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Halogen Bonding

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https://www.readbyqxmd.com/read/30097092/aminofutalosine-synthase-mqne-a-new-catalytic-motif-in-radical-sam-enzymology
#1
Sumedh Joshi, Dmytro Fedoseyenko, Nilkamal Mahanta, Tadhg P Begley
Aminofutalosine synthase (MqnE) is a radical SAM enzyme involved in the futalosine-dependent menaquinone biosynthetic pathway. Its ability to add the 5'-deoxyadenosyl radical to the substrate-rather than abstract a hydrogen atom-and to catalyze radical addition to a stable benzene ring gives it a unique place in the radical SAM superfamily and required the development of new strategies for trapping radical intermediates. This chapter describes the methodologies used for enzyme overexpression, purification, and in vitro reconstitution...
2018: Methods in Enzymology
https://www.readbyqxmd.com/read/30095189/direct-synthesis-of-heavy-grignard-reagents-challenges-limitations-and-derivatization
#2
Matthias Westerhausen, Alexander Koch, Quentin Dufrois, Marino Wirgenings, Helmar Görls, Sven Krieck, Michel Etienne, Georg Pohnert
The synthesis of organocalcium compounds (heavy Grignard reagents) via the reduction of organyl halides with calcium powder succeeds straightforwardly for organic bromides and iodides that are bound at sp2-hybridized carbon atoms. Extension of this strategy to alkyl halides is very limited and only the reduction of trialkylsilylmethyl bromides and iodides with activated calcium allows the isolation of corresponding heavy Grignard reagents. Substitution of only one hydrogen atom of the methylene moiety by a phenyl or methyl group directs this reduction toward the Wurtz-type coupling and the formation of calcium halide and the corresponding C-C coupling product...
August 10, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/30085389/a-general-approach-to-site-specific-intramolecular-c-h-functionalization-using-dithiocarbamates
#3
Christina Na, Erik John Alexanian
Intramolecular hydrogen-atom transfer is an established approach for the site-specific functionalization of unactivated, aliphatic C-H bonds. Transformations using this strategy typically require unstable intermediates formed using strong oxidants and have mainly targeted C-H halogenations or intramolecular aminations. Herein, we report a site-specific C-H functionalization that significantly increases the synthetic scope and convergency of reactions proceeding via intramolecular hydrogen atom transfer. Stable, isolable N-dithiocarbamates are used as precursors to amidyl radicals formed via either light or radical initiation to efficiently deliver highly versatile alkyl dithiocarbamates across a wide range of complex structures...
August 7, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/30080171/synthesis-and-characterization-of-two-one-dimensional-cd-ii-coordination-polymers-cps-with-5-amino-2-4-6-tribromoisophthalic-acid-and-flexible-n-donor-bipyridyl-ligands
#4
Chong Zhang, Kou Lin Zhang
The bromo-substituted aromatic dicarboxylic acid 5-amino-2,4,6-tribromoisophthalic acid (H2 ATBIP) was used to assemble with CdII ions in the presence of the N-donor flexible bipyridyl ligands 3,3'-(diazene-1,2-diyl)dipyridine (mzpy) and 1,3-bis(pyridin-3-ylmethyl)urea (3bpmu), leading to the formation of two chain coordination polymers by adopting solution methods, namely, catena-poly[[[triaqua(5-amino-2,4,6-tribromoisophthalato-κO)cadmium(II)]-μ-3,3'-(diazene-1,2-diyl)dipyridine-κ2 N1 :N1' ] dihydrate], {[Cd(C8 H2 Br3 NO4 )(C10 H8 N4 )(H2 O)3 ]·2H2 O}n or {[Cd(ATBIP)(mzpy)(H2 O)3 ]·2H2 O}n , (1), and catena-poly[[[tetraaquacadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2 N1 :N1' -[diaquabis(5-amino-2,4,6-tribromoisophthalato-κO)cadmium(II)]-μ-1,3-bis(pyridin-3-ylmethyl)urea-κ2 N1 :N1' ] octahydrate], {[Cd(C8 H2 Br3 NO4 )(C12 H12 N4 O)(H2 O)3 ]·4H2 O}n or {[Cd(ATBIP)(3bpmu)(H2 O)3 ]·4H2 O}n , (2)...
August 1, 2018: Acta Crystallographica. Section C, Structural Chemistry
https://www.readbyqxmd.com/read/30079726/functional-group-transposition-a-palladium-catalyzed-metathesis-of-ar-x-%C3%AF-bonds-and-acid-chloride-synthesis
#5
Maximiliano De La Higuera Macias, Bruce A Arndtsen
We describe the development of a new method to use palladium catalysis to form functionalized aromatics: via the metathesis of covalent σ-bonds between Ar-X fragments. This transformation demonstrates the dynamic nature of palladium-based oxidative addition/reductive elimination and offers a straightforward approach to incorporate reactive functional groups into aryl halides through exchange reactions. The reaction has been exploited to assemble acid chlorides without the use of high energy halogenating or toxic reagents and, instead, via the metathesis of aryl iodides with other acid chlorides...
August 6, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/30079217/selective-oxymetalation-of-terminal-alkynes-via-6-endo-cyclization-mechanistic-investigation-and-application-to-the-efficient-synthesis-of-4-substituted-isocoumarins
#6
Yuji Kita, Tetsuji Yata, Yoshihiro Nishimoto, Kouji Chiba, Makoto Yasuda
The cyclization of heteroatom-containing alkynes with π acidic metal salts is an attractive method to prepare heterocycles because the starting materials are readily available and the organometallic compounds are useful synthetic intermediates. A new organometallic species in the heterocyclization provides an opportunity to synthesize heterocycles that are difficult to obtain. Herein, we describe a novel cyclic oxymetalation of 2-alkynylbenzoate with indium or gallium salts that proceeds with an unusual regioselectivity to give isocoumarins bearing a carbon-metal bond at the 4-position...
July 28, 2018: Chemical Science
https://www.readbyqxmd.com/read/30079195/the-intramolecular-hydrogen-bonded-halogen-bond-a-new-strategy-for-preorganization-and-enhanced-binding
#7
Asia Marie S Riel, Daniel A Decato, Jiyu Sun, Casey J Massena, Morly J Jessop, Orion B Berryman
Natural and synthetic molecules use weak noncovalent forces to preorganize structure and enable remarkable function. Herein, we introduce the intramolecular hydrogen bonded-halogen bond (HB-XB) as a novel method to preorganize halogen bonding (XBing) molecules, while generating a polarization-enhanced XB. Positioning a fluoroaniline between two iodopyridinium XB donors engendered intramolecular hydrogen bonding (HBing) to the electron-rich belt of both XB donors. NMR solution studies established the efficacy of the HB-XB...
July 14, 2018: Chemical Science
https://www.readbyqxmd.com/read/30076632/the-halogen-bond-an-emerging-supramolecular-tool-in-the-design-of-functional-mesomorphic-materials
#8
Hao Wang, Hari Bisoyi, Augustine Urbas, Timothy Bunning, Quan Li
Owing to their dynamic attributes, non-covalent supramolecular interactions have enabled a new paradigm in the design and fabrication of multifunctional material systems with programmable properties, performances, and reconfigurable traits. Recently, the "halogen bond" is rising as an enticing supramolecular synthetic tool that displays a plethora of promising and advantageous characteristics. Consequently, this versatile and dynamic non-covalent interaction has been extensively harnessed in various fields such as crystal engineering, self-assembly, materials science, polymer chemistry, biochemistry, medicinal chemistry and nanotechnology...
August 3, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/30075056/solubility-of-halide-containing-organometallics-is-dramatically-enhanced-in-diiodomethane-can-the-solvent-complex-halogen-bonding-be-held-responsible
#9
Mikhail A Kinzhalov, Mariya V Kashina, Alexander S Mikherdov, Ekaterina A Mozheeva, Alexander S Novikov, Andrey S Smirnov, Daniil M Ivanov, Mariya A Kryukova, Aleksandr Yu Ivanov, Sergej N Smirnov, Vadim Yu Kukushkin, Konstantin V Luzyanin
In the current study, we evaluated a solubility of a number of organometallics and showed that it is noticeably improved in diiodomethane when compared to other haloalkane solvents. Better solvation properties of CH2I2 were associated with a dramatic growth of the s-hole donating ability of this solvent, and that results in the formation of the uniquely strong solvent-(metal complex) halogen bonding. The strength of halogen bonding is attenuated by the introduction of additional halogens to the organometallic species due to the competitive formation of more favourable intermolecular complex-complex halogen bonding...
August 3, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/30065221/engineering-cocrystals-of-poorlywater-soluble-drugs-to-enhance-dissolution-in-aqueous-medium
#10
REVIEW
Indumathi Sathisaran, Sameer Vishvanath Dalvi
Biopharmaceutics Classification System (BCS) Class II and IV drugs suffer from poor aqueous solubility and hence low bioavailability. Most of these drugs are hydrophobic and cannot be developed into a pharmaceutical formulation due to their poor aqueous solubility. One of the ways to enhance the aqueous solubility of poorlywater-soluble drugs is to use the principles of crystal engineering to formulate cocrystals of these molecules with water-soluble molecules (which are generally called coformers). Many researchers have shown that the cocrystals significantly enhance the aqueous solubility of poorly water-soluble drugs...
July 31, 2018: Pharmaceutics
https://www.readbyqxmd.com/read/30062353/controlled-growth-of-a-bicomponent-supramolecular-network-by-the-sergeants-soldiers-principle
#11
G Zhan, Y Makoudi, J Jeannoutot, M Féron, F Palmino, F Chérioux
The co-deposition of 1,4-di(4',4''-pyridyl)benzene and 1,4-di(4',4''-bromophenyl)benzene on Si(111)-B surface leads to the formation of a highly regular self-assembly. The formation of this network has been investigated by STM and has been elucidated in the light of sergeants & soldiers principle due to halogen bonding on a silicon surface.
July 31, 2018: Chemical Communications: Chem Comm
https://www.readbyqxmd.com/read/30058649/towards-the-systematic-crystallisation-of-molecular-ionic-cocrystals-insights-from-computed-crystal-form-landscapes
#12
Sharmarke Mohamed, Ahmad A Alwan, Tomislav Friščić, Andrew J Morris, Mihails Arhangelskis
The underlying molecular and crystal properties affecting the crystallisation of ionic cocrystals (ICCs) with the general formula A-B+N (A- = anion, B+ = cation and N = neutral acid molecule; 1 : 1 : 1 stoichiometry) are reported for a limited set of known crystal structures determined following the cocrystallisation of either 4-aminopyridine (which forms salts) or 4-dimethylaminopyridine (which forms salts and ICCs) with the same set of monoprotic acids with a single hydroxy or halogen substitution at the ortho or para position...
July 30, 2018: Faraday Discussions
https://www.readbyqxmd.com/read/30050071/immediate-hydroxylation-of-arenes-to-phenols-via-v-containing-all-silica-zsm-22-zeolite-triggered-non-radical-mechanism
#13
Yu Zhou, Zhipan Ma, Junjie Tang, Ning Yan, Yonghua Du, Shibo Xi, Kai Wang, Wei Zhang, Haimeng Wen, Jun Wang
Hydroxylation of arenes via activation of aromatic Csp2 -H bond has attracted great attention for decades but remains a huge challenge. Herein, we achieve the ring hydroxylation of various arenes with stoichiometric hydrogen peroxide (H2 O2 ) into the corresponding phenols on a robust heterogeneous catalyst series of V-Si-ZSM-22 (TON type vanadium silicalite zeolites) that is straightforward synthesized from an unusual ionic liquid involved dry-gel-conversion route. For benzene hydroxylation, the phenol yield is 30...
July 26, 2018: Nature Communications
https://www.readbyqxmd.com/read/30049210/ni-catalyzed-regioselective-alkylarylation-of-vinylarenes-via-c-sp-3-c-sp-3-c-sp-3-c-sp-2-bond-formation-and-mechanistic-studies
#14
Shekhar Kc, Roshan K Dhungana, Bijay Shrestha, Surendra Thapa, Namrata Khanal, Prakash Basnet, Robert W Lebrun, Ramesh Giri
We report a Ni-catalyzed regioselective alkylarylation of vinylarenes with alkyl halides and arylzinc reagents to generate 1,1-diarylalkanes. The reaction proceeds well with primary, secondary and tertiary alkyl halides, and electronically diverse arylzinc reagents. Mechanistic investigations by radical probes, competition studies and quantitative kinetics reveal that the current reaction proceeds via a Ni(0)/Ni(I)/Ni(II) catalytic cycle by a rate-limiting direct halogen atom abstraction via single electron transfer to alkyl halides by a Ni(0)-catalyst...
July 30, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/30048135/synthesis-of-halogenated-anilines-by-treatment-of-n-n-dialkylaniline-n-oxides-with-thionyl-halides
#15
Hayley Reed, Tyler R Paul, William J Chain
The special reactivity of N,N-dialkylaniline N-oxides allows practical and convenient access to electron-rich aryl halides. A complementary pair of reaction protocols allow for the selective para-bromination or ortho-chlorination of N,N-dialkylanilines in up to 69% isolated yield. The generation of a diverse array of halogenated anilines is made possible by a temporary oxidation level increase of N,N-dialkylanilines to the corresponding N,N-dialkylaniline N-oxides and the excision of the resultant weak N- O bond via treatment with thionyl bromide or thionyl chloride at low temperature...
August 9, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/30048124/iron-nickel-dual-catalysis-a-new-engine-for-olefin-functionalization-and-the-formation-of-quaternary-centers
#16
Samantha A Green, Suhelen Vásquez-Céspedes, Ryan A Shenvi
Alkene hydroarylation forms carbon-carbon bonds between two foundational building blocks of organic chemistry: olefins and aromatic rings. In the absence of electronic bias or directing groups, only the Friedel-Crafts reaction allows arenes to engage alkenes with Markovnikov selectivity to generate quaternary carbons. However, the intermediacy of carbocations precludes the use of electron-deficient arenes, including Lewis basic heterocycles. Here we report a highly Markovnikov-selective, dual-catalytic olefin hydroarylation that tolerates arenes and heteroarenes of any electronic character...
July 26, 2018: Journal of the American Chemical Society
https://www.readbyqxmd.com/read/30044526/ping-pong-tunneling-reactions-can-fluoride-jump-at-absolute-zero
#17
Sebastian Kozuch, Ashim Nandi, Adam Sucher
In a recent study, Scheiner designed a double Germanium-based fluoride receptor that binds the halogen by means of strong tetrel bonds (Chem. Eur. J. 2016, 22, 18850). In this system the F- sits in an asymmetric way, producing a double well potential where the fluoride can jump from one Ge to the other as in a ping-pong game. Herein we prove with computational tools that at cryogenic temperatures this rearrangement occurs by heavy atom quantum mechanical tunneling. The inductive strength of the substituents and the polarity of the solvent can adjust the barrier and the tunneling rate...
July 25, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/30039600/guest-induced-structural-transformations-in-a-porous-halogen-bonded-framework
#18
Varvara I Nikolayenko, Dominic C Castell, Dewald P van Heerden, Leonard J Barbour
Structural evidence obtained from in situ X-ray diffraction shows that halogen bonding is responsible for the formation of a dynamic porous molecular solid. This material is surprisingly robust and undergoes reversible switching of its pore volume by activation or by exposure to a series of gases of different sizes and shapes. Volumetric gas sorption and pressure-gradient differential scanning calorimetry (P-DSC) data provide further mechanistic insight into the breathing behavior.
July 23, 2018: Angewandte Chemie
https://www.readbyqxmd.com/read/30036470/stereoselective-synthesis-of-highly-substituted-tetrahydropyrans-through-an-evans-aldol-prins-strategy
#19
Sergio J Álvarez-Méndez, Marta Fariña-Ramos, María Luisa Villalba, Marcelle D Perretti, Celina García, Laila M Moujir, Miguel A Ramírez, Víctor S Martín
A direct and general method for the synthesis of naturally occurring 2,3,4,5,6-pentasubstituted tetrahydropyrans has been developed, employing β,γ-unsaturated N-acyl oxazolidin-2-ones as key starting materials. The combination of the Evans aldol addition and the Prins cyclization allowed the diastereoselective and efficient generation of the desired oxacycles in two fashions: a one-pot Evans aldol-Prins protocol, in which five new σ bonds and five contiguous stereocenters were straightforwardly generated, and a two-step version, which additionally permitted the isolation of β,γ-unsaturated alcohol precursors bearing an N-acyl oxazolidin-2-one in the α position...
August 6, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/30036060/how-meaningful-is-the-halogen-bonding-in-1-ethyl-3-methyl-imidazolium-based-ionic-liquids-for-co-2-capture
#20
Lucas Lodeiro, Renato Contreras, Rodrigo Ormazábal-Toledo
We report on several parameters that can be used to describe the 1-ethyl-3-methyl-4,5-(X2 )imidazolium cations (where X = H, Br, and I) within the Canongia-Lopez and Padua Force Field (CL&P) framework. Geometrical parameters like intramolecular distances and radial distribution functions are close to the experimental structure. Density values obtained with our force field are within the expected ones from CL&P calculations in related systems. This information is used to simulate through molecular dynamics the solubilization of CO2 by these ILs...
August 3, 2018: Journal of Physical Chemistry. B
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