein 6 from Arabidopsis thaliana (AtDIR6) with data to 1...
October 17, 2016: Plant Physiology
Xiang Chen, Zhi-Qiang Liu, Chao-Ping Lin, Yu-Guo Zheng
BACKGROUND: Ethyl (R)-4-chloro-3-hydroxybutyrate ((R)-CHBE) is a versatile chiral precursor for many pharmaceuticals. Although several biosynthesis strategies have been documented to convert ethyl 4-chloro-3-oxobutanoate (COBE) to (R)-CHBE, the catalytic efficiency and stereoselectivity are still too low to be scaled up for industrial applications. Due to the increasing demand of (R)-CHBE, it is essential to explore more robust biocatalyst capable of preparing (R)-CHBE efficiently. RESULTS: A stereoselective carbonyl reductase toolbox was constructed and employed into the asymmetric reduction of COBE to (R)-CHBE...
October 18, 2016: BMC Biotechnology
Michel Fischer, Klaus Harms, Ulrich Koert
An efficient stereoselective synthetic approach to 7-20 oxa-bridged abietane type natural products is reported. Key steps are an asymmetric Mukaiyama aldol addition to construct the C3 stereocenter and an intramolecular organocatalyzed Stetter-type Michael addition followed by a Tishchenko reaction. An intramolecular lactone-enolate arylation delivers the tetracyclic skeleton. This synthetic strategy was applied for the first total synthesis of (+)-elevenol, an antihepatitis C active compound from Fluegga virosa, and the first total synthesis of (+)-przewalskin...
October 18, 2016: Organic Letters
Dennis G Hall, Taras Rybak, Tristan Verdelet
Multicomponent reactions (MCR), transformations employing three or more simple substrates in a single and highly atom-economical operation, are very attractive in both natural product synthesis and diversity-oriented synthesis of druglike molecules. Several popular multicomponent reactions were designed by combining two well-established individual reactions that utilize mutually compatible substrates. In this regard, it is not surprising that the merging of two reactions deemed as workhorses of stereoselective synthesis, the Diels-Alder cycloaddition and carbonyl allylboration, would produce a powerful and highly versatile tandem MCR process...
October 18, 2016: Accounts of Chemical Research
Chandresakaran Prathipa, Lakshminarayanan Akilandeswari
There are eight possible pathways for the iron-tricarbonyl-assisted thermal electrocyclic ring opening of fluorocyclobutene due to variations in the orientation of the binding of Fe(CO)3 relative to the fluorine substituent (R1 or R2), stereoselectivity (conrotatory or disrotatory, i.e., C or D), and the torquoselectivity of fluorine (inward-facing or outward-facing, i.e., in or out). A density functional study revealed that the energetically favored pathway is R1 Din. Not only is the D mode favored energetically, but the in configuration was observed to be the lowest-lying mode of R1, despite the general tendency of fluorine substituents to prefer an out configuration...
November 2016: Journal of Molecular Modeling
Madeleine Peschke, Clara Brieke, Max J Cryle
The glycopeptide antibiotics are peptide-based natural products with impressive antibiotic function that derives from their unique three-dimensional structure. Biosynthesis of the glycopeptide antibiotics centres of the combination of peptide synthesis, mediated by a non-ribosomal peptide synthetase, and the crosslinking of aromatic side chains of the peptide, mediated by the action of a cascade of Cytochrome P450s. Here, we report the first example of in vitro activity of OxyE, which catalyses the F-O-G ring formation reaction in teicoplanin biosynthesis...
October 18, 2016: Scientific Reports
Raida Jallouli, Madiha Bouali, Youssef Gargouri, Sofiane Bezzine
Two lipases from Fusarium solani, FSL and FSL2, were efficiently expressed in Pichia pastoris. To check the influence of the expression on interfacial properties of FSL and to study kinetic properties of FSL2, interfacial parameters of FSL2, native FSL, untagged recombinant and tagged recombinant forms of FSL were compared using the monomolecular film technique. Kinetic study on the dependence of the stereoselectivity of these lipases on the surface pressure was performed using three dicaprin isomers spread in the form of monomolecular films at the air-water interface...
October 13, 2016: International Journal of Biological Macromolecules
Xiawen Liu, Lijun Zhu, Biyun Huang, Junjun Huang, Yi Cai, Liu Zhu, Bo Wu, Xiaojing Fu, Xingfei Zhang, Yi Rong, Qing Xiao, Jiewen Guo, Arong Li, Yifei Guo, Mu Yuan
Racemic naftopidil (NAF) is used to treat benign prostatic hyperplasia (BPH) and prostatic cancer (PCa). It exhibits greater efficacy but requires higher dose than other ɑ1-adrenoceptor blockers because of its poor bioavailability. It was previously shown that bioavailability of S(-)-NAF (14.5%) was twice that of R(+)-NAF (6.8%). The present study aimed to elucidate the major factors contributing to the poor and enantioselective bioavailability of NAF. First, absorption of NAF enantiomers was examined using a perfusated intestinal model...
September 27, 2016: Journal of Pharmaceutical and Biomedical Analysis
Harsha Amarasekara, David Crich
The synthesis and cyclization reactions, leading to spirocyclic medium ring-sized diolides, of o-(hydroxymethyl)xylylene monoesters of sialyl thioglycosides is described. Cyclization yields and stereoselectivities are found to vary as a function of the anomeric stereochemistry of the thioglycoside and of the N5 protecting group, and these effects are discussed in terms of the reaction mechanism. Cyclization in the presence of acetonitrile results in the isolation and characterization of a Ritter-type N-sialyl acetamide, which affords strong evidence for the participation of acetonitrile in the form of sialyl nitrilium ions...
October 8, 2016: Carbohydrate Research
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