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Acid ring closure

Johannes Gurke, Simon Budzak, Bernd Schmidt, Denis Jacquemin, Stefan Hecht
Photoswitchable acid-base pairs, allowing for a reversible alteration of their pKa values, are attractive molecular tools to control chemical and biological processes by light. A significant, light-induced pKa change of three units in aqueous medium has been realized involving two thermally stable states, which can be interconverted using UV and green light. The light-induced pKa modulation is based on incorporating a 3-H-thiazol-2-one moiety into the framework of a diarylethene photoswitch, which upon photochemical ring-closure loses the heteroaromatic stabilization of the corresponding, negatively charged base and hence, becomes significantly less acidic...
March 7, 2018: Angewandte Chemie
Yong Chan Park, Sandeep Chapagain, Cheol Seong Jang
RING (Really Interesting New Gene) finger proteins play crucial roles in abiotic stress responses in plants. We report the RING finger E3 ligase, an Oryza sativa salt, abscisic acid (ABA), and drought stress-induced RING finger protein 1 gene (OsSADR1). We demonstrated that although OsSAR1 possesses E3 ligase activity, a single amino acid substitution (OsSADR1C168A) in the RING domain exhibited no E3 ligase activity, suggesting that the activity of most E3s is specified by the RING domain. Additional assays substantiated that OsSADR1 interacts with three substrates-OsSNAC2, OsGRAS44, and OsPIRIN, and mediates their proteolysis via the 26S proteasome pathway...
January 18, 2018: Plant & Cell Physiology
Tímea Gonda, Péter Bérdi, István Zupkó, Ferenc Fülöp, Zsolt Szakonyi
Stereoselective synthesis of monoterpene-based 1,2,4- and 1,3,4-oxadiazole derivatives was accomplished starting from α,β-unsaturated carboxylic acids, obtained by the oxidation of (-)-2-carene-3-aldehyde and commercially available (-)-myrtenal. 1,2,4-Oxadiazoles were prepared in two steps via the corresponding O-acylamidoxime intermediates, which then underwent cyclisation induced by tetrabutylammonium fluoride (TBAF) under mild reaction conditions. Stereoselective dihydroxylation in highly stereospecific reactions with the OsO₄/NMO (N-methylmorpholine N-oxide) system produced α,β-dihydroxy 1,2,4-oxadiazoles...
December 28, 2017: International Journal of Molecular Sciences
Daniel Polyak, Ngan Phung, Jian Liu, Robert Barrows, Thomas J Emge, Spencer Knapp
Homophthalic anhydride (HPA) typically reacts rapidly with benzalimines to afford the formal [4+2] adduct, a 1,2,3,4-tetrahydroisoquinolin-1-one-4-carboxylic acid. The stereochemical outcome of this reaction is consistent with an open transition state comprising an iminium species and enolized HPA, leading to a short-lived amino-anhydride intermediate. In the case of N-tert-butylbenzalimine, this Mannich-type intermediate, which would normally cyclize at low temperature to a single isomer of the delta-lactam, is intercepted by base treatment to afford beta-lactam products...
October 4, 2017: Tetrahedron Letters
Elham Jafari, Najmeh Taghi Jarah-Najafabadi, Ali Jahanian-Najafabadi, Safoora Poorirani, Farshid Hassanzadeh, Sedighe Sadeghian-Rizi
Cyclic imides are a group of compounds which have valuable biological properties including cytotoxic, anti-inflammatory, antibacterial and antifungal activities. In this study, succinic and phthalic anhydrides were treated with glycinamide in pyridine to yield the corresponding amic acids. These amic acids underwent ring closure with acetic anhydride and anhydrous sodium acetate to form cyclic imides. In another procedure, succinic and phthalic anhydrides upon reaction with 2-amino-benzylamine in pyridine gave the corresponding cyclic imides...
December 2017: Research in Pharmaceutical Sciences
Marco Mottinelli, Mathew P Leese, Barry V L Potter
Background: 1,2,3,4-Tetrahydroisoquinolines (THIQs) are common motifs in alkaloids and in medicinal chemistry. Synthetic access to THIQs via the Pomeranz-Fritsch-Bobbit (PFB) methodology using mineral acids for deactivated, electron-poor aromatic systems, is scarcely represented in the literature. Here, the factors controlling the regiochemical outcome of cyclization are evaluated. Results: A double reductive alkylation was telescoped into a one-pot reaction delivering good to excellent yields of desired aminoacetals for cyclization...
2017: Beilstein Journal of Organic Chemistry
S Mirabella, G Fibbi, C Matassini, C Faggi, A Goti, F Cardona
A dual synthetic strategy to afford 2-substituted trihydroxypiperidines is disclosed. The procedure involved Grignard addition either to a carbohydrate-derived aldehyde or to a nitrone derived thereof, and took advantage of an efficient ring-closure reductive amination strategy in the final cyclization step. An opposite diastereofacial preference was demonstrated in the nucleophilic attack to the two electrophiles, which would finally produce the same piperidine diastereoisomer as the major product. However, use of a suitable Lewis acid in the Grignard addition to the nitrone allowed reversing the selectivity, giving access to 2-substituted piperidines with the opposite configuration at C-2...
November 7, 2017: Organic & Biomolecular Chemistry
Rezvan Rezaee Nasab, Farshid Hassanzadeh, Ghadam Ali Khodarahmi, Mahboubeh Rostami, Mahmoud Mirzaei, Ali Jahanian-Najafabadi, Mahboubeh Mansourian
A series of novel 4-anilinoquinazoline derivatives were designed and synthesized from benzoic acid through ring closure, chlorination or nucleophilic substitution. The structures of compounds were characterized by IR, (1)H-NMR and mass spectroscopy. All synthesized derivatives were screened for their antimicrobial activities against Gram-positive (Staphylococcus aurous, Bacillus subtilis, Listeria monocitogenes) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Salmonella entritidis) bacteria and also for antifungal activities against Candida albicans using the conventional micro dilution method...
October 2017: Research in Pharmaceutical Sciences
Furong Lin, Yunjun Shen, Yuanbin Zhang, Yuji Sun, Jiyong Liu, Simon Duttwyler
An iridium-catalyzed alkenylation/annulation sequence between monocarba-closo-dodecaborate carboxylic acids and diarylacetylenes is reported. Regioselective activation of the B2 position, followed by B-C bond formation and ring closure, affords 3D bora-analogs of isocoumarins. The reaction tolerates a variety of functional groups on the aromatic rings and can be extended to B12-substituted derivatives. Furthermore, subsequent alkenylation of the B4 vertex has been achieved in high yields.
September 29, 2017: Chemistry: a European Journal
Hui-Hong Wang, Tao Shi, Wei-Wei Gao, Hong-Hua Zhang, Yong-Qiang Wang, Jun-Fang Li, Yong-Sheng Hou, Jin-Hong Chen, Xue Peng, Zhen Wang
A simple and practical ring-closure procedure to prepare a range of diverse heterocycles has been developed. In this transformation, a variety of substituted (thio)salicylamides and thiosalicylic acids undergo a double 1,4-addition reaction with propiolate derivatives in the presence of an inorganic base (K3PO4), as a result benzothiazinones, benzoxazinones and benzoxathiinones were prepared in good to excellent yields, respectively, even in gram scales. In addition, further transformation towards more complex structures and oxicam drug analogues has also been successfully carried out...
October 4, 2017: Organic & Biomolecular Chemistry
Wataru Matsuoka, Hideto Ito, Kenichiro Itami
Efficient and rapid access to nanographenes and π-extended fused heteroaromatics is important in materials science. Herein, we report a palladium-catalyzed efficient one-step annulative π-extension (APEX) reaction of polycyclic aromatic hydrocarbons (PAHs) and heteroaromatics, producing various π-extended aromatics. In the presence of a cationic Pd complex, triflic acid, silver pivalate, and diiodobiaryls, diverse unfunctionalized PAHs and heteroaromatics were directly transformed into larger PAHs, nanographenes, and π-extended fused heteroaromatics in a single step...
August 11, 2017: Angewandte Chemie
Junya Suzuki, Natsumi Miyano, Shunpei Yashiro, Taiki Umezawa, Fuyuhiko Matsuda
A 3,4-disubstituted pyrrolidine ring was effectively cyclized through SmI2-mediated reductive coupling between allyl chloride and an α,β-unsaturated ester, although little has been reported about SmI2-promoted C-C bond formation of an allyl chloride with an α,β-unsaturated ester. Selection of either the 3,4-cis- or 3,4-trans-selective cyclization can be accomplished simply by changing the additives from NiI2 to HMPA during reductive cyclization conducted in H2O-THF. Total synthesis of (-)-kainic acid and (+)-allo-kainic acid, which are pyrrolidine alkaloids used in neuroscience and neuropharmacology as useful molecular probes, was successfully achieved by using the stereo-complementary ring closure reactions promoted by SmI2 for the construction of the 2,3,4-trisubsituted pyrrolidine scaffold of kainoids...
August 9, 2017: Organic & Biomolecular Chemistry
Francisco Martínez-Peña, Ana M Pizarro
The potential use of organoruthenium complexes as anticancer drugs is well known. Herein, a family of activatable tethered ruthenium(II) arene complexes of general formula [Ru{η(6) :κ(1) -C6 H5 (C6 H4 )NH2 }(XY)](n+) (closed tether ring) bearing different chelating XY ligands (XY=aliphatic diamine, phenylenediamine, oxalato, bis(phosphino)ethane) is reported. The activation of these complexes (closed- to open-tether conversion) occurs in methanol and DMSO at different rates and to different reaction extents at equilibrium...
July 22, 2017: Chemistry: a European Journal
Ruixiao Gao, Deyaa I AbuSalim, Timothy D Lash
The first examples of porphyrin analogues incorporating pyrene units are reported. Acid-catalyzed condensation of a pyrene dialdehyde with a tripyrrane, followed by oxidation with DDQ, afforded a polycyclic aromatic hydrocarbon (PAH)-porphyrin hybrid in 38% yield. Pyreniporphyrin proved to be devoid of global aromatic character, but upon protonation aromatic mono- and dicationic species were generated. In the proton NMR spectrum for the dication, the internal CH was shifted upfield to approximately +3 ppm. NICS calculations and ACID plots confirmed the diatropic nature of these structures...
June 15, 2017: Journal of Organic Chemistry
Ewout Ruysbergh, Kristof Van Hecke, Christian V Stevens, Norbert De Kimpe, Sven Mangelinckx
Several natural products containing a 1,4-oxazepane-2,5-dione-core are known. One example is serratin, isolated from Serratia marcescens. Because of the presence of a carboxylic amide, which has a preference for a trans-conformation, and the presence of a labile lactone in this core, many synthetic methodologies commonly used for the cyclization toward medium-sized heterocycles cannot be applied. As N-acyl amino acids lacking a third substituent at nitrogen failed to undergo ring-closure, several N-protecting groups were evaluated...
June 2, 2017: Journal of Organic Chemistry
Xin Fang, Jian-Xu Li, Jin-Quan Huang, You-Li Xiao, Peng Zhang, Xiao-Ya Chen
Terpene synthases (TPSs) are responsible for the extremely diversified and complex structure of terpenoids. Amorpha-4,11-diene synthase (ADS) has a high (90%) fidelity in generating the sesquiterpene precursor for the biosynthesis of artemisinin, an antimalarial drug, however, little is known about how active site residues of ADS are involved in carbocation rearrangement and cyclization reactions. Here, we identify seven residues that are key to most of the catalytic steps in ADS. By structural modeling and amino acid sequence alignments of ADS with two functionally relevant sesquiterpene synthases from Artemisia annua, we performed site-directed mutagenesis and found that a single substitution, T296V, impaired the ring closure activity almost completely, and tetra-substitutions (L374Y/L404V/L405I/G439S) led to an enzyme generating 80% monocyclic bisabolyl-type sesquiterpenes, whereas a double mutant (T399L/T447G) showed compromised activity in regioselective deprotonation to yield 34...
June 16, 2017: Biochemical Journal
Hyunhee Joo, Chae Woo Lim, Sang-Wook Han, Sung Chul Lee
Drought stress from soil or air limits plant growth and development, leading to a reduction in crop productivity. Several E3 ligases positively or negatively regulate the drought stress response. In the present study, we show that the pepper (Capsicum annuum) Drought Induced RING type E3 ligase 1, CaDIR1, regulates the drought stress response via abscisic acid (ABA)-mediated signaling. CaDIR1 contains a C3HC4-type RING finger domain in the N-terminal region; this domain functions during protein degradation via attachment of ubiquitins to the substrate target proteins...
2017: Frontiers in Plant Science
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
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
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
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