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Acid ring closure

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https://www.readbyqxmd.com/read/28225270/construction-of-the-bacteriochlorin-macrocycle-with-concomitant-nazarov-cyclization-to-form-the-annulated-isocyclic-ring-analogues-of-bacteriochlorophyll-a
#1
Shaofei Zhang, Jonathan S Lindsey
Bacteriochlorophylls contain a bacteriochlorin macrocycle bearing an annulated fifth ring. The fifth ring, termed the isocyclic ring or ring E, is equipped with 13(1)-oxo and 13(2)-carbomethoxy substituents. Herein, a general route to stable, synthetic bacteriochlorophyll analogues is described. Knoevenagel condensation (∼40 mM, rt, CH2Cl2, piperidine/AcOH/molecular sieves) of a dihydrodipyrrin-carboxaldehyde (AD half) and a dihydrodipyrrin substituted with a β-ketoester (BC half) forms a propenone bearing the two halves (a hydrobilin analogue)...
February 22, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28195725/theoretical-insight-into-the-conversion-mechanism-of-glucose-to-fructose-catalyzed-by-crcl2-in-imidazolium-chlorine-ionic-liquids
#2
Yaru Jing, Jun Gao, Chengbu Liu, Dongju Zhang
To better understand the efficient transformation of glucose to fructose catalyzed by chromium chlorides in imidazolium-based ionic liquids (ILs), density functional theory calculations have been carried out on a model system which describes the catalytic reaction by CrCl2 in 1,3-dimethylimidazolium chlorine (MMImCl) ionic liquid (IL). The reaction is shown to involve three fundamental processes: ring opening, 1,2-H migration, and ring closure. The reaction is calculated to exergonic by 3.8 kcal/mol with an overall barrier of 37...
February 22, 2017: Journal of Physical Chemistry. B
https://www.readbyqxmd.com/read/28184010/the-pepper-ring-type-e3-ligase-caairf1-regulates-the-aba-and-drought-signaling-via-caadip1-protein-phosphatase-degradation
#3
Chae Woo Lim, Woonhee Baek, Sung Chul Lee
Ubiquitin-mediated protein modification occurs at multiple steps of abscisic acid (ABA) signaling. Here, we sought proteins responsible for degradation of the pepper type 2C protein phosphatase CaADIP1 via the 26S proteasome system. We showed that the RING type E3 ligase CaAIRF1 (Capsicum annuum ADIP1 Interacting RING Finger Protein 1) interacts with and ubiquitinates CaADIP1. CaADIP1 degradation was slower in crude proteins from CaAIRF1-silenced peppers than in those from control plants. CaAIRF1-silenced pepper plants displayed reduced ABA sensitivity and decreased drought tolerance characterized by delayed stomatal closure and suppressed induction of ABA- and drought-responsive marker genes...
February 9, 2017: Plant Physiology
https://www.readbyqxmd.com/read/27934470/northern-southern-route-to-synthetic-bacteriochlorins
#4
Yizhou Liu, Jonathan S Lindsey
A new route to bacteriochlorins via Northern-Southern (N-S) self-condensation of a dihydrodipyrrin-acetal complements a prior Eastern-Western (E-W) route. Each bacteriochlorin was prepared in five steps from an α-halopyrrole and a 2,2-dimethylpent-4-ynoic acid. The first three steps follow Jacobi's synthesis of dihydrodipyrrins: Pd-mediated coupling to form a lactone-pyrrole, Petasis reagent treatment for methenylation, and Paal-Knorr type ring closure to form the 1,2,2-trimethyl-substituted dihydrodipyrrin...
December 2, 2016: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27911800/an-%C3%AE-%C3%AE-hydrolase-fold-protein-in-the-biosynthesis-of-thiostrepton-exhibits-a-dual-activity-for-endopeptidyl-hydrolysis-and-epoxide-ring-opening-macrocyclization
#5
Qingfei Zheng, Shoufeng Wang, Panpan Duan, Rijing Liao, Dandan Chen, Wen Liu
Thiostrepton (TSR), an archetypal bimacrocyclic thiopeptide antibiotic that arises from complex posttranslational modifications of a genetically encoded precursor peptide, possesses a quinaldic acid (QA) moiety within the side-ring system of a thiopeptide-characteristic framework. Focusing on selective engineering of the QA moiety, i.e., by fluorination or methylation, we have recently designed and biosynthesized biologically more active TSR analogs. Using these analogs as chemical probes, we uncovered an unusual indirect mechanism of TSR-type thiopeptides, which are able to act against intracellular pathogens through host autophagy induction in addition to direct targeting of bacterial ribosome...
December 13, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27875779/novel-pyrimidine-2-4-dione-1-2-3-triazole-and-furo-2-3-d-pyrimidine-2-one-1-2-3-triazole-hybrids-as-potential-anti-cancer-agents-synthesis-computational-and-x-ray-analysis-and-biological-evaluation
#6
Tomislav Gregorić, Mirela Sedić, Petra Grbčić, Andrea Tomljenović Paravić, Sandra Kraljević Pavelić, Mario Cetina, Robert Vianello, Silvana Raić-Malić
Regioselective 1,4-disubstituted 1,2,3-triazole tethered pyrimidine-2,4-dione derivatives (5-23) were successfully prepared by the copper(I)-catalyzed click chemistry. While known palladium/copper-cocatalyzed method based on Sonogashira cross-coupling followed by the intramolecular 5-endo-dig ring closure generated novel 6-alkylfuro[2,3-d]pyrimidine-2-one-1,2,3-triazole hybrids (24b-37b), a small library of their 5-alkylethynyl analogs (24a-37a) was synthesized and described for the first time by tandem terminal alkyne dimerization and subsequent 5-endo-trig cyclization, which was additionally corroborated with computational and X-ray crystal structure analyses...
January 5, 2017: European Journal of Medicinal Chemistry
https://www.readbyqxmd.com/read/27856760/molecular-mechanisms-of-substrate-controlled-ring-dynamics-and-substepping-in-a-nucleic-acid-dependent-hexameric-motor
#7
Nathan D Thomsen, Michael R Lawson, Lea B Witkowsky, Song Qu, James M Berger
Ring-shaped hexameric helicases and translocases support essential DNA-, RNA-, and protein-dependent transactions in all cells and many viruses. How such systems coordinate ATPase activity between multiple subunits to power conformational changes that drive the engagement and movement of client substrates is a fundamental question. Using the Escherichia coli Rho transcription termination factor as a model system, we have used solution and crystallographic structural methods to delineate the range of conformational changes that accompany distinct substrate and nucleotide cofactor binding events...
November 29, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27829907/microwave-assisted-cyclizations-promoted-by-polyphosphoric-acid-esters-a-general-method-for-1-aryl-2-iminoazacycloalkanes
#8
Jimena E Díaz, María C Mollo, Liliana R Orelli
The first general procedure for the synthesis of 5 to 7-membered 1-aryl-2-iminoazacycloalkanes is presented, by microwave-assisted ring closure of ω-arylaminonitriles promoted by polyphosphoric acid (PPA) esters. 1-Aryl-2-iminopyrrolidines were easily prepared from the acyclic precursors employing a chloroformic solution of ethyl polyphosphate (PPE). The use of trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes...
2016: Beilstein Journal of Organic Chemistry
https://www.readbyqxmd.com/read/27821776/ligand-induced-and-small-molecule-control-of-substrate-loading-in-a-hexameric-helicase
#9
Michael R Lawson, Kevin Dyer, James M Berger
Processive, ring-shaped protein and nucleic acid protein translocases control essential biochemical processes throughout biology and are considered high-prospect therapeutic targets. The Escherichia coli Rho factor is an exemplar hexameric RNA translocase that terminates transcription in bacteria. As with many ring-shaped motor proteins, Rho activity is modulated by a variety of poorly understood mechanisms, including small-molecule therapeutics, protein-protein interactions, and the sequence of its translocation substrate...
November 29, 2016: Proceedings of the National Academy of Sciences of the United States of America
https://www.readbyqxmd.com/read/27809535/charged-particle-imaging-of-the-deprotonated-octatrienoic-acid-anion-evidence-for-a-photoinduced-cyclization-reaction
#10
Christopher W West, James N Bull, Jan R R Verlet
Photoelectron spectroscopy of the deprotonated octatrienoic acid anion, [C7H9-CO2](-), shows the formation of [C7H9](-) and loss of H(-) at hν = 4.13 eV. Using velocity map imaging, the H(-) fragment was characterized to have a Boltzmann-like kinetic energy distribution consistent with dissociation on a ground electronic state. Similar dynamics were not observed at hν = 4.66 eV even though there is clear evidence for recovery of the ground electronic state of [C7H9-CO2](-). In accord with supporting electronic structure calculations, the production of H(-) at hν = 4...
November 17, 2016: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/27795589/a-novel-stereoselective-8-2-double-cycloaddition-route-to-hydronaphthalene-ring-systems
#11
Weijiang Ying, Lei Zhang, Paul A Wiget, James W Herndon
Substituted hydronaphthalenes where each of the ten carbons of the two-ring system contains functionality were obtained through a tandem [8+2] cycloaddition and base-catalyzed rearrangement process using dienylfurans and electron-deficient alkynes. If the [8+2] process is conducted under solvent-free conditions the process could be conducted in a single reaction flask without isolation of the chromatographically sensitive [8+2] cycloadducts. A mechanism involving base catalysed alkene positional isomerization followed by disrotatory electrocyclic ring closure was proposed for the key reaction step that converts [8+2] cycloadducts to hydronaphthalenes...
July 6, 2016: Tetrahedron Letters
https://www.readbyqxmd.com/read/27748978/the-br%C3%A3-nsted-acid-catalyzed-enantioselective-aza-diels-alder-reaction-for-the-direct-synthesis-of-chiral-piperidones
#12
Claudia Weilbeer, Marcel Sickert, Sergei Naumov, Christoph Schneider
We disclose herein the first enantioselective aza-Diels-Alder reaction of β-alkyl-substituted vinylketene silyl-O,O-acetals and imines furnishing a broad range of optically highly enriched 4-alkyl-substituted 2-piperidones. As a catalyst for this one-pot reaction we employed a chiral phosphoric acid which effects a vinylogous Mannich reaction directly followed by ring-closure to the lactam. Subsequent fully diastereoselective transformations including hydrogenation, enolate alkylation, and lactam alkylation/reduction processes converted the cycloadducts into various highly substituted piperidines of great utility for the synthesis of natural products and medicinally active compounds...
October 17, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27722531/intramolecular-lewis-pairs-with-two-acid-sites-reactivity-differences-between-p-and-n-based-systems
#13
Leif A Körte, Sebastian Blomeyer, Shari Heidemeyer, Jan Hendrick Nissen, Andreas Mix, Beate Neumann, Hans-Georg Stammler, Norbert W Mitzel
The doubly acid-functionalised aniline PhN[(CH2)3B(C6F5)2]2 shows rapidly exchanging boron acid groups at the central base function and is an active frustrated Lewis pair due to cooperative hydride binding by both Lewis acids. Here we report investigations on the effect of different substituents at the central nitrogen atom and on the effect of exchanging nitrogen by phosphorus. Treatment of diallyl-tert-butylaniline with one equivalent of HB(C6F5)2 led to formation of a seven-membered iminium hydridoborate ring; after mono-hydroboration the intermediately formed frustrated Lewis pair reacts with the second allylamine function under ring closure...
October 10, 2016: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/27680201/multiphase-ozonolysis-of-aqueous-%C3%AE-terpineol
#14
Dani H Leviss, Daryl A Van Ry, Ryan Z Hinrichs
Multiphase ozonolysis of aqueous organics presents a potential pathway for the formation of aqueous secondary organic aerosol (aqSOA). We investigated the multiphase ozonolysis of α-terpineol, an oxygenated derivative of limonene, and found that the reaction products and kinetics differ from the gas-phase ozonolysis of α-terpineol. One- and two-dimensional NMR spectroscopies along with GC-MS identified the aqueous ozonolysis reaction products as trans- and cis-lactols [4-(5-hydroxy-2,2-dimethyltetrahydrofuran-3-yl)butan-2-one] and a lactone [4-hydroxy-4-methyl-3-(3-oxobutyl)-valeric acid gamma-lactone], which accounted for 46%, 27%, and 20% of the observed products, respectively...
October 13, 2016: Environmental Science & Technology
https://www.readbyqxmd.com/read/27560135/precursor-directed-mutational-biosynthesis-facilitates-the-functional-assignment-of-two-cytochromes-p450-in-thiostrepton-biosynthesis
#15
Qingfei Zheng, Shoufeng Wang, Rijing Liao, Wen Liu
Side-ring-modified thiostrepton (TSR) derivatives that vary in their quinaldic acid (QA) substitution possess more potent biological activities and better pharmaceutical properties than the parent compound. In this work, we sought to introduce fluorine onto C-7' or C-8' of the TSR QA moiety via precursor-directed mutational biosynthesis to obtain new TSR variants. Unexpectedly, instead of the target product, the exogenous chemical feeding of 7-F-QA into the ΔtsrT mutant strain resulted in a unique TSR analog with an incomplete side-ring structure and an unoxidized QA moiety (1)...
October 21, 2016: ACS Chemical Biology
https://www.readbyqxmd.com/read/27554454/synthesis-properties-and-two-dimensional-adsorption-characteristics-of-6-hexahelicene-7-carboxylic-acid
#16
Maarten W van der Meijden, Tatyana Balandina, Oleksandr Ivasenko, Steven De Feyter, Klaus Wurst, Richard M Kellogg
A convergent synthesis of racemic [6]hexahelicene-7-carboxylic acid by cross-coupling of a bicyclic and a tricyclic component is described. A metal-catalyzed ring-closure is also a fundamental component of the synthetic approach. Scanning tunneling microscopy (STM) measurements of the racemate self-assembled on Au(111) at liquid-solid interface revealed the formation of ordered racemic 2D crystals.
October 4, 2016: Chemistry: a European Journal
https://www.readbyqxmd.com/read/27503217/the-pepper-ring-type-e3-ligase-caaip1-functions-as-a-positive-regulator-of-drought-and-high-salinity-stress-responses
#17
Chanmi Park, Chae Woo Lim, Sung Chul Lee
Plant adaptive responses to osmotic stress are co-ordinated by restriction of growth and developmental processes and by molecular and physiological activities. The phytohormone ABA is the primary regulator that induces and responds to osmotic stress, and its sensitivity markedly influences osmotic stress tolerance levels. Several E3 ubiquitin ligases act as positive or negative regulators of ABA, thereby mediating sensitivity to osmotic stress in higher plants. Here, we report that the C3H2C3-type RING finger E3 ligase, CaAIP1, regulates osmotic stress responses via ABA-mediated signaling...
October 2016: Plant & Cell Physiology
https://www.readbyqxmd.com/read/27487336/unexpected-ring-closure-products-derived-from-3-2-allylanilino-3-phenylacrylate-esters-crystal-and-molecular-structures-of-3-acetyl-8-allyl-6-methyl-2-phenylquinolin-4-yl-acetate-and-2rs-2-8-dimethyl-4-phenyl-1-2-dihydro-6h-pyrrolo-3-2-1-ij-quinolin-6-one
#18
Adriana L Luque, Carlos M Sanabria, Alirio Palma, Justo Cobo, Christopher Glidewell
The reactions of two 3-(2-allylanilino)-3-phenylacrylate esters with acetic anhydride and with strong acids has revealed a richly diverse reactivity providing a number of unexpected products. Thus, acetylation of ethyl 3-(2-allylanilino)-3-phenylacrylate, (Ia), or ethyl 3-(2-allyl-4-methylanilino)-3-phenylacrylate, (Ib), with acetic anhydride yields not only the expected acetylated esters, (II), as the major products but also the unexpected polysubstituted quinolines 3-acetyl-8-allyl-2-phenylquinolin-4-yl acetate, (IIIa), and 3-acetyl-8-allyl-6-methyl-2-phenylquinolin-4-yl acetate, (IIIb), as minor products...
August 1, 2016: Acta Crystallographica. Section C, Structural Chemistry
https://www.readbyqxmd.com/read/27464307/development-of-a-single-chain-peptide-agonist-of-the-relaxin-3-receptor-using-hydrocarbon-stapling
#19
Keiko Hojo, Mohammed Akhter Hossain, Julien Tailhades, Fazel Shabanpoor, Lilian L L Wong, Emma E K Ong-Pålsson, Hanna E Kastman, Sherie Ma, Andrew L Gundlach, K Johan Rosengren, John D Wade, Ross A D Bathgate
Structure-activity studies of the insulin superfamily member, relaxin-3, have shown that its G protein-coupled receptor (RXFP3) binding site is contained within its central B-chain α-helix and this helical structure is essential for receptor activation. We sought to develop a single B-chain mimetic that retained agonist activity. This was achieved by use of solid phase peptide synthesis together with on-resin ruthenium-catalyzed ring closure metathesis of a pair of judiciously placed i,i+4 α-methyl, α-alkenyl amino acids...
August 25, 2016: Journal of Medicinal Chemistry
https://www.readbyqxmd.com/read/27439598/identification-and-functional-expression-of-the-pepper-ring-type-e3-ligase-cadtr1-involved-in-drought-stress-tolerance-via-aba-mediated-signalling
#20
Hyunhee Joo, Chae Woo Lim, Sung Chul Lee
Drought negatively affects plant growth and development, thereby leading to loss of crop productivity. Several plant E3 ubiquitin ligases act as positive or negative regulators of abscisic acid (ABA) and thus play important roles in the drought stress response. Here, we show that the C3HC4-type RING finger E3 ligase, CaDTR1, regulates the drought stress response via ABA-mediated signalling. CaDTR1 contains an amino-terminal RING finger motif and two carboxyl-terminal hydrophobic regions; the RING finger motif functions during attachment of ubiquitins to the target proteins, and the carboxyl-terminal hydrophobic regions function during subcellular localisation...
2016: Scientific Reports
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