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Guangshui Na, Yao Yao, Hui Gao, Ruijing Li, Linke Ge, Ivan A Titaley, Lisandra Santiago-Delgado, Staci L Massey Simonich
The food web composition, assimilation efficiency of Dechlorane Plus (DP) in food web components, and even extrinsic conditions can affect the trophic biomagnification potentials of DP isomers in food webs. Antarctica ecological system is characterized by the presence of few consumers and simple trophic levels (TLs), which are crucial in discussing the behavior of contaminants. To assess the biomagnification potential of DP in the Antarctic food web, nine representative species were sampled and analyzed from the Fildes Peninsula...
February 14, 2017: Marine Pollution Bulletin
Friederike A Sandbaumhüter, Regula Theurillat, Wolfgang Thormann
The racemic N-methyl-d-aspartate receptor antagonist ketamine is used in anesthesia, analgesia and the treatment of depressive disorders. It is known that interactions of hydroxylated norketamine metabolites and 5,6-dehydronorketamine (DHNK) with the α7 -nicotinic acetylcholine receptor and the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor are responsible for the antidepressive effects. Ketamine and its first metabolite norketamine are not active on these receptors. As stereoselectivity plays a role in ketamine metabolism, a cationic capillary electrophoresis based method capable of resolving and analyzing the stereoisomers of four hydroxylated norketamine metabolites, norketamine and DHNK was developed...
February 18, 2017: Electrophoresis
Xiao-Yun Li, Wen-Qiang Yuan, Sheng Tang, Yi-Wei Huang, Jia-Hui Xue, Li Na Fu, Qi-Xiang Guo
A highly efficient alkenylation reaction of arylglyoxals with 3-vinylindoles catalyzed by chiral calcium phosphate is described. Structurally diverse allylic alcohols bearing indole and carbonyl units are prepared in excellent yields, good diastereoselectivities, and high to excellent enantioselectivities. These products are good building blocks for the synthesis of polysubstituted chiral tetrahydrocarbozol-2-ones. The mechanism study indicates that the most likely role of the catalyst is to activate the hydrate of arylglyoxal and control the stereoselectivity via desymmetric coordination...
February 17, 2017: Organic Letters
Wei-Chen Chang, Dev Sanyal, Jhih-Liang Huang, Kuljira Ittiamornkul, Qin Zhu, Xinyu Liu
In vitro reconstitution of a newly discovered isonitrile synthase (AmbI1 and AmbI2) and the detection of an elusive intermediate (S)-3-(1H-indol-3-yl)-2-isocyanopropanoic acid 1 in indolyl vinyl isocyanide biogenesis are reported. The characterization of iron/2-oxoglutarate (Fe/2OG) dependent desaturases IsnB and AmbI3 sheds light on the possible mechanism underlying stereoselective alkene installation to complete the biosynthesis of (E)- and (Z)-3-(2-isocyanovinyl)-1H-indole 2 and 5. Establishment of a tractable isonitrile synthase system (AmbI1 and AmbI2) paves the way to elucidate the enigmatic enzyme mechanism for isocyanide formation...
February 17, 2017: Organic Letters
Christopher G Newton, Shou-Guo Wang, Caio C Oliveira, Nicolai Cramer
The development of new methods for the direct functionalization of unactivated C-H bonds is ushering in a paradigm shift in the field of retrosynthetic analysis. In particular, the catalytic enantioselective functionalization of C-H bonds represents a highly atom- and step-economic approach toward the generation of structural complexity. However, as a result of their ubiquity and low reactivity, controlling both the chemo- and stereoselectivity of such processes constitutes a significant challenge. Herein we comprehensively review all asymmetric transition-metal-catalyzed methodologies that are believed to proceed via an inner-sphere-type mechanism, with an emphasis on the nature of stereochemistry generation...
February 17, 2017: Chemical Reviews
Abhijit Sau, Ryan Williams, Carlos Palo-Nieto, Antonio Franconetti, Sandra Medina, M Carmen Galan
Palladium(II) in combination with a monodentate phosphine ligand enables the unprecedented direct and α-stereoselective catalytic synthesis of deoxyglycosides from glycals. Initial mechanistic studies suggest that in the presence of N-phenyl-2-(di-tert-butylphosphino)pyrrole as the ligand, the reaction proceeds via an alkoxy palladium intermediate that increases the proton acidity and oxygen nucleophilicity of the alcohol. The method is demonstrated with a wide range of glycal donors and acceptors, including substrates bearing alkene functionalities...
February 17, 2017: Angewandte Chemie
Markus Neumeyer, Reinhard Brückner
We have accomplished the first total synthesis of an isomerically pure naphthoquinonopyrano-γ-lactone dimer, γ-actinorhodin, in eleven steps. Two steps exploit pairs of peri-MeO groups as unusual selectivity controls. The respective MeO groups convey the steric bulk of a bromo or iodo substituent located ortho to one MeO group as steric hindrance into the vicinity of the second MeO group. This relay effect was indispensable for exerting regiocontrol in an aromatic bromination and diastereocontrol in an oxa-Pictet-Spengler cyclization...
February 17, 2017: Angewandte Chemie
Carolina Pinto Vieira, Daniel Valente Neves, Evandro José Cesarino, Adriana Rocha, Séverine Poirier, Vera Lucia Lanchote
Nebivolol is a racemate of the d-isomer responsible for β1 adrenergic receptor antagonism and the l-isomer responsible for the release of nitric oxide from endothelial cells. Nebivolol is mainly metabolized to nebivolol glucuronide, which also contribute to the nebivolol β1 adrenoreceptor antagonism. This study reports the development and validation of an indirect stereoselective method of analysis of nebivolol glucuronides in plasma by LC-MS/MS. The method was applied to the investigation of stereoselectivity in the glucuronidation of nebivolol in elderly hypertensive patients (n=11) CYP2D6 phenotyped as EM and treated with a single oral dose of the racemate...
February 3, 2017: Journal of Pharmaceutical and Biomedical Analysis
Ileana Dragutan, Valerian Dragutan, Albert Demonceau
The organic chemistry of ruthenium has been one of the most vigorously growing research areas over the past decades. Considerable effort has been extended towards the design and application of a broad series of ruthenium complexes, which culminated with the development by Ryoji Noyori (2001 Nobel Prize for Chemistry) of chiral ruthenium catalysts for stereoselective hydrogenation reactions [1], and the discovery by Robert H. Grubbs (2005 Nobel Prize for Chemistry) of well-defined ruthenium- benzylidene catalysts for olefin metathesis [2] [...
February 8, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Bin Tang, Xiaojun Luo, Yan-Hong Zeng, Bi Xian Mai
Compound-specific and enantiomer-specific carbon isotope composition was investigated in terms of biotransformation of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) as well as atropisomers of chiral PCB congeners in fish by exposing common carp (Cyprinus carpio) to certain PCB and PBDE congeners. The calculated carbon isotope enrichment factors (εC) for PCBs 8, 18, and 45 were -1.99‰, -1.84‰, and -1.70‰, respectively, providing evidence for the metabolism of these congeners in fish...
February 16, 2017: Environmental Science & Technology
Pratik Pal, Samik Nanda
A short and flexible asymmetric synthesis of ramariolides A and C was accomplished. A bimetallic catalytic system consisting of Pd-Cu-mediated cascade cyclization, unprecedented Z-E isomerization by a Ru-based metathesis catalyst, and late-stage stereoselective epoxidation are the key steps involved in the synthesis.
February 16, 2017: Organic Letters
Tynchtyk Amatov, Radek Pohl, Ivana Cisařová, Ullrich Jahn
The most advanced approach, so far, to the asperparalines is developed. Consecutive oxidative and reductive radical cyclizations serve as the key steps to stereoselectively access the complex fully elaborated skeleton containing the cyclopentane and spiro-succinimide units.
February 16, 2017: Organic Letters
Siomenan Coulibali, Elsa Deruer, Elizabeth Godin, Sylvain Canesi
A new stereoselective arylative cyclopropanation process involving treatment of halogenated dienone systems in the presence of a Michael donor containing a nitro-aryl-sulfone has been developed. This transformation enables production of an arylated cyclopropane under mild conditions and occurs via a Michael-Smiles ring closure cascade process, reflecting the concepts of green chemistry and atom economy.
February 16, 2017: Organic Letters
Arturo Obregón-Zúñiga, Mario Milán, Eusebio Juaristi
For the first time, a highly efficient and stereoselective asymmetric aldol reaction employing (S)-proline in the presence of solvate ionic liquids is reported. The reaction seems to proceed via a supramolecular aggregate of (S)-proline, the solvate ionic liquid, and water, affording high yields and excellent stereoselectivities with low catalyst loadings.
February 15, 2017: Organic Letters
Ya-Mei Lin, Guo-Ping Lu, Rong-Kang Wang, Wen-Bin Yi
A radical-mediated approach has been introduced for the C-S bond activation of arylalkenyl sulfides. The protocol provides an efficient approach for the generation of various alkenes including alkenyl silanes, sulfones, phosphine oxides, and nitroolefins. In most cases, these radical substitutions are performed under metal-free conditions with stereospecificity.
February 15, 2017: Organic Letters
Bo-Liang Zhao, Da-Ming Du
A novel bifunctional squaramide-catalyzed one-pot electrophilic trifluoromethylthiolation-sulfur-Michael/aldol cascade reaction for the construction of CF3S-containing spiro-cyclopentanone-thiochromanes was developed. This convenient, one-pot cascade reaction serves as a powerful tool for the enantioselective construction of potential bioactive spiro-cyclopentanone-thiochromanes, which have one quaternary stereocenter containing a CF3S group and three contiguous stereocenters including one spiro all-carbon quaternary center, in moderate to good yields with excellent stereoselectivities (up to 15:1 dr, >99% ee)...
February 15, 2017: Organic Letters
Simon Krautwald, Mate J Bezdek, Paul J Chirik
A cobalt-catalyzed method for the 1,1-diboration of terminal alkynes with bis(pinacolato)diboron (B2Pin2) is described. The reaction proceeds efficiently at 23 °C with excellent 1,1-selectivity and broad functional group tolerance. With the unsymmetrical diboron reagent PinB-BDan (Dan = naphthalene-1,8-diaminato), stereoselective 1,1-diboration provided products with two boron substituents that exhibit differential reactivity. One example prepared by diboration of 1-octyne was crystallized and its stereochemistry established by X-ray crystallography...
February 15, 2017: Journal of the American Chemical Society
Jakub Szyling, Adrian Franczyk, Piotr Pawluć, Bogdan Marciniec, Jędrzej Walkowiak
A new stereoselective method for the synthesis of (E)-β-arylvinyl iodides and (E)- or (Z)-β-arylvinyl bromides from styrenes and vinyl boronates on the basis of a one-pot procedure via borylative coupling/halodeborylation is reported. Depending on the halogenating agent as well as the mode of the halodeborylation reaction, (E) or (Z) isomers are selectively formed.
February 15, 2017: Organic & Biomolecular Chemistry
Gen Li, Jiang-Yu Zhao, Chao Niu, Li-Fei Nie, Chang-Zhi Dong, Haji Akber Aisa
A series of 1-(1'-hydroxyalkyl)rupestonic acid methyl esters were synthesized via the condensation of methyl rupestonate with various aldehydes in the presence of LDA. This mixed aldol reaction was highly stereoselective and all the new compounds were elucidated by detailed NMR and MS analyses. The absolute configurations of the newly formed stereocenters were further confirmed by X-ray crystallographic analysis of 3d, the results of which were found to be opposite to the prediction based on Zimmerman-Traxler's and Houk's models...
June 6, 2016: Bioorganic & Medicinal Chemistry Letters
Zisis V Peitsinis, Achilleas G Mitrakas, Eirini A Nakiou, Dafni A Melidou, Dimitra Kalamida, Christos Kakouratos, Michael I Koukourakis, Alexandros E Koumbis
The synthesis of four new analogues of marine nucleoside trachycladine A was accomplished via direct regio- and stereoselective Vorbrüggen glycosylations of 2,6-dichloropurine and 2-chloropurine with a D-ribose derived chiron. Naturally occurring trachycladines (A and B) and a series of analogues were examined for their cytotoxic activity against a number of cancer cell lines (glioblastoma, lung and cervical cancer). Parent trachycladine A and two analogues (the diacetate of 2,6-dichloropurine derivative and N-cyclopropyl trachycladine A) were found to result in a significant reduction of cell viability, with the latter exhibiting a stronger effect...
February 14, 2017: ChemMedChem
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