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Acid ring closure

Claudia Weilbeer, Marcel Sickert, Sergej Naumov, Christoph Schneider
We disclose herein the first enantioselective aza-Diels-Alder reaction of b-alkyl-substituted vinylketene silyl-O,O-acetals and imines furnishing a broad range of optically highly enriched 4-alkyl-substituted 2-piperidones. As 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
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
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
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
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
Chanmi Park, Chae Woo Lim, Sung Chul Lee
Plant adaptive responses to osmotic stress are coordinated by restriction of growth and developmental processes and by molecular and physiological activities. The phytohormone abscisic acid (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 signalling...
August 8, 2016: Plant & Cell Physiology
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
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
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
Naohiko Ikuma, Koji Nakagawa, Ken Kokubo, Takumi Oshima
Grignard reagents (RMgBr: R = Et, p-tolyl) selectively attacked the β-position of the bridgehead double bond of tosylazafulleroid through interaction of Mg with the S[double bond, length as m-dash]O group. The following [5,6] ring closure and C-N bond scission led to aryl/alkyl aminylfullerenes with 1,2-configuration. Tolyl-substituted aminylfullerene was further converted into 1,4-di(p-tolyl)fullerene on treatment in acidic toluene.
August 7, 2016: Organic & Biomolecular Chemistry
Daria Yu Dzhons, Andrei V Budruev
The base-mediated photochemical cyclization of 2-azidobenzoic acids with the formation of 2,1-benzisoxazole-3(1H)-ones is reported. The optimization and scope of this cyclization reaction is discussed. It is shown that an essential step of the ring closure of 2-azidobenzoic acids is the formation and photolysis of 2-azidobenzoate anions.
2016: Beilstein Journal of Organic Chemistry
Wei Zhang, Yang Wang, Donghui Wei, Mingsheng Tang, Xinju Zhu
A systematic theoretical study has been carried out to understand the mechanism and stereoselectivity of N-heterocyclic carbene (NHC)-catalyzed intramolecular crossed-benzoin reaction of enolizable keto-aldehyde using density functional theory (DFT) calculations. The calculated results reveal that the most favorable pathway contains four steps, i.e., the nucleophilic attack of NHC on the carbonyl carbon atom of a formyl group, the formation of a Breslow intermediate, a ring-closure process coupled with proton transfer, and regeneration of the catalyst...
July 6, 2016: Organic & Biomolecular Chemistry
Katarzyna Ciesielska, Sophie L K W Roelants, Inge N A Van Bogaert, Stijn De Waele, Isabel Vandenberghe, Sara Groeneboer, Wim Soetaert, Bart Devreese
We recently discovered a novel enzyme in the exoproteome of Starmerella bombicola, which is structurally related to Candida antarctica lipase A. A knockout strain for this enzyme does no longer produce lactonic sophorolipids, prompting us to believe that this protein is the missing S. bombicola lactone esterase (SBLE). SBLE catalyzes a rather unusual reaction, i.e., an intramolecular esterification (lactonization) of acidic sophorolipids in an aqueous environment, which raised questions about its activity and mode of action...
June 2, 2016: Applied Microbiology and Biotechnology
Nils Widderich, Stefanie Kobus, Astrid Höppner, Ramona Riclea, Andreas Seubert, Jeroen S Dickschat, Johann Heider, Sander H J Smits, Erhard Bremer
Ectoine is a compatible solute and chemical chaperone widely used by members of the Bacteria and a few Archaea to fend-off the detrimental effects of high external osmolarity on cellular physiology and growth. Ectoine synthase (EctC) catalyzes the last step in ectoine production and mediates the ring closure of the substrate N-gamma-acetyl-L-2,4-diaminobutyric acid through a water elimination reaction. However, the crystal structure of ectoine synthase is not known and a clear understanding of how its fold contributes to enzyme activity is thus lacking...
2016: PloS One
Mandy L Wallace, Gary W Ellison, Christopher Batich, J Brad Case, Stanley E Kim
OBJECTIVE: To develop a device intended for gradual venous occlusion over 4 to 6 weeks. SAMPLE: Silicone tubing filled with various inorganic salt and polyacrylic acid (PAA) formulations and mounted within a polypropylene or polyether ether ketone (PEEK) outer ring. PROCEDURES: 15 polypropylene prototype rings were initially filled with 1 of 5 formulations and placed in PBSS. In a second test, 10 polypropylene and 7 PEEK prototype rings were filled with 1 formulation and placed in PBSS...
March 2016: American Journal of Veterinary Research
Alexey O Chagarovskiy, Ekaterina M Budynina, Olga A Ivanova, Victor B Rybakov, Igor V Trushkov, Mikhail Ya Melnikov
A convenient general approach to 2-(pyrazol-4-yl)- and 2-(isoxazol-4-yl)ethanols based on the Brønsted acid-initiated reaction of 3-acyl-4,5-dihydrofurans with hydrazines or hydroxylamine was developed. Further transformation of the alcohol moiety in 2-(pyrazolyl)ethanols affording 2-(pyrazolyl)ethylamine as potent bioactive compounds as well as pyrazole-substituted derivatives of antitumor alkaloid crispine A was elaborated.
March 14, 2016: Organic & Biomolecular Chemistry
Éva Bokor, Zsolt Széles, Tibor Docsa, Pál Gergely, László Somsák
Various C-glucopyranosyl-1,2,4-triazolones were designed as potential inhibitors of glycogen phosphorylase. Syntheses of these compounds were performed with O-perbenzoylated glucose derivatives as precursors. High temperature ring closure of N(1)-carbamoyl-C-β-D-glucopyranosyl formamidrazone gave 3-β-D-glucopyranosyl-1,2,4-triazol-5-one. Reaction of N(1)-tosyl-C-β-D-glucopyranosyl formamidrazone with ClCOOEt furnished 3-β-D-glucopyranosyl-1-tosyl-1,2,4-triazol-5-one. In situ prepared β-D-glucopyranosylcarbonyl isocyanate was transformed by PhNHNHBoc into 3-β-D-glucopyranosyl-1-phenyl-1,2,4-triazol-5-one, while the analogous 1-(2-naphthyl) derivative was obtained from the unsubstituted triazolone by naphthalene-2-boronic acid in a Cu(II) catalyzed N-arylation...
June 24, 2016: Carbohydrate Research
Tobias Michael Brütsch, Pascal Bucher, Karl-Heinz Altmann
A new convergent total synthesis of the marine macrolide mandelalide A (1) has been developed that is based on macrocyclic ring closure by a Shiina-type macrolactonization and the construction of the requisite precursor seco acid by a highly efficient Sonogashira cross-coupling reaction between two fragments of comparable complexity. Key steps in the elaboration of the acid building block were the enantioselective, catalytic addition of a protected acetylene to crotonaldehyde and the construction of the tetrahydropyran unit that is embedded in the macrocycle by means of an acid-catalyzed Prins reaction...
January 22, 2016: Chemistry: a European Journal
Ji Yeon Suh, Soo Jin Kim, Tae Rin Oh, Seok Keun Cho, Seong Wook Yang, Woo Taek Kim
Plants have developed a variety of complicated responses to cope with drought, one of the most challenging environmental stresses. As a quick response, plants rapidly inhibit stomatal opening under the control of abscisic acid (ABA) signaling pathway, in order to preserve water. Here, we report that Arabidopsis Tóxicos en Levadura (ATL), a RING-type E3 ubiquitin ligase, mediates the ABA-dependent stomatal closure. In contrast to wild-type plants, the stomatal closure was fully impaired in atatl78 mutant plants even in the presence of exogenous ABA and reactive oxygen species (ROS)...
January 1, 2016: Biochemical and Biophysical Research Communications
Shuangcheng Ding, Bin Zhang, Feng Qin
Abscisic acid (ABA) is a phytohormone that plays a fundamental role in plant development and stress response, especially in the regulation of stomatal closure in response to water deficit stress. The signal transduction that occurs in response to ABA and drought stress is mediated by protein phosphorylation and ubiquitination. This research identified Arabidopsis thaliana RING ZINC-FINGER PROTEIN34 (RZP34; renamed here as CHY ZINC-FINGER AND RING PROTEIN1 [CHYR1]) as an ubiquitin E3 ligase. CHYR1 expression was significantly induced by ABA and drought, and along with its corresponding protein, was expressed mainly in vascular tissues and stomata...
November 2015: Plant Cell
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