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Sreenath Pappuru, Debashis Chakraborty, Venkatachalam Ramkumar
A series of novel mononuclear (1a-7a and 1b-6b) as well as tetranuclear (8a and 9a) niobium (Nb) and tantalum (Ta) complexes of benzotriazole or benzoxazole phenoxide pro-ligands bearing different substituents at the ortho and para positions of the phenol rings were synthesized and characterized. The reaction of NbCl5 or TaCl5 with one equivalent of benzotriazole or benzoxazole phenoxide pro-ligands (L1H-L6H) in dry toluene or chloroform produced the corresponding chloride (1a-6a and 1b-6b) and ethoxy (7a) mononuclear Nb and Ta complexes in high yields...
November 23, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
T B Ward, E Miliordos, P D Carnegie, S S Xantheas, M A Duncan
Vanadium and niobium cation-water complexes, V(+)(H2O) and Nb(+)(H2O), are produced by laser vaporization in a pulsed supersonic expansion, mass selected in a time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy using rare gas atom (Ar, Ne) complex predissociation. The vibrational bands measured in the O-H stretching region contain K-type rotational sub-band structure, which provides insight into the structures of these complexes. However, rotational sub-bands do not exhibit the simple patterns seen previously for other metal ion-water complexes...
June 14, 2017: Journal of Chemical Physics
Yinghua Yu, Qianqian Lu, Gui Chen, Chunsen Li, Xueliang Huang
In this work, we describe a palladium-catalyzed intermolecular O-acylation of α-diazoesters with ortho-bromo benzaldehydes. The C(sp2)-H bond activation of the aldehyde was enabled by migratory insertion of palladium carbene intermediate. As such, the diazoesters were found to act as modular three-atom units to build up the key seven-membered palladacycles, from which a variety of isocoumarin derivatives were produced after reductive elimination. Mechanistic experiments and DFT calculations have provided deep insights on the reaction pathway...
November 22, 2017: Angewandte Chemie
Thomas Wurm, Ben W H Turnbull, Brett R Ambler, Michael J Krische
Benzocyclobutenones 1a-1g undergo cycloreversion at 150 °C in m-xylene solvent to form transient α-oxo-ortho-quinodimethanes or "ortho-quinoid ketene methides", which engage in intermolecular [4+2] cycloadditions with isatins 2a-2f to form 2-oxindole spirolactones 3a-3l. This process tolerates an array of different functional groups and substitution patterns, and is applicable to unprotected isatins 2b-2f bearing free NH-functionalities. The superior performance of isatins compared to other carbonyl based dienophiles was demonstrated and rationalized with the aid of quantum chemical calculations...
November 22, 2017: Journal of Organic Chemistry
Johanna Nyffeler, Petra Chovancova, Xenia Dolde, Anna-Katharina Holzer, Vladimir Purvanov, Ilona Kindinger, Anna Kerins, David Higton, Steve Silvester, Barbara M A van Vugt-Lussenburg, Enrico Glaab, Bart van der Burg, Richard Maclennan, Daniel F Legler, Marcel Leist
Migration of neural crest cells (NCC) is a fundamental developmental process, and test methods to identify interfering toxicants have been developed. By examining cell function endpoints, as in the 'migration-inhibition of NCC (cMINC)' assay, a large number of toxicity mechanisms and protein targets can be covered. However, the key events that lead to the adverse effects of a given chemical or group of related compounds are hard to elucidate. To address this issue, we explored here, whether the establishment of two overlapping structure-activity relationships (SAR)-linking chemical structure on the one hand to a phenotypic test outcome, and on the other hand to a mechanistic endpoint-was useful as strategy to identify relevant toxicity mechanisms...
November 21, 2017: Archives of Toxicology
Muthulakshmi T, Dhanadeep Dutta, Priya Maheshwari, P K Pujari
We report an experimental evidence for the phase separation of ethanol-water mixture confined in mesoporous silica with different pore size using positron annihilation lifetime spectroscopy (PALS). A bulk-like liquid in the core of the pore and a distinct interfacial region near the pore surface have been identified based on ortho-positronium lifetime components. The lifetime corresponding to the core liquid shows similar behavior as the bulk liquid mixture while the interfacial lifetime shows an abrupt rise within a particular range of ethanol concentration depending on the pore size...
November 21, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Joseph Tsemeugne, Emmanuel Sopbué Fondjo, Jean-de-Dieu Tamokou, Ignas Tonle, Irene Chinda Kengne, Arnaud Djintchui Ngongang, Stephen Tamekou Lacmata, Taoufik Rohand, Jules Roger Kuiate, Beibam Luc Sondengam
BACKGROUND: A series of recently reported phenolic azo dyes 7a-e were prepared by coupling the thienyl diazonium sulfate of 3-Amino-4H-benzo[f]thieno[3,4-c](2H)chromen-4-one with selected diversely substituted phenolic and naphtholic derivatives. These compounds were evaluated for their antibacterial and antifungal activities. Furthermore their voltammetric behavior was compared at a glassy carbon electrode. RESULTS: The voltammetric behavior of the five recently reported azo dyes has been compared at a glassy carbon electrode...
November 21, 2017: Chemistry Central Journal
Colet Te Grotenhuis, Naudin van den Heuvel, Jarl Ivar van der Vlugt, Bas de Bruin
Metalloradical activation of N-tosyl hydrazones 1 (o-benzallyl-aryl-tosylhydrazones), using [Co(TPP)] as a catalyst (TPP = tetraphenylporphyrin), allows controlled exploitation of single-electron reactivity of the redox non-innocent carbene intermediate. This method offers a novel route to prepare 8-membered rings, using base metal catalysis to construct a series of unique dibenzocyclooctenes via selective CcarbeneCaryl cyclization, producing the desired 8 membered ring products in good to excellent yields...
November 20, 2017: Angewandte Chemie
Xue-An Chen, Ya-Hua Zhang, Xin-An Chang, Wei-Qiang Xiao
Two new penta-borates, tris-odium zinc cadmium penta-borate, Na3Zn0.912Cd0.088B5O10, and tris-odium zinc magnesium penta-borate, Na3Zn0.845Mg0.155B5O10, have been synthesized by high-temperature solution reactions at 1023 K. Their crystal structures were determined by single-crystal X-ray diffraction. Both solid solutions crystallize in the ortho-rhom-bic form of the parent compound Na3ZnB5O10 (space group type Pbca, Z = 8) and contain the double ring [B5O10](5-) anion composed of one BO4 tetra-hedron and four BO3 triangles as the basic structural motif...
November 1, 2017: Acta Crystallographica. Section E, Crystallographic Communications
Dieter Enders, Xiang-Yu Chen, Jia-Wen Xiong, Qiang Liu, Sun Li, He Sheng, Carolina von Essen, Kari Rissanen
A strategy to control the switchable linear and cycloaddition reactions of enals through NHC catalyisis has been developed. The new scalable protocol leads to γ-amino acid esters bearing a tetrasubstituted stereocenter in good yields and high stereoselectivities via homo-Mannich reactions of enals and isatin-derived ketimines. By simply changing the N-ketimine substituent to an ortho-hydroxy phenyl group, the corresponding spirocyclic oxindolo-γ-lactams are obtained.
November 17, 2017: Angewandte Chemie
Ramesh Samineni, Jaipal Madapa, Srihari Pabbaraja, Goverdhan Mehta
A general, transition-metal-free, one-pot, domino Michael-SNAr or AdNE substitution protocol was devised for spiroannulation of oxindoles with ortho-bromoaryl ynones, β-bromoalkenyl ynones, and β-bromoalkenyl enones in a convenient and efficient manner. As an application, a short synthesis of tetracyclic alkaloid spindomycin B was accomplished.
November 17, 2017: Organic Letters
Yunxiang Wu, Zhaoqiang Chen, Yaxi Yang, Weiliang Zhu, Bing Zhou
A Rh(III)-catalyzed unsymmetrical C-H alkylation and amidation of N-phenoxyacetamides with diazo compounds has been developed under mild and redox-neutral conditions, producing dinitrogen as the only by-product. The reaction represents the first example of one-step, unsymmetrical difunctionalization of two orthoC-H bonds. Experimental and computational studies support that N-phenoxyacetamides most likely undergo an initial ortho C-H alkylation with diazo compounds via a Rh(III)-catalyzed C-H activation, and the resulting Rh(III) intermediate subse-quently undergo an intramolecular oxidative addition into the O-N bond to form a Rh(V) nitrenoid species that is pro-tonated and further directed toward electrophilic addition to the second ortho position of the phenyl ring...
November 17, 2017: Journal of the American Chemical Society
Pamela T Wong, Shengzhuang Tang, Jayme Cannon, Dexin Chen, Rachel Sun, Jennifer Lee, James Phan, Ke Tao, Kang Sun, Biqiong Chen, James R Baker, Seok Ki Choi
Despite their proven ability for precise and targeted release, nanoplatform systems for photocontrolled delivery often face formidable synthetic challenges, in part, due to the paucity of advanced linker strategies. Here we report on a novel linker strategy using a thioacetal ortho-nitrobenzaldehyde (TNB) cage, demonstrating its application for delivery of doxorubicin (Dox) in two nanoscale systems. This photocleavable linker, TNB(OH), which presents two identical arms, each terminated with a hydroxyl functionality, was prepared in a single step from 6-nitroverataldehyde...
November 17, 2017: Bioconjugate Chemistry
Peter M Felker, Vojtěch Vlček, Isaac Hietanen, Stephen FitzGerald, Daniel Neuhauser, Zlatko Bačić
Symmetry breaking has been recently observed in the endofullerenes M@C60 (M = H2, HF, H2O), manifesting in the splittings of the three-fold degenerate ground states of the endohedral ortho-H2, ortho-H2O and the j = 1 level of HF. The nature of the interaction causing the symmetry breaking is established in this study. A fragment of the solid C60 is considered, comprised of the central C60 molecule surrounded by twelve nearest-neighbor (NN) C60 molecules. The fullerenes have either P (major) or H (minor) orientational orderings, and are assumed to be rigid with Ih symmetry...
November 17, 2017: Physical Chemistry Chemical Physics: PCCP
Atsuhiro Osuka, Kota Yoshida
Pyrrole-modified subporphyrins bearing a non-pyrrolic cyclic unit, subporpholactone, subporpholactam, and imidazolosubporphyrin were newly synthesized. They show subporphyrin-like absorption and fluorescence spectra that are red-shifted in the order of subporpholactam < subporpholactone < imidazolosubporphyrin. Metalation of the imidazolosubporphyrin with (pentamethylcyclopentadienyl)iridium(III) dichloride dimer gave a complex, in which the Ir(III) atom was attached at the peripheral nitrogen atom of the imidazole moiety and the ortho-position of the meso-phenyl group...
November 15, 2017: Angewandte Chemie
Ratchanok Pingaew, Prasit Mandi, Veda Prachayasittikul, Supaluk Prachayasittikul, Somsak Ruchirawat, Virapong Prachayasittikul
Thirty four of indoles bearing sulfonamides (11-44) were synthesized and evaluated for their anti-aromatase activities. Interestingly, all indole derivatives inhibited the aromatase with IC50 range of 0.7-15.3 μM. Indoles (27-36) exerted higher aromatase inhibitory activity than that of ketoconazole. The phenoxy analogs 28 and 34 with methoxy group were shown to be the most potent compounds with sub-micromolar IC50 values (i.e., 0.7 and 0.8 μM, respectively) without affecting to the normal cell line. Molecular docking demonstrated that the indoles 28, 30 and 34 could occupy the same binding site on the aromatase pocket and share several binding residues with those of the natural substrate (androstenedione), which suggested the competitive binding could be the mode of inhibition of the compounds...
October 20, 2017: European Journal of Medicinal Chemistry
Antonio Garcia-Jimenez, Jose Antonio Teruel-Puche, Pedro Antonio Garcia-Ruiz, Adrian Saura-Sanmartin, Jose Berna, Francisco Garcia-Canovas, José Neptuno Rodriguez-Lopez
Deoxyarbutin, a potent inhibitor of tyrosinase, could act as substrate of the enzyme. Oxytyrosinase is able to hydroxylate deoxyarbutin and finishes the catalytic cycle by oxidizing the formed o-diphenol to quinone, while the enzyme becomes deoxytyrosinase, which evolves to oxytyrosinase in the presence of oxygen. This compound is the only one described that does not release o-diphenol after the hydroxylation step. Oxytyrosinase hydroxylates the deoxyarbutin in ortho position of the phenolic hydroxyl group by means of an aromatic electrophilic substitution...
2017: PloS One
Hana Pizova, Marketa Havelkova, Sarka Stepankova, Andrzej Bak, Tereza Kauerova, Violetta Kozik, Michal Oravec, Ales Imramovsky, Peter Kollar, Pavel Bobal, Josef Jampilek
Series of twenty-five benzyl (2S)-2-(arylcarbamoyl)pyrrolidine-1-carboxylates was prepared and completely characterized. All the compounds were tested for their in vitro ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and the selectivity of compounds to individual cholinesterases was determined. Screening of the cytotoxicity of all the compounds was performed using a human monocytic leukaemia THP-1 cell line, and the compounds demonstrated insignificant toxicity. All the compounds showed rather moderate inhibitory effect against AChE; benzyl (2S)-2-[(2-chlorophenyl)carbamoyl]pyrrolidine-1-carboxylate (IC50 = 46...
November 14, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Andrew Edwards, Michael Rubin, Marina Rubina
A full account on rhodium-catalyzed asymmetric, directed hydroboration of functionalized prochiral cyclopropenes affording enantiomerically enriched cyclopropylboronates is reported. The scope and limitations of two alternate directing groups, ester and carboxamide, are evaluated. It was found that hydroboration of esters appeared to be more sensitive to substitution in the aromatic ring of the substrates. Specifically, ortho-halogens were detrimental for diastereo- and enantioselectivity, potentially, due to additional coordination with rhodium...
November 13, 2017: Chemistry: a European Journal
Ilija N Cvijetić, Tatjana Ž Verbić, Pedro Ernesto de Resende, Paul Stapleton, Simon Gibbons, Ivan O Juranić, Branko J Drakulić, Mire Zloh
Antimicrobial resistance (AMR) is a major health problem worldwide, because of ability of bacteria, fungi and viruses to evade known therapeutic agents used in treatment of infections. Aryldiketo acids (ADK) have shown antimicrobial activity against several resistant strains including Gram-positive Staphylococcus aureus bacteria. Our previous studies revealed that ADK analogues having bulky alkyl group in ortho position on a phenyl ring have up to ten times better activity than norfloxacin against the same strains...
November 10, 2017: European Journal of Medicinal Chemistry
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