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https://www.readbyqxmd.com/read/28420174/an-expedient-total-synthesis-of-triciribine
#1
Chen Hu, Zhizhong Ruan, Haixin Ding, Yirong Zhou, Qiang Xiao
In the present paper, we report an expedient total synthesis of triciribine, a tricyclic 7-deazapurine nucleoside and protein kinase B (AKT ) inhibitor, in 35% overall yield. Our synthesis route features a highly regioselective substitution of 1-N-Boc-2-methylhydrazine and a trifluoroacetic acid catalyzed one-pot transformation which combined the deprotection of the tert-butylcarbonyl (Boc) group and ring closure reaction together to give a tricyclic nucleobase motif.
April 17, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28406463/synthesis-of-pyrrolo-1-2-a-pyrimidine-enantiomers-via-domino-ring-closure-followed-by-retro-diels-alder-protocol
#2
Beáta Fekete, Márta Palkó, Matti Haukka, Ferenc Fülöp
From 2-aminonorbornene hydroxamic acids, a simple and efficient method for the preparation of pyrrolo[1,2-a]pyrimidine enantiomers is reported. The synthesis is based on domino ring-closure followed by microwave-induced retro Diels-Alder (RDA) protocols, where the chirality of the desired products is transferred from norbornene derivatives. The stereochemistry of the synthesized compounds was proven by X-ray crystallography. The absolute configuration of the product is determined by the configuration of the starting amino hydroxamic acid...
April 13, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28394400/the-missing-link-in-leguminous-pterocarpan-biosynthesis-is-a-dirigent-domain-containing-protein-with-isoflavanol-dehydratase-activity
#3
Kai Uchida, Tomoyoshi Akashi, Toshio Aoki
Pterocarpan forms the basic structure of leguminous phytoalexins, and most of the isoflavonoid pathway genes encoding the enzymes responsible for its biosynthesis have been identified. However, the last step of pterocarpan biosynthesis is a ring closure reaction, and the enzyme that catalyzes this step, 2'-hydroxyisoflavanol 4,2'-dehydratase or pterocarpan synthase (PTS), remains as an unidentified 'missing link'. This last ring formation is assumed to be the key step in determining the stereochemistry of pterocarpans, which plays a role in their antimicrobial activity...
February 1, 2017: Plant & Cell Physiology
https://www.readbyqxmd.com/read/28358517/total-synthesis-of-scholarisine-k-and-alstolactine-a
#4
Dan Wang, Min Hou, Yue Ji, Shuanhu Gao
The first asymmetric total syntheses of scholarisine K and alstolactine A have been accomplished. Our syntheses feature (1) ring closure metathesis and an intramolecular Heck reaction to construct the 1,3-bridged [3,3,1] bicycle (C-D ring), (2) intramolecular alkylation followed by Fischer indolization to form the basic skeleton of akuammilines, and (3) bioinspired, acid-promoted epoxide opening/lactonization to generate the second lactone ring of alstolactine A. These results provide evidence of a biogenetic relationship between scholarisine K and alstolactine A, which should facilitate the preparation of other akuammiline-type natural products and their derivatives for functional studies...
April 7, 2017: Organic Letters
https://www.readbyqxmd.com/read/28352121/pepper-carel1-a-ubiquitin-e3-ligase-regulates-drought-tolerance-via-the-aba-signalling-pathway
#5
Chae Woo Lim, Chanmi Park, Jung-Hyun Kim, Hyunhee Joo, Eunji Hong, Sung Chul Lee
Drought stress conditions in soil or air hinder plant growth and development. Here, we report that the hot pepper (C apsicum a nnuum) RING type E3 Ligase 1 gene (CaREL1) is essential to the drought stress response. CaREL1 encodes a cytoplasmic- and nuclear-localized protein with E3 ligase activity. CaREL1 expression was induced by abscisic acid (ABA) and drought. CaREL1 contains a C3H2C3-type RING finger motif, which functions in ubiquitination of the target protein. We used CaREL1-silenced pepper plants and CaREL1-overexpressing (OX) transgenic Arabidopsis plants to evaluate the in vivo function of CaREL1 in response to drought stress and ABA treatment...
March 28, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28271894/altering-the-cyclization-modes-temperature-dependent-intramolecular-7-endo-dig-vs-6-endo-dig-electrophilic-ring-closures
#6
Maloy Nayak, Young Kee Kang, Ikyon Kim
In an attempt to construct 10-acyl-5H-benzo[e]pyrrolo[1,2-a]azepines via acid-catalyzed intramolecular alkyne carbonyl metathesis, two distinctive modes of cyclization were revealed to depend on the reaction temperatures. 5H-Benzo[e]pyrrolo[1,2-a]azepine-1-carbaldehydes with a substituent at the C11 position were obtained as major products at 90 °C as a result of intramolecular 7-endo-dig cyclization, while 6-endo-dig ring closure by electrophilic addition of nitrogen of the pyrrole to a vinyl cation generated under acidic medium followed by an unprecedented domino rearrangement process was observed at 40 °C in some cases, resulting in 5-aryl-11H-benzo[d]pyrrolo[1,2-a]azepine-1-carbaldehydes along with the former products...
March 8, 2017: Organic Letters
https://www.readbyqxmd.com/read/28245117/octadentate-zirconium-iv-loaded-macrocycles-with-varied-stoichiometry-assembled-from-hydroxamic-acid-monomers-using-metal-templated-synthesis
#7
William Tieu, Tulip Lifa, Andrew Katsifis, Rachel Codd
The reaction between Zr(IV) and the forward endo-hydroxamic acid monomer 4-[(5-aminopentyl)(hydroxy)amino]-4-oxobutanoic acid (for-PBH) in a 1:4 stoichiometry in the presence of diphenylphosphoryl azide and triethylamine gave the octadentate Zr(IV)-loaded tetrameric hydroxamic acid macrocycle for-[Zr(DFOT1)] ([M + H](+) calc 887.3, obs 887.2). In this metal-templated synthesis (MTS) approach, the coordination preferences of Zr(IV) directed the preorganization of four oxygen-rich bidentate for-PBH ligands about the metal ion prior to ring closure under peptide coupling conditions...
February 28, 2017: Inorganic Chemistry
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
#8
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
#9
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-aba-and-drought-signaling-via-caadip1-protein-phosphatase-degradation
#10
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 (Capsicum annuum) 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...
April 2017: Plant Physiology
https://www.readbyqxmd.com/read/27934470/northern-southern-route-to-synthetic-bacteriochlorins
#11
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
#12
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
#13
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
#14
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
#15
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
#16
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
#17
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
#18
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
#19
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
#20
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
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