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Organic & Biomolecular Chemistry

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https://www.readbyqxmd.com/read/27910989/catalytic-asymmetric-aldol-addition-reactions-of-3-fluoro-indolinone-derived-enolates
#1
Lijun Zhang, Wenzhong Zhang, Haibo Mei, Jianlin Han, Vadim A Soloshonok, Yi Pan
Reported herein is a Cu(i)/bisoxazoline ligand-catalyzed aldol reaction of unprotected tertiary enolates generated in situ from 3-(1,1-dihydroxy-2,2,2-trifluoroethyl)-substituted derivatives of 3-fluoro-2-oxindoles. A range of α-fluoro-β-aryl/hetaryl/alkyl-β-hydroxy-indolin-2-ones containing C-F quaternary stereogenic centers of high pharmaceutical importance were furnished in good yields and satisfactory diastereo- and enantioselectivities. The reactions were conducted under operationally convenient conditions and displayed wide substrate/functional group generality including unprotected N-H on the tertiary enolates, and aromatic, hetero-aromatic and aliphatic aldehydes...
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910982/synthesis-of-6-methyl-3-4-dihydropyrazinones-using-an-ugi-4-cr-allenamide-cycloisomerization-protocol
#2
Estefanía Icelo-Ávila, Yoarhy A Amador-Sánchez, Luis A Polindara-García, Luis D Miranda
A synthetic approach to the 6-methyl-3,4-dihydropyrazinone core from Ugi adducts is described. This methodology relies on the regioselective C-N bond formation between an allenamide moiety at C-β and an amide anion formed under base-mediated conditions. This protocol allows easy access to tricyclic systems such as pyrazino[2,1-a]isoindole and pyrazino[2,1-a]isoquinoline nuclei.
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910980/carbonylation-as-a-novel-method-for-the-assembly-of-pyrazine-based-oligoamide-alpha-helix-mimetics
#3
Seger Van Mileghem, Brecht Egle, Philippe Gilles, Cedrick Veryser, Luc Van Meervelt, Wim M De Borggraeve
The design and synthesis of oligoamide α-helix peptidomimetics is reported. The oligoamide type systems are prepared in a modular fashion by coupling the monomers using palladium-catalyzed carbonylation chemistry. This enabled us to use substrates with a low nucleophilicity, leading to previously unreported pyrazine based oligoamide α-helix mimetics. The proof of principle is given by synthesizing a small set of compounds. Various end-capping groups were introduced and also a mixed multimer was successfully prepared...
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910979/efficient-synthesis-of-cysteine-rich-cyclic-peptides-through-intramolecular-native-chemical-ligation-of-n-hnb-cys-peptide-crypto-thioesters
#4
Victor P Terrier, Agnès F Delmas, Vincent Aucagne
We herein introduce a straightforward synthetic route to cysteine-containing cyclic peptides based on the intramolecular native chemical ligation of in situ generated thioesters. Key precursors are N-Hnb-Cys crypto-thioesters, easily synthesized by Fmoc-based SPPS. The strategy is applied to a representative range of naturally occurring cyclic disulfide-rich peptide sequences.
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910978/indium-catalysed-amide-allylation-of-%C3%AE-iminoamide-highly-enantioselective-synthesis-of-amide-functionalised-%C3%AE-methylene-%C3%AE-butyrolactams
#5
Tetsuya Sengoku, Kana Kokubo, Masami Sakamoto, Masaki Takahashi, Hidemi Yoda
A highly enantioselective amide allylation of α-iminoamides has been achieved using catalytic amounts of InCl3, ZnCl2 and a BINOL derivative. This reaction allowed facile access to a variety of amide functionalised α-methylene-γ-butyrolactams in excellent yields with high enantioselectivities.
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910977/acylboranes-synthetic-strategies-and-applications
#6
REVIEW
Florian Korbinian Scharnagl, Shubhankar Kumar Bose, Todd B Marder
An overview of the synthesis and chemistry of acylborane compounds is presented. Acylboranes are a rare class of boron compounds, previously proposed as intermediates in several transformations and considered to be difficult to prepare. Methodologies for the preparation of acylborane compounds are based on both electrophilic and nucleophilic sources of boron. The former methods include addition of electrophilic boron reagents to acyl-anion equivalents, while the latter methods are based on boryl anion reagents which are trapped by electrophiles, such as aldehydes, diethyl carbonate and ethyl acetate...
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27910976/the-first-example-of-palladium-catalyzed-cascade-amidine-arylation-intramolecular-ester-amidation-for-the-synthesis-of-hypoxanthines-application-to-the-synthesis-of-8-azanebularine-analogues
#7
Wu Yang, Haoran Ma, Qian Yang, Jingwen Wang, Yuan Liu, Qinghua Yang, Jie Wu, Chuanjun Song, Junbiao Chang
8-Azanebularine analogues display interesting antiviral, antitumour and biochemical activities. However, typical glycosylation of 8-azapurines always resulted in the desired products in low yields due to the lack of stereo- and regioselectivity of the glycosylation reaction. Herein, a concise synthetic route toward 8-azanebularine analogues has been developed. Key steps involve a copper-catalyzed 1,3-dipolar cycloaddition of a 1-β-azido sugar moiety with ethyl 3-bromopropiolate and a palladium-catalyzed cascade amidine arylation-intramolecular ester amidation reaction to build the hypoxanthine structural motif...
December 2, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27906394/formal-nucleophilic-borylation-and-borylative-cyclization-of-organic-halides
#8
REVIEW
K Kubota, H Iwamoto, H Ito
This review describes recent advances in direct borylation reactions of organic halides, including both transition-metal-catalyzed and metal-free methods. Since the pioneering work on palladium-catalyzed boryl substitution of aryl halides with a diboron compound reported by Miyaura and co-workers in 1995, various catalytic systems for the borylation of aryl, alkneyl, and alkyl halides have been developed to give a wide range of organoboronate esters that cannot be synthesized using conventional methods. Borylative cyclization of alkyl halides is also discussed...
December 1, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27905615/viability-of-dodecahedrane-forming-radical-polycyclizations
#9
Selina C Wang, Dean J Tantillo
The results of density functional theory calculations on thiyl radical-promoted polycyclization to form dodecahedrane are described. On the basis of these results, the proposed polycyclization is predicted to be both highly exergonic and fast. These results showcase the potential power of radical polycyclization reactions in constructing complex molecular architectures.
December 1, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901535/intermolecular-interactions-boost-aggregation-induced-emission-in-carbazole-schiff-base-derivatives
#10
Xiaoping Gan, Guangjin Liu, Mingjie Chu, Wengang Xi, Zili Ren, Xiuli Zhang, Yupeng Tian, Hongping Zhou
Six D-π-A model compounds (compounds 1-6) were conveniently synthesized and characterized by (1)H NMR, (13)C NMR, MS and single crystal X-ray diffraction. One photon absorption and emission properties were studied by using a series of UV-visible and fluorescence spectra and theoretical calculations were applied to investigate the structure-property relationships, which showed that all six compounds possessed an obvious intramolecular charge transfer process which could be attributed to their optical properties...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901171/role-of-lewis-acid-additives-in-a-palladium-catalyzed-directed-c-h-functionalization-reaction-of-benzohydroxamic-acid-to-isoxazolone
#11
C Athira, Raghavan B Sunoj
Metallic salts as well as protic additives are widely employed in transition metal catalyzed C-H bond functionalization reactions to improve the efficiency of catalytic protocols. In one such example, ZnCl2 and pivalic acid are used as additives in a palladium catalyzed synthesis of isoxazolone from a readily available benzohydroxamic acid under one pot conditions. In this article, we present some important mechanistic insights into the role of ZnCl2 and pivalic acid, gained by using density functional theory (M06) computations...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901167/dearomatisation-approaches-to-spirocyclic-dienones-via-the-electrophilic-activation-of-alkynes
#12
Aimee K Clarke, John T R Liddon, James D Cuthbertson, Richard J K Taylor, William P Unsworth
Two complementary dearomatising spirocyclisation protocols to generate spirocyclic dienones from anisole and phenol-tethered ynones are described, each proceeding via electrophilic alkyne activation. The first approach focuses on the spirocyclisation of para-substituted anisoles using either SnCl2·2H2O or Cu(OTf)2. The second approach, which enables the spirocyclisation of both ortho- and para-substituted phenols, uses silica-supported AgNO3 to generate similar scaffolds with much greater efficiency. Initial asymmetric studies are also outlined...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901165/the-requirements-at-the-c-3-position-of-alkylquinolones-for-signalling-in-pseudomonas-aeruginosa
#13
Rachel Shanahan, F Jerry Reen, Rafael Cano, Fergal O'Gara, Gerard P McGlacken
The 'perfect storm' of increasing bacterial antibiotic resistance and a decline in the discovery of new antibiotics, has made it necessary to search for new and innovative strategies to treat bacterial infections. Interruption of bacterial cell-to-cell communication signalling (Quorum Sensing), thus neutralizing virulence in pathogenic bacteria, is a growing area. 2-Alkyl-4-quinolones, HHQ and PQS, play a key role in the quorum sensing circuitry of P. aeruginosa. We report a new set of isosteres of 2-heptyl-6-nitroquinolin-4-one, with alterations at C-3, and evaluate the key structural requirements for agonistic and antagonistic activity in Pseudomonas aeruginosa...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901164/metal-catalyst-free-cyclization-of-3-alkynyl-substituted-2-indol-3-yl-quinoxalines-in-tfa-alone-a-new-synthesis-of-indolophenazines
#14
K Shiva Kumar, Boyapally Bhaskar, Meesa Siddi Ramulu, N Praveen Kumar, Mohd Ashraf Ashfaq, Manojit Pal
TFA alone was found to be remarkably effective for the intramolecular hydroarylation (IMHA) of alkynes when employed as a solvent in the cyclization of 3-alkynyl substituted 2-(indol-3-yl)quinoxalines. This simple and metal free cyclization method afforded a range of indolophenazines as new and potential cytotoxic agents. The use of excess TFA was found to be crucial for the success of this reaction.
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901163/synthesis-and-biological-evaluation-of-simplified-pironetin-analogues-with-modifications-in-the-side-chain-and-the-lactone-ring
#15
Steven Roldán, Adrià Cardona, Laura Conesa, Juan Murga, Eva Falomir, Miguel Carda, J Alberto Marco
The preparation of several new analogues of the natural dihydropyrone pironetin is described. They differ from the natural product mainly in the nature of the side chain and the lactone ring. Their cytotoxic activity has been measured. In addition, their interaction with tubulin, their ability to inhibit the secretion of the vascular endothelial growth factor (VEGF) and the expression of angiogenesis and telomerase-related genes have been determined. Unexpectedly, and unlike pironetin, the lactones studied in this work do not interact with tubulin...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27901161/optical-control-of-girk-channels-using-visible-light
#16
Julie B Trads, Jessica Burgstaller, Laura Laprell, David B Konrad, Luis de la Osa de la Rosa, C David Weaver, Herwig Baier, Dirk Trauner, David M Barber
G-protein coupled inwardly rectifying potassium (GIRK) channels are an integral part of inhibitory signal transduction pathways, reducing the activity of excitable cells via hyperpolarization. They play crucial roles in processes such as cardiac output, cognition and the coordination of movement. Therefore, the precision control of GIRK channels is of critical importance. Here, we describe the development of the azobenzene containing molecule VLOGO (Visible Light Operated GIRK channel Opener), which activates GIRK channels in the dark and is promptly deactivated when illuminated with green light...
November 30, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27897299/diastereoselective-synthesis-of-trifluoromethylated-1-3-dioxanes-by-intramolecular-oxa-michael-reaction
#17
Liliana Becerra-Figueroa, Elodie Brun, Michael Mathieson, Louis J Farrugia, Claire Wilson, Joëlle Prunet, Diego Gamba-Sánchez
A highly diastereoselective synthesis of trifluoromethylated 1,3-dioxanes is described. The reaction proceeds by an addition/oxa-Michael sequence and works efficiently under mild reaction conditions, with a good substrate scope and acceptable to good yields.
November 29, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27896353/pseudopeptidic-compounds-for-the-generation-of-dynamic-combinatorial-libraries-of-chemically-diverse-macrocycles-in-aqueous-media
#18
Joan Atcher, Jordi Solà, Ignacio Alfonso
A straightforward four-step synthesis leads to the preparation of C2-symmetric dithiols containing a central aromatic core and amino acid side chains. These building blocks allow the preparation of dynamic covalent libraries of pseudopeptidic macrocycles in aqueous media that cover a broad range of polarities, functional groups and bulkiness mirroring the diversity found in natural peptides. The versatility of the generated dynamic libraries has been illustrated by the amplification of two different members from the same library upon the action of two biologically relevant templates...
November 29, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27892591/pd-mediated-cross-coupling-of-c-17-lithiated-androst-16-en-3-ol-access-to-functionalized-arylated-steroid-derivatives
#19
Vanessa Koch, Stefan Bräse
Herein, we report on Pd-mediated cross-coupling of vinyllithium steroids and aryl bromides to introduce various substituted aryls at C-17 of steroidal frameworks based on the structure of epi-androsterone. Compared to other C-C cross-couplings, this method turned out to be an easy and competitive access to biologically interesting C-17 modified steroids.
November 28, 2016: Organic & Biomolecular Chemistry
https://www.readbyqxmd.com/read/27892589/intramolecular-oxidative-deselenization-of-acylselenoureas-a-facile-synthesis-of-benzoxazole-amides-and-carbonic-anhydrase-inhibitors
#20
A Angeli, T S Peat, G Bartolucci, A Nocentini, C T Supuran, F Carta
A mild, efficient and one pot procedure to access benzoxazoles using easily accessible acylselenoureas as starting materials has been discovered. Mechanistic studies revealed a pH dependent intramolecular oxidative deselenization, with ring closure due to an intramolecular nucleophilic attack of a phenoxide ion. All the benzoxazoles herein reported possessed a primary sulfonamide zinc binding group and showed effective inhibitory action on the enzymes, carbonic anhydrases.
November 28, 2016: Organic & Biomolecular Chemistry
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